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Internet Engineering Task Force (IETF)                       C. HolmbergRequest for Comments: 7549                                       J. HolmCategory: Standards Track                                       EricssonISSN: 2070-1721                                                R. Jesske                                                        Deutsche Telekom                                                                M. Dolly                                                                    AT&T                                                                May 2015           3GPP SIP URI Inter-Operator Traffic Leg ParameterAbstract   In 3GPP networks, the signaling path between a calling user and a   called user can be partitioned into segments, referred to as traffic   legs.  Each traffic leg may span networks belonging to different   operators and will have its own characteristics that can be different   from other traffic legs in the same call.  A traffic leg might be   associated with multiple SIP dialogs, e.g., in case a Back-to-Back   User Agent (B2BUA) that modifies the SIP dialog identifier is located   within the traffic leg.   This document defines a new SIP URI parameter, 'iotl' (an   abbreviation for Inter-Operator Traffic Leg).  The parameter can be   used in a SIP URI to indicate that the entity associated with the   address, or an entity responsible for the host part of the address,   represents the end of a specific traffic leg (or multiple traffic   legs).   The SIP URI 'iotl' parameter defined in this document has known uses   in 3GPP networks.  Usage in other networks is also possible.Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7549.Holmberg, et al.             Standards Track                    [Page 1]

RFC 7549                       3GPP 'iotl'                      May 2015Copyright Notice   Copyright (c) 2015 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Holmberg, et al.             Standards Track                    [Page 2]

RFC 7549                       3GPP 'iotl'                      May 2015Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .42.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .63.  Applicability . . . . . . . . . . . . . . . . . . . . . . . .64.  Traffic Leg Examples  . . . . . . . . . . . . . . . . . . . .64.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .64.2.  Originating Roaming Call  . . . . . . . . . . . . . . . .64.3.  Terminating Roaming Call  . . . . . . . . . . . . . . . .74.4.  Call from Originating Home to Terminating Home  . . . . .75.  'iotl' SIP URI Parameter  . . . . . . . . . . . . . . . . . .75.1.  Usage . . . . . . . . . . . . . . . . . . . . . . . . . .75.2.  Parameter Values  . . . . . . . . . . . . . . . . . . . .85.2.1.  General . . . . . . . . . . . . . . . . . . . . . . .85.2.2.  homea-homeb . . . . . . . . . . . . . . . . . . . . .85.2.3.  homeb-visitedb  . . . . . . . . . . . . . . . . . . .85.2.4.  visiteda-homea  . . . . . . . . . . . . . . . . . . .95.2.5.  homea-visiteda  . . . . . . . . . . . . . . . . . . .95.2.6.  visiteda-homeb  . . . . . . . . . . . . . . . . . . .96.  Syntax  . . . . . . . . . . . . . . . . . . . . . . . . . . .106.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .106.2.  ABNF  . . . . . . . . . . . . . . . . . . . . . . . . . .107.  Security Considerations . . . . . . . . . . . . . . . . . . .108.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .109.  References  . . . . . . . . . . . . . . . . . . . . . . . . .119.1.  Normative References  . . . . . . . . . . . . . . . . . .119.2.  Informative References  . . . . . . . . . . . . . . . . .11Appendix A.  3GPP Examples  . . . . . . . . . . . . . . . . . . .12A.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .12A.2.  The UE Registers via P-CSCF . . . . . . . . . . . . . . .12A.3.  Originating IMS Call  . . . . . . . . . . . . . . . . . .14A.4.  Terminating IMS Call  . . . . . . . . . . . . . . . . . .15     A.5.  Call between Originating Home and Terminating Home           Network . . . . . . . . . . . . . . . . . . . . . . . . .16   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .17   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .17Holmberg, et al.             Standards Track                    [Page 3]

RFC 7549                       3GPP 'iotl'                      May 20151.  Introduction   In a 3GPP network, an end-user device can be attached (e.g., using a   radio access network) to its own operator network (home network)   [TS.3GPP.24.229] or to another operator's network (visited network)   [TS.3GPP.24.229].  In the latter case, the user is referred to as a   roaming user.   3GPP operator networks are often not connected directly to each   other.  Instead, there might be intermediate networks, referred to as   3GPP transit networks, between them.  Such transit networks act on   the SIP level or the IP level.   In 3GPP networks, the signaling path between a calling user and a   called user can be partitioned into segments, referred to as traffic   legs.  Each traffic leg may span networks belonging to different   operators and will have its own characteristics that can be different   from other traffic legs in the same call.  A traffic leg might be   associated with multiple SIP dialogs, e.g., in case a B2BUA [RFC3261]   that modifies the SIP dialog identifier is located within the traffic   leg.   The traffic leg information can be used by intermediary entities to   make policy decisions related to, e.g., media anchoring, signaling   policy, insertion of media functions (e.g., transcoder), and   charging.   The figure below shows two users (Alice and Bob) and the different   type of networks that the signaling might traverse.  The signaling   path can be divided into multiple traffic legs, and the type of   traffic legs depends on how the signaling is routed.Holmberg, et al.             Standards Track                    [Page 4]

RFC 7549                       3GPP 'iotl'                      May 2015   Alice -- ORIG HNW +++++ TRANSIT NW +++++ TERM HNW -- Bob   Home           +     +                +    +   +    Home                  +     ++++++++++++++++++    +   +                  +                           +   +                  +                           +   +                  +     +++++++++++++++++++++++   +                  +     +              +          +   Alice -- ORIG VNW +++++ TRANSIT NW ++    TERM VNW -- Bob   Visited                                           Visited   ORIG HNW  =     Originating 3GPP Home Network   TERM HNW  =     Terminating 3GPP Home Network   ORIG VNW  =     Originating 3GPP Visited Network   TERM VNW  =     Terminating 3GPP Visited Network   TRANSIT NW =    3GPP Transit Network               Figure 1: 3GPP Operator Network Roaming Roles   In Figure 1, Alice is a user initiating communication with Bob. Also,   consider the following information:   Alice is attached to an originating network, which is either the home   network of Alice or a visited network (in case Alice is roaming).  In   both cases, any originating service is provided by the home network   of Alice.   Bob is attached to a terminating network, which is either the home   network of Bob or a visited network (in case Bob is roaming).  In   both cases, any terminating service is provided by the home network   of Bob.   A transit network providing transit functions (e.g., translation of   free phone numbers) may be included between the originating and   terminating networks and between visited and home networks.   This document defines a new SIP URI parameter [RFC3261], 'iotl' (an   abbreviation for Inter-Operator Traffic Leg).  The parameter can be   used in a SIP URI to indicate that the entity associated with the   address, or an entity responsible for the host part of the address,   represents the end of a specific traffic leg (or multiple traffic   legs).Holmberg, et al.             Standards Track                    [Page 5]

RFC 7549                       3GPP 'iotl'                      May 2015   This document defines the following 'iotl' parameter values:   o  homea-homeb   o  homeb-visitedb   o  visiteda-homea   o  homea-visiteda   o  visiteda-homeb   SIP entities that do not support the SIP URI 'iotl' parameter will   simply ignore it, if received, as defined in [RFC3261].2.  Conventions   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 in [RFC2119].3.  Applicability   The SIP URI 'iotl' parameter defined in this document has known uses   in 3GPP networks.  Usage in other networks is also possible.4.  Traffic Leg Examples4.1.  General   This section describes examples of different types of traffic legs in   3GPP networks.4.2.  Originating Roaming Call   In this case, Alice is located in a visited network.  When Alice   sends the initial SIP INVITE request for a call, one traffic leg   (referred to as the 'visiteda-homea' traffic leg) represents the   signaling path between the User Agent (UA) of Alice and the home   Serving Call Session Control Function (S-CSCF) [TS.3GPP.24.229] of   Alice.Holmberg, et al.             Standards Track                    [Page 6]

RFC 7549                       3GPP 'iotl'                      May 20154.3.  Terminating Roaming Call   In this case, Bob is located in a visited network.  When the home   S-CSCF of Bob forwards the initial SIP INVITE request for a call   towards Bob, one traffic leg (referred to as the 'homeb-visitedb'   traffic leg) represents the signaling path between the home S-CSCF of   Bob and the UA of Bob.4.4.  Call from Originating Home to Terminating Home   In this case, the home S-CSCF of Alice forwards the initial SIP   INVITE request towards the home S-CSCF of Bob. The signaling path   between the S-CSCFs represents one traffic leg (referred to as the   'homea-homeb' traffic leg).5.  'iotl' SIP URI Parameter5.1.  Usage   As specified in [RFC3261], when a SIP entity inserts a SIP URI in an   initial request for a dialog, or in a stand-alone request, the SIP   URI will be used to route the request to another SIP entity,   addressed by the SIP URI, or to a SIP entity responsible for the host   part of the SIP URI (e.g., a SIP registrar).  If such an entity   represents the end of one or more traffic legs, the SIP entity   inserting the SIP URI can add a SIP URI 'iotl' parameter to the SIP   URI to indicate the type(s) of traffic leg.  Each parameter value   indicates a type of traffic leg.   For routing of an initial SIP request for a dialog, or a stand-alone   SIP request, a SIP entity can add the 'iotl' parameter to (a) the SIP   URI of the Request-URI [RFC3261] or (b) the SIP URI of a Route header   field [RFC3261] of the SIP request.  SIP entities can add the 'iotl'   parameter to the SIP URI of a Path header field [RFC3327] or a   Service-Route header field [RFC3608] in order for the parameter to   later occur in a Route header field.   When a SIP entity receives an initial request for a dialog or a   stand-alone request, which contains one or more SIP URI 'iotl'   parameters, it identifies the type of traffic leg in the following   way:   o  if the SIP request contains a single Route header field containing      a SIP URI with an 'iotl' parameter, that parameter identifies the      type of traffic leg;Holmberg, et al.             Standards Track                    [Page 7]

RFC 7549                       3GPP 'iotl'                      May 2015   o  if the SIP request contains multiple Route header fields      containing a SIP URI with an 'iotl' parameter, the 'iotl'      parameter associated with the SIP URI of the topmost Route header      field (or, if the SIP URI of the topmost Route header field does      not contain an 'iotl' parameter, the SIP URI of the Route header      field closest to the topmost) identifies the type of traffic leg;      or   o  if a SIP request contains an 'iotl' parameter only in the Request-      URI SIP URI, the 'iotl' parameter identifies the type of traffic      leg.   During SIP registration [RFC3261], entities can add the 'iotl'   parameter to the SIP URI of a Path or Service-Route header field if   the entity is aware that the SIP URI will be used to indicate the end   of a specific traffic leg for initial requests for dialogs or stand-   alone requests sent on the registration path.   As defined in [RFC3261], a SIP proxy must not modify or remove URI   parameters from SIP URIs associated with other entities.  This also   applies to the 'iotl' parameter.5.2.  Parameter Values5.2.1.  General   This section describes the SIP URI 'iotl' parameter values defined in   this specification.   Note that, when a request is routed between different networks, the   request might traverse one or more IBCFs (Interconnection Border   Control Functions) acting as network border entities.5.2.2.  homea-homeb   This value indicates that a SIP entity responsible for the host part   of the SIP URI associated with the parameter represents the end of a   traffic leg between the home network (originating) of the calling   user and the home network (terminating) of the called user.   In 3GPP, this traffic leg is between two S-CSCFs.5.2.3.  homeb-visitedb   This value indicates that the SIP entity addressed by the SIP URI   associated with the parameter represents the end of a traffic leg   between the home network (terminating) of the called user and the   visited network (terminating) in which the called user is located.Holmberg, et al.             Standards Track                    [Page 8]

RFC 7549                       3GPP 'iotl'                      May 2015   In 3GPP, this traffic leg is between the home S-CSCF and the User   Equipment (UE) of the called user or between the Service   Centralization and Continuity Application Server (SCC AS) in the home   network of the called user and Access Transfer Control Function   (ATCF) in the visited network of the called user.5.2.4.  visiteda-homea   This value indicates that a SIP entity responsible for the host part   of the SIP URI associated with the parameter represents the end of a   traffic leg between the visited network (originating) in which the   calling user is located and the home network (originating) of the   calling user.   In 3GPP, this traffic leg is between the UE and the home S-CSCF of   the calling user or between the Proxy Call Session Control Function   (P-CSCF) in the visited network, serving the calling user and the   home S-CSCF of the calling user.5.2.5.  homea-visiteda   This value indicates that the SIP entity addressed by the SIP URI   associated with the parameter represents the end of a traffic leg   between the home network (originating) and the visited network   (originating) in which the calling user is located.   In 3GPP, this traffic leg is between the home S-CSCF of the calling   user and the Transit and Roaming Function (TRF) [TS.3GPP.24.229]   serving the calling user and exists in scenarios where the home   S-CSCF of the calling user forwards a request back to the visited   network where the UE of the calling user is located.  An example of   this is when the Roaming Architecture for Voice over IMS with Local   Breakout (RAVEL) [TS.3GPP.24.229] feature is enabled.5.2.6.  visiteda-homeb   This value indicates that a SIP entity responsible for the host part   of the SIP URI associated with the parameter represents the end of a   traffic leg between the visited network (originating) of the calling   user and the home network (terminating) of the called user.   In 3GPP, this traffic leg is between the TRF [TS.3GPP.24.229] serving   the calling user and the home S-CSCF of the called user and exists in   scenarios where a request is forwarded from the visited network where   the calling user is located directly to the home S-CSCF of the called   user.  An example of this is when the RAVEL [TS.3GPP.24.229] feature   is enabled.Holmberg, et al.             Standards Track                    [Page 9]

RFC 7549                       3GPP 'iotl'                      May 20156.  Syntax6.1.  General   This section defines the ABNF for the 'iotl' SIP URI parameter.  The   ABNF defined in this specification is conformant toRFC 5234   [RFC5234].   This specification does not create an IANA registry for 'iotl'   parameter values.  A registry should be considered if new parameter   values are defined in the future.6.2.  ABNF   The ABNF [RFC5234] grammar for this SIP URI parameter is:   uri-parameter =/ iotl-param   iotl-param    = iotl-tag "=" iotl-value ["." iotl-value]   iotl-tag      = "iotl"   iotl-value    = "homea-homeb" / "homeb-visitedb" / "visiteda-homea"                    / "homea-visiteda" / "visiteda-homeb" / other-iotl   other-iotl    = 1*iotl-char   iotl-char     = alphanum / "-"   ;; alphanum defined inRFC 32617.  Security Considerations   The information in the 'iotl' parameter is used for making policy   decisions.  Such policies can be related to charging and triggering   of services.  In order to prevent abuse, which could cause user   billing or service failure, the parameter SHOULD only be used for   making policy decisions based on the role by nodes within the same   trust domain [RFC3325], and network boundary entities MUST NOT   forward information received from untrusted entities.  In addition,   an agreement MUST exist between the operators for usage of the   roaming role information.   General security considerations for SIP are defined in [RFC3261]8.  IANA Considerations   Per this specification, IANA has added one new value to the "SIP/SIPS   URI Parameters" registry as defined in [RFC3969].         Parameter Name  Predefined Values  Reference         ____________________________________________                   iotl      YesRFC 7549Holmberg, et al.             Standards Track                   [Page 10]

RFC 7549                       3GPP 'iotl'                      May 20159.  References9.1.  Normative References   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119,              DOI 10.17487/RFC2119, March 1997,              <http://www.rfc-editor.org/info/rfc2119>.   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,              A., Peterson, J., Sparks, R., Handley, M., and E.              Schooler, "SIP: Session Initiation Protocol",RFC 3261,              DOI 10.17487/RFC3261, June 2002,              <http://www.rfc-editor.org/info/rfc3261>.   [RFC3327]  Willis, D. and B. Hoeneisen, "Session Initiation Protocol              (SIP) Extension Header Field for Registering Non-Adjacent              Contacts",RFC 3327, DOI 10.17487/RFC3327, December 2002,              <http://www.rfc-editor.org/info/rfc3327>.   [RFC3608]  Willis, D. and B. Hoeneisen, "Session Initiation Protocol              (SIP) Extension Header Field for Service Route Discovery              During Registration",RFC 3608, DOI 10.17487/RFC3608,              October 2003, <http://www.rfc-editor.org/info/rfc3608>.   [RFC3969]  Camarillo, G., "The Internet Assigned Number Authority              (IANA) Uniform Resource Identifier (URI) Parameter              Registry for the Session Initiation Protocol (SIP)",BCP99,RFC 3969, DOI 10.17487/RFC3969, December 2004,              <http://www.rfc-editor.org/info/rfc3969>.   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax              Specifications: ABNF", STD 68,RFC 5234,              DOI 10.17487/RFC5234, January 2008,              <http://www.rfc-editor.org/info/rfc5234>.   [TS.3GPP.24.229]              3GPP, "Vocabulary for 3GPP Specifications", 3GPP TS 24.229              12.6.0, September 2014.9.2.  Informative References   [RFC3325]  Jennings, C., Peterson, J., and M. Watson, "Private              Extensions to the Session Initiation Protocol (SIP) for              Asserted Identity within Trusted Networks",RFC 3325,              DOI 10.17487/RFC3325, November 2002,              <http://www.rfc-editor.org/info/rfc3325>.Holmberg, et al.             Standards Track                   [Page 11]

RFC 7549                       3GPP 'iotl'                      May 2015Appendix A.  3GPP ExamplesA.1.  General   This section contains example call flows based on 3GPP usage of the   SIP URI 'iotl' parameter.A.2.  The UE Registers via P-CSCF   The Visited Proxy (P-CSCF) adds the 'iotl' value 'homeb-visitedb' to   the Path header field of the REGISTER request to be used for   terminating routing towards Alice.  The Home Proxy (S-CSCF) adds the   'iotl' value 'visiteda-homea' to the Service-Route header field to be   used for originating initial/stand-alone requests from Alice.             Visited Proxy    Visited Proxy      Home Proxy   Home ProxyAlice's . . . . P-CSCF . . . . .  IBCF-V . . . . . IBCF-H . . . . S-CSCF  |                |                |                |                |  |   REGISTER F1  |                |                |                |  |--------------->|   REGISTER F2  |                |                |  |                |--------------->|   REGISTER F3  |                |  |                |                |--------------->|  REGISTER F4   |  |                |                |                |--------------->|  |                |                |                |                |  |                |                |                |  200 (OK) F5   |  |                |                |                |<---------------|  |                |                |  200 (OK) F6   |                |  |                |                |<---------------|                |  |                |  200 (OK) F7   |                |                |  |                |<---------------|                |                |  |  200 (OK) F8   |                |                |                |  |<---------------|                |                |                |   F1 REGISTER Alice -> P-CSCF   REGISTER sip:registrar.home1.net SIP/2.0   F2 REGISTER P-CSCF -> IBCF-V   REGISTER sip:registrar.home1.net SIP/2.0   Path: <p-cscf URI;iotl=homeb-visitedb>   F3 REGISTER IBCF-V -> IBCF-H   REGISTER sip:registrar.home1.net SIP/2.0   Path: <p-cscf URI;iotl=homeb-visitedb>   F4 REGISTER IBCF-H -> S-CSCF   REGISTER sip:registrar.home1.net SIP/2.0   Path: <p-cscf URI;iotl=homeb-visitedb>Holmberg, et al.             Standards Track                   [Page 12]

RFC 7549                       3GPP 'iotl'                      May 2015   F5 200 OK S-CSCF -> IBCF-H   200 OK   Path: <p-cscf URI;iotl=homeb-visitedb>   Service-Route: <s-cscf URI;iotl=visiteda-homea>   F6 200 OK IBCF-H -> IBCF-V   200 OK   Path: <p-cscf URI;iotl=homeb-visitedb>   Service-Route: <s-cscf URI;iotl=visiteda-homea>   F7 200 OK IBCF-V -> P-CSCF   200 OK   Path: <p-cscf URI;iotl=homeb-visitedb>   Service-Route: <s-cscf URI;iotl=visiteda-homea>   F8 200 OK P-CSCF -> Alice   200 OK   Path: <p-cscf URI;iotl=homeb-visitedb>   Service-Route: <s-cscf URI;iotl=visiteda-homea>                   Figure 2: The UE Registers via P-CSCFHolmberg, et al.             Standards Track                   [Page 13]

RFC 7549                       3GPP 'iotl'                      May 2015A.3.  Originating IMS Call   In the originating INVITE request from Alice, the 'iotl' value   'visiteda-homea', received in the Service-Route header field during   registration, is added to the Route header field representing the   Home Proxy (S-CSCF) to indicate the traffic leg type between the   Visited Proxy (P-CSCF) and the Home Proxy (S-CSCF).             Visited Proxy    Visited Proxy      Home Proxy   Home ProxyAlice's . . . . P-CSCF . . . . .  IBCF-V . . . . . IBCF-H . . . . S-CSCF  |                |                |                |                |  |   INVITE F1    |                |                |                |  |--------------->|   INVITE F2    |                |                |  |                |--------------->|   INVITE F3    |                |  |                |                |--------------->|   INVITE F4    |  |                |                |                |--------------->|  |                |                |                |                |  |                |                |                |    180   F5    |  |                |                |    180   F6    |<---------------|  |                |    180   F7    |<---------------|                |  |    180   F8    |<---------------|                |                |  |<---------------|                |                |                |  |                |                |                |                |   F1 INVITE Alice -> P-CSCF   INVITE sip:Bob@homeb.net SIP/2.0   Route: <p-cscf URI>,<s-cscf URI;iotl=visiteda-homea>   F2 INVITE P-CSCF -> IBCF-V   INVITE sip:Bob@homeb.net SIP/2.0   Route: <ibcf-v URI>,<s-cscf URI;iotl=visiteda-homea>   F3 INVITE IBCF-V -> IBCF-H   INVITE sip:Bob@homeb.net SIP/2.0   Route: <ibcf-h URI>,<s-cscf URI;iotl=visiteda-homea>   F4 INVITE IBCF-H -> S-CSCF   INVITE sip:Bob@homeb.net SIP/2.0   Route: <s-cscf URI;iotl=visiteda-homea>         Figure 3: Originating IP Multimedia Subsystem (IMS) CallHolmberg, et al.             Standards Track                   [Page 14]

RFC 7549                       3GPP 'iotl'                      May 2015A.4.  Terminating IMS Call   In the terminating INVITE request towards Alice, the 'iotl' value   'homeb-visitedb' provided to the Home Proxy (S-CSCF) during   registration is added to the Route header field representing the   Visited Proxy (P-CSCF) to indicate the traffic leg type between the   Home Proxy (S-CSCF) and the Visited Proxy (P-CSCF).Home Proxy    Home Proxy      Visited Proxy     Visited ProxyS-CSCF  . . . . IBCF-H . . . . .  IBCF-V . . . . . P-CSCF . . . . .  Bob  |                |                |                |                |  |   INVITE F1    |                |                |                |  |--------------->|   INVITE F2    |                |                |  |                |--------------->|   INVITE F3    |                |  |                |                |--------------->|   INVITE F4    |  |                |                |                |--------------->|  |                |                |                |                |  |                |                |                |    180   F5    |  |                |                |    180   F6    |<---------------|  |                |    180   F7    |<---------------|                |  |    180   F8    |<---------------|                |                |  |<---------------|                |                |                |  |                |                |                |                |   F1 INVITE S-CSCF -> IBCF-H   INVITE sip:Bob@visitedb.net SIP/2.0   Route: <ibcf-h URI>,<p-cscf-v URI;iotl=homeb-visitedb   F2 INVITE IBCF-H -> IBCF-V   INVITE sip:Bob@visitedb.net SIP/2.0   Route: <ibcf-v URI>,<p-cscf-v URI;iotl=homeb-visitedb   F3 INVITE IBCF-V -> P-CSCF   INVITE sip:Bob@visitedb.net SIP/2.0   Route: <p-cscf-v URI;iotl=homeb-visitedb   F4 INVITE P-CSCF -> Bob   INVITE sip:Bob@visitedb.net SIP/2.0                      Figure 4: Terminating IMS CallHolmberg, et al.             Standards Track                   [Page 15]

RFC 7549                       3GPP 'iotl'                      May 2015A.5.  Call between Originating Home and Terminating Home Network   The S-CSCF of the originating home network adds the 'iotl' value   'homea-homeb' in the Request-URI of the INVITE, sent towards the   S-CSCF of the terminating network to indicate the traffic leg type   between the S-CSCFs.Home-A Proxy   Home-A Proxy    Home-B Proxy    Home-B Proxy Home-B ProxyS-CSCF-A  . . . . IBCF-A . . . . .IBCF-B . . . . .I-CSCF-B . . .S-CSCF-B  |                |                |                |                |  |   INVITE F1    |                |                |                |  |--------------->|   INVITE F2    |                |                |  |                |--------------->|   INVITE F3    |                |  |                |                |--------------->|   INVITE F4    |  |                |                |                |--------------->|  |                |                |                |                |  |                |                |                |    180   F5    |  |                |                |    180   F6    |<---------------|  |                |    180   F7    |<---------------|                |  |    180   F8    |<---------------|                |                |  |<---------------|                |                |                |  |                |                |                |                |   F1 INVITE S-CSCF-A -> IBCF-A   INVITE sip:Bob@visitedb.net;iotl=homea-homeb SIP/2.0   F2 INVITE IBCF-a -> IBCF-B   INVITE sip:Bob@visitedb.net;iotl=homea-homeb SIP/2.0   F3 INVITE IBCF-B -> I-CSCF-B   INVITE sip:Bob@visitedb.net;iotl=homea-homeb SIP/2.0   F4 INVITE I-CSCF-B -> S-CSCF-B   INVITE sip:Bob@visitedb.net;iotl=homea-homeb SIP/2.0   Figure 5: Call between Originating Home and Terminating Home NetworkHolmberg, et al.             Standards Track                   [Page 16]

RFC 7549                       3GPP 'iotl'                      May 2015Acknowledgements   The authors wish to thank everyone in the 3GPP community that gave   comments on the initial version of this document and contributed with   comments and suggestions during the work.  A special thanks to Paul   Kyziwat, Dale Worley, and Michael Hammer.  Robert Sparks performed   the Gen-ART review of the document.Authors' Addresses   Christer Holmberg   Ericsson   Hirsalantie 11   Jorvas  02420   Finland   EMail: christer.holmberg@ericsson.com   Jan Holm   Ericsson   Kistavagen 25   Stockholm16480   Sweden   EMail: jan.holm@ericsson.com   Roland Jesske   Deutsche Telekom   Heinrich-Hertz-Strasse 3-7   Darmstadt  64307   Germany   Phone: +4961515812766   EMail: r.jesske@telekom.de   Martin Dolly   AT&T   718 Clairmore Ave   Lanoka Harbor  08734   United States   EMail: md3135@att.comHolmberg, et al.             Standards Track                   [Page 17]

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