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Internet Engineering Task Force (IETF)                          P. JonesRequest for Comments: 7206                                  G. SalgueiroCategory: Informational                                          J. PolkISSN: 2070-1721                                            Cisco Systems                                                                L. Liess                                                        Deutsche Telekom                                                               H. Kaplan                                                                  Oracle                                                                May 2014Requirements for an End-to-End Session Identifierin IP-Based Multimedia Communication NetworksAbstract   This document specifies the requirements for an end-to-end session   identifier in IP-based multimedia communication networks.  This   identifier would enable endpoints, intermediate devices, and   management and monitoring systems to identify a session end-to-end   across multiple SIP devices, hops, and administrative domains.Status of This Memo   This document is not an Internet Standards Track specification; it is   published for informational purposes.   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).  Not all documents   approved by the IESG are a candidate for any level of Internet   Standard; seeSection 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/rfc7206.Jones, et al.                 Informational                     [Page 1]

RFC 7206         Requirements for End-to-End Session ID         May 2014Copyright Notice   Copyright (c) 2014 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.Table of Contents1. Introduction ....................................................32. Conventions Used in This Document ...............................33. Terminology .....................................................43.1. What Does the Session Identifier Identify? .................43.2. Communication Session ......................................53.3. End-to-End .................................................64. Session Identifier Use Cases ....................................64.1. End-to-End Identification of a Communication Session .......64.2. Protocol Interworking ......................................64.3. Traffic Monitoring .........................................74.4. Tracking Transferred Sessions ..............................74.5. Session Signal Logging .....................................84.6. Identifier Syntax ..........................................84.7. 3PCC Use Case ..............................................95. Requirements for the End-to-End Session Identifier ..............96. Related Work in Other Standards Organizations ..................106.1. Coordination with the ITU-T ...............................106.2. Requirements within 3GPP ..................................117. Security Considerations ........................................118. Acknowledgments ................................................129. Contributors ...................................................1210. References ....................................................1210.1. Normative References .....................................1210.2. Informative References ...................................12Jones, et al.                 Informational                     [Page 2]

RFC 7206         Requirements for End-to-End Session ID         May 20141.  Introduction   IP-based multimedia communication systems like SIP [1] and H.323 [2]   have the concept of a "call identifier" that is globally unique.  The   identifier is intended to represent an end-to-end communication   session from the originating device to the terminating device.  Such   an identifier is useful for troubleshooting, session tracking, and   so forth.   Unfortunately, there are a number of factors that mean that the   current call identifiers defined in SIP and H.323 are not suitable   for end-to-end session identification.  Perhaps most significant is   the fact that the syntax for the call identifier in SIP and H.323 is   different between the two protocols.  This important fact makes it   impossible for call identifiers to be exchanged end-to-end when a   network uses both of these session protocols.   Another reason why the current call identifiers are not suitable to   identify the session end-to-end is that in real-world deployments,   devices like Back-to-Back User Agents (B2BUAs) often change the   values as the session signaling passes through.  This is true even   when a single session protocol is employed and is not a byproduct of   protocol interworking.   Lastly, identifiers that might have been used to identify a session   end-to-end fail to meet that need when sessions are manipulated   through supplementary service interactions.  For example, when a   session is transferred or if a private branch exchange (PBX) joins or   merges two communication sessions together locally, the end-to-end   properties of currently defined identifiers are lost.   This document specifies the requirements for an end-to-end session   identifier in IP-based multimedia communication networks.  This   identifier would enable endpoints, intermediate devices, and   management and monitoring systems to identify a session end-to-end   across multiple SIP devices, hops, and administrative domains.2.  Conventions Used in This Document   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 inRFC 2119 [3] when they   appear in ALL CAPS.  These words may also appear in this document in   lower case as plain English words, absent their normative meanings.Jones, et al.                 Informational                     [Page 3]

RFC 7206         Requirements for End-to-End Session ID         May 20143.  Terminology3.1.  What Does the Session Identifier Identify?   The identifier on which this document places requirements, the   session identifier, identifies a set of signaling messages associated   with exactly two endpoints that, from each endpoint's perspective,   are related to a single invocation of a communication application.   How the endpoints determine which signaling messages share a given   identifier (that is, what constitutes a single invocation of a   communication application) is intentionally left loosely defined.   The term "call" is often used as an example of such an invocation for   voice and video communication, but different protocols and   deployments define the scope of a "call" in different ways.  For   instance, some systems would associate all of the activity between   all three parties involved in a transfer as a single "call".   Similarly, the term "session" is often used as an example of such an   invocation, but this term is overloaded to describe both signaling   and media-level interaction.  A single invocation of the   communication application, as described above, may involve multiple   RTP "sessions" as described byRFC 3550 [4], and possibly even   multiple concurrent sessions.   In this document, unless otherwise qualified, the term "communication   session", or simply "session", will refer only to the set of   signaling messages identified by the common session identifier.  That   is, a "session" is a set of signaling messages associated with   exactly two endpoints that, from each endpoint's perspective, are   related to a single invocation of a communication application.   The requirements in this document put some constraints on what an   endpoint will consider the same, or a different, invocation of a   communication session.  They also ensure that related sessions (as   this document is using the term) can be correlated using only the   session identifiers for each session.  Again, what constitutes a   "related" session is intentionally left loosely defined.   The definition considers messages associated with exactly two   endpoints instead of messages sent between two endpoints to allow for   intermediaries that create messages on an endpoint's behalf.  It is   possible that an endpoint may not see all of the messages in a   session (as this document is using the term) associated with it.Jones, et al.                 Informational                     [Page 4]

RFC 7206         Requirements for End-to-End Session ID         May 2014   This definition, along with the constraints imposed by the   requirements in this document, facilitates specifying an identifier   that allows the two endpoints to use two entirely different protocols   (and hence to potentially have different ideas of what a single   invocation means) or use two applications that have a different idea   of what a single invocation means.3.2.  Communication Session   A communication session may exist between two SIP User Agents (UAs)   and may pass through one or more intermediary devices, including   B2BUAs or SIP proxies.  For example:            UA A               Middlebox(es)                UA B            SIP message(s) -------[]---[]-------> SIP message(s)            SIP message(s)  <-----[]---[]-------  SIP message(s)           Figure 1: Communication Session through Middlebox(es)   The following are examples of acceptable communication sessions as   described inSection 3.1 and are not exhaustive:   o  A call directly between two user agents   o  A call between two user agents with one or more SIP middleboxes in      the signaling path   o  A call between two user agents that was initiated using third-      party call control (3PCC) [5]   o  A call between two user agents (e.g., between Alice and Carol)      that results from a different communication session (e.g., Alice      and Bob) wherein one of those user agents (Alice) is transferred      to another user agent (Carol) using a REFER request or a re-INVITE      request   The following are not considered communication sessions:   o  A call between any two user agents wherein two or more user agents      are engaged in a conference call via a conference focus:      - each call between the user agent and the conference focus would        be a communication session, and      - each of these is a distinct communication session.Jones, et al.                 Informational                     [Page 5]

RFC 7206         Requirements for End-to-End Session ID         May 2014   o  A call between three user agents (e.g., Alice, Bob, and Carol)      wherein the first user agent (Alice) ad hoc conferences the other      two user agents (Bob and Carol):      - The call between Alice and Bob would be one communication        session.      - The call between Alice and Carol would be a different        communication session.3.3.  End-to-End   The term "end-to-end" in this document means the communication   session from the point of origin, passing through any number of   intermediaries, to the ultimate point of termination.  It is   recognized that legacy devices may not support the end-to-end session   identifier.  Since such an endpoint will not create a session   identifier, an intermediary device that supports this identifier can   inject an identifier into the session signaling.4.  Session Identifier Use Cases4.1.  End-to-End Identification of a Communication Session   For SIP messaging that either does not involve SIP servers or only   involves SIP proxies, the Call-ID header field value sufficiently   identifies each SIP message within a transaction (see Section 17 of   [1]) or dialog (seeSection 12 of [1]).  This is not the case when   either B2BUAs or Session Border Controllers (SBCs) [6] are in the   signaling path between User Agents (UAs).  Therefore, we need the   ability to identify each communication session through a single SIP   header field, regardless of which types of SIP servers are in the   signaling path between UAs.  For messages that create a dialog, each   message within the same dialog MUST use the same session identifier.   Derived Requirements: All Requirements inSection 5.4.2.  Protocol Interworking   A communication session might originate on an H.323 [2] endpoint and   pass through an SBC before ultimately reaching a terminating SIP user   agent.  Likewise, a call might originate on a SIP user agent and   terminate on an H.323 endpoint.  It MUST be possible to identify such   sessions end-to-end across the plurality of devices, networks, or   administrative domains.Jones, et al.                 Informational                     [Page 6]

RFC 7206         Requirements for End-to-End Session ID         May 2014   It is anticipated that the ITU-T will define protocol elements for   H.323 to make the end-to-end signaling possible.   Derived Requirements: REQ5, REQ7 (Section 5).4.3.  Traffic Monitoring   UA A and UA B communicate using SIP messaging with a SIP B2BUA acting   as a middlebox that belongs to a SIP service provider.  For privacy   reasons, the B2BUA changes the SIP header fields that reveal   information related to the SIP users, devices, or domain identities.   The service provider uses an external device to monitor and log all   SIP traffic coming to and from the B2BUA.  In the case of failures   reported by the customer or when security issues arise (e.g., theft   of service), the service provider has to analyze the logs from the   past several days or weeks and then correlates those messages that   were messages for a single end-to-end SIP session.   For this scenario, we must consider three particular use cases:   a) UAs A and B support the end-to-end session identifier.      Derived Requirements: REQ1, REQ3, REQ4, REQ6.   b) Only UA A supports the end-to-end session identifier; UA B      does not.      Derived Requirements: REQ1, REQ3, REQ4, REQ5, REQ6.   c) UAs A and B do not support the end-to-end session identifier.      Derived Requirements: REQ1, REQ3, REQ4, REQ5, REQ6.4.4.  Tracking Transferred Sessions   It is difficult to track which SIP messages were involved in the same   call across transactions, especially when invoking supplementary   services such as call transfer or call join.  There exists a need for   the ability to track communication sessions as they are transferred,   one side at a time, until completion of the session (i.e., until a   BYE is sent).   Derived Requirements: REQ1, REQ2, REQ9.Jones, et al.                 Informational                     [Page 7]

RFC 7206         Requirements for End-to-End Session ID         May 20144.5.  Session Signal Logging   An after-the-fact search of SIP messages to determine which messages   were part of the same transaction or call is difficult when B2BUAs   and SBCs are involved in the signaling between UAs.  Mapping more   than one Call-ID together can be challenging because all of the   values in SIP header fields on one side of the B2BUA or SBC will   likely be different than those on the other side.  If multiple B2BUAs   and/or SBCs are in the signaling path, more than two sets of header   field values will exist, creating more of a challenge.  Creating a   common header field value through all SIP entities will greatly   reduce any challenge for the purposes of debugging, communication   tracking (such as for security purposes in case of theft of   service), etc.   Derived Requirements: REQ1, REQ3, REQ5, REQ6.4.6.  Identifier Syntax   A syntax that is too lax (e.g., one that allows special characters or   a very long identifier) would make it difficult to encode the   identifier in other protocols.  Therefore, the syntax of the   identifier should be reasonably constrained.   Derived Requirement: REQ8.Jones, et al.                 Informational                     [Page 8]

RFC 7206         Requirements for End-to-End Session ID         May 20144.7.  3PCC Use Case   Third-party call control refers to the ability of an entity to create   a call in which communication is actually between two or more parties   other than the one setting up the call.  For example, a B2BUA acting   as a third-party controller could establish a call between two SIP   UAs using 3PCC procedures as described inSection 4.1 of RFC 3725   [5], the flow for which is reproduced below.                A              Controller               B                |(1) INVITE no SDP  |                   |                |<------------------|                   |                |(2) 200 offer1     |                   |                |------------------>|                   |                |                   |(3) INVITE offer1  |                |                   |------------------>|                |                   |(4) 200 OK answer1 |                |                   |<------------------|                |                   |(5) ACK            |                |                   |------------------>|                |(6) ACK answer1    |                   |                |<------------------|                   |                |(7) RTP            |                   |                |.......................................|                Figure 2: Session Identifier 3PCC Scenario   Such a flow must result in a single session identifier being used for   the communication session between UA A and UA B.  This use case does   not extend to three SIP UAs.   Derived Requirement: REQ9.5.  Requirements for the End-to-End Session Identifier   The following requirements are derived from the use cases and   additional constraints regarding the construction of the identifier.   REQ1: It MUST be possible for an administrator or an external device      that monitors the SIP traffic to use the identifier to identify      those dialogs, transactions, and messages that were at some point      in time components of a single end-to-end SIP session (e.g., parts      of the same call).   REQ2: It MUST be possible to correlate two end-to-end sessions when a      session is transferred or if two different sessions are joined      together via an intermediary (e.g., a PBX).Jones, et al.                 Informational                     [Page 9]

RFC 7206         Requirements for End-to-End Session ID         May 2014   REQ3: The solution MUST require that the identifier, if present, pass      unchanged through SIP B2BUAs or other intermediaries.   REQ4: The identifier MUST NOT reveal any information related to any      SIP user, device, or domain identity.  Additionally, it MUST NOT      be possible to correlate a set of session identifiers produced      over a period of time with one another, or with a particular user      or device.  This includes any IP address, port, hostname, domain      name, username, Address-of-Record, Media Access Control (MAC)      address, IP address family, transport type, subscriber ID,      Call-ID, tags, or other SIP header field or body parts.   REQ5: It MUST be possible to identify SIP traffic with an end-to-end      session identifier from and to end devices that do not support      this new identifier, such as by allowing an intermediary to inject      an identifier into the session signaling.   REQ6: The identifier SHOULD be unique in time and space, similar to      the Call-ID.   REQ7: The identifier SHOULD be constructed in such a way as to make      it suitable for transmission in SIP [1] and H.323 [2].   REQ8: The identifier SHOULD use a restricted syntax and length so as      to allow the identifier to be used in other protocols.   REQ9: It MUST be possible to correlate two end-to-end sessions when      the sessions are created by a third-party controller using 3PCC      procedures as shown in Figure 1 ofRFC 3725 [5].6.  Related Work in Other Standards Organizations6.1.  Coordination with the ITU-T   IP multimedia networks are often comprised of a mix of session   protocols like SIP [1] and H.323 [2].  A benefit of the session   identifier is that it uniquely identifies a communication session   end-to-end across session protocol boundaries.  Therefore, the need   for coordinated standardization activities across Standards   Development Organizations (SDOs) is imperative.   To facilitate this, a parallel effort is underway in the ITU-T to   introduce the session identifier for H.323 in such a way as to be   interoperable with the procedures defined by the IETF.Jones, et al.                 Informational                    [Page 10]

RFC 7206         Requirements for End-to-End Session ID         May 20146.2.  Requirements within 3GPP   The Third Generation Partnership Project (3GPP) identified in their   Release 9 the need for a session identifier for operation and   maintenance purposes to correlate flows in an end-to-end   communication session.  3GPP TS24.229 [7] points to the fact that the   session identifier can be used to correlate SIP messages belonging to   the same session.  In the case where signaling passes through SIP   entities like B2BUAs, the end-to-end session identifier indicates   that these dialogs belong to the same end-to-end SIP communication   session.7.  Security Considerations   The security vulnerabilities, attacks, and threat models affecting   other similar SIP identifiers are well documented inRFC 3261 [1] and   are equally applicable to the end-to-end session identifier and   subject to the same mitigating security best practices.  Further,   storage of the session identifier in a log file is also subject to   the security considerations specified inRFC 6872 [8].   An end-to-end identifier, if not properly constructed, could provide   confidential information that would allow one to identify the   individual, device, or domain initiating or terminating a   communication session.  In adhering to REQ4, the solution produced in   accordance with these requirements MUST take appropriate measures to   properly secure and obfuscate sensitive or private information that   might allow one to identify a person, device, or domain.  This means   that the end-to-end session identifier MUST NOT reveal information   elements such as the MAC address or IP address.  It is outside the   scope of this document to specify the implementation details of such   security and privacy measures.  Those details may vary with the   specific construction mechanism selected for the end-to-end session   identifier and therefore will be discussed in the document specifying   the actual end-to-end identifier.   A key security consideration is to ensure that an attacker cannot   surreptitiously spoof the identifier and effectively render it   useless to diagnostic equipment that cannot properly correlate   signaling messages due to the duplicate session identifiers that   exist in the same space and time.  In accordance with REQ6, this   end-to-end identifier MUST be sufficiently long and random to prevent   it from being guessable as well as avoid collision with another   identifier.  The secure transport of the identifier, need for   authentication, encryption, etc. should be appropriately evaluated   based on the network infrastructure, transport domain, and usage   scenarios for the end-to-end session identifier.Jones, et al.                 Informational                    [Page 11]

RFC 7206         Requirements for End-to-End Session ID         May 20148.  Acknowledgments   The authors would like to acknowledge Paul Kyzivat, Christer   Holmberg, Charles Eckel, Andy Hutton, Salvatore Loreto, Keith Drage,   and Chris Pearce for their contribution and collaboration in   developing this document.9.  Contributors   Roland Jesske and Parthasarathi Ravindran provided substantial   contributions to this document during its initial creation.10.  References10.1.  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]  Recommendation ITU-T H.323, "Packet-based multimedia        communications systems", December 2009.   [3]  Bradner, S., "Key words for use in RFCs to Indicate Requirement        Levels",BCP 14,RFC 2119, March 1997.10.2.  Informative References   [4]  Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,        "RTP: A Transport Protocol for Real-Time Applications", STD 64,RFC 3550, July 2003.   [5]  Rosenberg, J., Peterson, J., Schulzrinne, H., and G. Camarillo,        "Best Current Practices for Third Party Call Control (3pcc) in        the Session Initiation Protocol (SIP)",BCP 85,RFC 3725,        April 2004.   [6]  Hautakorpi, J., Ed., Camarillo, G., Penfield, R., Hawrylyshen,        A., and M. Bhatia, "Requirements from Session Initiation        Protocol (SIP) Session Border Control (SBC) Deployments",RFC 5853, April 2010.Jones, et al.                 Informational                    [Page 12]

RFC 7206         Requirements for End-to-End Session ID         May 2014   [7]  3GPP TS 24.229, "IP multimedia call control protocol based on        Session Initiation Protocol (SIP) and Session Description        Protocol (SDP); Stage 3".   [8]  Gurbani, V., Ed., Burger, E., Ed., Anjali, T., Abdelnur, H., and        O. Festor, "The Common Log Format (CLF) for the Session        Initiation Protocol (SIP): Framework and Information Model",RFC 6872, February 2013.Jones, et al.                 Informational                    [Page 13]

RFC 7206         Requirements for End-to-End Session ID         May 2014Authors' Addresses   Paul E. Jones   Cisco Systems, Inc.   7025 Kit Creek Rd.   Research Triangle Park, NC  27709   USA   Phone: +1 919 476 2048   EMail: paulej@packetizer.com   IM: xmpp:paulej@packetizer.com   Gonzalo Salgueiro   Cisco Systems, Inc.   7025 Kit Creek Rd.   Research Triangle Park, NC  27709   USA   Phone: +1 919 392 3266   EMail: gsalguei@cisco.com   IM: xmpp:gsalguei@cisco.com   James Polk   Cisco Systems, Inc.   3913 Treemont Circle   Colleyville, TX   USA   Phone: +1 817 271 3552   EMail: jmpolk@cisco.com   IM: xmpp:jmpolk@cisco.com   Laura Liess   Deutsche Telekom NP   64295 Darmstadt   Heinrich-Hertz-Str. 3-7   Germany   Phone: +49 6151 268 2761   EMail: laura.liess.dt@gmail.comJones, et al.                 Informational                    [Page 14]

RFC 7206         Requirements for End-to-End Session ID         May 2014   Hadriel Kaplan   Oracle   71 Third Ave.   Burlington, MA  01803   USA   EMail: hadriel.kaplan@oracle.comJones, et al.                 Informational                    [Page 15]