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Network Working Group                                        A. JohnstonRequest for Comments: 3665                                           MCIBCP: 75                                                       S. DonovanCategory: Best Current Practice                                R. Sparks                                                           C. Cunningham                                                             dynamicsoft                                                              K. Summers                                                                   Sonus                                                           December 2003Session Initiation Protocol (SIP) Basic Call Flow ExamplesStatus of this Memo   This document specifies an Internet Best Current Practices for the   Internet Community, and requests discussion and suggestions for   improvements.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2003).  All Rights Reserved.Abstract   This document gives examples of Session Initiation Protocol (SIP)   call flows.  Elements in these call flows include SIP User Agents and   Clients, SIP Proxy and Redirect Servers.  Scenarios include SIP   Registration and SIP session establishment.  Call flow diagrams and   message details are shown.Johnston, et al.         Best Current Practice                  [Page 1]

RFC 3665              SIP Basic Call Flow Examples         December 2003Table of Contents1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .21.1.  General Assumptions. . . . . . . . . . . . . . . . . . .31.2.  Legend for Message Flows . . . . . . . . . . . . . . . .31.3.  SIP Protocol Assumptions . . . . . . . . . . . . . . . .42.  SIP Registration . . . . . . . . . . . . . . . . . . . . . . .42.1.  Successful New Registration. . . . . . . . . . . . . . .52.2.  Update of Contact List . . . . . . . . . . . . . . . . .72.3.  Request for Current Contact List . . . . . . . . . . . .82.4.  Cancellation of Registration . . . . . . . . . . . . . .92.5.  Unsuccessful Registration. . . . . . . . . . . . . . . .103.  SIP Session Establishment. . . . . . . . . . . . . . . . . . .123.1.  Successful Session Establishment . . . . . . . . . . . .123.2.  Session Establishment Through Two Proxies. . . . . . . .153.3.  Session with Multiple Proxy Authentication . . . . . . .263.4.  Successful Session with Proxy Failure. . . . . . . . . .373.5.  Session Through a SIP ALG. . . . . . . . . . . . . . . .46       3.6.  Session via Redirect and Proxy Servers with SDP in ACK . 543.7.  Session with re-INVITE (IP Address Change) . . . . . . .613.8.  Unsuccessful No Answer . . . . . . . . . . . . . . . . .673.9.  Unsuccessful Busy. . . . . . . . . . . . . . . . . . . .753.10. Unsuccessful No Response from User Agent . . . . . . . .803.11. Unsuccessful Temporarily Unavailable . . . . . . . . . .854.  Security Considerations. . . . . . . . . . . . . . . . . . . .915.  References . . . . . . . . . . . . . . . . . . . . . . . . . .915.1.  Normative References . . . . . . . . . . . . . . . . . .915.2.  Informative References . . . . . . . . . . . . . . . . .916.  Intellectual Property Statement. . . . . . . . . . . . . . . .917.  Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . .928.  Authors' Addresses . . . . . . . . . . . . . . . . . . . . . .939.  Full Copyright Statement . . . . . . . . . . . . . . . . . . .941.  Overview   The call flows shown in this document were developed in the design of   a SIP IP communications network.  They represent an example minimum   set of functionality.   It is the hope of the authors that this document will be useful for   SIP implementers, designers, and protocol researchers alike and will   help further the goal of a standard implementation ofRFC 3261 [1].   These flows represent carefully checked and working group reviewed   scenarios of the most basic examples as a companion to the   specifications.Johnston, et al.         Best Current Practice                  [Page 2]

RFC 3665              SIP Basic Call Flow Examples         December 2003   These call flows are based on the current version 2.0 of SIP inRFC3261 [1] with SDP usage described inRFC 3264 [2].  Other RFCs also   comprise the SIP standard but are not used in this set of basic call   flows.   Call flow examples of SIP interworking with the PSTN through gateways   are contained in a companion document,RFC 3666 [5].   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this   document are to be interpreted as described inBCP 14,RFC 2119 [4].1.1.  General Assumptions   A number of architecture, network, and protocol assumptions underlie   the call flows in this document.  Note that these assumptions are not   requirements.  They are outlined in this section so that they may be   taken into consideration and to aid in the understanding of the call   flow examples.   The authentication of SIP User Agents in these example call flows is   performed using HTTP Digest as defined in [1] and [3].   Some Proxy Servers in these call flows insert Record-Route headers   into requests to ensure that they are in the signaling path for   future message exchanges.   These flows show TCP, TLS, and UDP for transport.  See the discussion   inRFC 3261 for details on the transport issues for SIP.1.2.  Legend for Message Flows   Dashed lines (---) represent signaling messages that are mandatory to   the call scenario.  These messages can be SIP or PSTN signaling.  The   arrow indicates the direction of message flow.   Double dashed lines (===) represent media paths between network   elements.   Messages with parentheses around their name represent optional   messages.   Messages are identified in the Figures as F1, F2, etc.  This   references the message details in the list that follows the Figure.   Comments in the message details are shown in the following form:    /* Comments. */Johnston, et al.         Best Current Practice                  [Page 3]

RFC 3665              SIP Basic Call Flow Examples         December 20031.3.  SIP Protocol Assumptions   This document does not prescribe the flows precisely as they are   shown, but rather the flows illustrate the principles for best   practice.  They are best practices usages (orderings, syntax,   selection of features for the purpose, handling of error) of SIP   methods, headers and parameters.  IMPORTANT: The exact flows here   must not be copied as is by an implementer due to specific incorrect   characteristics that were introduced into the document for   convenience and are listed below.  To sum up, the basic flows   represent well-reviewed examples of SIP usage, which are best common   practice according to IETF consensus.   For simplicity in reading and editing the document, there are a   number of differences between some of the examples and actual SIP   messages.  For example, the HTTP Digest responses are not actual MD5   encodings.  Call-IDs are often repeated, and CSeq counts often begin   at 1.  Header fields are usually shown in the same order.  Usually   only the minimum required header field set is shown, others that   would normally be present such as Accept, Supported, Allow, etc are   not shown.   Actors:   Element       Display Name   URI                         IP Address   -------       ------------   ---                         ----------   User Agent    Alice          alice@atlanta.example.com   192.0.2.101   User Agent    Bob            bob@biloxi.example.com      192.0.2.201   User Agent                   bob@chicago.example.com     192.0.2.100   Proxy Server                 ss1.atlanta.example.com     192.0.2.111   Proxy/Registrar              ss2.biloxi.example.com      192.0.2.222   Proxy Server                 ss3.chicago.example.com     192.0.2.233   ALG                          alg1.atlanta.example.com    192.0.2.1282.  SIP Registration   Registration binds a particular device Contact URI with a SIP user   Address of Record (AOR).Johnston, et al.         Best Current Practice                  [Page 4]

RFC 3665              SIP Basic Call Flow Examples         December 20032.1.  Successful New Registration    Bob                        SIP Server     |                               |     |          REGISTER F1          |     |------------------------------>|     |      401 Unauthorized F2      |     |<------------------------------|     |          REGISTER F3          |     |------------------------------>|     |            200 OK F4          |     |<------------------------------|     |                               |   Bob sends a SIP REGISTER request to the SIP server.  The request   includes the user's contact list.  This flow shows the use of HTTP   Digest for authentication using TLS transport.  TLS transport is used   due to the lack of integrity protection in HTTP Digest and the danger   of registration hijacking without it, as described inRFC 3261 [1].   The SIP server provides a challenge to Bob.  Bob enters her/his valid   user ID and password.  Bob's SIP client encrypts the user information   according to the challenge issued by the SIP server and sends the   response to the SIP server.  The SIP server validates the user's   credentials.  It registers the user in its contact database and   returns a response (200 OK) to Bob's SIP client.  The response   includes the user's current contact list in Contact headers.  The   format of the authentication shown is HTTP digest.  It is assumed   that Bob has not previously registered with this Server.   Message Details   F1 REGISTER Bob -> SIP Server   REGISTER sips:ss2.biloxi.example.com SIP/2.0   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7   Max-Forwards: 70   From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl   To: Bob <sips:bob@biloxi.example.com>   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com   CSeq: 1 REGISTER   Contact: <sips:bob@client.biloxi.example.com>   Content-Length: 0Johnston, et al.         Best Current Practice                  [Page 5]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F2 401 Unauthorized SIP Server -> Bob   SIP/2.0 401 Unauthorized   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7    ;received=192.0.2.201   From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl   To: Bob <sips:bob@biloxi.example.com>;tag=1410948204   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com   CSeq: 1 REGISTER   WWW-Authenticate: Digest realm="atlanta.example.com", qop="auth",    nonce="ea9c8e88df84f1cec4341ae6cbe5a359",    opaque="", stale=FALSE, algorithm=MD5   Content-Length: 0   F3 REGISTER Bob -> SIP Server   REGISTER sips:ss2.biloxi.example.com SIP/2.0   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashd92   Max-Forwards: 70   From: Bob <sips:bob@biloxi.example.com>;tag=ja743ks76zlflH   To: Bob <sips:bob@biloxi.example.com>   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com   CSeq: 2 REGISTER   Contact: <sips:bob@client.biloxi.example.com>   Authorization: Digest username="bob", realm="atlanta.example.com"    nonce="ea9c8e88df84f1cec4341ae6cbe5a359", opaque="",    uri="sips:ss2.biloxi.example.com",    response="dfe56131d1958046689d83306477ecc"   Content-Length: 0   F4 200 OK SIP Server -> Bob   SIP/2.0 200 OK   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashd92    ;received=192.0.2.201   From: Bob <sips:bob@biloxi.example.com>;tag=ja743ks76zlflH   To: Bob <sips:bob@biloxi.example.com>;tag=37GkEhwl6   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com   CSeq: 2 REGISTER   Contact: <sips:bob@client.biloxi.example.com>;expires=3600   Content-Length: 0Johnston, et al.         Best Current Practice                  [Page 6]

RFC 3665              SIP Basic Call Flow Examples         December 20032.2.  Update of Contact List   Bob                        SIP Server     |                               |     |          REGISTER F1          |     |------------------------------>|     |            200 OK F2          |     |<------------------------------|     |                               |   Bob wishes to update the list of addresses where the SIP server will   redirect or forward INVITE requests.   Bob sends a SIP REGISTER request to the SIP server.  Bob's request   includes an updated contact list.  Since the user already has   authenticated with the server, the user supplies authentication   credentials with the request and is not challenged by the server. The   SIP server validates the user's credentials.  It registers the user   in its contact database, updates the user's contact list, and returns   a response (200 OK) to Bob's SIP client.  The response includes the   user's current contact list in Contact headers.   Message Details   F1 REGISTER Bob -> SIP Server   REGISTER sips:ss2.biloxi.example.com SIP/2.0   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7   Max-Forwards: 70   From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl   To: Bob <sips:bob@biloxi.example.com>   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com   CSeq: 1 REGISTER   Contact: mailto:bob@biloxi.example.com   Authorization: Digest username="bob", realm="atlanta.example.com",    qop="auth", nonce="1cec4341ae6cbe5a359ea9c8e88df84f", opaque="",    uri="sips:ss2.biloxi.example.com",    response="71ba27c64bd01de719686aa4590d5824"   Content-Length: 0   F2 200 OK SIP Server -> Bob   SIP/2.0 200 OK   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7    ;received=192.0.2.201   From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl   To: Bob <sips:bob@biloxi.example.com>;tag=34095828jhJohnston, et al.         Best Current Practice                  [Page 7]

RFC 3665              SIP Basic Call Flow Examples         December 2003   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com   CSeq: 1 REGISTER   Contact: <sips:bob@client.biloxi.example.com>;expires=3600   Contact: <mailto:bob@biloxi.example.com>;expires=4294967295   Content-Length: 02.3.  Request for Current Contact List   Bob                        SIP Server     |                               |     |          REGISTER F1          |     |------------------------------>|     |            200 OK F2          |     |<------------------------------|     |                               |   Bob sends a register request to the Proxy Server containing no   Contact headers, indicating the user wishes to query the server for   the user's current contact list.  Since the user already has   authenticated with the server, the user supplies authentication   credentials with the request and is not challenged by the server.   The SIP server validates the user's credentials.  The server returns   a response (200 OK) which includes the user's current registration   list in Contact headers.   Message Details   F1 REGISTER Bob -> SIP Server   REGISTER sips:ss2.biloxi.example.com SIP/2.0   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7   Max-Forwards: 70   From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl   To: Bob <sips:bob@biloxi.example.com>   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com   CSeq: 1 REGISTER   Authorization: Digest username="bob", realm="atlanta.example.com",    nonce="df84f1cec4341ae6cbe5ap359a9c8e88", opaque="",    uri="sips:ss2.biloxi.example.com",    response="aa7ab4678258377c6f7d4be6087e2f60"   Content-Length: 0   F2 200 OK SIP Server -> Bob   SIP/2.0 200 OK   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7    ;received=192.0.2.201Johnston, et al.         Best Current Practice                  [Page 8]

RFC 3665              SIP Basic Call Flow Examples         December 2003   From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl   To: Bob <sips:bob@biloxi.example.com>;tag=jqoiweu75   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com   CSeq: 1 REGISTER   Contact: <sips:bob@client.biloxi.example.com>;expires=3600   Contact: <mailto:bob@biloxi.example.com>;expires=4294967295   Content-Length: 02.4.  Cancellation of Registration   Bob                         SIP Server     |                               |     |          REGISTER F1          |     |------------------------------>|     |            200 OK F2          |     |<------------------------------|     |                               |   Bob wishes to cancel their registration with the SIP server.  Bob   sends a SIP REGISTER request to the SIP server.  The request has an   expiration period of 0 and applies to all existing contact locations.   Since the user already has authenticated with the server, the user   supplies authentication credentials with the request and is not   challenged by the server.  The SIP server validates the user's   credentials.  It clears the user's contact list, and returns a   response (200 OK) to Bob's SIP client.   Message Details   F1 REGISTER Bob -> SIP Server   REGISTER sips:ss2.biloxi.example.com SIP/2.0   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7   Max-Forwards: 70   From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl   To: Bob <sips:bob@biloxi.example.com>   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com   CSeq: 1 REGISTER   Expires: 0   Contact: *   Authorization: Digest username="bob", realm="atlanta.example.com",    nonce="88df84f1cac4341aea9c8ee6cbe5a359", opaque="",    uri="sips:ss2.biloxi.example.com",    response="ff0437c51696f9a76244f0cf1dbabbea"   Content-Length: 0   F2 200 OK SIP Server -> BobJohnston, et al.         Best Current Practice                  [Page 9]

RFC 3665              SIP Basic Call Flow Examples         December 2003   SIP/2.0 200 OK   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7    ;received=192.0.2.201   From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl   To: Bob <sips:bob@biloxi.example.com>;tag=1418nmdsrf   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com   CSeq: 1 REGISTER   Content-Length: 02.5.  Unsuccessful Registration   Bob                        SIP Server     |                               |     |          REGISTER F1          |     |------------------------------>|     |      401 Unauthorized F2      |     |<------------------------------|     |          REGISTER F3          |     |------------------------------>|     |      401 Unauthorized F4      |     |<------------------------------|     |                               |   Bob sends a SIP REGISTER request to the SIP Server.  The SIP server   provides a challenge to Bob.  Bob enters her/his user ID and   password.  Bob's SIP client encrypts the user information according   to the challenge issued by the SIP server and sends the response to   the SIP server.  The SIP server attempts to validate the user's   credentials, but they are not valid (the user's password does not   match the password established for the user's account).  The server   returns a response (401 Unauthorized) to Bob's SIP client.   Message Details   F1 REGISTER Bob -> SIP Server   REGISTER sips:ss2.biloxi.example.com SIP/2.0   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7    ;received=192.0.2.201   From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl   To: Bob <sips:bob@biloxi.example.com>   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com   CSeq: 1 REGISTER   Contact: <sips:bob@client.biloxi.example.com>   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 10]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F2 Unauthorized SIP Server -> Bob   SIP/2.0 401 Unauthorized   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7    ;received=192.0.2.201   From: Bob <sips:bob@biloxi.example.com>;tag=a73kszlfl   To: Bob <sips:bob@biloxi.example.com>;tag=1410948204   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com   CSeq: 1 REGISTER   WWW-Authenticate: Digest realm="atlanta.example.com", qop="auth",    nonce="f1cec4341ae6ca9c8e88df84be55a359",    opaque="", stale=FALSE, algorithm=MD5   Content-Length: 0   F3 REGISTER Bob -> SIP Server   REGISTER sips:ss2.biloxi.example.com SIP/2.0   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashd92   Max-Forwards: 70   From: Bob <sips:bob@biloxi.example.com>;tag=JueHGuidj28dfga   To: Bob <sips:bob@biloxi.example.com>   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com   CSeq: 2 REGISTER   Contact: <sips:bob@client.biloxi.example.com>   Authorization: Digest username="bob", realm="atlanta.example.com",    nonce="f1cec4341ae6ca9c8e88df84be55a359", opaque="",    uri="sips:ss2.biloxi.example.com",    response="61f8470ceb87d7ebf508220214ed438b"   Content-Length: 0   /*  The response above encodes the incorrect password */   F4 401 Unauthorized SIP Server -> Bob   SIP/2.0 401 Unauthorized   Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashd92    ;received=192.0.2.201   From: Bob <sips:bob@biloxi.example.com>;tag=JueHGuidj28dfga   To: Bob <sips:bob@biloxi.example.com>;tag=1410948204   Call-ID: 1j9FpLxk3uxtm8tn@biloxi.example.com   CSeq: 2 REGISTER   WWW-Authenticate: Digest realm="atlanta.example.com", qop="auth",    nonce="84f1c1ae6cbe5ua9c8e88dfa3ecm3459",    opaque="", stale=FALSE, algorithm=MD5   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 11]

RFC 3665              SIP Basic Call Flow Examples         December 20033.  SIP Session Establishment   This section details session establishment between two SIP User   Agents (UAs): Alice and Bob.  Alice (sip:alice@atlanta.example.com)   and Bob (sip:bob@biloxi.example.com) are assumed to be SIP phones or   SIP-enabled devices.  The successful calls show the initial   signaling, the exchange of media information in the form of SDP   payloads, the establishment of the media session, then finally the   termination of the call.   HTTP Digest authentication is used by Proxy Servers to authenticate   the caller Alice.  It is assumed that Bob has registered with Proxy   Server Proxy 2 as perSection 2 to be able to receive the calls via   the Proxy.3.1.  Successful Session Establishment   Alice                     Bob     |                        |     |       INVITE F1        |     |----------------------->|     |    180 Ringing F2      |     |<-----------------------|     |                        |     |       200 OK F3        |     |<-----------------------|     |         ACK F4         |     |----------------------->|     |   Both Way RTP Media   |     |<======================>|     |                        |     |         BYE F5         |     |<-----------------------|     |       200 OK F6        |     |----------------------->|     |                        |   In this scenario, Alice completes a call to Bob directly.   Message Details   F1 INVITE Alice -> Bob   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>Johnston, et al.         Best Current Practice                 [Page 12]

RFC 3665              SIP Basic Call Flow Examples         December 2003   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:alice@client.atlanta.example.com;transport=tcp>   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F2 180 Ringing Bob -> Alice   SIP/2.0 180 Ringing   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=8321234356   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:bob@client.biloxi.example.com;transport=tcp>   Content-Length: 0   F3 200 OK Bob -> Alice   SIP/2.0 200 OK   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=8321234356   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:bob@client.biloxi.example.com;transport=tcp>   Content-Type: application/sdp   Content-Length: 147   v=0   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com   s=-   c=IN IP4 192.0.2.201   t=0 0   m=audio 3456 RTP/AVP 0   a=rtpmap:0 PCMU/8000Johnston, et al.         Best Current Practice                 [Page 13]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F4 ACK Alice -> Bob   ACK sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bd5   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=8321234356   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 1 ACK   Content-Length: 0   /* RTP streams are established between Alice and Bob */   /* Bob Hangs Up with Alice. Note that the CSeq is NOT 2, since      Alice and Bob maintain their own independent CSeq counts.      (The INVITE was request 1 generated by Alice, and the BYE is      request 1 generated by Bob) */   F5 BYE Bob -> Alice   BYE sip:alice@client.atlanta.example.com SIP/2.0   Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7   Max-Forwards: 70   From: Bob <sip:bob@biloxi.example.com>;tag=8321234356   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 1 BYE   Content-Length: 0   F6 200 OK Alice -> Bob   SIP/2.0 200 OK   Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7    ;received=192.0.2.201   From: Bob <sip:bob@biloxi.example.com>;tag=8321234356   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 1 BYE   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 14]

RFC 3665              SIP Basic Call Flow Examples         December 20033.2.  Session Establishment Through Two Proxies   Alice           Proxy 1          Proxy 2            Bob     |                |                |                |     |   INVITE F1    |                |                |     |--------------->|                |                |     |     407 F2     |                |                |     |<---------------|                |                |     |     ACK F3     |                |                |     |--------------->|                |                |     |   INVITE F4    |                |                |     |--------------->|   INVITE F5    |                |     |     100  F6    |--------------->|   INVITE F7    |     |<---------------|     100  F8    |--------------->|     |                |<---------------|                |     |                |                |     180 F9     |     |                |    180 F10     |<---------------|     |     180 F11    |<---------------|                |     |<---------------|                |     200 F12    |     |                |    200 F13     |<---------------|     |     200 F14    |<---------------|                |     |<---------------|                |                |     |     ACK F15    |                |                |     |--------------->|    ACK F16     |                |     |                |--------------->|     ACK F17    |     |                |                |--------------->|     |                Both Way RTP Media                |     |<================================================>|     |                |                |     BYE F18    |     |                |    BYE F19     |<---------------|     |     BYE F20    |<---------------|                |     |<---------------|                |                |     |     200 F21    |                |                |     |--------------->|     200 F22    |                |     |                |--------------->|     200 F23    |     |                |                |--------------->|     |                |                |                |   In this scenario, Alice completes a call to Bob using two proxies   Proxy 1 and Proxy 2.  The initial INVITE (F1) contains a pre-loaded   Route header with the address of Proxy 1 (Proxy 1 is configured as a   default outbound proxy for Alice).  The request does not contain the   Authorization credentials Proxy 1 requires, so a 407 Proxy   Authorization response is sent containing the challenge information.   A new INVITE (F4) is then sent containing the correct credentials and   the call proceeds.  The call terminates when Bob disconnects by   initiating a BYE message.Johnston, et al.         Best Current Practice                 [Page 15]

RFC 3665              SIP Basic Call Flow Examples         December 2003   Proxy 1 inserts a Record-Route header into the INVITE message to   ensure that it is present in all subsequent message exchanges.  Proxy   2 also inserts itself into the Record-Route header.  The ACK (F15)   and BYE (F18) both have a Route header.   Message Details   F1 INVITE Alice -> Proxy 1   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74b43   Max-Forwards: 70   Route: <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:alice@client.atlanta.example.com;transport=tcp>   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   /* Proxy 1 challenges Alice for authentication */   F2 407 Proxy Authorization Required Proxy 1 -> Alice   SIP/2.0 407 Proxy Authorization Required   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74b43    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=3flal12sf   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 1 INVITE   Proxy-Authenticate: Digest realm="atlanta.example.com", qop="auth",    nonce="f84f1cec41e6cbe5aea9c8e88d359",    opaque="", stale=FALSE, algorithm=MD5   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 16]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F3 ACK Alice -> Proxy 1   ACK sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74b43   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=3flal12sf   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 1 ACK   Content-Length: 0   /* Alice responds be re-sending the INVITE with authentication      credentials in it. */   F4 INVITE Alice -> Proxy 1   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9   Max-Forwards: 70   Route: <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 2 INVITE   Contact: <sip:alice@client.atlanta.example.com;transport=tcp>   Proxy-Authorization: Digest username="alice",    realm="atlanta.example.com",    nonce="wf84f1ceczx41ae6cbe5aea9c8e88d359", opaque="",    uri="sip:bob@biloxi.example.com",    response="42ce3cef44b22f50c6a6071bc8"   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   /* Proxy 1 accepts the credentials and forwards the INVITE to Proxy   2.  Client for Alice prepares to receive data on port 49172 from the   network. */Johnston, et al.         Best Current Practice                 [Page 17]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F5 INVITE Proxy 1 -> Proxy 2   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Max-Forwards: 69   Record-Route: <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 2 INVITE   Contact: <sip:alice@client.atlanta.example.com;transport=tcp>   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F6 100 Trying Proxy 1 -> Alice   SIP/2.0 100 Trying   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 2 INVITE   Content-Length: 0   F7 INVITE Proxy 2 -> Bob   INVITE sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Max-Forwards: 68   Record-Route: <sip:ss2.biloxi.example.com;lr>,    <sip:ss1.atlanta.example.com;lr>Johnston, et al.         Best Current Practice                 [Page 18]

RFC 3665              SIP Basic Call Flow Examples         December 2003   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 2 INVITE   Contact: <sip:alice@client.atlanta.example.com;transport=tcp>   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F8 100 Trying Proxy 2 -> Proxy 1   SIP/2.0 100 Trying   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 2 INVITE   Content-Length: 0   F9 180 Ringing Bob -> Proxy 2   SIP/2.0 180 Ringing   Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1    ;received=192.0.2.222   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss2.biloxi.example.com;lr>,    <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 3848276298220188511@atlanta.example.com   Contact: <sip:bob@client.biloxi.example.com;transport=tcp>   CSeq: 2 INVITE   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 19]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F10 180 Ringing Proxy 2 -> Proxy 1   SIP/2.0 180 Ringing   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss2.biloxi.example.com;lr>,    <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 3848276298220188511@atlanta.example.com   Contact: <sip:bob@client.biloxi.example.com;transport=tcp>   CSeq: 2 INVITE   Content-Length: 0   F11 180 Ringing Proxy 1 -> Alice   SIP/2.0 180 Ringing   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss2.biloxi.example.com;lr>,    <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 3848276298220188511@atlanta.example.com   Contact: <sip:bob@client.biloxi.example.com;transport=tcp>   CSeq: 2 INVITE   Content-Length: 0   F12 200 OK Bob -> Proxy 2   SIP/2.0 200 OK   Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1    ;received=192.0.2.222   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss2.biloxi.example.com;lr>,    <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 2 INVITEJohnston, et al.         Best Current Practice                 [Page 20]

RFC 3665              SIP Basic Call Flow Examples         December 2003   Contact: <sip:bob@client.biloxi.example.com;transport=tcp>   Content-Type: application/sdp   Content-Length: 147   v=0   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com   s=-   c=IN IP4 192.0.2.201   t=0 0   m=audio 3456 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F13 200 OK Proxy 2 -> Proxy 1   SIP/2.0 200 OK   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss2.biloxi.example.com;lr>,    <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 2 INVITE   Contact: <sip:bob@client.biloxi.example.com;transport=tcp>   Content-Type: application/sdp   Content-Length: 147   v=0   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com   s=-   c=IN IP4 192.0.2.201   t=0 0   m=audio 3456 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F14 200 OK Proxy 1 -> Alice   SIP/2.0 200 OK   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss2.biloxi.example.com;lr>,    <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159Johnston, et al.         Best Current Practice                 [Page 21]

RFC 3665              SIP Basic Call Flow Examples         December 2003   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 2 INVITE   Contact: <sip:bob@client.biloxi.example.com;transport=tcp>   Content-Type: application/sdp   Content-Length: 147   v=0   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com   s=-   c=IN IP4 192.0.2.201   t=0 0   m=audio 3456 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F15 ACK Alice -> Proxy 1   ACK sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74b76   Max-Forwards: 70   Route: <sip:ss1.atlanta.example.com;lr>,    <sip:ss2.biloxi.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 2 ACK   Content-Length: 0   F16 ACK Proxy 1 -> Proxy 2   ACK sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74b76    ;received=192.0.2.101   Max-Forwards: 69   Route: <sip:ss2.biloxi.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 2 ACK   Content-Length: 0   F17 ACK Proxy 2 -> Bob   ACK sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1Johnston, et al.         Best Current Practice                 [Page 22]

RFC 3665              SIP Basic Call Flow Examples         December 2003   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74b76    ;received=192.0.2.101   Max-Forwards: 68   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 2 ACK   Content-Length: 0   /* RTP streams are established between Alice and Bob */   /* Bob Hangs Up with Alice. */   /* Again, note that the CSeq is NOT 3.  Alice and Bob maintain      their own separate CSeq counts */   F18 BYE Bob -> Proxy 2   BYE sip:alice@client.atlanta.example.com SIP/2.0   Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7   Max-Forwards: 70   Route: <sip:ss2.biloxi.example.com;lr>,    <sip:ss1.atlanta.example.com;lr>   From: Bob <sip:bob@biloxi.example.com>;tag=314159   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 1 BYE   Content-Length: 0   F19 BYE Proxy 2 -> Proxy 1   BYE sip:alice@client.atlanta.example.com SIP/2.0   Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1   Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7    ;received=192.0.2.201   Max-Forwards: 69   Route: <sip:ss1.atlanta.example.com;lr>   From: Bob <sip:bob@biloxi.example.com>;tag=314159   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 1 BYE   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 23]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F20 BYE Proxy 1 -> Alice   BYE sip:alice@client.atlanta.example.com SIP/2.0   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1   Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1    ;received=192.0.2.222   Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7    ;received=192.0.2.201   Max-Forwards: 68   From: Bob <sip:bob@biloxi.example.com>;tag=314159   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 1 BYE   Content-Length: 0   F21 200 OK Alice -> Proxy 1   SIP/2.0 200 OK   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1    ;received=192.0.2.222   Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7    ;received=192.0.2.201   From: Bob <sip:bob@biloxi.example.com>;tag=314159   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 1 BYE   Content-Length: 0   F22 200 OK Proxy 1 -> Proxy 2   SIP/2.0 200 OK   Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1    ;received=192.0.2.222   Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7    ;received=192.0.2.101   From: Bob <sip:bob@biloxi.example.com>;tag=314159   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 1 BYE   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 24]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F23 200 OK Proxy 2 -> Bob   SIP/2.0 200 OK   Via: SIP/2.0/TCP client.biloxi.example.com:5060;branch=z9hG4bKnashds7    ;received=192.0.2.201   From: Bob <sip:bob@biloxi.example.com>;tag=314159   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   Call-ID: 3848276298220188511@atlanta.example.com   CSeq: 1 BYE   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 25]

RFC 3665              SIP Basic Call Flow Examples         December 20033.3.  Session with Multiple Proxy Authentication     Alice        Proxy 1     Proxy 2         Bob       |            |           |             |       |  INVITE F1 |           |             |       |----------->|           |             |       |  407 Proxy Authorization Required F2 |       |<-----------|           |             |       |   ACK F3   |           |             |       |----------->|           |             |       |  INVITE F4 |           |             |       |----------->|           |             |       |   100 F5   |           |             |       |<-----------| INVITE F6 |             |       |            |---------->|             |       |            |  407 Proxy Authorization Required F7       |            |<----------|             |       |            |   ACK F8  |             |       |            |---------->|             |       |  407 Proxy Authorization Required F9 |       |<-----------|           |             |       |   ACK F10  |           |             |       |----------->|           |             |       |  INVITE F11|           |             |       |----------->|           |             |       |   100 F12  |           |             |       |<-----------| INVITE F13|             |       |            |---------->|             |       |            |  100 F14  |             |       |            |<----------|  INVITE F15 |       |            |           |------------>|       |            |           | 200 OK F16  |       |            | 200 OK F17|<------------|       | 200 OK F18 |<----------|             |       |<-----------|           |             |       |   ACK F19  |           |             |       |----------->|  ACK F20  |             |       |            |---------->|   ACK F21   |       |            |           |------------>|       |           RTP Media Path             |       |<====================================>|   In this scenario, Alice completes a call to Bob using two proxies   Proxy 1 and Proxy 2.  Alice has valid credentials in both domains.   Since the initial INVITE (F1) does not contain the Authorization   credentials Proxy 1 requires, so a 407 Proxy Authorization response   is sent containing the challenge information. A new INVITE (F4) isJohnston, et al.         Best Current Practice                 [Page 26]

RFC 3665              SIP Basic Call Flow Examples         December 2003   then sent containing the correct credentials and the call proceeds   after Proxy 2 challenges and receives valid credentials.  The call   terminates when Bob disconnects by initiating a BYE message.   Proxy 1 inserts a Record-Route header into the INVITE message to   ensure that it is present in all subsequent message exchanges.  Proxy   2 also inserts itself into the Record-Route header.   Message Details   F1 INVITE Alice -> Proxy 1   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b03   Max-Forwards: 70   Route: <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   /* Proxy 1 challenges Alice for authentication */   F2 407 Proxy Authorization Required Proxy 1 -> Alice   SIP/2.0 407 Proxy Authorization Required   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b03    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=876321   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Proxy-Authenticate: Digest realm="atlanta.example.com", qop="auth",    nonce="wf84f1cczx41ae6cbeaea9ce88d359",    opaque="", stale=FALSE, algorithm=MD5   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 27]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F3 ACK Alice -> Proxy 1   ACK sip:bob@biloxi.example.com SIP/2.0   Max-Forwards: 70   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b03   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=876321   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 ACK   Content-Length: 0   /* Alice responds be re-sending the INVITE with authentication      credentials in it.  The same Call-ID is used, so the CSeq is      increased. */   F4 INVITE Alice -> Proxy 1   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b21   Max-Forwards: 70   Route: <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 2 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Proxy-Authorization: Digest username="alice",    realm="atlanta.example.com",    nonce="wf84f1ceczx41ae6cbe5aea9c8e88d359", opaque="",    uri="sip:bob@biloxi.example.com",    response="42ce3cef44b22f50c6a6071bc8"   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   /* Proxy 1 accepts the credentials and forwards the INVITE to Proxy   2.  Client for Alice prepares to receive data on port 49172 from the   network. */Johnston, et al.         Best Current Practice                 [Page 28]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F5 100 Trying Proxy 1 -> Alice   SIP/2.0 100 Trying   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b21    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 2 INVITE   Content-Length: 0   F6 INVITE Proxy 1 -> Proxy 2   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b21    ;received=192.0.2.101   Max-Forwards: 69   Record-Route: <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 2 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   /* Proxy 2 challenges Alice for authentication */   F7 407 Proxy Authorization Required Proxy 2 -> Proxy 1   SIP/2.0 407 Proxy Authorization Required   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1    ;received=192.0.2.111   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b21    ;received=192.0.2.101Johnston, et al.         Best Current Practice                 [Page 29]

RFC 3665              SIP Basic Call Flow Examples         December 2003   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=838209   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 2 INVITE   Proxy-Authenticate: Digest realm="biloxi.example.com", qop="auth",    nonce="c1e22c41ae6cbe5ae983a9c8e88d359",    opaque="", stale=FALSE, algorithm=MD5   Content-Length: 0   F8 ACK Proxy 1 -> Proxy 2   ACK sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b21   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=838209   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 2 ACK   Content-Length: 0   /* Proxy 1 forwards the challenge to Alice for authentication from   Proxy 2 */   F9 407 Proxy Authorization Required Proxy 1 -> Alice   SIP/2.0 407 Proxy Authorization Required   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b21    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=838209   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 2 INVITE   Proxy-Authenticate: Digest realm="biloxi.example.com", qop="auth",    nonce="c1e22c41ae6cbe5ae983a9c8e88d359",    opaque="", stale=FALSE, algorithm=MD5   Content-Length: 0   F10 ACK Alice -> Proxy 1   ACK sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b21   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=838209   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.comJohnston, et al.         Best Current Practice                 [Page 30]

RFC 3665              SIP Basic Call Flow Examples         December 2003   CSeq: 2 ACK   Proxy-Authorization: Digest username="alice",    realm="atlanta.example.com",    nonce="wf84f1ceczx41ae6cbe5aea9c8e88d359", opaque="",    uri="sip:bob@biloxi.example.com",    response="42ce3cef44b22f50c6a6071bc8"   Content-Length: 0   /* Alice responds be re-sending the INVITE with authentication   credentials for Proxy 1 AND Proxy 2.  */   F11 INVITE Alice -> Proxy 1   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 3 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Proxy-Authorization: Digest username="alice",    realm="atlanta.example.com",    nonce="wf84f1ceczx41ae6cbe5aea9c8e88d359", opaque="",    uri="sip:bob@biloxi.example.com",    response="42ce3cef44b22f50c6a6071bc8"   Proxy-Authorization: Digest username="alice",    realm="biloxi.example.com",    nonce="c1e22c41ae6cbe5ae983a9c8e88d359", opaque="",    uri="sip:bob@biloxi.example.com", response="f44ab22f150c6a56071bce8"   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   /* Proxy 1 finds its credentials and authorizes Alice, forwarding the   INVITE to Proxy.  */Johnston, et al.         Best Current Practice                 [Page 31]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F12 100 Trying Proxy 1 -> Alice   SIP/2.0 100 Trying   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 3 INVITE   Content-Length: 0   F13 INVITE Proxy 1 -> Proxy 2   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Max-Forwards: 69   Record-Route: <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 3 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Proxy-Authorization: Digest username="alice",    realm="biloxi.example.com",    nonce="c1e22c41ae6cbe5ae983a9c8e88d359", opaque="",    uri="sip:bob@biloxi.example.com", response="f44ab22f150c6a56071bce8"   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   /* Proxy 2 finds its credentials and authorizes Alice, forwarding the   INVITE to Bob.  */Johnston, et al.         Best Current Practice                 [Page 32]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F14 100 Trying Proxy 2 -> Proxy 1   SIP/2.0 100 Trying   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1    ;received=192.0.2.111   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 3 INVITE   Content-Length: 0   F15 INVITE Proxy 2 -> Bob   INVITE sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK31972.1   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1    ;received=192.0.2.111   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Max-Forwards: 68   Record-Route: <sip:ss2.biloxi.example.com;lr>,    <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 3 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   /* Bob answers the call immediately */Johnston, et al.         Best Current Practice                 [Page 33]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F16 200 OK Bob -> Proxy 2   SIP/2.0 200 OK   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK31972.1    ;received=192.0.2.222   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1    ;received=192.0.2.111   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss2.biloxi.example.com;lr>,    <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=9103874   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 3 INVITE   Contact: <sip:bob@client.biloxi.example.com>   Content-Type: application/sdp   Content-Length: 147   v=0   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com   s=-   c=IN IP4 192.0.2.201   t=0 0   m=audio 3456 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F17 200 OK Proxy 2 -> Proxy 1   SIP/2.0 200 OK   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1    ;received=192.0.2.111   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss2.biloxi.example.com;lr>,    <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=9103874   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 3 INVITE   Contact: <sip:bob@client.biloxi.example.com>   Content-Type: application/sdp   Content-Length: 147   v=0   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com   s=-Johnston, et al.         Best Current Practice                 [Page 34]

RFC 3665              SIP Basic Call Flow Examples         December 2003   c=IN IP4 192.0.2.201   t=0 0   m=audio 3456 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F18 200 OK Proxy 1 -> Alice   SIP/2.0 200 OK   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss2.biloxi.example.com;lr>,    <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=9103874   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 3 INVITE   Contact: <sip:bob@client.biloxi.example.com>   Content-Type: application/sdp   Content-Length: 147   v=0   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com   s=-   c=IN IP4 192.0.2.201   t=0 0   m=audio 3456 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F19 ACK Alice -> Proxy 1   ACK sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b44   Max-Forwards: 70   Route: <sip:ss1.atlanta.example.com;lr>,    <sip:ss2.biloxi.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=9103874   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 3 ACK   Proxy-Authorization: Digest username="alice",    realm="atlanta.example.com",    nonce="wf84f1ceczx41ae6cbe5aea9c8e88d359", opaque="",    uri="sip:bob@biloxi.example.com",    response="42ce3cef44b22f50c6a6071bc8"   Proxy-Authorization: Digest username="alice",    realm="biloxi.example.com",Johnston, et al.         Best Current Practice                 [Page 35]

RFC 3665              SIP Basic Call Flow Examples         December 2003    nonce="c1e22c41ae6cbe5ae983a9c8e88d359", opaque="",    uri="sip:bob@biloxi.example.com", response="f44ab22f150c6a56071bce8"   Content-Length: 0   F20 ACK Proxy 1 -> Proxy 2   ACK sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b44    ;received=192.0.2.101   Max-Forwards: 69   Route: <sip:ss2.biloxi.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=9103874   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 3 ACK   Contact: <sip:bob@client.biloxi.example.com>   Proxy-Authorization: Digest username="alice",    realm="biloxi.example.com",    nonce="c1e22c41ae6cbe5ae983a9c8e88d359", opaque="",    uri="sip:bob@biloxi.example.com", response="f44ab22f150c6a56071bce8"   Content-Length: 0   F21 ACK Proxy 2 -> Bob   ACK sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK31972.1   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK230f2.1    ;received=192.0.2.111   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b44    ;received=192.0.2.101   Max-Forwards: 68   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=9103874   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 3 ACK   Contact: <sip:bob@client.biloxi.example.com>   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 36]

RFC 3665              SIP Basic Call Flow Examples         December 20033.4.  Successful Session with Proxy Failure    Alice           Proxy 1          Proxy 2            Bob      |                |                |                |      |   INVITE F1    |                |                |      |--------------->|                |                |      |   INVITE F2    |                |                |      |--------------->|                |                |      |   INVITE F3    |                |                |      |--------------->|                |                |      |   INVITE F4    |                |                |      |--------------->|                |                |      |   INVITE F5    |                |                |      |--------------->|                |                |      |   INVITE F6    |                |                |      |--------------->|                |                |      |   INVITE F7    |                |                |      |--------------->|                |                |      |     INVITE F8                   |                |      |-------------------------------->|                |      |            407 F9               |                |      |<--------------------------------|                |      |             ACK F10             |                |      |-------------------------------->|                |      |           INVITE F11            |                |      |-------------------------------->|   INVITE F12   |      |             100  F13            |--------------->|      |<--------------------------------|                |      |                                 |     180 F14    |      |             180 F15             |<---------------|      |<--------------------------------|                |      |                                 |     200 F16    |      |             200 F17             |<---------------|      |<--------------------------------|                |      |             ACK F18             |                |      |-------------------------------->|     ACK F19    |      |                                 |--------------->|      |                Both Way RTP Media                |      |<================================================>|      |                                 |     BYE F20    |      |             BYE F21             |<---------------|      |<--------------------------------|                |      |             200 F22             |                |      |-------------------------------->|     200 F23    |      |                                 |--------------->|      |                                 |                |Johnston, et al.         Best Current Practice                 [Page 37]

RFC 3665              SIP Basic Call Flow Examples         December 2003   In this scenario, Alice completes a call to Bob via a Proxy Server.   Alice is configured for a primary SIP Proxy Server Proxy 1 and a   secondary SIP Proxy Server Proxy 2 (Or is able to use DNS SRV records   to locate Proxy 1 and Proxy 2).  Alice has valid credentials for both   domains.  Proxy 1 is out of service and does not respond to INVITEs   (it is reachable, but unresponsive).  Alice then completes the call   to Bob using Proxy 2.   Message Details   F1 INVITE Alice -> Proxy 1   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK465b6d   Max-Forwards: 70   Route: <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F2 INVITE Alice -> Proxy 1   Same as Message F1   F3 INVITE Alice -> Proxy 1   Same as Message F1   F4 INVITE Alice -> Proxy 1   Same as Message F1Johnston, et al.         Best Current Practice                 [Page 38]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F5 INVITE Alice -> Proxy 1   Same as Message F1   F6 INVITE Alice -> Proxy 1   Same as Message F1   F7 INVITE Alice -> Proxy 1   Same as Message F1   /* Alice gives up on the unresponsive proxy */   F8 INVITE Alice -> Proxy 2   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b8a   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   /* Proxy 2 challenges Alice for authentication */   F9 407 Proxy Authorization Required Proxy 2 -> Alice   SIP/2.0 407 Proxy Authorization Required   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b8a    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=2421452Johnston, et al.         Best Current Practice                 [Page 39]

RFC 3665              SIP Basic Call Flow Examples         December 2003   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com   CSeq: 1 INVITE   Proxy-Authenticate: Digest realm="biloxi.example.com", qop="auth",    nonce="1ae6cbe5ea9c8e8df84fqnlec434a359",    opaque="", stale=FALSE, algorithm=MD5   Content-Length: 0   F10 ACK Alice -> Proxy 2   ACK sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b8a   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=2421452   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com   CSeq: 1 ACK   Content-Length: 0   /* Alice responds by re-sending the INVITE with authentication   credentials in it.  */   F11 INVITE Alice -> Proxy 2   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com   CSeq: 2 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Proxy-Authorization: Digest username="alice",    realm="biloxi.example.com",    nonce="1ae6cbe5ea9c8e8df84fqnlec434a359", opaque="",    uri="sip:bob@biloxi.example.com",    response="8a880c919d1a52f20a1593e228adf599"   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000Johnston, et al.         Best Current Practice                 [Page 40]

RFC 3665              SIP Basic Call Flow Examples         December 2003   /* Proxy 2 accepts the credentials and forwards the INVITE to Bob.   Client for Alice prepares to receive data on port 49172 from the   network.   */   F12 INVITE Proxy 2 -> Bob   INVITE sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Max-Forwards: 69   Record-Route: <sip:ss2.biloxi.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com   CSeq: 2 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F13 100 Trying Proxy 2 -> Alice   SIP/2.0 100 Trying   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com   CSeq: 2 INVITE   Content-Length: 0   F14 180 Ringing Bob -> Proxy 2   SIP/2.0 180 Ringing   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1    ;received=192.0.2.222Johnston, et al.         Best Current Practice                 [Page 41]

RFC 3665              SIP Basic Call Flow Examples         December 2003   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss2.biloxi.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com   CSeq: 2 INVITE   Contact: <sip:bob@client.biloxi.example.com>   Content-Length: 0   F15 180 Ringing Proxy 2 -> Alice   SIP/2.0 180 Ringing   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss2.biloxi.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com   CSeq: 2 INVITE   Contact: <sip:bob@client.biloxi.example.com>   Content-Length: 0   F16 200 OK Bob -> Proxy 2   SIP/2.0 200 OK   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1    ;received=192.0.2.222   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss2.biloxi.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com   CSeq: 2 INVITE   Contact: <sip:bob@client.biloxi.example.com>   Content-Type: application/sdp   Content-Length: 147   v=0   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com   s=-   c=IN IP4 192.0.2.201   t=0 0   m=audio 3456 RTP/AVP 0   a=rtpmap:0 PCMU/8000Johnston, et al.         Best Current Practice                 [Page 42]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F17 200 OK Proxy 2 -> Alice   SIP/2.0 200 OK   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss2.biloxi.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com   CSeq: 2 INVITE   Contact: <sip:bob@client.biloxi.example.com>   Content-Type: application/sdp   Content-Length: 147   v=0   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com   s=-   c=IN IP4 192.0.2.201   t=0 0   m=audio 3456 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F18 ACK Alice -> Proxy 2   ACK sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b8g   Max-Forwards: 70   Route: <sip:ss2.biloxi.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com   CSeq: 2 ACK   Content-Length: 0   F19 ACK Proxy 2 -> Bob   ACK sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b8g    ;received=192.0.2.101   Max-Forwards: 69   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.comJohnston, et al.         Best Current Practice                 [Page 43]

RFC 3665              SIP Basic Call Flow Examples         December 2003   CSeq: 2 ACK   Content-Length: 0   /* RTP streams are established between Alice and Bob */   /* Bob Hangs Up with Alice. */   F20 BYE Bob -> Proxy 2   BYE sip:alice@client.atlanta.example.com SIP/2.0   Via: SIP/2.0/UDP client.biloxi.example.com:5060;branch=z9hG4bKnashds7   Max-Forwards: 70   Route: <sip:ss2.biloxi.example.com;lr>   From: Bob <sip:bob@biloxi.example.com>;tag=314159   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com   CSeq: 1 BYE   Content-Length: 0   F21 BYE Proxy 2 -> Alice   BYE sip:alice@client.atlanta.example.com SIP/2.0   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1   Via: SIP/2.0/UDP client.biloxi.example.com:5060;branch=z9hG4bKnashds7    ;received=192.0.2.201   Max-Forwards: 69   From: Bob <sip:bob@biloxi.example.com>;tag=314159   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com   CSeq: 1 BYE   Content-Length: 0   F22 200 OK Alice -> Proxy 2   SIP/2.0 200 OK   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1    ;received=192.0.2.222   Via: SIP/2.0/UDP client.biloxi.example.com:5060;branch=z9hG4bKnashds7    ;received=192.0.2.201   From: Bob <sip:bob@biloxi.example.com>;tag=314159   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com   CSeq: 1 BYE   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 44]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F23 200 OK Proxy 2 -> Bob   SIP/2.0 200 OK   Via: SIP/2.0/UDP client.biloxi.example.com:5060;branch=z9hG4bKnashds7    ;received=192.0.2.201   From: Bob <sip:bob@biloxi.example.com>;tag=314159   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   Call-ID: 4Fde34wkd11wsGFDs3@atlanta.example.com   CSeq: 1 BYE   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 45]

RFC 3665              SIP Basic Call Flow Examples         December 20033.5.  Session Through a SIP ALG   Alice             ALG           Proxy 2            Bob     |                |                |                |     |   INVITE F1    |                |                |     |--------------->|   INVITE F2    |                |     |     100 F3     |--------------->|   INVITE F4    |     |<---------------|     100 F5     |--------------->|     |                |<---------------|      180 F6    |     |                |     180 F7     |<---------------|     |     180 F8     |<---------------|                |     |<---------------|                |      200 F9    |     |                |    200 F10     |<---------------|     |     200 F11    |<---------------|                |     |<---------------|                                 |     |     ACK F12    |                                 |     |--------------->|             ACK F13             |     |                |-------------------------------->|     |    RTP Media   |        Both Way RTP Media       |     |<==============>|<===============================>|     |     BYE F14    |                                 |     |--------------->|             BYE F15             |     |                |-------------------------------->|     |                |             200 F16             |     |     200 F17    |<--------------------------------|     |<---------------|                                 |     |                |                                 |   Alice completes a call to Bob through a ALG (Application Layer   Gateway) and a SIP Proxy.  The routing through the ALG is   accomplished using a pre-loaded Route header in the INVITE F1.  Note   that the media stream setup is not end-to-end - the ALG terminates   both media streams and bridges them.  This is done by the ALG   modifying the SDP in the INVITE (F1) and 200 OK (F10) messages, and   possibly any 18x or ACK messages containing SDP.   In addition to firewall traversal, this Back-to-Back User Agent   (B2BUA) could be used as part of an anonymizer service (in which all   identifying information on Alice would be removed), or to perform   codec media conversion, such as mu-law to A-law conversion of PCM on   an international call.   Also note that Proxy 2 does not Record-Route in this call flow.Johnston, et al.         Best Current Practice                 [Page 46]

RFC 3665              SIP Basic Call Flow Examples         December 2003   Message Details   F1 INVITE Alice -> SIP ALG   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Route: <sip:alg1.atlanta.example.com;lr>   Proxy-Authorization: Digest username="alice",    realm="biloxi.example.com",    nonce="85b4f1cen4341ae6cbe5a3a9c8e88df9", opaque="",    uri="sip:bob@biloxi.example.com",    response="b3f392f9218a328b9294076d708e6815"   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   /* Client for Alice prepares to receive data on port 49172 from the   network. */   F2 INVITE SIP ALG -> Proxy 2   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Max-Forwards: 69   Record-Route: <sip:alg1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Proxy-Authorization: Digest username="alice",    realm="biloxi.example.com",Johnston, et al.         Best Current Practice                 [Page 47]

RFC 3665              SIP Basic Call Flow Examples         December 2003    nonce="85b4f1cen4341ae6cbe5a3a9c8e88df9", opaque="",    uri="sip:bob@biloxi.example.com",    response="b3f392f9218a328b9294076d708e6815"   Content-Type: application/sdp   Content-Length: 150   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.128   t=0 0   m=audio 2000 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F3 100 Trying SIP ALG -> Alice   SIP/2.0 100 Trying   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Content-Length: 0   /* SIP ALG prepares to proxy data from port 192.0.2.128/2000 to   192.0.2.101/49172.   Proxy 2 uses a Location Service function to   determine where Bob is located. Based upon location analysis the call   is forwarded to Bob */   F4 INVITE Proxy 2 -> Bob   INVITE sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK2d4790.1   Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1    ;received=192.0.2.128   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Max-Forwards: 68   Record-Route: <sip:alg1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Content-Type: application/sdpJohnston, et al.         Best Current Practice                 [Page 48]

RFC 3665              SIP Basic Call Flow Examples         December 2003   Content-Length: 150   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.128   t=0 0   m=audio 2000 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F5 100 Trying Proxy 2 -> SIP ALG   SIP/2.0 100 Trying   Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1    ;received=192.0.2.128   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Content-Length: 0   F6 180 Ringing Bob -> Proxy 2   SIP/2.0 180 Ringing   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.222   Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1    ;received=192.0.2.128   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:alg1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:bob@client.biloxi.example.com>   Content-Length: 0   F7 180 Ringing Proxy 2 -> SIP ALG   SIP/2.0 180 Ringing   Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1    ;received=192.0.2.128Johnston, et al.         Best Current Practice                 [Page 49]

RFC 3665              SIP Basic Call Flow Examples         December 2003   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:alg1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:bob@client.biloxi.example.com>   Content-Length: 0   F8 180 Ringing SIP ALG -> Alice   SIP/2.0 180 Ringing   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:alg1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:bob@client.biloxi.example.com>   Content-Length: 0   F9 200 OK Bob -> Proxy 2   SIP/2.0 200 OK   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.222   Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1    ;received=192.0.2.128   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:alg1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:bob@client.biloxi.example.com>   Content-Type: application/sdp   Content-Length: 147   v=0   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com   s=-   c=IN IP4 192.0.2.201   t=0 0Johnston, et al.         Best Current Practice                 [Page 50]

RFC 3665              SIP Basic Call Flow Examples         December 2003   m=audio 3456 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F10 200 OK Proxy 2 -> SIP ALG   SIP/2.0 200 OK   Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1    ;received=192.0.2.128   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:alg1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:bob@client.biloxi.example.com>   Content-Type: application/sdp   Content-Length: 147   v=0   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com   s=-   c=IN IP4 192.0.2.201   t=0 0   m=audio 3456 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F11 200 OK SIP ALG -> Alice   SIP/2.0 200 OK   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:alg1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:bob@client.biloxi.example.com>   Content-Type: application/sdp   Content-Length: 147   v=0   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com   s=-   c=IN IP4 192.0.2.128   t=0 0Johnston, et al.         Best Current Practice                 [Page 51]

RFC 3665              SIP Basic Call Flow Examples         December 2003   m=audio 1734 RTP/AVP 0   a=rtpmap:0 PCMU/8000   /* The ALG prepares to proxy packets from 192.0.2.128/      1734 to 192.0.2.201/3456 */   F12 ACK Alice -> SIP ALG   ACK sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bhh   Max-Forwards: 70   Route: <sip:alg1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 ACK   Content-Length: 0   F13 ACK SIP ALG -> Bob   ACK sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bhh    ;received=192.0.2.101   Max-Forwards: 69   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 ACK   Content-Length: 0   /* RTP streams are established between Alice and the ALG and   between the ALG and B*/   /* Alice Hangs Up with Bob. */   F14 BYE Alice -> SIP ALG   BYE sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74be5   Max-Forwards: 70   Route: <sip:alg1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.comJohnston, et al.         Best Current Practice                 [Page 52]

RFC 3665              SIP Basic Call Flow Examples         December 2003   CSeq: 2 BYE   Content-Length: 0   F15 BYE SIP ALG -> Bob   BYE sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74be5    ;received=192.0.2.101   Max-Forwards: 69   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 2 BYE   Content-Length: 0   F16 200 OK Bob -> SIP ALG   SIP/2.0 200 OK   Via: SIP/2.0/UDP alg1.atlanta.example.com:5060;branch=z9hG4bK739578.1    ;received=192.0.2.128   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74be5    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 2 BYE   Content-Length: 0   F17 200 OK SIP ALG -> Alice   SIP/2.0 200 OK   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74be5    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 2 BYE   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 53]

RFC 3665              SIP Basic Call Flow Examples         December 20033.6.  Session via Redirect and Proxy Servers with SDP in ACK   Alice        Redirect Server     Proxy 3             Bob     |                |                |                |     |   INVITE F1    |                |                |     |--------------->|                |                |     |     302 F2     |                |                |     |<---------------|                |                |     |     ACK F3     |                |                |     |--------------->|                |                |     |     INVITE F4                   |                |     |-------------------------------->|    INVITE F5   |     |             100  F6             |--------------->|     |<--------------------------------|      180 F7    |     |             180 F8              |<---------------|     |<--------------------------------|                |     |                                 |     200 F9     |     |             200 F10             |<---------------|     |<--------------------------------|                |     |             ACK F11             |                |     |-------------------------------->|     ACK F12    |     |                                 |--------------->|     |                Both Way RTP Media                |     |<================================================>|     |                                 |     BYE F13    |     |             BYE F14             |<---------------|     |<--------------------------------|                |     |             200 F15             |                |     |-------------------------------->|     200 F16    |     |                                 |--------------->|     |                                 |                |   In this scenario, Alice places a call to Bob using first a Redirect   server then a Proxy Server.  The INVITE message is first sent to the   Redirect Server.  The Server returns a 302 Moved Temporarily response   (F2) containing a Contact header with Bob's current SIP address.   Alice then generates a new INVITE and sends to Bob via the Proxy   Server and the call proceeds normally.  In this example, no SDP is   present in the INVITE, so the SDP is carried in the ACK message.   The call is terminated when Bob sends a BYE message.Johnston, et al.         Best Current Practice                 [Page 54]

RFC 3665              SIP Basic Call Flow Examples         December 2003   Message Details   F1 INVITE Alice -> Redirect Server   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bKbf9f44   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Content-Length: 0   F2 302 Moved Temporarily Redirect Proxy -> Alice   SIP/2.0 302 Moved Temporarily   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bKbf9f44    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=53fHlqlQ2   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:bob@chicago.example.com;transport=tcp>   Content-Length: 0   F3 ACK Alice -> Redirect Server   ACK sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bKbf9f44   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=53fHlqlQ2   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 ACK   Content-Length: 0   F4 INVITE Alice -> Proxy 3   INVITE sip:bob@chicago.example.com SIP/2.0   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.comJohnston, et al.         Best Current Practice                 [Page 55]

RFC 3665              SIP Basic Call Flow Examples         December 2003   CSeq: 2 INVITE   Contact: <sip:alice@client.atlanta.example.com;transport=tcp>   Content-Length: 0   F5 INVITE Proxy 3 -> Bob   INVITE sip:bob@client.chicago.example.com SIP/2.0   Via: SIP/2.0/TCP ss3.chicago.example.com:5060;branch=z9hG4bK721e.1   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Max-Forwards: 69   Record-Route: <sip:ss3.chicago.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 2 INVITE   Contact: <sip:alice@client.atlanta.example.com;transport=tcp>   Content-Length: 0   F6 100 Trying Proxy 3 -> Alice   SIP/2.0 100 Trying   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 2 INVITE   Content-Length: 0   F7 180 Ringing Bob -> Proxy 3   SIP/2.0 180 Ringing   Via: SIP/2.0/TCP ss3.chicago.example.com:5060;branch=z9hG4bK721e.1    ;received=192.0.2.233   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss3.chicago.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 2 INVITE   Contact: <sip:bob@client.chicago.example.com;transport=tcp>   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 56]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F8 180 Ringing Proxy 3 -> Alice   SIP/2.0 180 Ringing   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss3.chicago.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 2 INVITE   Contact: <sip:bob@client.chicago.example.com;transport=tcp>   Content-Length: 0   F9 200 OK Bob -> Proxy 3   SIP/2.0 200 OK   Via: SIP/2.0/TCP ss3.chicago.example.com:5060;branch=z9hG4bK721e.1    ;received=192.0.2.233   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss3.chicago.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 2 INVITE   Contact: <sip:bob@client.chicago.example.com;transport=tcp>   Content-Type: application/sdp   Content-Length: 148   v=0   o=bob 2890844527 2890844527 IN IP4 client.chicago.example.com   s=-   c=IN IP4 192.0.2.100   t=0 0   m=audio 3456 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F10 200 OK Proxy -> Alice   SIP/2.0 200 OK   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss3.chicago.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159Johnston, et al.         Best Current Practice                 [Page 57]

RFC 3665              SIP Basic Call Flow Examples         December 2003   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 2 INVITE   Contact: <sip:bob@client.chicago.example.com;transport=tcp>   Content-Type: application/sdp   Content-Length: 148   v=0   o=bob 2890844527 2890844527 IN IP4 client.chicago.example.com   s=-   c=IN IP4 192.0.2.100   t=0 0   m=audio 3456 RTP/AVP 0   a=rtpmap:0 PCMU/8000   /* ACK contains SDP of Alice since none present in INVITE */   F11 ACK Alice -> Proxy 3   ACK sip:bob@client.chicago.example.com SIP/2.0   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bq9   Max-Forwards: 70   Route: <sip:ss3.chicago.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 2 ACK   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F12 ACK Proxy 3 -> Bob   ACK sip:bob@client.chicago.example.com SIP/2.0   Via: SIP/2.0/TCP ss3.chicago.example.com:5060;branch=z9hG4bK721e.1   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bq9    ;received=192.0.2.101   Max-Forwards: 69   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159Johnston, et al.         Best Current Practice                 [Page 58]

RFC 3665              SIP Basic Call Flow Examples         December 2003   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 2 ACK   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   /* RTP streams are established between Alice and Bob */   /* Bob Hangs Up with Alice. */   F13 BYE Bob -> Proxy 3   BYE sip:alice@client.atlanta.example.com SIP/2.0   Via: SIP/2.0/TCP client.chicago.example.com:5060;branch=z9hG4bKfgaw2   Max-Forwards: 70   Route: <sip:ss3.chicago.example.com;lr>   From: Bob <sip:bob@biloxi.example.com>;tag=314159   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 BYE   Content-Length: 0   F14 BYE Proxy 3 -> Alice   BYE sip:alice@client.atlanta.example.com SIP/2.0   Via: SIP/2.0/TCP ss3.chicago.example.com:5060;branch=z9hG4bK721e.1    ;received=192.0.2.100   Via: SIP/2.0/TCP client.chicago.example.com:5060;branch=z9hG4bKfgaw2   Max-Forwards: 69   From: Bob <sip:bob@biloxi.example.com>;tag=314159   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 BYE   Content-Length: 0   F15 200 OK Alice -> Proxy 3   SIP/2.0 200 OKJohnston, et al.         Best Current Practice                 [Page 59]

RFC 3665              SIP Basic Call Flow Examples         December 2003   Via: SIP/2.0/TCP ss3.chicago.example.com:5060;branch=z9hG4bK721e.1    ;received=192.0.2.233   Via: SIP/2.0/TCP client.chicago.example.com:5060;branch=z9hG4bKfgaw2    ;received=192.0.2.100   From: Bob <sip:bob@biloxi.example.com>;tag=314159   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 BYE   Content-Length: 0   F16 200 OK Proxy 3 -> Bob   SIP/2.0 200 OK   Via: SIP/2.0/TCP client.chicago.example.com:5060;branch=z9hG4bKfgaw2    ;received=192.0.2.100   From: Bob <sip:bob@biloxi.example.com>;tag=314159   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 BYE   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 60]

RFC 3665              SIP Basic Call Flow Examples         December 20033.7.  Session with re-INVITE (IP Address Change)     Alice                Proxy 2                Bob        |   F1 INVITE        |                    |        |------------------->|      F2 INVITE     |        |   F3 100 Trying    |------------------->|        |<-------------------|   F4 180 Ringing   |        |   F5 180 Ringing   |<-------------------|        |<-------------------|                    |        |                    |    F6 200 OK       |        |    F7 200 OK       |<-------------------|        |<-------------------|                    |        |                 F8  ACK                 |        |---------------------------------------->|        |      Both Way RTP Media Established     |        |<=======================================>|        |                                         |        |           Bob changes IP address        |        |                                         |        |                 F9 INVITE               |        |<----------------------------------------|        |                F10 200 OK               |        |---------------------------------------->|        |                 F11  ACK                |        |<----------------------------------------|        |         New RTP Media Stream            |        |<=======================================>|        |                 F12 BYE                 |        |---------------------------------------->|        |               F13 200 OK                |        |<----------------------------------------|        |                                         |   This example shows a session in which the media changes midway   through the session.  When Bob's IP address changes during the   session, Bob sends a re-INVITE containing a new Contact and SDP   (version number incremented) information to A.  In this flow, the   proxy does not Record-Route so is not in the SIP messaging path after   the initial exchange.Johnston, et al.         Best Current Practice                 [Page 61]

RFC 3665              SIP Basic Call Flow Examples         December 2003   Message Details   F1 INVITE Alice -> Proxy 2   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F2 INVITE Proxy 2 -> Bob   INVITE sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK2d4790.1   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Max-Forwards: 69   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000Johnston, et al.         Best Current Practice                 [Page 62]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F3 100 Trying Proxy 2 -> Alice   SIP/2.0 100 Trying   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Content-Length: 0   F4 180 Ringing Bob -> Proxy 2   SIP/2.0 180 Ringing   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.222   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:bob@client.biloxi.example.com>   Content-Length: 0   F5 180 Ringing Proxy 2 -> Alice   SIP/2.0 180 Ringing   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:bob@client.biloxi.example.com>   Content-Length: 0   F6 200 OK Bob -> Proxy 2   SIP/2.0 200 OK   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.222   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76slJohnston, et al.         Best Current Practice                 [Page 63]

RFC 3665              SIP Basic Call Flow Examples         December 2003   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:bob@client.biloxi.example.com>   Content-Type: application/sdp   Content-Length: 147   v=0   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com   s=-   c=IN IP4 192.0.2.201   t=0 0   m=audio 3456 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F7 200 OK Proxy 2 -> Alice   SIP/2.0 200 OK   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:bob@client.biloxi.example.com>   Content-Type: application/sdp   Content-Length: 147   v=0   o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com   s=-   c=IN IP4 192.0.2.201   t=0 0   m=audio 3456 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F8 ACK Alice -> Bob   ACK sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74b7b   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 ACK   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 64]

RFC 3665              SIP Basic Call Flow Examples         December 2003   /* RTP streams are established between Alice and Bob */   /* Bob changes IP address and re-INVITEs Alice with new Contact and   SDP */   F9 INVITE Bob -> Alice   INVITE sip:alice@client.atlanta.example.com SIP/2.0   Via: SIP/2.0/UDP client.chicago.example.com:5060;branch=z9hG4bKlkld5l   Max-Forwards: 70   From: Bob <sip:bob@biloxi.example.com>;tag=314159   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 14 INVITE   Contact: <sip:bob@client.chicago.example.com>   Content-Type: application/sdp   Content-Length: 149   v=0   o=bob 2890844527 2890844528 IN IP4 client.chicago.example.com   s=-   c=IN IP4 192.0.2.100   t=0 0   m=audio 47172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F10 200 OK Alice -> Bob   SIP/2.0 200 OK   Via: SIP/2.0/UDP client.chicago.example.com:5060;branch=z9hG4bKlkld5l    ;received=192.0.2.100   Max-Forwards: 70   From: Bob <sip:bob@biloxi.example.com>;tag=314159   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 14 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Content-Type: application/sdp   Content-Length: 150   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0Johnston, et al.         Best Current Practice                 [Page 65]

RFC 3665              SIP Basic Call Flow Examples         December 2003   m=audio 1000 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F11 ACK Bob -> Alice   ACK sip:alice@client.atlanta.example.com SIP/2.0   Via: SIP/2.0/UDP client.chicago.example.com:5060;branch=z9hG4bKlkldcc   Max-Forwards: 70   From: Bob <sip:bob@biloxi.example.com>;tag=314159   To: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 14 ACK   Content-Length: 0   /* New RTP stream established between Alice and Bob */   /* Alice hangs up with Bob */   F12 BYE Alice -> Bob   BYE sip:bob@client.chicago.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bo4   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 2 BYE   Content-Length: 0   F13 200 OK Bob -> Alice   SIP/2.0 200 OK   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bo4    ;received=192.0.2.101   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 2 BYE   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 66]

RFC 3665              SIP Basic Call Flow Examples         December 20033.8.  Unsuccessful No Answer   Alice           Proxy 1          Proxy 2            Bob     |                |                |                |     |   INVITE F1    |                |                |     |--------------->|   INVITE F2    |                |     |     100  F3    |--------------->|   INVITE F4    |     |<---------------|     100  F5    |--------------->|     |                |<---------------|                |     |                |                |      180 F6    |     |                |     180 F7     |<---------------|     |     180 F8     |<---------------|                |     |<---------------|                |                |     |   CANCEL F9    |                |                |     |--------------->|                |                |     |     200 F10    |                |                |     |<---------------|   CANCEL F11   |                |     |                |--------------->|                |     |                |     200 F12    |                |     |                |<---------------|                |     |                |                |   CANCEL F13   |     |                |                |--------------->|     |                |                |     200 F14    |     |                |                |<---------------|     |                |                |     487 F15    |     |                |                |<---------------|     |                |                |     ACK F16    |     |                |     487 F17    |--------------->|     |                |<---------------|                |     |                |     ACK F18    |                |     |     487 F19    |--------------->|                |     |<---------------|                |                |     |     ACK F20    |                |                |     |--------------->|                |                |     |                |                |                |   In this scenario, Alice gives up on the call before Bob answers   (sends a 200 OK response).  Alice sends a CANCEL (F9) since no final   response had been received from Bob.  If a 200 OK to the INVITE had   crossed with the CANCEL, Alice would have sent an ACK then a BYE to   Bob in order to properly terminate the call.   Note that the CANCEL message is acknowledged with a 200 OK on a hop   by hop basis, rather than end to end.Johnston, et al.         Best Current Practice                 [Page 67]

RFC 3665              SIP Basic Call Flow Examples         December 2003   Message Details   F1 INVITE Alice -> Proxy 1   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9   Max-Forwards: 70   Route: <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Proxy-Authorization: Digest username="alice",    realm="atlanta.example.com",    nonce="ze7k1ee88df84f1cec431ae6cbe5a359", opaque="",    uri="sip:bob@biloxi.example.com",    response="b00b416324679d7e243f55708d44be7b"   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   /*Client for Alice prepares to receive data on port 49172 from the   network.*/   F2 INVITE Proxy 1 -> Proxy 2   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Max-Forwards: 69   Record-Route: <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Content-Type: application/sdp   Content-Length: 151Johnston, et al.         Best Current Practice                 [Page 68]

RFC 3665              SIP Basic Call Flow Examples         December 2003   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F3 100 Trying Proxy 1 -> Alice   SIP/2.0 100 Trying   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Content-Length: 0   F4 INVITE Proxy 2 -> Bob   INVITE sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss2.biloxi.example.com;lr>,    <sip:ss1.atlanta.example.com;lr>   Max-Forwards: 68   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000Johnston, et al.         Best Current Practice                 [Page 69]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F5 100 Trying Proxy 2 -> Proxy 1   SIP/2.0 100 Trying   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Content-Length: 0   F6 180 Ringing Bob -> Proxy 2   SIP/2.0 180 Ringing   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1    ;received=192.0.2.222   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss2.biloxi.example.com;lr>,    <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:bob@client.biloxi.example.com>   Content-Length: 0   F7 180 Ringing Proxy 2 -> Proxy 1   SIP/2.0 180 Ringing   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss2.biloxi.example.com;lr>,    <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITEJohnston, et al.         Best Current Practice                 [Page 70]

RFC 3665              SIP Basic Call Flow Examples         December 2003   Contact: <sip:bob@client.biloxi.example.com>   Content-Length: 0   F8 180 Ringing Proxy 1 -> Alice   SIP/2.0 180 Ringing   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss2.biloxi.example.com;lr>,    <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:bob@client.biloxi.example.com>   Content-Length: 0   F9 CANCEL Alice -> Proxy 1   CANCEL sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Route: <sip:ss1.atlanta.example.com;lr>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 CANCEL   Content-Length: 0   F10 200 OK Proxy 1 -> Alice   SIP/2.0 200 OK   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 CANCEL   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 71]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F11 CANCEL Proxy 1 -> Proxy 2   CANCEL sip:alice@atlanta.example.com SIP/2.0   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 CANCEL   Content-Length: 0   F12 200 OK Proxy 2 -> Proxy 1   SIP/2.0 200 OK   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 CANCEL   Content-Length: 0   F13 CANCEL Proxy 2 -> Bob   CANCEL sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 CANCEL   Content-Length: 0   F14 200 OK Bob -> Proxy 2   SIP/2.0 200 OK   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1    ;received=192.0.2.222   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 CANCEL   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 72]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F15 487 Request Terminated Bob -> Proxy 2   SIP/2.0 487 Request Terminated   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1    ;received=192.0.2.222   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Content-Length: 0   F16 ACK Proxy 2 -> Bob   ACK sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 ACK   Content-Length: 0   F17 487 Request Terminated Proxy 2 -> Proxy 1   SIP/2.0 487 Request Terminated   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 73]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F18 ACK Proxy 1 -> Proxy 2   ACK sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 ACK   Content-Length: 0   F19 487 Request Terminated Proxy 1 -> Alice   SIP/2.0 487 Request Terminated   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   F20 ACK Alice -> Proxy 1   ACK sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   Proxy-Authorization: Digest username="alice",    realm="atlanta.example.com",    nonce="ze7k1ee88df84f1cec431ae6cbe5a359", opaque="",    uri="sip:bob@biloxi.example.com",    response="b00b416324679d7e243f55708d44be7b"   CSeq: 1 ACK   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 74]

RFC 3665              SIP Basic Call Flow Examples         December 20033.9.  Unsuccessful Busy   Alice           Proxy 1          Proxy 2            Bob     |                |                |                |     |   INVITE F1    |                |                |     |--------------->|   INVITE F2    |                |     |     100  F3    |--------------->|   INVITE F4    |     |<---------------|     100  F5    |--------------->|     |                |<---------------|                |     |                |                |      486 F6    |     |                |                |<---------------|     |                |                |     ACK F7     |     |                |      486 F8    |--------------->|     |                |<---------------|                |     |                |      ACK F9    |                |     |     486 F10    |--------------->|                |     |<---------------|                |                |     |     ACK F11    |                |                |     |--------------->|                |                |     |                |                |                |   In this scenario, Bob is busy and sends a 486 Busy Here response to   Alice's INVITE.  Note that the non-2xx response is acknowledged on a   hop-by-hop basis instead of end-to-end.  Also note that many SIP UAs   will not return a 486 response, as they have multiple line and other   features.   Message Details   F1 INVITE Alice -> Proxy 1   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9   Max-Forwards: 70   Route: <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:alice@client.atlanta.example.com;transport=tcp>   Proxy-Authorization: Digest username="alice",    realm="atlanta.example.com",    nonce="dc3a5ab2530aa93112cf5904ba7d88fa", opaque="",    uri="sip:bob@biloxi.example.com",    response="702138b27d869ac8741e10ec643d55be"   Content-Type: application/sdp   Content-Length: 151Johnston, et al.         Best Current Practice                 [Page 75]

RFC 3665              SIP Basic Call Flow Examples         December 2003   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   /*Client for Alice prepares to receive data on port 49172 from the   network.*/   F2 INVITE Proxy 1 -> Proxy 2   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Max-Forwards: 69   Record-Route: <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:alice@client.atlanta.example.com;transport=tcp>   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F3 100 Trying Proxy 1 -> Alice   SIP/2.0 100 Trying   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 76]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F4 INVITE Proxy 2 -> Bob   INVITE sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Max-Forwards: 68   Record-Route: <sip:ss2.biloxi.example.com;lr>,    <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:alice@client.atlanta.example.com;transport=tcp>   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F5 100 Trying Proxy 2 -> Proxy 1   SIP/2.0 100 Trying   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Content-Length: 0   F6 486 Busy Here Bob -> Proxy 2   SIP/2.0  486 Busy Here   Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1    ;received=192.0.2.222   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1Johnston, et al.         Best Current Practice                 [Page 77]

RFC 3665              SIP Basic Call Flow Examples         December 2003    ;received=192.0.2.111   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Content-Length: 0   F7 ACK Proxy 2 -> Bob   ACK sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/TCP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 ACK   Content-Length: 0   F8 486 Busy Here Proxy 2 -> Proxy 1   SIP/2.0  486 Busy Here   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Content-Length: 0   F9 ACK Proxy 1 -> Proxy 2   ACK sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/TCP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 ACK   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 78]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F10 486 Busy Here Proxy 1 -> Alice   SIP/2.0  486 Busy Here   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Content-Length: 0   F11 ACK Alice -> Proxy 1   ACK sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/TCP client.atlanta.example.com:5060;branch=z9hG4bK74bf9   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 ACK   Proxy-Authorization: Digest username="alice",    realm="atlanta.example.com",    nonce="dc3a5ab2530aa93112cf5904ba7d88fa", opaque="",    uri="sip:bob@biloxi.example.com",    response="702138b27d869ac8741e10ec643d55be"   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 79]

RFC 3665              SIP Basic Call Flow Examples         December 20033.10.  Unsuccessful No Response from User Agent   Alice           Proxy 1          Proxy 2            Bob     |                |                |                |     |   INVITE F1    |                |                |     |--------------->|   INVITE F2    |                |     |     100  F3    |--------------->|   INVITE F4    |     |<---------------|     100  F5    |--------------->|     |                |<---------------|   INVITE F6    |     |                |                |--------------->|     |                |                |   INVITE F7    |     |                |                |--------------->|     |                |                |   INVITE F8    |     |                |                |--------------->|     |                |                |   INVITE F9    |     |                |                |--------------->|     |                |                |   INVITE F10   |     |                |                |--------------->|     |                |                |   INVITE F11   |     |                |     480 F12    |--------------->|     |                |<---------------|                |     |                |     ACK F13    |                |     |     480 F14    |--------------->|                |     |<---------------|                |                |     |     ACK F15    |                |                |     |--------------->|                |                |     |                |                |                |   In this example, there is no response from Bob to Alice's INVITE   messages being re-transmitted by Proxy 2.  After the sixth   re-transmission, Proxy 2 gives up and sends a 480 No Response to   Alice.   Message Details   F1 INVITE Alice -> Proxy 1   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9   Max-Forwards: 70   Route: <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Proxy-Authorization: Digest username="alice",    realm="atlanta.example.com",Johnston, et al.         Best Current Practice                 [Page 80]

RFC 3665              SIP Basic Call Flow Examples         December 2003    nonce="cf5904ba7d8dc3a5ab2530aa931128fa", opaque="",    uri="sip:bob@biloxi.example.com",    response="7afc04be7961f053c24f80e7dbaf888f"   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   /*Client for Alice prepares to receive data on port 49172 from the   network.*/   F2 INVITE Proxy 1 -> Proxy 2   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Max-Forwards: 69   Record-Route: <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F3 100 Trying Proxy 1 -> Alice   SIP/2.0 100 Trying   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101Johnston, et al.         Best Current Practice                 [Page 81]

RFC 3665              SIP Basic Call Flow Examples         December 2003   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Content-Length: 0   F4 INVITE Proxy 2 -> Bob   INVITE sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Max-Forwards: 68   Record-Route: <sip:ss2.biloxi.example.com;lr>,   <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F5 100 Trying Proxy 2 -> Proxy 1   SIP/2.0 100 Trying   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 82]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F6 INVITE Proxy 2 -> Bob   Resend of Message F4   F7 INVITE Proxy 2 -> Bob   Resend of Message F4   F8 INVITE Proxy 2 -> Bob   Resend of Message F4   F9 INVITE Proxy 2 -> Bob   Resend of Message F4   F10 INVITE Proxy 2 -> Bob   Resend of Message F4   F11 INVITE Proxy 2 -> Bob   Resend of Message F4   /* Proxy 2 gives up */   F12 480 No Response Proxy 2 -> Proxy 1   SIP/2.0 480 No Response   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 83]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F13 ACK Proxy 1 -> Proxy 2   ACK sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 ACK   Content-Length: 0   F14 480 No Response Proxy 1 -> Alice   SIP/2.0 480 No Response   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Content-Length: 0   F15 ACK Alice -> Proxy 1   ACK sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 ACK   Proxy-Authorization: Digest username="alice",    realm="atlanta.example.com",    nonce="cf5904ba7d8dc3a5ab2530aa931128fa", opaque="",    uri="sip:bob@biloxi.example.com",    response="7afc04be7961f053c24f80e7dbaf888f"   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 84]

RFC 3665              SIP Basic Call Flow Examples         December 20033.11.  Unsuccessful Temporarily Unavailable   Alice          Proxy 1          Proxy 2            Bob     |                |                |                |     |   INVITE F1    |                |                |     |--------------->|   INVITE F2    |                |     |     100  F3    |--------------->|   INVITE F4    |     |<---------------|     100  F5    |--------------->|     |                |<---------------|      180 F6    |     |                |     180 F7     |<---------------|     |     180 F8     |<---------------|                |     |<---------------|                |     480 F9     |     |                |                |<---------------|     |                |                |     ACK F10    |     |                |     480 F11    |--------------->|     |                |<---------------|                |     |                |     ACK F12    |                |     |     480 F13    |--------------->|                |     |<---------------|                |                |     |     ACK F14    |                |                |     |--------------->|                |                |     |                |                |                |   In this scenario, Bob initially sends a 180 Ringing response to   Alice, indicating that alerting is taking place.  However, then a   480 Unavailable is then sent to Alice.  This response is   acknowledged then proxied back to Alice.   Message Details   F1 INVITE Alice -> Proxy 1   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9   Max-Forwards: 70   Route: <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Proxy-Authorization: Digest username="alice",    realm="atlanta.example.com",    nonce="aa9311cf5904ba7d8dc3a5ab253028fa", opaque="",    uri="sip:bob@biloxi.example.com",    response="59a46a91bf1646562a4d486c84b399db"   Content-Type: application/sdpJohnston, et al.         Best Current Practice                 [Page 85]

RFC 3665              SIP Basic Call Flow Examples         December 2003   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   /*Client for Alice prepares to receive data on port 49172 from the   network.*/   F2 INVITE Proxy 1 -> Proxy 2   INVITE sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Max-Forwards: 69   Record-Route: <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F3 100 Trying Proxy 1 -> Alice   SIP/2.0 100 Trying   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITEJohnston, et al.         Best Current Practice                 [Page 86]

RFC 3665              SIP Basic Call Flow Examples         December 2003   Content-Length: 0   F4 INVITE Proxy 2 -> Bob   INVITE sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Max-Forwards: 68   Record-Route: <sip:ss2.biloxi.example.com;lr>,    <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:alice@client.atlanta.example.com>   Content-Type: application/sdp   Content-Length: 151   v=0   o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com   s=-   c=IN IP4 192.0.2.101   t=0 0   m=audio 49172 RTP/AVP 0   a=rtpmap:0 PCMU/8000   F5 100 Trying Proxy 2 -> Proxy 1   SIP/2.0 100 Trying   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 87]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F6 180 Ringing Bob -> Proxy 2   SIP/2.0 180 Ringing   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1    ;received=192.0.2.222   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss2.biloxi.example.com;lr>,    <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:bob@client.biloxi.example.com>   Content-Length: 0   F7 180 Ringing Proxy 2 -> Proxy 1   SIP/2.0 180 Ringing   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss2.biloxi.example.com;lr>,    <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:bob@client.biloxi.example.com>   Content-Length: 0   F8 180 Ringing Proxy 1 -> Alice   SIP/2.0 180 Ringing   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   Record-Route: <sip:ss2.biloxi.example.com;lr>,    <sip:ss1.atlanta.example.com;lr>   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Contact: <sip:bob@client.biloxi.example.com>Johnston, et al.         Best Current Practice                 [Page 88]

RFC 3665              SIP Basic Call Flow Examples         December 2003   Content-Length: 0   F9 480 Temporarily Unavailable Bob -> Proxy 2   SIP/2.0 480 Temporarily Unavailable   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1    ;received=192.0.2.222   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Content-Length: 0   F10 ACK Proxy 2 -> Bob   ACK sip:bob@client.biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP ss2.biloxi.example.com:5060;branch=z9hG4bK721e4.1   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 ACK   Content-Length: 0   F11 480 Temporarily Unavailable Proxy 2 -> Proxy 1   SIP/2.0 480 Temporarily Unavailable   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1    ;received=192.0.2.111   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 89]

RFC 3665              SIP Basic Call Flow Examples         December 2003   F12 ACK Proxy 1 -> Proxy 2   ACK sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP ss1.atlanta.example.com:5060;branch=z9hG4bK2d4790.1   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 ACK   Content-Length: 0   F13 480 Temporarily Unavailable Proxy 1 -> Alice   SIP/2.0 480 Temporarily Unavailable   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9    ;received=192.0.2.101   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   CSeq: 1 INVITE   Content-Length: 0   F14 ACK Alice -> Proxy 1   ACK sip:bob@biloxi.example.com SIP/2.0   Via: SIP/2.0/UDP client.atlanta.example.com:5060;branch=z9hG4bK74bf9   Max-Forwards: 70   From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl   To: Bob <sip:bob@biloxi.example.com>;tag=314159   Call-ID: 2xTb9vxSit55XU7p8@atlanta.example.com   Proxy-Authorization: Digest username="alice",    realm="atlanta.example.com",    nonce="aa9311cf5904ba7d8dc3a5ab253028fa", opaque="",    uri="sip:bob@biloxi.example.com",    response="59a46a91bf1646562a4d486c84b399db"   CSeq: 1 ACK   Content-Length: 0Johnston, et al.         Best Current Practice                 [Page 90]

RFC 3665              SIP Basic Call Flow Examples         December 20034.  Security Considerations   Since this document contains examples of SIP session establishment,   the security considerations inRFC 3261 [1] apply.RFC 3261   describes the basic threats including registration hijacking, server   impersonation, message body tampering, session modifying or teardown,   and denial of service and amplification attacks.  The use of HTTP   Digest as shown in this document provides one-way authentication and   protection against replay attacks.  TLS transport is used in   registration scenarios due to the lack of integrity protection in   HTTP Digest and the danger of registration hijacking without it, as   described inRFC 3261 [1].  A full discussion of the weaknesses of   HTTP Digest is provided inRFC 3261 [1].  The use of TLS and the   Secure SIP (sips) URI scheme provides a better level of security   including two-way authentication.  S/MIME can provide end-to-end   confidentiality and integrity protection of message bodies, as   described inRFC 3261.5.  References5.1.  Normative References   [1] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,       Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:       Session Initiation Protocol",RFC 3261, June 2002.   [2] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with       SDP",RFC 3264, April 2002.   [3] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., Leach,       P., Luotonen, A. and L. Stewart, "HTTP authentication: Basic and       Digest Access Authentication",RFC 2617, June 1999.   [4] Bradner, S., "Key words for use in RFCs to Indicate Requirement       Levels",BCP 14,RFC 2119, March 1997.5.2.  Informative References   [5] Johnston, A., Donovan, S., Sparks, R., Cunningham, C. and K.       Summers, "Session Initiation Protocol (SIP) Public Switched       Telephone Network (PSTN) Call Flows",BCP 76,RFC 3666, December       2003.6.  Intellectual Property Statement   The IETF takes no position regarding the validity or scope of any   intellectual property or other rights that might be claimed to   pertain to the implementation or use of the technology described inJohnston, et al.         Best Current Practice                 [Page 91]

RFC 3665              SIP Basic Call Flow Examples         December 2003   this document or the extent to which any license under such rights   might or might not be available; neither does it represent that it   has made any effort to identify any such rights.  Information on the   IETF's procedures with respect to rights in standards-track and   standards-related documentation can be found inBCP-11.  Copies of   claims of rights made available for publication and any assurances of   licenses to be made available, or the result of an attempt made to   obtain a general license or permission for the use of such   proprietary rights by implementors or users of this specification can   be obtained from the IETF Secretariat.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights which may cover technology that may be required to practice   this standard.  Please address the information to the IETF Executive   Director.7.  Acknowledgments   This document is has been a group effort by the SIP and SIPPING WGs.   The authors wish to thank everyone who has read, reviewed, commented,   or made suggestions to improve this document.   Thanks to Rohan Mahy, Adam Roach, Gonzalo Camarillo, Cullen Jennings,   and Tom Taylor for their detailed comments during the final review.   Thanks to Dean Willis for his early contributions to the development   of this document.   The authors wish to thank Kundan Singh for performing parser   validation of messages.   The authors wish to thank the following individuals for their   participation in the review of this call flows document: Aseem   Agarwal, Rafi Assadi, Ben Campbell, Sunitha Kumar, Jon Peterson, Marc   Petit-Huguenin, Vidhi Rastogi, and Bodgey Yin Shaohua.   The authors also wish to thank the following individuals for their   assistance: Jean-Francois Mule, Hemant Agrawal, Henry Sinnreich,   David Devanatham, Joe Pizzimenti, Matt Cannon, John Hearty, the whole   MCI WorldCom IPOP Design team, Scott Orton, Greg Osterhout, Pat   Sollee, Doug Weisenberg, Danny Mistry, Steve McKinnon, and Denise   Ingram, Denise Caballero, Tom Redman, Ilya Slain, Pat Sollee, John   Truetken, and others from MCI WorldCom, 3Com, Cisco, Lucent and   Nortel.Johnston, et al.         Best Current Practice                 [Page 92]

RFC 3665              SIP Basic Call Flow Examples         December 20038.  Authors' Addresses   All listed authors actively contributed large amounts of text to this   document.   Alan Johnston   MCI   100 South 4th Street   St. Louis, MO 63102   USA   EMail: alan.johnston@mci.com   Steve Donovan   dynamicsoft, Inc.   5100 Tennyson Parkway   Suite 1200   Plano, Texas 75024   USA   EMail: sdonovan@dynamicsoft.com   Robert Sparks   dynamicsoft, Inc.   5100 Tennyson Parkway   Suite 1200   Plano, Texas 75024   USA   EMail: rsparks@dynamicsoft.com   Chris Cunningham   dynamicsoft, Inc.   5100 Tennyson Parkway   Suite 1200   Plano, Texas 75024   USA   EMail: ccunningham@dynamicsoft.com   Kevin Summers   Sonus   1701 North Collins Blvd, Suite 3000   Richardson, TX 75080   USA   EMail: kevin.summers@sonusnet.comJohnston, et al.         Best Current Practice                 [Page 93]

RFC 3665              SIP Basic Call Flow Examples         December 20039.  Full Copyright Statement   Copyright (C) The Internet Society (2003).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assignees.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Johnston, et al.         Best Current Practice                 [Page 94]