path: root/doc/rfc/rfc8497.txt

Internet Engineering Task Force (IETF)                          P. Dawes
Request for Comments: 8497                                Vodafone Group
Category: Standards Track                                 C. Arunachalam
ISSN: 2070-1721                                            Cisco Systems
                                                           November 2018


                   Marking SIP Messages to Be Logged

Abstract

   SIP networks use signaling monitoring tools to diagnose user-reported
   problems and to perform regression testing if network or user agent
   (UA) software is upgraded.  As networks grow and become
   interconnected, including connection via transit networks, it becomes
   impractical to predict the path that SIP signaling will take between
   user agents and therefore impractical to monitor SIP signaling end to
   end.

   This document describes an indicator for the SIP protocol that can be
   used to mark signaling as being of interest to logging.  Such marking
   will typically be applied as part of network testing controlled by
   the network operator and is not used in normal user agent signaling.
   Operators of all networks on the signaling path can agree to carry
   such marking end to end, including the originating and terminating
   SIP user agents, even if a session originates and terminates in
   different networks.

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 in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8497.










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Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://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 Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
   3.  "Log Me" Marking Protocol Aspects . . . . . . . . . . . . . .   4
     3.1.  Session-ID "logme" Parameter  . . . . . . . . . . . . . .   4
     3.2.  Starting and Stopping Logging . . . . . . . . . . . . . .   5
     3.3.  Identifying Test Cases  . . . . . . . . . . . . . . . . .   6
     3.4.  Passing the Marker  . . . . . . . . . . . . . . . . . . .   6
       3.4.1.  To/From a User Device . . . . . . . . . . . . . . . .   6
       3.4.2.  To/From an External Network . . . . . . . . . . . . .   6
       3.4.3.  Across a Non-supporting SIP Intermediary  . . . . . .   6
     3.5.  Logging Multiple Simultaneous Dialogs . . . . . . . . . .   6
     3.6.  Format of Logged Signaling  . . . . . . . . . . . . . . .   7
     3.7.  Marking-Related Dialogs . . . . . . . . . . . . . . . . .   7
     3.8.  Forked Requests . . . . . . . . . . . . . . . . . . . . .  13
   4.  SIP Entity Behavior . . . . . . . . . . . . . . . . . . . . .  13
     4.1.  Scope of Marking  . . . . . . . . . . . . . . . . . . . .  13
     4.2.  Endpoints . . . . . . . . . . . . . . . . . . . . . . . .  13
     4.3.  SIP Intermediaries Acting on Behalf of Endpoints  . . . .  15
     4.4.  B2BUAs  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     4.5.  "Log Me" Marker Processing by SIP Intermediaries  . . . .  17
       4.5.1.  Stateless Processing  . . . . . . . . . . . . . . . .  17
       4.5.2.  Stateful Processing . . . . . . . . . . . . . . . . .  17
         4.5.2.1.  "Log Me" Marking Not Supported by Originating UA   18
         4.5.2.2.  "Log Me" Marking Not Supported by Terminating UA   21
         4.5.2.3.  "Log Me" Marking Removed by Originating Network .  23
         4.5.2.4.  "Log Me" Marking Removed by Supporting
                   Terminating Network . . . . . . . . . . . . . . .  26
         4.5.2.5.  "Log Me" Marking Passed by Non-supporting
                   Terminating Network . . . . . . . . . . . . . . .  28





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   5.  Errors  . . . . . . . . . . . . . . . . . . . . . . . . . . .  31
     5.1.  Error Cases . . . . . . . . . . . . . . . . . . . . . . .  31
       5.1.1.  Missing "Log Me" Marker Error Case  . . . . . . . . .  31
       5.1.2.  "Log Me" Marker Appears Mid-dialog Error Case . . . .  35
     5.2.  Non-error Cases . . . . . . . . . . . . . . . . . . . . .  36
       5.2.1.  Missing "Log Me" Marker Non-error Case  . . . . . . .  36
       5.2.2.  "Log Me" Marker Appears Mid-dialog Non-error Case . .  37
       5.2.3.  Combining Dialogs Non-error Case  . . . . . . . . . .  37
     5.3.  Error Handling  . . . . . . . . . . . . . . . . . . . . .  38
   6.  Augmented BNF for the "logme" Parameter . . . . . . . . . . .  38
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  39
     7.1.  "Log Me" Authorization  . . . . . . . . . . . . . . . . .  39
     7.2.  "Log Me" Marker Removal . . . . . . . . . . . . . . . . .  39
     7.3.  Denial-of-Service Attacks . . . . . . . . . . . . . . . .  39
     7.4.  Data Protection . . . . . . . . . . . . . . . . . . . . .  40
   8.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  40
     8.1.  Personal Identifiers  . . . . . . . . . . . . . . . . . .  40
     8.2.  Data Stored at SIP Intermediaries . . . . . . . . . . . .  41
     8.3.  Data Visible at Network Elements  . . . . . . . . . . . .  41
     8.4.  Preventing Fingerprinting . . . . . . . . . . . . . . . .  41
     8.5.  Retaining Logs  . . . . . . . . . . . . . . . . . . . . .  42
     8.6.  User Control of Logging . . . . . . . . . . . . . . . . .  42
     8.7.  Recommended Defaults  . . . . . . . . . . . . . . . . . .  42
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  43
     9.1.  Registration of the "logme" Parameter . . . . . . . . . .  43
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  43
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  43
     10.2.  Informative References . . . . . . . . . . . . . . . . .  45
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  46
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  46

1.  Introduction

   When users experience problems with setting up sessions using SIP,
   enterprise or service provider network operators often have to
   identify the root cause by examining the SIP signaling.  Also, when
   network or user agent (UA) software or hardware is upgraded,
   regression testing is needed.  Such diagnostics apply to a small
   proportion of network traffic and can apply end to end, even if
   signaling crosses several networks possibly belonging to several
   different network operators.  It may not be possible to predict the
   path through those networks in advance, therefore, a mechanism is
   needed to mark a session as being of interest so that SIP entities
   along the signaling path can provide diagnostic logging.  [RFC8123]
   illustrates this motivating scenario.  This document describes a
   solution that meets the requirements for such "log me" marking of SIP
   signaling also defined in [RFC8123].




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   This document also defines a new header field parameter, "logme", for
   the Session-ID header field [RFC7989].  Implementations of this
   document MUST implement [RFC7989].

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  "Log Me" Marking Protocol Aspects

3.1.  Session-ID "logme" Parameter

   Logging for diagnostic purposes is most effective when it is applied
   end to end in a communication session.  This ability requires a "log
   me" marker to be passed through SIP intermediaries.  The Session-ID
   header field defined in [RFC7989] was chosen to carry the "log me"
   marker as a "logme" parameter since the session identifier is
   typically passed through SIP Back-to-Back User Agents (B2BUAs)
   (described in [RFC7092]) or other intermediaries, as per the Session-
   ID requirement REQ3 in [RFC7206].  The "logme" parameter shown in
   Figure 1 does not introduce any device-specific or user-specific
   information and MUST be passed unchanged with the Session-ID header
   field.  There is an exception, however, for the cases specified in
   Section 3.4.2 where the "log me" marker may be removed at a network
   boundary.

       Alice              Proxy            Registrar
       u1.example.com     p1.example.com   r1.example.com
         |                  |                  |
         |(1) INVITE        |                  |
         | Session-ID: ab30317f1a784dc48ff824d0d3715d86;
         |  remote=47755a9de7794ba387653f2099600ef2;logme
         |----------------->|                  |
         |                  |                  |

                   Figure 1: "Log Me" Marking Using the
                 "logme" Session-ID Header Field Parameter










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3.2.  Starting and Stopping Logging

   If a dialog is to be "log me" marked, then marking MUST start with
   the SIP request that initiates that dialog (dialog-initiating
   requests are described in Section 12.1 of [RFC3261]).  For the most
   effective testing and troubleshooting, marking continues for the
   lifetime of the dialog, applies to each request and response in the
   dialog, and applies uninterrupted end to end (including user
   devices).  The "log me" marking mechanism described in this document
   allows for parts of the signaling path to not be marked, e.g, because
   an endpoint does not support the "log me" marking mechanism (see
   Section 4.5.2) or because an endpoint or intermediary deliberately
   removes the "log me" marker (see Section 4.5.2.4).  Also, marking
   errors can terminate marking before the dialog ends (see
   Section 5.3).

   A UA or intermediary adds a "log me" marker in an unmarked request or
   response in two cases: first, because it is configured to add the
   marking to a dialog-creating request, or second, because it has
   received a dialog-creating request that is being "log me" marked
   causing it to maintain state to ensure that all requests and
   responses in the dialog are similarly "log me" marked.  Once the "log
   me" marking is started for a dialog, all subsequent requests and
   responses in this dialog are "log me" marked.  Marking is stopped
   when this dialog and its related dialogs end.  It is considered an
   error (see Section 5.1.2) if "log me" marking is started in a mid-
   dialog request or response.

   For the first case, "log me" marking trigger condition configurations
   that define whether a UA or intermediary can initiate "log me"
   marking for a given dialog are out of scope of this document.  As an
   example of trigger condition configurations, the UA or intermediary
   could be configured to add a "log me" marker for all dialogs
   initiated during a specific time period (e.g., 9:00 am - 10:00 am
   every day) or for specific dialogs that have a particular "User-
   Agent" header field value.  They could also be configured to add a
   "log me" marker for a specific set of called party numbers for which
   users are experiencing call setup failures.

   For the second case of a UA or intermediary detecting that a dialog-
   initiating request is being "log me" marked, the scope of such
   marking extends to the lifetime of the dialog.  In addition, as
   discussed in Section 3.7, "log me" marked dialogs that create related
   dialogs (e.g., REFER) may transfer the marking to the related
   dialogs.  In such cases, the entire "session", identified by the
   Session-ID header field, is "log me" marked.





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3.3.  Identifying Test Cases

   The local Universally Unique Identifier (UUID) portion of the
   Session-ID header field value [RFC7989] in the initial SIP request of
   a dialog is used as a random test case identifier (described in REQ 5
   in [RFC8123]).  This provides the ability to collate all logged SIP
   requests and responses to the initial SIP request in a dialog or
   standalone transaction.

3.4.  Passing the Marker

3.4.1.  To/From a User Device

   When a user device inserts the "log me" marker, the marker MUST be
   passed unchanged in the Session-ID header field across an edge proxy
   or a B2BUA adjacent to the user device.

3.4.2.  To/From an External Network

   An external network is a peer network connected at a network boundary
   as defined in [RFC8123].

   External networks may be connected directly or via a peering network,
   and such networks often have specific connection agreements.  Whether
   "log me" marking is removed depends on the policy applied at the
   network-to-network interface.  Troubleshooting and testing will be
   easier if peer networks endeavor to make agreements to pass "log me"
   marking unchanged.  However, since a "log me" marker may cause a SIP
   entity to log the SIP header and body of a request or response, the
   "log me" marker MUST be removed at a network boundary if no agreement
   exists between peer networks.

3.4.3.  Across a Non-supporting SIP Intermediary

   "Log me" marking is most effective if passed end to end.  However,
   intermediaries that do not comply with this document might pass the
   "log me" marker unchanged or even drop it entirely.

3.5.  Logging Multiple Simultaneous Dialogs

   Multiple SIP dialogs can be simultaneously logged by an originating
   UA, terminating UA, and SIP entities on the signaling path.  These
   dialogs are differentiated by their test case identifier (the local
   UUID portion of the Session-ID header field value at the originating
   device).






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3.6.  Format of Logged Signaling

   The entire SIP message (SIP request line, response line, header
   fields, and message body) SHOULD be logged since troubleshooting
   might be difficult if information is missing.  Logging SHOULD use
   common standard formats such as SIP Common Log Format (CLF) defined
   in [RFC6873] and Libpcap as defined in "vnd.tcpdump.pcap" in the
   Media Types registry [MEDIA-TYPES].  If SIP CLF is used, the entire
   message is logged using Vendor-ID = 00000000 and Tag = 02 in the
   <OptionalFields> portion of the SIP CLF record (see Section 4.4 of
   [RFC6873]).  Header fields SHOULD be logged in the form in which they
   appear in the message; they SHOULD NOT be converted between long and
   compact forms described in Section 7.3.3 of [RFC3261].

3.7.  Marking Related Dialogs

   "Log me" marking is done per dialog; typically, it begins at dialog
   creation and ends when the dialog ends.  However, dialogs related to
   a "log me" marked dialog MAY also be "log me" marked for call control
   features such as call forward, transfer, park, and join.  As
   described in Section 6 of [RFC7989], related dialogs can occur when
   an endpoint receives a 3xx message, a REFER that directs the endpoint
   to a different peer, an INVITE request with Replaces that also
   potentially results in communicating with a new peer, or an INVITE
   with a Join header field as described in [RFC3911].  An example is
   the call transfer feature described in Section 6.1 of [RFC5589].  The
   logged signaling for related dialogs can be correlated using Session-
   ID header field values as described in Section 10.9 of [RFC7989].

   In the example shown in Figure 2, Alice has reported problems making
   call transfers.  Her terminal is placed in debug mode in preparation
   for "log me" marked signaling from the network administrator,
   Bob. Bob's terminal is configured to "log me" mark and log signaling
   for calls originated during the troubleshooting session (e.g., for a
   duration of 15 minutes).  Bob, who is troubleshooting the problem,
   arranges to make a call that Alice can attempt to transfer.  Bob
   calls Alice, which creates initial dialog1, and then Alice transfers
   the call to connect Bob to Carol.  Logged signaling is correlated
   using the test case identifier, which is the local UUID
   ab30317f1a784dc48ff824d0d3715d86 in the Session-ID header field of
   INVITE request F1.  Logging by Alice's terminal begins when it
   receives and echoes the "log me" marker in INVITE F1 and ends when
   the last request or response in the dialog is sent or received (200
   OK F7 of dialog1).  Also during dialog1, Alice's terminal logs
   related REFER dialog2, which it initiates and terminates as part of
   the call transfer.  Alice's terminal inserts a "log me" marker in the
   REFER request and 200 OK responses to NOTIFY requests in dialog2.
   Both dialog1 and dialog2 have the same test case identifier.



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   Logging by Bob's terminal begins when it sends INVITE F1, which
   includes the "log me" marker, and ends when dialog3, initiated by
   Bob, ends.  Logging by Carol's terminal begins when it receives the
   INVITE F5 with the "log me" marker and ends when dialog3 ends.

   dialog3 is not logged by Alice's terminal; however, the test case
   identifier ab30317f1a784dc48ff824d0d3715d86 is also the test case
   identifier (local-uuid) in INVITE F5.  Also, the test case identifier
   of dialog2, which is logged by Alice's terminal, can be linked to
   dialog1 and dialog3 because the remote-uuid component of dialog2 is
   the test case identifier ab30317f1a784dc48ff824d0d3715d86.








































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                 Alice                 Bob                  Carol
               Transferor           Transferee             Transfer
                    |                    |                  Target
                    |          INVITE F1 |                    |
            dialog1 |<-------------------|                    |
                    |          200 OK F2 |                    |
            dialog1 |------------------->|                    |
                    |            ACK     |                    |
            dialog1 |<-------------------|                    |
                    |  INVITE (hold)     |                    |
            dialog1 |------------------->|                    |
                    |  200 OK            |                    |
            dialog1 |<-------------------|                    |
                    |  ACK               |                    |
            dialog1 |------------------->|                    |
                    |  REFER F3 (Target-Dialog:1)             |
            dialog2 |------------------->|                    |
                    |  200 OK            |                    |
            dialog2 |<-------------------|                    |
                    | NOTIFY (100 Trying) F4                  |
            dialog2 |<-------------------|                    |
                    |            200 OK  |                    |
            dialog2 |------------------->|                    |
                    |                    |  INVITE F5         |
            dialog3 |                    |------------------->|
                    |                    |  200 OK            |
            dialog3 |                    |<-------------------|
                    |                    |  ACK               |
            dialog3 |                    |------------------->|
                    |  NOTIFY (200 OK) F6|                    |
            dialog2 |<-------------------|                    |
                    |            200 OK  |                    |
            dialog2 |------------------->|                    |
                    |  BYE               |                    |
            dialog1 |------------------->|                    |
                    |  200 OK F7         |                    |
            dialog1 |<-------------------|                    |
                    |                    |             BYE    |
            dialog3 |                    |<-------------------|
                    |                    |             200 OK |
            dialog3 |                    |------------------->|

        Figure 2: "Log Me" Marking Related Dialogs in Call Transfer








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   F1:   Bob's UA inserts the "logme" parameter in the Session-ID header
         field of the INVITE request that creates dialog1.

   F3:   Alice's UA inserts the "logme" parameter in the Session-ID
         header field of the REFER request that creates dialog2, which
         is related to dialog1.

   F5:   Bob's UA inserts the "logme" parameter in the Session-ID header
         field of the INVITE request that creates dialog3, which is
         related to dialog1.


          F1 INVITE Transferee -> Transferor

          INVITE sips:transferor@atlanta.example.com SIP/2.0
          Via: SIP/2.0/TLS [2001:db8::1];branch=z9hG4bKnas432
          Max-Forwards: 70
          To: <sips:transferor@atlanta.example.com>
          From: <sips:transferee@biloxi.example.com>;tag=7553452
          Call-ID: 090459243588173445
          Session-ID: ab30317f1a784dc48ff824d0d3715d86
             ;remote=00000000000000000000000000000000;logme
          CSeq: 29887 INVITE
          Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
          Supported: replaces, gruu, tdialog
          Contact: <sips:3ld812adkjw@biloxi.example.com;gr=3413kj2ha>
          Content-Type: application/sdp
          Content-Length: ...


          F2 200 OK Transferor -> Transferee

          SIP/2.0 200 OK
          Via: SIP/2.0/TLS [2001:db8::1];branch=z9hG4bKnas432
          To: <sips:transferor@atlanta.example.com>;tag=31kdl4i3k
          From: <sips:transferee@biloxi.example.com>;tag=7553452
          Call-ID: 090459243588173445
          Session-ID: 47755a9de7794ba387653f2099600ef2
             ;remote=ab30317f1a784dc48ff824d0d3715d86;logme
          CSeq: 29887 INVITE
          Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
          Supported: replaces, gruu, tdialog
          Contact: <sips:4889445d8kjtk3@atlanta.example.com;gr=723jd2d>
          Content-Type: application/sdp
          Content-Length: ...






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          F3 REFER Transferor -> Transferee

          REFER sips:3ld812adkjw@biloxi.example.com;gr=3413kj2ha SIP/2.0
          Via: SIP/2.0/TLS pc33.atlanta.example.com;branch=z9hG4bKna9
          Max-Forwards: 70
          To: <sips:3ld812adkjw@biloxi.example.com;gr=3413kj2ha>
          From: <sips:transferor@atlanta.example.com>;tag=1928301774
          Call-ID: a84b4c76e66710
          Session-ID: 47755a9de7794ba387653f2099600ef2
             ;remote=ab30317f1a784dc48ff824d0d3715d86;logme
          CSeq: 314159 REFER
          Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
          Supported: gruu, replaces, tdialog
          Require: tdialog
          Refer-To: <sips:transfertarget@chicago.example.com>
          Target-Dialog: 090459243588173445;local-tag=7553452
           ;remote-tag=31kdl4i3k
          Contact: <sips:4889445d8kjtk3@atlanta.example.com;gr=723jd2d>
          Content-Length: 0


          F4 NOTIFY Transferee -> Transferor

          NOTIFY sips:4889445d8kjtk3@atlanta.example.com
             ;gr=723jd2d SIP/2.0
          Via: SIP/2.0/TLS [2001:db8::1];branch=z9hG4bKnas432
          Max-Forwards: 70
          To: <sips:transferor@atlanta.example.com>;tag=1928301774
          From: <sips:3ld812adkjw@biloxi.example.com;gr=3413kj2ha>
           ;tag=a6c85cf
          Call-ID: a84b4c76e66710
          Session-ID: ab30317f1a784dc48ff824d0d3715d86
             ;remote=47755a9de7794ba387653f2099600ef2;logme
          CSeq: 73 NOTIFY
          Contact: <sips:3ld812adkjw@biloxi.example.com;gr=3413kj2ha>
          Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
          Supported: replaces, tdialog
          Event: refer
          Subscription-State: active;expires=60
          Content-Type: message/sipfrag
          Content-Length: ...










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          F5 INVITE Transferee -> Transfer Target

          INVITE sips:transfertarget@chicago.example.com SIP/2.0
          Via: SIP/2.0/TLS [2001:db8::1];branch=z9hG4bKnas41234
          Max-Forwards: 70
          To: <sips:transfertarget@chicago.example.com>
          From: <sips:transferee@biloxi.example.com>;tag=j3kso3iqhq
          Call-ID: 90422f3sd23m4g56832034
          Session-ID: ab30317f1a784dc48ff824d0d3715d86
             ;remote=00000000000000000000000000000000;logme
          CSeq: 521 REFER
          Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
          Supported: replaces, gruu, tdialog
          Contact: <sips:3ld812adkjw@biloxi.example.com;gr=3413kj2ha>
          Content-Type: application/sdp
          Content-Length: ...


          F6 NOTIFY Transferee -> Transferor

          NOTIFY sips:4889445d8kjtk3@atlanta.example.com
             ;gr=723jd2d SIP/2.0
          Via: SIP/2.0/TLS [2001:db8::1];branch=z9hG4bKnas432
          Max-Forwards: 70
          To: <sips:transferor@atlanta.example.com>;tag=1928301774
          From: <sips:3ld812adkjw@biloxi.example.com;gr=3413kj2ha>
           ;tag=a6c85cf
          Call-ID: a84b4c76e66710
          Session-ID: ab30317f1a784dc48ff824d0d3715d86
             ;remote=47755a9de7794ba387653f2099600ef2;logme
          CSeq: 74 NOTIFY
          Contact: <sips:3ld812adkjw@biloxi.example.com;gr=3413kj2ha>
          Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
          Supported: replaces, tdialog
          Event: refer
          Subscription-State: terminated;reason=noresource
          Content-Type: message/sipfrag
          Content-Length: ...













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3.8.  Forked Requests

   A SIP intermediary is required to copy the "log me" marker into
   forked requests.  SIP request forking is discussed in Sections 4 and
   16.6 of [RFC3261].

4.  SIP Entity Behavior

4.1.  Scope of Marking

   "Log me" marking is intended to be limited, in time period and number
   of dialogs marked, to the minimum needed to troubleshoot a particular
   problem or perform a particular test.

   o  SIP entities MUST be configured to "log me" mark only dialogs
      needed for the current testing purpose, e.g., troubleshooting or
      regression testing.  The mechanisms in this section ensure that
      "log me" marking begins at dialog creation and, other than cases
      of marking related dialogs or premature ending, ends when the
      dialog being "log me" marked ends.

   o  If a dialog is to be marked, the only way to initiate "log me"
      marking is at the dialog-creating request (e.g., SIP INVITE) sent
      by an originating endpoint or an intermediary that marks on behalf
      of the originating endpoint.  Marking that appears mid-dialog is
      an error as described in Section 5.1.2.  The final terminating
      endpoint, or intermediary that marks on behalf of the terminating
      endpoint, cannot initiate marking, but it takes action as defined
      in Sections 4.2 and 4.3 if it receives an incoming "log me"
      marker.

   Note that the error cases described in Section 5.1 cause SIP entities
   to stop "log me" marking, and the requirements in Section 7 also
   place requirements on SIP entities, including allowing SIP entities
   to not log signaling based on local policies (see Section 8.6).

4.2.  Endpoints

   A common scenario is to have both originating and terminating
   endpoints support "log me" marking with the originating endpoint
   configured to initiate "log me" marking.  In this simplest use case,
   the originating UA inserts a "log me" marker in the dialog-creating
   SIP request and all subsequent SIP requests within that dialog.  The
   "log me" marker is passed through the SIP intermediaries and arrives
   at the terminating UA, which echoes the "log me" marker in the
   corresponding responses.  If the terminating UA sends an in-dialog
   request on a dialog that is being "log me" marked, it inserts a "log
   me" marker and the originating UA echoes the "log me" marker in



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   responses.  The terminating UA logs the "log me" marked SIP requests
   and responses if it is allowed as per policy defined in the
   terminating network.  This basic use case suggests the following
   rules for originating and terminating UAs.

   For originating UAs:

   o  The originating UA configured for "log me" marking MUST insert a
      "log me" marker into the dialog-creating SIP request and
      subsequent in-dialog SIP requests.

   o  The originating UA itself logs marked requests and responses.

   o  The originating UA echoes, in responses, the "log me" marker
      received in in-dialog requests from the terminating side.

   o  The originating UA logs the SIP responses that it sends in
      response to received "log me" marked in-dialog requests.

   o  The originating UA MAY also apply these rules to any subsequent
      related SIP dialogs as described in Section 3.7.

   For terminating UAs:

   o  The terminating UA detects that a dialog is of interest to logging
      by the existence of a "log me" marker in an incoming dialog-
      creating SIP request.

   o  The terminating UA itself logs marked requests and corresponding
      marked responses if allowed as per policy.

   o  The terminating UA MUST echo a "log me" marker in responses to a
      SIP request that included a "log me" marker.

   o  If the terminating UA has detected that a dialog is being "log me"
      marked, it MUST insert a "log me" marker in any in-dialog SIP
      requests that it sends.

   o  The terminating UA itself logs any in-dialog SIP requests that it
      sends if allowed as per policy.

   o  The terminating UA MAY also apply these rules to any subsequent
      related SIP dialogs as described in Section 3.7.








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4.3.  SIP Intermediaries Acting on Behalf of Endpoints

   A network operator may know that some of the UAs connected to the
   network do not support "log me" marking.  Subject to the
   authorizations in Section 7.1, a SIP intermediary close to the UA
   (e.g., edge proxy, B2BUA) on the originating and/or terminating sides
   inserts the "log me" marker instead in order to test sessions
   involving such UAs.

   The originating and terminating SIP intermediaries are not identified
   by protocol means but are designated and explicitly configured by the
   network administrator to "log me" mark on behalf of endpoints.  The
   intermediaries that are known to be closest to the terminals can be
   configured to "log me" mark on behalf of terminals that do not
   support "log me" marking.  The originating SIP intermediary is the
   first one to be traversed by a SIP request sent by the originating
   endpoint.  Similarly, the terminating SIP intermediary is the last
   intermediary traversed before the terminating endpoint is reached.

   The SIP intermediary at the originating side is configured to insert
   the "log me" marker on behalf of the originating endpoint.  If the
   terminating UA does not echo the "log me" marker in responses to a
   marked request, then the SIP intermediary closest to the terminating
   UA, if configured to mark on behalf of the terminating UA, inserts a
   "log me" marker in responses to the request.  Likewise, if the
   terminating UA sends an in-dialog request, the SIP intermediary at
   the terminating side inserts a "log me" marker and the SIP
   intermediary at the originating side echoes the "log me" marker in
   responses to that request.  Originating and terminating
   intermediaries that are configured for "log me" marking on behalf of
   the endpoint must also mark dialog-creating requests that contain
   Target-Dialog [RFC4538], Join [RFC3911], and Replaces [RFC3891]
   header fields and corresponding responses.  The SIP intermediaries at
   the originating and terminating sides log the "log me" marked SIP
   requests and responses if it is allowed as per policy defined in the
   originating and terminating networks.  This scenario suggests the
   following rules when a SIP intermediary is configured to initiate or
   handle "log me" marking on behalf of a UA.

   For the originating SIP intermediary:

   o  The originating SIP intermediary configured for "log me" marking
      MUST insert a "log me" marker into the dialog-creating SIP request
      and subsequent in-dialog SIP requests.

   o  The originating SIP intermediary itself logs marked requests and
      responses.




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   o  The originating SIP intermediary detects the "log me" marker
      received in in-dialog requests and echoes the "log me" marker in
      the corresponding SIP responses.

   o  The originating SIP intermediary logs the SIP responses that it
      sends in response to "log me" marked in-dialog requests.

   o  The originating SIP intermediary MAY also apply these rules to any
      subsequent related SIP dialogs as described in Section 3.7.

   For the terminating SIP intermediary:

   o  The terminating SIP intermediary detects that a dialog is of
      interest to logging by the existence of a "log me" marker in an
      incoming dialog-creating SIP request.

   o  The terminating SIP intermediary itself logs marked requests and
      corresponding responses if allowed as per policy.

   o  The terminating SIP intermediary MUST echo a "log me" marker in
      responses to a SIP request that included a "log me" marker.

   o  If the terminating SIP intermediary has detected that a dialog is
      being "log me" marked, it MUST insert a "log me" marker in any
      in-dialog SIP requests from the terminating UA.

   o  The terminating SIP intermediary itself logs any in-dialog SIP
      requests that it sends if allowed as per policy.

   o  The terminating SIP intermediary MAY also apply these rules to any
      subsequent related SIP dialogs as described in Section 3.7.

4.4.  B2BUAs

   B2BUA "log me" behavior is specified based on its different signaling
   plane roles described in [RFC7092].

   A Proxy-B2BUA SHOULD copy "log me" marking in requests and responses
   from its terminating side to the originating side without needing
   explicit configuration to do so.

   A dialog on one "side" of the B2BUA may or may not be coupled to a
   related dialog on the other "side" for "log me" purposes.  To allow
   end-to-end troubleshooting of user problems and regression testing, a
   signaling-only and SDP-modifying signaling-only B2BUA [RFC7092]
   SHOULD couple related dialogs for "log me" marking purposes and pass
   on the received "log me" parameter from the originating side to the
   terminating side and vice versa.  For example, a SIP B2BUA handling



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   an end-to-end session between an external caller and an agent in a
   contact center environment can couple the dialog between itself and
   an agent with the dialog between itself and the external caller.  It
   can pass on the "log me" marking from the originating side to the
   terminating side to enable end-to-end logging of specific sessions of
   interest.

   For dialogs that are being "log me" marked, all B2BUAs MUST "log me"
   mark in-dialog SIP requests that they generate on their own, without
   needing explicit configuration to do so.  This rule applies to both
   the originating and terminating sides of a B2BUA.

4.5.  "Log Me" Marker Processing by SIP Intermediaries

4.5.1.  Stateless Processing

   Typically, "log me" marking will be done by an originating UA and
   echoed by a terminating UA.  SIP intermediaries on the signaling path
   between these UAs that do not perform the tasks described in Sections
   4.3 or 4.4 MUST simply log any request or response that contains a
   "log me" marker in a stateless manner, if it is allowed per local
   policy.

4.5.2.  Stateful Processing

   The originating and terminating SIP intermediaries that "log me" mark
   on behalf of endpoints and SIP intermediaries that remove "log me"
   marking at the network boundary must maintain state to enable "log
   me" marking.  Applicable scenarios are as follows:

   o  The originating UA does not support "log me" marking.  This
      scenario was described in Section 4.3 and requires support by the
      originating SIP intermediary.  "Log me" marker processing is
      illustrated in Section 4.5.2.1.

   o  The terminating UA does not support "log me" marking.  This
      scenario was described in Section 4.3 and requires support by the
      terminating SIP intermediary.  "Log me" marker processing is
      illustrated in Section 4.5.2.2.

   o  The originating network ensures that it does not pass marking
      outside its boundaries in order to not impact any external
      networks.  The originating network removes "log me" marking from
      SIP requests and responses before forwarding them from its network
      boundary to external networks, but it adds marking back to any
      incoming SIP requests and responses belonging to any "log me"





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      marked dialog.  This scenario requires support by the SIP
      intermediary at the originating network boundary.  "Log me" marker
      processing is illustrated in Section 4.5.2.3.

   o  The terminating network ensures that it does not allow "log me"
      marking from external networks to pass through its boundary to its
      internal entities.  The terminating network removes "log me"
      marking from SIP requests and responses before forwarding them
      internally, but it adds marking back to any outgoing SIP requests
      and responses belonging to any "log me" marked dialog.  This
      scenario requires support by the SIP intermediary at the
      terminating network boundary.  "Log me" marker processing is
      illustrated in Section 4.5.2.4.

   o  The terminating network does not support "log me" marking and does
      not echo marking that it receives.  The originating network adds
      marking back to any incoming SIP requests and responses belonging
      to the "log me" marked dialog.  This scenario requires support by
      the SIP intermediary at the originating network boundary and "log
      me" marker processing is illustrated in Section 4.5.2.5.

   SIP intermediary behavior in these scenarios is illustrated using
   [RFC3665] example call flow "Session Establishment Through Two
   Proxies".

4.5.2.1.  "Log Me" Marking Not Supported by Originating UA

   Alice's UA does not support "log me" marking; hence, Proxy 1, which
   is the SIP intermediary closest to Alice, is configured to act on
   behalf of Alice's UA to "log me" mark specific dialogs of interest
   that are created by Alice for troubleshooting purposes.

   In Figure 3, Proxy 1 in the originating network maintains state of
   which dialogs are being logged in order to "log me" mark all SIP
   requests and responses that it receives from Alice's UA before
   forwarding them to Proxy 2.















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        [ NETWORK A           ]          [ NETWORK B          ]
        Alice           Proxy 1          Proxy 2            Bob
          |                |                |                |
          |   INVITE F1    |                |                |
          |  (no logme)    |                |                |
          |--------------->|                |                |
          |                |   INVITE F2    |                |
          |                |    (logme)     |                |
          |                |--------------->|                |
          |                |                |                |
          |                |                |                |
          |   100  F3      |                |   INVITE F4    |
          |   (logme)      |                |     (logme)    |
          |<---------------|     100  F5    |--------------->|
          |                |    (logme)     |                |
          |                |<---------------|                |
          |                |                |     180 F6     |
          |                |                |     (logme)    |
          |                |    180 F7      |<---------------|
          |                |    (logme)     |                |
          |     180 F8     |<---------------|                |
          |     (logme)    |                |                |
          |<---------------|                |     200 F9     |
          |                |                |     (logme)    |
          |                |    200 F10     |<---------------|
          |                |    (logme)     |                |
          |     200 F11    |<---------------|                |
          |     (logme)    |                |                |
          |<---------------|                |                |
          |     ACK F12    |                |                |
          |  (no logme)    |                |                |
          |--------------->|                |                |
          |                |                |                |
          |                |    ACK F13     |                |
          |                |    (logme)     |                |
          |                |--------------->|                |
          |                |                |                |
          |                |                |     ACK F14    |
          |                |                |     (logme)    |
          |                |                |--------------->|
          |                Both Way RTP Media                |
          |<================================================>|









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          |                |                |     BYE F15    |
          |                |                |     (logme)    |
          |                |    BYE F16     |<---------------|
          |                |    (logme)     |                |
          |     BYE F17    |<---------------|                |
          |     (logme)    |                |                |
          |<---------------|                |                |
          |     200 F18    |                |                |
          |  (no logme)    |                |                |
          |--------------->|                |                |
          |                |     200 F19    |                |
          |                |    (logme)     |                |
          |                |--------------->|                |
          |                |                |                |
          |                |                |     200 F20    |
          |                |                |     (logme)    |
          |                |                |--------------->|
          |                |                |                |

      Figure 3: The Originating UA Does Not Support "Log Me" Marking

   F1:   Alice's UA does not insert a "log me" marker in the dialog-
         creating INVITE request F1.  Nevertheless, Proxy 1 is
         configured to initiate logging on behalf of Alice.  Proxy 1
         logs INVITE request F1 and maintains state that this dialog is
         being logged.

   F2:   Proxy 1 inserts a "log me" marker in INVITE request F2 before
         forwarding it to Proxy 2.  Proxy 1 logs this request.

   F3:   Proxy 1 inserts a "log me" marker in 100 response F3 before
         forwarding it to Alice's UA since this is a response sent on a
         dialog that is being "log me" marked.  Proxy 1 logs this
         response.

   F4:   "Bob's UA detects the "log me" marker and logs the INVITE
         request F4 if allowed as per policy.

   F6:   Bob's UA echoes the "log me" marker in INVITE request F4 into
         180 response F6.  It logs this response if allowed as per
         policy.

   F7 and F8:  Proxy 1 logs the received "180" response F7 and passes
         the "log me" marker to Alice's UA in F8.

   F12:  Proxy 1 receives ACK with no "log me" marker.  It doesn't
         consider this an error since it is configured to "log me" mark
         on behalf of Alice's UA.



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   F13:  Proxy 1 inserts a "log me" marker in ACK request F13 before
         forwarding it to Proxy 2.  Proxy 1 logs this request.

   F15:  Bob's UA inserts a "log me" marker in the in-dialog BYE request
         and this "log me" marker is carried back to Alice's UA in F16
         and F17.  Bob's UA logs this request if allowed as per policy.

   F18:  Alice's UA does not echo the "log me" marker from BYE request
         F17 into 200 response F18.

   F19:  Proxy 1 inserts a "log me" marker in 200 response F19 before
         forwarding it to Proxy 2.  Proxy 1 logs this response.

4.5.2.2.  "Log Me" Marking Not Supported by Terminating UA

   In Figure 4, Bob's UA does not support "log me" marking, so Proxy 2
   in the terminating network maintains state to ensure "log me" marking
   of SIP requests and responses from Bob's UA.

































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       [ NETWORK A           ]          [ NETWORK B          ]
       Alice           Proxy 1          Proxy 2            Bob
         |                |                |                |
         |   INVITE F1    |                |                |
         |    (log me)    |                |                |
         |--------------->|                |                |
         |                |    INVITE F2   |                |
         |                |     (log me)   |                |
         |                |--------------->|                |
         |                |                |                |
         |                |                |                |
         |     100  F3    |                |                |
         |     (log me)   |                |                |
         |<---------------|                |                |
         |                |                |   INVITE F4    |
         |                |                |    (log me)    |
         |                |     100  F5    |--------------->|
         |                |     (log me)   |                |
         |                |<---------------|                |
         |                |                |     180 F6     |
         |                |                |   (no log me)  |
         |                |                |<---------------|
         |                |                |                |
         |                |                |                |
         |                |    180 F7      |                |
         |                |   (log me)     |                |
         |                |<---------------|                |
         |                |                |                |
         |                |                |                |
         |     180 F8     |                |                |
         |     (log me)   |                |                |
         |<---------------|                |     200 F9     |
         |                |                |    (no log me) |
         |                |    200 F10     |<---------------|
         |                |    (log me)    |                |
         |     200 F11    |<---------------|                |
         |     (log me)   |                |                |
         |<---------------|                |                |
         |     ACK F12    |                |                |
         |    (log me)    |                |                |
         |--------------->|                |                |
         |                |    ACK F13     |                |
         |                |    (log me)    |                |
         |                |--------------->|     ACK F14    |
         |                |                |    (log me)    |
         |                |                |--------------->|
         |                Both Way RTP Media                |
         |<================================================>|



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         |                |                |     BYE F15    |
         |                |                |   (no log me)  |
         |                |    BYE F16     |<---------------|
         |                |   (log me)     |                |
         |     BYE F17    |<---------------|                |
         |    (log me)    |                |                |
         |<---------------|                |                |
         |     200 F18    |                |                |
         |    (log me)    |                |                |
         |--------------->|                |                |
         |                |     200 F19    |                |
         |                |    (log me)    |                |
         |                |--------------->|     200 F20    |
         |                |                |    (log me)    |
         |                |                |--------------->|
         |                |                |                |

      Figure 4: The Terminating UA Does Not Support "Log Me" Marking.

   F1:   Alice's UA inserts a "log me" marker in the dialog-creating
         INVITE request F1.

   F2:   INVITE F2 is "log me" marked; therefore, Proxy 2 maintains
         state that this dialog is to be logged.  Proxy 2 logs the
         request and responses of this dialog if allowed per policy.

   F5:   Proxy 2 inserts a "log me" marker in the 100 response it sends
         to Proxy 1.

   F6:   Bob's UA does not support "log me" marking; therefore, the 180
         response to the INVITE request doesn't have a "log me" marker.

   F7:   Proxy 2 inserts a "log me" marker in the 180 response on behalf
         of Bob's UA before forwarding it.  The same applies to response
         F10 and the BYE request in F16.

4.5.2.3.  "Log Me" Marking Removed by Originating Network

   If network A in Figure 5 is performing testing independently of
   network B, then network A removes "log me" marking from SIP requests
   and responses forwarded to network B to prevent triggering unintended
   logging in network B.  Proxy 1 removes "log me" marking from requests
   and responses that it forwards to Proxy 2 and maintains state of
   which dialogs are being "log me" marked in order to "log me" mark
   requests and responses that it forwards from Proxy 2 to Alice's UA.
   For troubleshooting purposes, Proxy 1 MAY also log the requests and
   responses sent to or received from Proxy 2 even though it removed
   "log me" marker prior to forwarding the messages to Proxy 2.



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          [ NETWORK A           ]          [ NETWORK B          ]
        Alice           Proxy 1          Proxy 2            Bob
          |                |                |                |
          |   INVITE F1    |                |                |
          |   (logme)      |                |                |
          |--------------->|                |                |
          |                |   INVITE F2    |                |
          |                |  (no logme)    |                |
          |                |--------------->|                |
          |                |                |                |
          |                |                |                |
          |     100  F3    |                |                |
          |     (logme)    |                |   INVITE F4    |
          |                |                |  (no logme)    |
          |<---------------|     100  F5    |--------------->|
          |                |  (no logme)    |                |
          |                |<---------------|                |
          |                |                |     180 F6     |
          |                |                |  (no logme)    |
          |                |    180 F7      |<---------------|
          |                |  (no logme)    |                |
          |     180 F8     |<---------------|                |
          |     (logme)    |                |                |
          |<---------------|                |     200 F9     |
          |                |                |  (no logme)    |
          |                |    200 F10     |<---------------|
          |                |  (no logme)    |                |
          |     200 F11    |<---------------|                |
          |     (logme)    |                |                |
          |<---------------|                |                |
          |     ACK F12    |                |                |
          |     (logme)    |                |                |
          |--------------->|                |                |
          |                |                |                |
          |                |    ACK F13     |                |
          |                |  (no logme)    |                |
          |                |--------------->|                |
          |                |                |                |
          |                |                |     ACK F14    |
          |                |                |   (no logme)   |
          |                |                |--------------->|
          |                Both Way RTP Media                |
          |<================================================>|








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          |                |                |     BYE F15    |
          |                |                |   (no logme)   |
          |                |    BYE F16     |<---------------|
          |                |  (no logme)    |                |
          |     BYE F17    |<---------------|                |
          |     (logme)    |                |                |
          |<---------------|                |                |
          |     200 F18    |                |                |
          |    (logme)     |                |                |
          |--------------->|                |                |
          |                |     200 F19    |                |
          |                |   (no logme)   |                |
          |                |--------------->|                |
          |                |                |                |
          |                |                |     200 F20    |
          |                |                |   (no logme)   |
          |                |                |--------------->|
          |                |                |                |

      Figure 5: The Originating Network Removes "Log Me" Marking from
                Outgoing SIP Messages at its Network Edge.

   F1:   Alice's UA inserts a "log me" marker in the dialog-creating
         INVITE request, and Proxy 1 therefore maintains state that this
         dialog is to be logged.

   F2:   Proxy 1 removes "log me" marking from INVITE request before
         forwarding it to Proxy 2.  Proxy 1 logs INVITE request F2.

   F3:   Proxy 1 inserts a "log me" marker in the 100 response sent to
         Alice's UA.  Proxy 1 logs this response.

   F8:   Proxy 1 inserts a "log me" marker in the 180 response before
         forwarding it to Alice's UA.  Proxy 1 logs this response.  The
         same applies to responses F11 and F17.

   F13:  Proxy 1 removes "log me" marking from the ACK request.  Proxy 1
         logs this request before forwarding it to Proxy 2.

   F19:  Proxy 1 removes "log me" marking from the 200 response of the
         BYE request.  Proxy 1 logs this response before forwarding it
         to Proxy 2.









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4.5.2.4.  "Log Me" Marking Removed by Supporting Terminating Network

   In Figure 6, Proxy 2 removes "log me" marking from all SIP requests
   and responses entering network B.  However, Proxy 2 supports
   maintaining the marking state of the dialog and "log me" marks
   requests and responses that it sends towards Proxy 1.  For
   troubleshooting purposes, Proxy 2 MAY also log the requests and
   responses received from or sent to Bob even though it removed the
   "log me" marker prior to forwarding the messages to Bob.  This
   scenario might be used for troubleshooting a signaling path between
   two enterprise or carrier networks, or across a transit network, with
   minimal logging (i.e., only at the network boundaries).







































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       [ NETWORK A           ]          [ NETWORK B          ]
       Alice           Proxy 1          Proxy 2            Bob
         |                |                |                |
         |   INVITE F1    |                |                |
         |   (log me)     |                |                |
         |--------------->|                |                |
         |                |    INVITE F2   |                |
         |                |    (log me)    |                |
         |                |--------------->|                |
         |                |                |                |
         |                |                |                |
         |     100  F3    |                |                |
         |    (log me)    |                |                |
         |<---------------|                |                |
         |                |                |   INVITE F4    |
         |                |                |   (no log me)  |
         |                |     100  F5    |--------------->|
         |                |    (log me)    |                |
         |                |<---------------|                |
         |                |                |     180 F6     |
         |                |                |   (no log me)  |
         |                |                |<---------------|
         |                |    180 F7      |                |
         |                |   (log me)     |                |
         |                |<---------------|                |
         |                |                |                |
         |                |                |                |
         |     180 F8     |                |                |
         |    (log me)    |                |                |
         |<---------------|                |     200 F9     |
         |                |                |   (no log me)  |
         |                |    200 F10     |<---------------|
         |                |   (log me)     |                |
         |     200 F11    |<---------------|                |
         |    (log me)    |                |                |
         |<---------------|                |                |
         |     ACK F12    |                |                |
         |    (log me)    |                |                |
         |--------------->|                |                |
         |                |    ACK F13     |                |
         |                |   (log me)     |                |
         |                |--------------->|     ACK F14    |
         |                |                |   (no log me)  |
         |                |                |--------------->|
         |                Both Way RTP Media                |
         |<================================================>|





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         |                |                |     BYE F15    |
         |                |                |   (no log me)  |
         |                |    BYE F16     |<---------------|
         |                |   (log me)     |                |
         |     BYE F17    |<---------------|                |
         |    (log me)    |                |                |
         |<---------------|                |                |
         |     200 F18    |                |                |
         |    (log me)    |                |                |
         |--------------->|                |                |
         |                |     200 F19    |                |
         |                |    (log me)    |                |
         |                |--------------->|     200 F20    |
         |                |                |   (no log me)  |
         |                |                |--------------->|
         |                |                |                |

      Figure 6: The terminating network removes "log me" marking from
                incoming SIP messages at its network edge.

   F1:   Alice's UA inserts a "log me" marker in the dialog-creating
         INVITE request F1.  Proxy 1 detects the "log me" marker, logs
         the request, and maintains state that this dialog is to be
         logged.

   F2:   Proxy 2 removes the "log me" marker in the INVITE request F2
         before forwarding it as F4.  The same applies to responses F13
         and F19.

   F6:   Proxy 2 inserts a "log me" marker in the 180 response to the
         INVITE request and logs the request before forwarding it as F7.
         The same applies to response F9 and the BYE request in F15.

4.5.2.5.  "Log Me" Marking Passed by Non-supporting Terminating Network

   In Figure 6, Proxy 2 is not "log me" aware and therefore passes
   marking in all SIP requests and responses entering network B
   according to the rules in Sections 16.6 and 16.7 of [RFC3261].  Proxy
   2 does not log requests and responses in the dialog.  Proxy 1
   supports maintaining the marking state of the dialog.  When Proxy 1
   observes that requests and responses received from Proxy 2 are not
   marked, it adds the marking.

   For troubleshooting purposes, Proxy 1 MAY also log the requests and
   responses received from or sent to Proxy 2 even though Proxy 2 didn't
   add "log me" to messages sent to Proxy 1.





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       [ NETWORK A           ]          [ NETWORK B          ]
       Alice           Proxy 1          Proxy 2            Bob
         |                |                |                |
         |   INVITE F1    |                |                |
         |   (log me)     |                |                |
         |--------------->|                |                |
         |                |    INVITE F2   |                |
         |                |   (log me)     |                |
         |                |--------------->|                |
         |                |                |                |
         |                |                |                |
         |     100  F3    |                |                |
         |   (log me)     |                |                |
         |<---------------|                |                |
         |                |                |   INVITE F4    |
         |                |                |   (log me)     |
         |                |     100  F5    |--------------->|
         |                |   (no log me)  |                |
         |                |<---------------|                |
         |                |                |     180 F6     |
         |                |                |  (no log me)   |
         |                |                |<---------------|
         |                |    180 F7      |                |
         |                |   (no log me)  |                |
         |                |<---------------|                |
         |                |                |                |
         |                |                |                |
         |     180 F8     |                |                |
         |   (log me)     |                |                |
         |<---------------|                |     200 F9     |
         |                |                |   (no log me)  |
         |                |    200 F10     |<---------------|
         |                |  (no log me)   |                |
         |     200 F11    |<---------------|                |
         |   (log me)     |                |                |
         |<---------------|                |                |
         |     ACK F12    |                |                |
         |   (log me)     |                |                |
         |--------------->|                |                |
         |                |    ACK F13     |                |
         |                |   (log me)     |                |
         |                |--------------->|     ACK F14    |
         |                |                |    (log me)    |
         |                |                |--------------->|
         |                Both Way RTP Media                |
         |<================================================>|





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         |                |                |     BYE F15    |
         |                |                |  (no log me)   |
         |                |    BYE F16     |<---------------|
         |                |   (no log me)  |                |
         |     BYE F17    |<---------------|                |
         |   (log me)     |                |                |
         |<---------------|                |                |
         |     200 F18    |                |                |
         |   (log me)     |                |                |
         |--------------->|                |                |
         |                |     200 F19    |                |
         |                |    (log me)    |                |
         |                |--------------->|     200 F20    |
         |                |                |    (log me)    |
         |                |                |--------------->|
         |                |                |                |

      Figure 7: The Terminating Network Removes "Log Me" Marking from
                Incoming SIP Messages at its Network Edge.

   F1:   Alice's UA inserts a "log me" marker in the dialog-creating
         INVITE request F1.  Proxy 1 detects the "log me" marker, logs
         the request, and maintains state that this dialog is to be
         logged.

   F2:   Proxy 2 passes the "log me" marker in the INVITE request F2
         before forwarding it as F4.  The same applies to request F13
         and response F19.

   F6:   Bob's UA does not support "log me" marking and does not echo
         the "log me" marker in response F6.  The same applies to
         response F9 and the BYE request F15.

   F7:   Proxy 1 inserts a "log me" marker in the 180 response of the
         INVITE request before forwarding it as F8.  The same applies to
         response F10 and the BYE request F16.















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5.  Errors

5.1.  Error Cases

   The following error cases are possible for "log me" marking:

   1.  A "log me" marker is unexpectedly missing from a dialog that is
       being logged.

   2.  A "log me" marker unexpectedly appears in a dialog that is not
       being logged.

   3.  A "log me" marker unexpectedly disappears and then reappears in a
       dialog being logged.  This is treated in the same way as case 1.

   4.  A "log me" marker is unexpectedly missing from a retransmission
       in a dialog being logged.  This is treated in the same way as
       case 1.

   These cases apply to any request or response sent by any entity and
   in any direction in a dialog being "log me" marked.  Detection of
   these error cases is described in this section.

5.1.1.  Missing "Log Me" Marker Error Case

   Since "log me" marking is per-dialog, if a dialog is being marked and
   marking is missing from a request or response then this is an error.

   However, detecting such errors is not as simple as checking for
   missing markers because of cases such as non-supporting terminals
   where it is normal that marking is not done.

   Detecting errors must be evaluated separately for each neighbor.  It
   is an error if a particular neighbor has previously sent "log me" in
   the dialog and then stops, independently of what has been happening
   with other neighbors.

   UAs and intermediaries that are stateless with respect to "log me"
   marking are not able detect such errors.  User agents and
   intermediaries that are stateful with respect to "log me" marking are
   able to detect that a marker is missing from a dialog that has
   previously been "log me" marked.  Error cases are illustrated in this
   section, and non-error cases in Section 5.2.1.








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   The following figures illustrate missing "log me" marker errors.

   Figure 8 shows an error detected at Proxy 1, where an expected "log
   me" marker is missing.

       [ NETWORK A           ]          [ NETWORK B          ]
       Alice           Proxy 1          Proxy 2            Bob
         |                |                |                |
         |   INVITE F1    |                |                |
         |    (log me)    |  INVITE F2     |                |
         |--------------->|   (log me)     |  INVITE F3     |
         |                |--------------->|   (log me)     |
         |                |                |--------------->|
         |                |                |                |
         |                |                |   200 F4       |
         |                |     200 F5     |   (log me)     |
         |     200 F6     |    (log me)    |<---------------|
         |    (log me)    |<---------------|                |
         |<---------------|                |                |
         |                |                |                |
         |     ACK F7     |                |                |
         |  (no log me)   |                |                |
         |--------------->|                |                |
         |                |     ACK F8     |                |
         |                |  (no log me)   |                |
         |                |--------------->|                |
         |                |                |     ACK F9     |
         |                |                |  (no log me)   |
         |                |                |--------------->|

               Figure 8: Error Case: Missing "Log Me" Marker

   F1:   Proxy 1 detects the "log me" marker and maintains state that
         this dialog is to be logged.

   F7:   Proxy 1 detects that the expected "log me" marker is missing,
         considers it to be an error, and stops "log me" marking in
         subsequent requests and responses in this dialog.

   Figure 9 shows an error detected at both Proxy 2 and Bob's UA.











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       [ NETWORK A           ]          [ NETWORK B          ]
       Alice           Proxy 1          Proxy 2            Bob
         |   INVITE F1    |                |                |
         |   (log me)     |                |                |
         |--------------->|                |                |
         |                |    INVITE F2   |                |
         |                |   (log me)     |                |
         |                |--------------->|                |
         |                |                |                |
         |                |                |                |
         |     100  F3    |                |                |
         |   (log me)     |                |                |
         |<---------------|                |                |
         |                |                |   INVITE F4    |
         |                |                |   (log me)     |
         |                |     100  F5    |--------------->|
         |                |   (log me)     |                |
         |                |<---------------|                |
         |                |                |     180 F6     |
         |                |                |     (log me)   |
         |                |                |<---------------|
         |                |    180 F7      |                |
         |                |   (log me)     |                |
         |                |<---------------|                |
         |                |                |                |
         |                |                |                |
         |     180 F8     |                |                |
         |   (log me)     |                |                |
         |<---------------|                |     200 F9     |
         |                |                |    (log me)    |
         |                |    200 F10     |<---------------|
         |                |   (log me)     |                |
         |     200 F11    |<---------------|                |
         |   (log me)     |                |                |
         |<---------------|                |                |
         |     ACK F12    |                |                |
         |  (no log me)   |                |                |
         |--------------->|                |                |
         |                |    ACK F13     |                |
         |                | (no log me)    |                |
         |                |--------------->|     ACK F14    |
         |                |                |   (no log me)  |
         |                |                |--------------->|

               Figure 9: Error Case: Missing "Log Me" Marker






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   F2:   Proxy 2 detects the "log me" marker and maintains state that
         this dialog is to be logged.

   F4:   Bob's UA detects the "log me" marker and maintains state that
         this dialog is to be logged.

   F12:  Proxy 1 detects that the expected "log me" marker is missing,
         considers it to be an error, and stops "log me" marking in
         subsequent requests and responses in this dialog.  Hence, it
         does not insert a "log me" marker in F13.

   F13:  Proxy 2 detects that the expected "log me" marker is missing,
         considers it to be an error, and stops "log me" marking in
         subsequent requests and responses in this dialog.

   F14:  Proxy 2 does not insert a "log me" marker because it has
         stopped "log me" marking due to an error observed in F13.
         Bob's UA detects that the expected "log me" marker is missing,
         considers it to be an error, and stops "log me" marking in
         subsequent requests and responses in this dialog.































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5.1.2.  "Log Me" Marker Appears Mid-dialog Error Case

   SIP endpoints, intermediaries acting on behalf of endpoints, and
   B2BUAs that can perform "log me" marking are stateful.  Such entities
   will expect a "log me" marker only for dialogs where the initial
   dialog-creating request was "log me" marked, either by themselves or
   by an upstream entity.  "Log me" marking that subsequently begins
   mid-dialog is an error.

   Figure 10 illustrates a "log me" marking error observed in the middle
   of a dialog.  Alice's UA supports "log me" marking but the call is
   not initially marked for logging, i.e., INVITE F1 is not "log me"
   marked.  But Alice's UA starts to "log me" mark at the ACK request
   F7.  Proxy 1 supports "log me" marking at the originating network
   boundary and therefore detects the error, does not log signaling, and
   removes the "log me" marker before forwarding the ACK request F8.

          [ NETWORK A           ]          [ NETWORK B          ]
          Alice           Proxy 1          Proxy 2            Bob
            |                |                |                |
            |   INVITE F1    |                |                |
            |  (no log me)   |    INVITE F2   |                |
            |--------------->|   (no log me)  |    INVITE F3   |
            |                |--------------->|   (no log me)  |
            |                |                |--------------->|
            |                |                |                |
            |                |                |    200 F4      |
            |                |    200 F5      |  (no log me)   |
            |    200 F6      |  (no log me)   |<---------------|
            |  (no log me)   |<---------------|                |
            |<---------------|                |                |
            |                |                |                |
            |    ACK F7      |                |                |
            |   (log me)     |                |                |
            |--------------->|                |                |
            |                |    ACK F8      |                |
            |                |  (no log me)   |                |
            |                |--------------->|                |
            |                |                |    ACK F9      |
            |                |                |   (log me)     |
            |                |                |--------------->|

         Figure 10: Error Case: "Log Me" Marker Begins Mid-dialog








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5.2.  Non-error Cases

5.2.1.  Missing "Log Me" Marker Non-error Case

   The following figure illustrates a non-error case.

   Figure 11 shows Proxy 2 receiving a response with no "log me" marker
   that is not an error case.  Proxy 2 is configured by network B to
   perform "log me" marking on behalf of Bob's UA, which does not
   support "log me" marking.  Proxy 2 does not therefore expect
   responses from Bob to include a "log me" marker.

       [ NETWORK A           ]          [ NETWORK B          ]
       Alice           Proxy 1          Proxy 2            Bob
         |                |                |                |
         |   INVITE F1    |                |                |
         |   (log me)     |                |                |
         |--------------->|                |                |
         |                |    INVITE F2   |                |
         |                |   (log me)     |                |
         |                |--------------->|                |
         |                |                |                |
         |                |                |                |
         |     100  F3    |                |                |
         |   (log me)     |                |                |
         |<---------------|                |                |
         |                |                |   INVITE F4    |
         |                |                |   (log me)     |
         |                |     100  F5    |--------------->|
         |                |   (log me)     |                |
         |                |<---------------|                |
         |                |                |     180 F6     |
         |                |                |   (no log me)  |
         |                |                |<---------------|
         |                |    180 F7      |                |
         |                |   (log me)     |                |
         |                |<---------------|                |
         |     180  F8    |                |                |
         |    (log me)    |                |                |
         |<---------------|                |                |

            Figure 11: Non-error Case: Missing "Log Me" Marker

   F2:   Proxy 2 detects the "log me" marker and maintains state that
         this dialog is to be logged.  Proxy 2 inserts "log me" markers
         on behalf of Bob's user agent, such as in F7.





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   F6:   Proxy 2 detects that the "log me" marker is missing from the
         response but considers "log me" marking to be ongoing as a
         marker was not expected.

   F7:   Proxy 2 continues to "log me" mark requests and responses on
         behalf of Bob's UA.

5.2.2.  "Log Me" Marker Appears Mid-dialog Non-error Case

   A SIP intermediary that can perform "log me" marking on behalf of an
   endpoint MAY optionally mark a request or response towards a
   non-supporting endpoint, such as the 100 response F3 in Figure 3.  In
   this case, the endpoint will receive a "log me" marker mid-dialog,
   and this is not considered an error.

   Another use case is a network in which some (but not all) endpoints
   support "log me" marking and that wants to avoid treating endpoints
   differently by always managing "log me" marking at a SIP
   intermediary.  In this case, the endpoint that supports "log me" is
   not configured to mark a dialog; instead, the SIP intermediary is
   configured to perform "log me" marking on behalf of that endpoint.
   This case still requires authorization as described in Section 7.1.
   This SIP intermediary MAY optionally mark a request or response
   towards the endpoint, such as the 100 response F3 in Figure 3.  The
   endpoint will receive a "log me" marker mid-dialog, which is not
   considered an error.

5.2.3.  Combining Dialogs Non-error Case

   When troubleshooting call flows that involve the SIP Join header
   field specified in [RFC3911], the ideal scenario is to have "log me"
   marking enabled on all UAs and intermediaries participating in the
   end-to-end session.  If the ideal scenario is not feasible, the
   following rules apply:

   o  If an endpoint or an intermediary that is "log me" aware and is
      already "log me" marking a dialog receives a SIP INVITE with a
      Join header field and without a "log me" marker, it MUST NOT "log
      me" mark responses and requests exchanged within the new dialog
      established as a result of processing the SIP INVITE.

   o  If an endpoint or an intermediary that is "log me" aware and is
      not "log me" marking a dialog receives a SIP INVITE with a Join
      header field and with a "log me" marker, it MUST "log me" mark
      responses and requests exchanged within the new dialog established
      as a result of processing the SIP INVITE as per Section 4 of this
      document.




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5.3.  Error Handling

   The two error types that SIP entities must handle are defined in
   Section 5.1: a missing marker error and an error of "log me" marking
   that begins mid-dialog.  Section 5.2 gives exceptions that have
   marking that begins mid-dialog or a missing marker but are not
   errors.

   If a missing marker error is detected by a UA, SIP intermediary, or
   B2BUA, it SHOULD consider this to be an error condition in the "log
   me" functionality.  It MUST NOT mark subsequent requests and
   responses, and it MUST stop logging messages in the same dialog.  Any
   previously logged messages SHOULD be retained, for the time period
   defined in Section 8.5, and not deleted.

   If a "log me" marking that begins mid-dialog error is detected by a
   UA, SIP intermediary, or B2BUA, it SHOULD consider this to be an
   error condition in the "log me" functionality.  It MUST NOT forward
   the "log me" marker, and it MUST NOT log the message.  It MUST NOT
   mark subsequent requests and responses, and it MUST NOT log
   subsequent messages in the same dialog.

   "Log me" marking errors can be detected and handled only by
   supporting UAs or B2BUAs.  A SIP proxy as defined in [RFC3261] cannot
   detect or handle marking errors and will simply forward any "log me"
   marker it receives.

6.  Augmented BNF for the "logme" Parameter

   ABNF is described in [RFC5234].  This document introduces a new
   "logme" parameter for the Session-ID header field defined in
   Section 5 of [RFC7989].

          sess-id-param       =/ logme-param

          logme-param         = "logme"

            Figure 12: Augmented BNF for the "logme" Parameter













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7.  Security Considerations

7.1.  "Log Me" Authorization

   "Log me" marking MUST be disabled by default both at the endpoints
   and intermediaries and MUST be enabled only by authorized users.  For
   example, an end user or network administrator must give permission
   for a terminal that supports "log me" marking in order to initiate
   marking.  Similarly, a network administrator must enable a
   configuration at the SIP intermediary to perform "log me" marking on
   behalf of a terminal that does not support "log me" marking.  The
   permission MUST be limited to only specific calls of interest that
   are originated in a given time duration.

   Activating a debug mode affects the operation of a terminal;
   therefore, the debugging configuration MUST be supplied by an
   authorized party to an authorized terminal through a secure
   communication channel.

7.2.  "Log Me" Marker Removal

   The "log me" marker is not sensitive information, though it will
   sometimes be inserted because a particular device is experiencing
   problems.

   The presence of a "log me" marker will cause some SIP entities to log
   signaling messages.  Therefore, this marker MUST be removed at the
   earliest opportunity if it has been incorrectly inserted, such as
   appearing mid-dialog in a dialog that was not being logged or outside
   the configured start and stop of logging.

   If SIP requests and responses are exchanged with an external network
   with which there is no agreement to pass "log me" marking, then the
   "log me" marking is removed as mandated in Section 3.4.2.  This
   behavior applies to incoming and outgoing requests and responses.

7.3.  Denial-of-Service Attacks

   Maliciously configuring a large number of terminals to simultaneously
   mark dialogs with a "log me" marker will cause high processor load on
   SIP entities that are logging signaling.  Since "log me" marking is
   for the small number of dialogs subject to troubleshooting or
   regression testing, the number of dialogs that can be simultaneously
   logged can be statically limited without adversely affecting the
   usefulness of "log me" marking.  Also, the SIP intermediary closest
   to the terminal and SIP intermediary at network edge (e.g., Session
   Border Controllers) can be configured to screen-out "log me" markers
   when troubleshooting or regression testing is not in progress.



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7.4.  Data Protection

   A SIP entity that has logged information MUST protect the logs.
   Storage of the log files are subject to the security considerations
   specified in [RFC6872].

8.  Privacy Considerations

   Logging includes all SIP header fields.  The SIP privacy mechanisms
   defined in [RFC3323] can be used to ensure that logs do not divulge
   personal identity information in the core SIP header fields specified
   in [RFC3261].

   Privacy mechanisms might also need to be applied to header fields
   defined by SIP extensions and for managing the confidentiality of the
   Request-URI and SIP header fields and bodies.

8.1.  Personal Identifiers

   "Log me" marking is defined for the SIP protocol, and SIP has header
   fields such as From, Contact, and P-Asserted-Identity that can carry
   personal identifiers.  Different protocol interactions can be
   correlated using the Session-ID and Call-ID header fields, but such
   correlation is limited to a single end-to-end session.

   In order to protect user privacy during logging, privacy settings can
   be enabled or requested by the terminal used by the end user.
   [RFC3323] suggests two mechanisms:

   o  By using the value "anonymous" in the From header field

   o  By requesting header-level and session-level privacy from SIP
      intermediaries using the Privacy header

   Endpoints that support Globally Routable User Agent URIs (GRUUs) can
   use a temporary GRUU (see Section 3.1.2 of [RFC5627]) assigned by the
   Registrar in order to protect user privacy as discussed in
   Section 10.3 of [RFC5627].

   Intermediaries that perform "log me" marking on behalf of the
   endpoints (see Section 4.3) may also be configured to apply privacy
   (as defined in Section 3.3 of [RFC3323]) on messages that belong to a
   dialog that is "log me" marked.

   Complete anonymization (e.g., the Request-URI and the "username"
   field in the "o=" parameter of an SDP body) may not be possible in
   all circumstances; therefore, administrators of the originating and




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   terminating networks should consider how privacy will be ensured when
   providing consent for "log me" marking.

   "Log me" marking is typically used for troubleshooting and regression
   testing; in some cases, a service-provider-owned device with a dummy
   account can be used instead of a customer device.  In such cases, no
   personal identifiers are included in the logged signaling messages.

8.2.  Data Stored at SIP Intermediaries

   SIP endpoints and intermediaries that honor the "log me" request
   store all the SIP messages that are exchanged within a given dialog.
   SIP messages can contain the personal identifiers listed in
   Section 8.1 and additionally a user identity, calling party number,
   IP address, hostname, and other user-related or device-related items.
   The SIP message bodies describe the kind of session being set up by
   the identified end user and device.

   "Log me" marking does not introduce any additional user or device
   data to SIP but might indicate that a specific user is experiencing a
   problem.

   If the SIP SDP parameters [SDP-PARAMETERS] contain sensitive security
   information (e.g., encryption keys) such as "crypto" [RFC4568], 3GPP-
   Integrity-Key, or 3GPP-SRTP-Config [RFC6064] attributes, then the
   attribute value MUST be masked with a dummy value prior to storing
   the message in a log file.  For example, the attribute value can be
   replaced with a string of special characters like "X", "*", and "#"
   as shown in the example below.

   a=crypto:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
    XXXXXXXXXXXXX

8.3.  Data Visible at Network Elements

   SIP messages that are logged due to "log me" requests are stored only
   by the SIP initiators, intermediaries, and recipients.  Enablers as
   defined in Section 3.1 of [RFC6973], such as firewalls and DNS
   servers, do not log messages due to the "log me" marking.

8.4.  Preventing Fingerprinting

   "Log me" functionality is typically used to troubleshoot a given
   problem and, hence, can be used as a method to identify users and
   devices that are experiencing issues.  The best way to prevent
   fingerprinting of users is to enable or request SIP privacy for the
   logged dialog.




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8.5.  Retaining Logs

   The lifetime of "log me" marking is equivalent to the lifetime of the
   dialog that initiated the "log me" request.  When "log me" is
   extended to related dialogs, the lifetime is extended until there is
   no remaining related dialog for the end-to-end session.

   "Log me" automatically expires at the end of the dialog, and there is
   no explicit mechanism to turn off logging within a dialog.

   The scope of "log me" marking is limited, i.e., a user or the network
   administrator has to enable it on a per-session basis or for a
   specific time period.  This minimizes the risk of exposing user data
   for an indefinite time.

   The retention time period for logged messages SHOULD be the minimum
   needed for each particular troubleshooting or testing case.  The
   retention period is configured based on the data-retention policies
   of service providers and enterprises.

8.6.  User Control of Logging

   Consent to turn on "log me" marking for a given session MUST be
   provided by the end user or by the network administrator.  It is
   handled outside of the protocol through user interface or application
   programming interfaces at the endpoint, call control elements, and
   network management systems.

   Originating and terminating endpoints that are "log me" aware and
   have a user interface MUST indicate (using text, icon, etc.) to the
   user that a session is being logged.

   SIP entities across the communication path MAY be configured to pass
   through the "log me" marking but not honor the request, i.e., not log
   the data based on local policies.

8.7.  Recommended Defaults

   The recommended defaults for "log me" marking are:

   o  Turn on SIP privacy as described in Section 8 or use a device that
      is service provider owned with a dummy user identity for test
      calls.

   o  Use the local UUID portion of the Session-ID header field value at
      the originating device as the test case identifier as described in
      Section 3.3.




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9.  IANA Considerations

9.1.  Registration of the "logme" Parameter

   The following parameter has been added to the "Header Field
   Parameters and Parameter Values" section of the "Session Initiation
   Protocol (SIP) Parameters" registry:

   +-------------+---------------+-------------------------+-----------+
   | Header      | Parameter     | Predefined Values       | Reference |
   | Field       | Name          |                         |           |
   +-------------+---------------+-------------------------+-----------+
   | Session-ID  | logme         | No (no values are       | [RFC8497] |
   |             |               | allowed)                |           |
   +-------------+---------------+-------------------------+-----------+

                                  Table 1

10.  References

10.1.  Normative References

   [MEDIA-TYPES]
              IANA, "Media Types",
              <https://www.iana.org/assignments/media-types/>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://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,
              <https://www.rfc-editor.org/info/rfc3261>.

   [RFC3323]  Peterson, J., "A Privacy Mechanism for the Session
              Initiation Protocol (SIP)", RFC 3323,
              DOI 10.17487/RFC3323, November 2002,
              <https://www.rfc-editor.org/info/rfc3323>.

   [RFC3891]  Mahy, R., Biggs, B., and R. Dean, "The Session Initiation
              Protocol (SIP) "Replaces" Header", RFC 3891,
              DOI 10.17487/RFC3891, September 2004,
              <https://www.rfc-editor.org/info/rfc3891>.





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   [RFC3911]  Mahy, R. and D. Petrie, "The Session Initiation Protocol
              (SIP) "Join" Header", RFC 3911, DOI 10.17487/RFC3911,
              October 2004, <https://www.rfc-editor.org/info/rfc3911>.

   [RFC4538]  Rosenberg, J., "Request Authorization through Dialog
              Identification in the Session Initiation Protocol (SIP)",
              RFC 4538, DOI 10.17487/RFC4538, June 2006,
              <https://www.rfc-editor.org/info/rfc4538>.

   [RFC4568]  Andreasen, F., Baugher, M., and D. Wing, "Session
              Description Protocol (SDP) Security Descriptions for Media
              Streams", RFC 4568, DOI 10.17487/RFC4568, July 2006,
              <https://www.rfc-editor.org/info/rfc4568>.

   [RFC5627]  Rosenberg, J., "Obtaining and Using Globally Routable User
              Agent URIs (GRUUs) in the Session Initiation Protocol
              (SIP)", RFC 5627, DOI 10.17487/RFC5627, October 2009,
              <https://www.rfc-editor.org/info/rfc5627>.

   [RFC6064]  Westerlund, M. and P. Frojdh, "SDP and RTSP Extensions
              Defined for 3GPP Packet-Switched Streaming Service and
              Multimedia Broadcast/Multicast Service", RFC 6064,
              DOI 10.17487/RFC6064, January 2011,
              <https://www.rfc-editor.org/info/rfc6064>.

   [RFC6872]  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, DOI 10.17487/RFC6872,
              February 2013, <https://www.rfc-editor.org/info/rfc6872>.

   [RFC6873]  Salgueiro, G., Gurbani, V., and A. Roach, "Format for the
              Session Initiation Protocol (SIP) Common Log Format
              (CLF)", RFC 6873, DOI 10.17487/RFC6873, February 2013,
              <https://www.rfc-editor.org/info/rfc6873>.

   [RFC7989]  Jones, P., Salgueiro, G., Pearce, C., and P. Giralt, "End-
              to-End Session Identification in IP-Based Multimedia
              Communication Networks", RFC 7989, DOI 10.17487/RFC7989,
              October 2016, <https://www.rfc-editor.org/info/rfc7989>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [SDP-PARAMETERS]
              IANA, "Session Description Protocol (SDP) Parameters",
              <https://www.iana.org/assignments/sdp-parameters/>.



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10.2.  Informative References

   [RFC3665]  Johnston, A., Donovan, S., Sparks, R., Cunningham, C., and
              K. Summers, "Session Initiation Protocol (SIP) Basic Call
              Flow Examples", BCP 75, RFC 3665, DOI 10.17487/RFC3665,
              December 2003, <https://www.rfc-editor.org/info/rfc3665>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

   [RFC5589]  Sparks, R., Johnston, A., Ed., and D. Petrie, "Session
              Initiation Protocol (SIP) Call Control - Transfer",
              BCP 149, RFC 5589, DOI 10.17487/RFC5589, June 2009,
              <https://www.rfc-editor.org/info/rfc5589>.

   [RFC6973]  Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
              Morris, J., Hansen, M., and R. Smith, "Privacy
              Considerations for Internet Protocols", RFC 6973,
              DOI 10.17487/RFC6973, July 2013,
              <https://www.rfc-editor.org/info/rfc6973>.

   [RFC7092]  Kaplan, H. and V. Pascual, "A Taxonomy of Session
              Initiation Protocol (SIP) Back-to-Back User Agents",
              RFC 7092, DOI 10.17487/RFC7092, December 2013,
              <https://www.rfc-editor.org/info/rfc7092>.

   [RFC7206]  Jones, P., Salgueiro, G., Polk, J., Liess, L., and H.
              Kaplan, "Requirements for an End-to-End Session
              Identification in IP-Based Multimedia Communication
              Networks", RFC 7206, DOI 10.17487/RFC7206, May 2014,
              <https://www.rfc-editor.org/info/rfc7206>.

   [RFC8123]  Dawes, P. and C. Arunachalam, "Requirements for Marking
              SIP Messages to be Logged", RFC 8123,
              DOI 10.17487/RFC8123, March 2017,
              <https://www.rfc-editor.org/info/rfc8123>.













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Acknowledgments

   The authors wish to thank Paul Giralt, Paul Kyzivat, Jorgen Axell,
   Christer Holmberg, Vijay Gurbani, Ben Campbell, Gonzalo Salgueiro,
   Francesca Palombini, Adam Roach, Mirja Kuhlewind, Benjamin Kaduk,
   Eric Rescorla, Alissa Cooper, Warren Kumari, and Alexey Melnikov for
   their constructive review comments and guidance while developing this
   document.

Authors' Addresses

   Peter Dawes
   Vodafone Group
   The Connection
   Newbury, Berkshire  RG14 2FN
   United Kingdom

   Phone: +44 7717 275009
   Email: peter.dawes@vodafone.com


   Chidambaram Arunachalam
   Cisco Systems
   7200-12 Kit Creek Road
   Research Triangle Park, NC  27709
   United States of America

   Email: carunach@cisco.com























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