Internet Engineering Task Force P. Dawes Internet-Draft Vodafone Group Intended status: Standards Track C. Arunachalam Expires: February 7, 2018 Cisco Systems August 6, 2017 Marking SIP Messages to be Logged draft-ietf-insipid-logme-marking-08 Abstract SIP networks use signaling monitoring tools to diagnose user reported problems and for regression testing if network or user agent 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 which 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 not used in normal user agent signaling. However, such marking can be carried 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 Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on February 7, 2018. Dawes & Arunachalam Expires February 7, 2018 [Page 1] Internet-Draft log me marking August 2017 Copyright Notice Copyright (c) 2017 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 (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 3. "Log Me" Marking Protocol Aspects . . . . . . . . . . . . . . 4 3.1. Session-ID logme Parameter . . . . . . . . . . . . . . . 4 3.2. Starting and Stopping Logging . . . . . . . . . . . . . . 4 3.3. Identifying Test Cases . . . . . . . . . . . . . . . . . 5 3.4. Passing the Marker . . . . . . . . . . . . . . . . . . . 5 3.4.1. To and From a User Device . . . . . . . . . . . . . . 5 3.4.2. To and From an External Network . . . . . . . . . . . 5 3.5. Logging Multiple Simultaneous Dialogs . . . . . . . . . . 5 3.6. Format of Logged Signaling . . . . . . . . . . . . . . . 6 3.7. Marking Related Dialogs . . . . . . . . . . . . . . . . . 6 3.8. Forked Requests . . . . . . . . . . . . . . . . . . . . . 11 4. SIP Entity Behavior . . . . . . . . . . . . . . . . . . . . . 11 4.1. Endpoints . . . . . . . . . . . . . . . . . . . . . . . . 11 4.2. SIP Intermediaries . . . . . . . . . . . . . . . . . . . 12 4.2.1. B2BUAs . . . . . . . . . . . . . . . . . . . . . . . 13 4.2.2. "Log me" Marker Processing . . . . . . . . . . . . . 14 4.2.2.1. Stateless processing . . . . . . . . . . . . . . 14 4.2.2.2. Stateful processing . . . . . . . . . . . . . . . 14 5. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 23 5.1. Missing "Log me" Marker in Dialog Being Logged . . . . . 24 5.1.1. Error Cases . . . . . . . . . . . . . . . . . . . . . 24 5.1.2. Non-Error Cases . . . . . . . . . . . . . . . . . . . 27 5.2. "Log Me" Marker Appears Mid-Dialog . . . . . . . . . . . 28 6. Security Considerations . . . . . . . . . . . . . . . . . . . 29 6.1. "Log Me" Authorization . . . . . . . . . . . . . . . . . 29 6.2. "Log Me" Marker Removal . . . . . . . . . . . . . . . . . 29 6.3. Denial of Service Attacks . . . . . . . . . . . . . . . . 29 6.4. Privacy . . . . . . . . . . . . . . . . . . . . . . . . . 29 6.4.1. Personal Identifiers . . . . . . . . . . . . . . . . 30 Dawes & Arunachalam Expires February 7, 2018 [Page 2] Internet-Draft log me marking August 2017 6.4.2. Data Stored at SIP Intermediaries . . . . . . . . . . 30 6.4.3. Data Visible at Network Elements . . . . . . . . . . 30 6.4.4. Preventing Fingerprinting . . . . . . . . . . . . . . 31 6.4.5. Retaining Logs . . . . . . . . . . . . . . . . . . . 31 6.4.6. User Control of Logging . . . . . . . . . . . . . . . 31 6.4.7. Recommended Defaults . . . . . . . . . . . . . . . . 31 6.5. Data Protection . . . . . . . . . . . . . . . . . . . . . 32 7. Augmented BNF for the "logme" Parameter . . . . . . . . . . . 32 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32 8.1. Registration of the "logme" Parameter . . . . . . . . . . 32 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 32 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 32 10.1. Normative References . . . . . . . . . . . . . . . . . . 33 10.2. Informative References . . . . . . . . . . . . . . . . . 33 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34 1. Introduction When users experience problems with setting up sessions using SIP, enterprise or service provider network operators need to identify root cause by examining the SIP signaling. Also, when network or user agent 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]. This document defines a new header field parameter "logme" for the "Session-ID" header field. Implementations of this document MUST implement session identity specified in [RFC7989]. 2. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119], except that rather than describing interoperability requirements, they are used to describe requirements to be satisfied by the "log me" marking solution. Dawes & Arunachalam Expires February 7, 2018 [Page 3] Internet-Draft log me marking August 2017 3. "Log Me" Marking Protocol Aspects 3.1. Session-ID logme Parameter Logging is most effective when it is applied end-to-end in a communication session. This ability requires "log me" marker to be passed through SIP intermediaries. Session-ID header defined in ([RFC7989]) was chosen to carry the "log me" marker as a "logme" parameter since the session identifier is passed through SIP B2BUAs or other intermediaries. The "logme" parameter shown in Figure 1 does not introduce any device-specific or user-specific information and MUST be passed unchanged through SIP B2BUAs or other intermediaries. (See Section 3.4.2 where this normative behavior may be relaxed for intermediaries in an external network.) 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 3.2. Starting and Stopping Logging A user agent or proxy adds a "log me" marker in a request or response for two reasons: either it is configured to do so or it has detected that a dialog 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. When a user agent or proxy is configured to add a "log me" marker in messages, the start and stop times or events that the user agent or proxy will be configured with is out of the scope of this document. As example possible configurations, the user agent client or proxy could be configured to add a "log me" marker for a certain number of requests, or could be configured to mark messages with a temporal scope (e.g., 9:00am - 10:00am every day), or could be configured to mark messages when it encounters a specific "User-Agent" header, or for a specific set of called party numbers for which users are experiencing call setup failures. Dawes & Arunachalam Expires February 7, 2018 [Page 4] Internet-Draft log me marking August 2017 On the other hand, when a user agent or proxy detects 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 (REFER) may transfer the marking to the related dialogs. In such cases, the entire "session", identified by the Session-ID header, is "log me" marked. 3.3. Identifying Test Cases The local Universally Unique Identifier (UUID) portion of Session-ID [RFC7989] in the initial SIP request of a dialog is used as a random test case identifier. 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 and From a User Device When a user device inserts the "log me" marker, the marker MUST be passed unchanged in the Session-ID header across an edge proxy or a B2BUA adjacent to the user device. 3.4.2. To and 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 SHOULD have specific connection agreements. Whether "log me" marking is removed depends upon the policy applied at the network to network interface. Peer networks SHOULD 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, if no agreement exists between peer networks then the "log me" marker MUST be removed at a network boundary. 3.5. Logging Multiple Simultaneous Dialogs An originating or terminating user agent and SIP entities on the signaling path can log multiple SIP dialogs simultaneously, these dialogs are differentiated by their test case identifier (the local UUID of the Session-ID header field at the originating device). Dawes & Arunachalam Expires February 7, 2018 [Page 5] Internet-Draft log me marking August 2017 3.6. Format of Logged Signaling The entire SIP message (SIP headers and message body) is logged. Logging SHOULD use common standard formats such as the SIP CLF defined in [RFC6873] and Libpcap. If SIP CLF format is used, the entire message is logged using Vendor-ID = 00000000 and Tag = 02 in the portion of the SIP CLF record (see [RFC6873] clause 4.4). 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 [RFC3261] clause 7.3.3. 3.7. Marking Related Dialogs "Log me" marking is done per-dialog and typically 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. An example is call transfer described in section 6.1 of [RFC5589] and the logged signalling for related dialogs can be correlated using Session-ID values as described in section 10.9 of [RFC7989]. In the example shown in Figure 2 below, Alice has reported problems making call transfers and her terminal is configured to log signalling for a call transfer. Alice calls Bob, which creates initial dialog1, and then transfers the call to connect Bob to Carol. Logged signalling 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 with INVITE request F1 and ends with the final 200 OK of dialog1. Also during dialog1, Alice's terminal logs related REFER dialog2 that it initiates and terminates as part of the call transfer. Both dialog1 and dialog2 have the same test case identifier. Logging by Bob's terminal begins when it receives and echoes the "logme" marker in INVITE F1 and ends when dialog3, initiated by Bob, ends. Logging by Carol's terminal begins when it receives and echoes the "log me" marker in INVITE F5 that creates dialog3 and ends when dialog3 ends. dialog3 is not logged by Alice's terminal and the test case identifier ab30317f1a784dc48ff824d0d3715d86 is not the local-uuid in INVITE F5. However, Alice's test case identifier can be linked to dialog3 because dialog3 is initiated by the remote party of dialog1 i.e., the remote-uuid component of the Session-ID header field in requests and responses sent from Alice to Bob is the local-uuid component in INVITE F5. Dawes & Arunachalam Expires February 7, 2018 [Page 6] Internet-Draft log me marking August 2017 F1 - Alice's UA inserts "logme" parameter in the Session-ID header of the INVITE request that creates dialog1. F3 - Alice's UA inserts "logme" parameter in the Session-ID header of the REFER request that creates dialog2 which is related to dialog1. F5 - Bob's UA inserts "logme" parameter in the Session-ID header of the INVITE request that creates dialog3 which is related to dialog1. Dawes & Arunachalam Expires February 7, 2018 [Page 7] Internet-Draft log me marking August 2017 Bob Alice Carol Transferee Transferor 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 |<-------------------| | | 202 Accepted | | 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 | | dialog1 |------------------->| | | | BYE | dialog3 |<----------------------------------------| | | 200 OK | dialog3 |---------------------------------------->| Figure 2: "Log me" marking related dialogs in call transfer F1 INVITE Transferor -> Transferee Dawes & Arunachalam Expires February 7, 2018 [Page 8] Internet-Draft log me marking August 2017 INVITE sips:transferor@atlanta.example.com SIP/2.0 Via: SIP/2.0/TLS 192.0.2.4;branch=z9hG4bKnas432 Max-Forwards: 70 To: From: ;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: Content-Type: application/sdp Content-Length: ... F2 200 OK Transferee -> Transferor SIP/2.0 200 OK Via: SIP/2.0/TLS 192.0.2.4;branch=z9hG4bKnas432 To: ;tag=31kdl4i3k From: ;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: Content-Type: application/sdp Content-Length: ... 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: From: ;tag=1928301774 Call-ID: a84b4c76e66710 Session-ID: ab30317f1a784dc48ff824d0d3715d86 ;remote=47755a9de7794ba387653f2099600ef2;logme CSeq: 314159 REFER Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY Supported: gruu, replaces, tdialog Require: tdialog Refer-To: Dawes & Arunachalam Expires February 7, 2018 [Page 9] Internet-Draft log me marking August 2017 Target-Dialog: 090459243588173445;local-tag=7553452 ;remote-tag=31kdl4i3k Contact: Content-Length: 0 F4 NOTIFY Transferee -> Transferor NOTIFY sips:4889445d8kjtk3@atlanta.example.com;gr=723jd2d SIP/2.0 Via: SIP/2.0/TLS 192.0.2.4;branch=z9hG4bKnas432 Max-Forwards: 70 To: ;tag=1928301774 From: ;tag=a6c85cf Call-ID: a84b4c76e66710 Session-ID: 47755a9de7794ba387653f2099600ef2 ;remote=ab30317f1a784dc48ff824d0d3715d86;logme CSeq: 73 NOTIFY Contact: Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY Supported: replaces, tdialog Event: refer Subscription-State: active;expires=60 Content-Type: message/sipfrag Content-Length: ... F5 INVITE Transferee -> Transfer Target INVITE sips:transfertarget@chicago.example.com SIP/2.0 Via: SIP/2.0/TLS 192.0.2.4;branch=z9hG4bKnas41234 Max-Forwards: 70 To: From: ;tag=j3kso3iqhq Call-ID: 90422f3sd23m4g56832034 Session-ID: 47755a9de7794ba387653f2099600ef2 ;remote=00000000000000000000000000000000;logme CSeq: 521 REFER Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY Supported: replaces, gruu, tdialog Contact: Content-Type: application/sdp Content-Length: ... F6 NOTIFY Transferee -> Transferor NOTIFY sips:4889445d8kjtk3@atlanta.example.com;gr=723jd2d SIP/2.0 Dawes & Arunachalam Expires February 7, 2018 [Page 10] Internet-Draft log me marking August 2017 Via: SIP/2.0/TLS 192.0.2.4;branch=z9hG4bKnas432 Max-Forwards: 70 To: ;tag=1928301774 From: ;tag=a6c85cf Call-ID: a84b4c76e66710 Session-ID: 47755a9de7794ba387653f2099600ef2 ;remote=ab30317f1a784dc48ff824d0d3715d86;logme CSeq: 74 NOTIFY Contact: Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY Supported: replaces, tdialog Event: refer Subscription-State: terminated;reason=noresource Content-Type: message/sipfrag Content-Length: ... 3.8. Forked Requests The "log me" marker MUST be copied into forked requests. 4. SIP Entity Behavior "Log me" marking is initiated on a dialog creating side controlled by configuration. The dialog terminating side detects an incoming "log me" marker and reacts accordingly. 4.1. Endpoints A common scenario is to have both originating and terminating endpoints support "log me" marking specification with the originating endpoint configured to initiate "log me" marking. In this simplest use case, the originating user agent 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 user agent which echoes the "log me" marker in the corresponding responses. If the terminating user agent sends an in-dialog request on a dialog that is being "log me" marked, it inserts a "log me" marker and the originating user agent echoes the "log me" marker in responses. The terminating user agent logs the "log me" marked SIP requests and responses if it is allowed as per policy defined in the termination network. This basic use case suggests the following principles: Dawes & Arunachalam Expires February 7, 2018 [Page 11] Internet-Draft log me marking August 2017 o The originating user agent 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 user agent itself logs signaling. o The terminating user agent 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 user agent itself logs marked requests and corresponding responses if allowed as per policy. o The terminating user agent MUST echo a "log me" marker in responses to a SIP request that included a "log me" marker. o If the terminating user agent 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 user agent itself logs any in-dialog SIP requests that it sends if allowed as per policy. o The originating user agent echoes, in responses, the "log me" marker received in in-dialog requests from the terminating side. o The originating user agent logs the SIP responses that it sends in response to received "log me" marked in-dialog requests. 4.2. SIP Intermediaries A network operator may know that some of the user agents connected to the network do not support "log me" marking. In order to test sessions involving such user agents, the SIP intermediary closest to the user agent (e.g. edge proxies, B2BUA) on the originating and terminating sides insert the "log me" marker instead. If the terminating user agent does not echo this "log me" marker in responses to that request then the the SIP intermediary closest to the terminating user agent inserts a "log me" marker in responses to the request. Likewise, if the terminating user agent sends an in- dialog request, the SIP intermediary at the termination side inserts a "log me" marker and the SIP intermediary at the origination side echoes the "log me" marker in responses to that request. The SIP intermediary at the terminating side logs the "log me" marked SIP requests and responses if it is allowed as per policy defined in the termination network. This scenario suggests the following principles when a SIP intermediary is configured to initiate or handle "log me" marking on behalf of user agent: Dawes & Arunachalam Expires February 7, 2018 [Page 12] Internet-Draft log me marking August 2017 o The originating SIP intermediary 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 signaling. 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 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 user agent. o The terminating SIP intermediary itself logs any in-dialog SIP requests that it sends if allowed as per policy. 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. 4.2.1. 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 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 terminating side and vice versa. For example, a SIP B2BUA handling end-to-end session between an external caller and an agent in a contact center environment can couple the dialog between itself and Dawes & Arunachalam Expires February 7, 2018 [Page 13] Internet-Draft log me marking August 2017 an agent with the dialog between itself and external caller and pass on the "log me" marking from originating side to 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. 4.2.2. "Log me" Marker Processing 4.2.2.1. Stateless processing Typically, "log me" marking will be done by an originating UA and echoed by a terminating UA. Any SIP intermediary on the signalling path between these UAs MAY be stateless and simply log any SIP request or response that contains a "log me" marker, if configured to do so. 4.2.2.2. Stateful processing It is possible that some or all user agents connected to a SIP network do not support "log me" marking, or that "log me" marking is removed from SIP messages by the originating or terminating network. These scenarios require SIP intermediaries to maintain state to enable "log me" marking: o The originating UA does not support "log me" marking. o The originating network removes "log me" marking from SIP requests and responses before forwarding them from its network edge to external network. o The terminating UA does not support "log me" marking. o The terminating network removes "log me" marking from SIP requests and responses received from its network edge to internal network. The sections below illustrate SIP intermediary behavior in these scenarios using [RFC3665] example call flow "Session Establishment Through Two Proxies". 4.2.2.2.1. "Log Me" marking not supported by Originating UA Alice's user agent does not support "log me" marking and hence Proxy 1 which is the SIP intermediary closest to Alice is configured to act on behalf of Alice's user agent to "log me" mark dialogs created by Alice. Dawes & Arunachalam Expires February 7, 2018 [Page 14] Internet-Draft log me marking August 2017 In Figure 3 below, 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 user agent before forwarding them to Proxy 2. Dawes & Arunachalam Expires February 7, 2018 [Page 15] Internet-Draft log me marking August 2017 [ 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 | |<================================================>| | | | BYE F15 | | | | (logme) | | | BYE F16 |<---------------| | | (logme) | | | BYE F17 |<---------------| | | (logme) | | | Dawes & Arunachalam Expires February 7, 2018 [Page 16] Internet-Draft log me marking August 2017 |<---------------| | | | 200 F18 | | | | (no logme) | | | |--------------->| | | | | 200 F19 | | | | (logme) | | | |--------------->| | | | | | | | | 200 F20 | | | | (logme) | | | |--------------->| | | | | Figure 3: Case 1: 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 and also 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 and also 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 the "180" response F7 and passes the "log me" marker to Alice's UA in F8. F13 - Proxy 1 inserts a "log me" marker in ACK request F13 before forwarding it to Proxy 2 and also 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. Dawes & Arunachalam Expires February 7, 2018 [Page 17] Internet-Draft log me marking August 2017 F19 - Proxy 1 inserts a "log me" marker in 200 response F19 before forwarding it to Proxy 2 and also logs this response. 4.2.2.2.2. "Log Me" marking removed by Originating Network If network A in Figure 4 below 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 user agent. Proxy 1 also logs requests and responses for the duration of the dialog. [ 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) | | | |--------------->| | | Dawes & Arunachalam Expires February 7, 2018 [Page 18] Internet-Draft log me marking August 2017 | | | | | | ACK F13 | | | | (no logme) | | | |--------------->| | | | | | | | | ACK F14 | | | | (no logme) | | | |--------------->| | Both Way RTP Media | |<================================================>| | | | BYE F15 | | | | (no logme) | | | BYE F16 |<---------------| | | (no logme) | | | BYE F17 |<---------------| | | (logme) | | | |<---------------| | | | 200 F18 | | | | (logme) | | | |--------------->| | | | | 200 F19 | | | | (no logme) | | | |--------------->| | | | | | | | | 200 F20 | | | | (no logme) | | | |--------------->| | | | | Figure 4: Case 2: 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 does not log INVITE request F2. F3 - Proxy 1 inserts a "log me" marker in 100 response sent to Alice's user agent. F8 - Proxy 1 inserts a "log me" marker in 180 response before forwarding it to Alice's user agent. The same applies to responses F11, F17. Dawes & Arunachalam Expires February 7, 2018 [Page 19] Internet-Draft log me marking August 2017 F13 - Proxy 1 removes "log me" marking from ACK request before forwarding it to Proxy 2. F19 - Proxy 1 removes "log me" marking from the 200 response of the BYE request before forwarding it to Proxy 2. 4.2.2.2.3. "Log Me" marking not supported by Terminating UA In Figure 5 below 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. [ 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 |<---------------| | Dawes & Arunachalam Expires February 7, 2018 [Page 20] Internet-Draft log me marking August 2017 | (log me) | | | |<---------------| | | | ACK F12 | | | | (log me) | | | |--------------->| | | | | ACK F13 | | | | (log me) | | | |--------------->| ACK F14 | | | | (log me) | | | |--------------->| | Both Way RTP Media | |<================================================>| | | | 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 5: Case 3: The terminating UA does not support "log me" marking. F1 - Alice's UA inserts a "log me" marker in the the dialog-creating INVITE request F1. F2 - INVITE F2 is "log me" marked and Proxy 2 therefore 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. Dawes & Arunachalam Expires February 7, 2018 [Page 21] Internet-Draft log me marking August 2017 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. 4.2.2.2.4. "Log Me" marking removed by Terminating Network In Figure 6 below Proxy 2 removes "log me" marking from all SIP requests and responses entering network B. Proxy 1 maintains 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. [ 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 |--------------->| | | (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) | | | |<---------------| | | Dawes & Arunachalam Expires February 7, 2018 [Page 22] Internet-Draft log me marking August 2017 | ACK F12 | | | | (log me) | | | |--------------->| | | | | ACK F13 | | | | (log me) | | | |--------------->| ACK F14 | | | | (no log me) | | | |--------------->| | Both Way RTP Media | |<================================================>| | | | BYE F15 | | | | (no log me) | | | BYE F16 |<---------------| | | (no log me) | | | BYE F17 |<---------------| | | (log me) | | | |<---------------| | | | 200 F18 | | | | (log me) | | | |--------------->| | | | | 200 F19 | | | | (log me) | | | |--------------->| 200 F20 | | | | (no log me) | | | |--------------->| | | | | Figure 6: Case 2: 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 "log me" marker in the INVITE request F2 before forwarding it as F7. F7 - Proxy 1 inserts a "log me" marker in 180 response of the INVITE request before forwarding it as F8. The same applies to response F10 and the BYE request in F16. 5. Error Handling Dawes & Arunachalam Expires February 7, 2018 [Page 23] Internet-Draft log me marking August 2017 5.1. Missing "Log me" Marker in Dialog Being Logged "log me" marking is done per dialog, therefore if a user agent or edge proxy that has been "log me" marking requests and responses in a given dialog receives a SIP request or response that has not been "log me" marked as expected, this is an error. User agents and proxies that are stateless with respect to "log me" marking are not able detect such errors. User agents and proxies 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. In such cases, the user agent or proxy SHOULD consider "log me" marking to have ended and MUST NOT mark the forwarded request or response to the unmarked request, responses to subsequent requests in the dialog, or in-dialog requests sent from the terminating side. 5.1.1. Error Cases The following figures illustrate error cases. Figure 7 shows an error detected at Proxy 1. [ NETWORK A ] [ NETWORK B ] Alice Proxy 1 Proxy 2 Bob | | | | | INVITE F1 | | | | (log me) | | | |--------------->| | | | | | | | | | | | 200 F2 | | | | (log me) | | | |<---------------| | | | | | | | ACK F3 | | | | (no log me) | | | |--------------->| | | Figure 7: Error cases: missing "log me" marker F1 - Proxy 1 detects the "log me" marker and maintains state that this dialog is to be logged. Dawes & Arunachalam Expires February 7, 2018 [Page 24] Internet-Draft log me marking August 2017 F3 - Proxy 1 detects that the expected "log me" marker is missing and considers "log me" marking to have ended. Figure 8 shows an error detected at Proxy 2 and Bob's user agent. Dawes & Arunachalam Expires February 7, 2018 [Page 25] Internet-Draft log me marking August 2017 [ 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 8: Error cases: missing "log me" marker Dawes & Arunachalam Expires February 7, 2018 [Page 26] Internet-Draft log me marking August 2017 F2 - Proxy 2 detects the "log me" marker and maintains state that this dialog is to be logged. F4 - Bob's user agent 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 and considers "log me" marking to have ended. Hence it does not insert a "log me" marker in F13. F13 - Proxy 2 detects that the expected "log me" marker is missing and considers "log me" marking to have ended. F14 - Proxy 2 does not insert a "log me" marker because it considers "log me" marking to have ended. Bob's UA detects that the expected "log me" marker is missing and considers "log me" marking to have ended. 5.1.2. Non-Error Cases The following figures illustrate non-error cases. Figure 9 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. Dawes & Arunachalam Expires February 7, 2018 [Page 27] Internet-Draft log me marking August 2017 [ 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) | | | |<---------------| | | | | | Figure 9: Non-error cases: 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. 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 user agent. 5.2. "Log Me" Marker Appears Mid-Dialog "log me" marking that begins mid-dialog is an error case and the terminating user agent or edge proxy MUST NOT "log me" mark responses to the marked request, responses to subsequent requests in the dialog, or in-dialog requests from the terminating side. Dawes & Arunachalam Expires February 7, 2018 [Page 28] Internet-Draft log me marking August 2017 6. Security Considerations 6.1. "Log Me" Authorization An end user or network administrator MUST give permission for a terminal to perform "log me" marking. The configuration of a SIP intermediary to perform "log me" marking on behalf of a terminal MUST be authorized by the network administrator. Activating a debug mode affects the operation of a terminal, therefore debugging configuration MUST be supplied by an authorized party to an authorized terminal through a secure communication channel. 6.2. "Log Me" Marker Removal The log me marker is not sensitive information, although 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. 6.3. Denial of Service Attacks Maliciously configuring a large number of terminals to simultaneously "log me" mark dialogs will cause high processor load on SIP entities that are logging signalling. 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. 6.4. Privacy 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. Dawes & Arunachalam Expires February 7, 2018 [Page 29] Internet-Draft log me marking August 2017 6.4.1. Personal Identifiers "Log me" marking is defined for the SIP Protocol, and SIP has header fields such as From, Contact, 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 privacy from SIP intermediaries using the Privacy header "Log me" marking is typically used for troubleshooting and regression testing, and 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. 6.4.2. 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 6.4.1 and additionally a user identity, calling party number, IP address, hostname, and other user and 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. 6.4.3. 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. Dawes & Arunachalam Expires February 7, 2018 [Page 30] Internet-Draft log me marking August 2017 6.4.4. Preventing Fingerprinting "Log me" functionality is typically used to troubleshoot a given problem and hence it can be used as an method to identify users and devices that are experiencing issues. The best way to prevent fingerprinting is to enable or request SIP privacy for the logged dialog. 6.4.5. 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 more 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. an 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 is out of scope for this document and is expected to be configured based on the data storage policies of service providers and enterprises. 6.4.6. User Control of Logging Consent to turn on "log me" 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 end point, call control elements and network management systems. SIP entities across the communication path can be configured to pass through the "log me" marking but not honor the request i.e. not log the data based on local policies. 6.4.7. Recommended Defaults The recommended defaults for "log me" marking are: o turn on SIP privacy as described in Section 6.4 or use a service provider owned device with a dummy user identity for test calls o use the local UUID of Session-ID header at the originating device as the test case identifier as described in Section 3.3 Dawes & Arunachalam Expires February 7, 2018 [Page 31] Internet-Draft log me marking August 2017 6.5. 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]. 7. 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 10: Augmented BNF for the "logme" Parameter 8. IANA Considerations 8.1. Registration of the "logme" Parameter The following parameter is to be added to the "Header Field Parameters and Parameter Values" section of the SIP parameter registry: +--------------+----------------+-------------------+-----------+ | Header Field | Parameter Name | Predefined Values | Reference | +--------------+----------------+-------------------+-----------+ | Session-ID | logme | No | [RFCXXXX] | +--------------+----------------+-------------------+-----------+ Table 1 9. Acknowledgments The authors wish to thank Paul Giralt, Paul Kyzivat, Jorgen Axell and Vijay Gurbani for their constructive review comments and guidance while developing this document. 10. References Dawes & Arunachalam Expires February 7, 2018 [Page 32] Internet-Draft log me marking August 2017 10.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [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, . [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, . [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, . [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, . [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, . 10.2. Informative References [RFC3323] Peterson, J., "A Privacy Mechanism for the Session Initiation Protocol (SIP)", RFC 3323, DOI 10.17487/RFC3323, November 2002, . [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, . Dawes & Arunachalam Expires February 7, 2018 [Page 33] Internet-Draft log me marking August 2017 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/RFC5234, January 2008, . [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, . [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, . [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, . [RFC8123] Dawes, P. and C. Arunachalam, "Requirements for Marking SIP Messages to be Logged", RFC 8123, DOI 10.17487/RFC8123, March 2017, . Authors' Addresses Peter Dawes Vodafone Group The Connection Newbury, Berkshire RG14 2FN UK Email: peter.dawes@vodafone.com Chidambaram Arunachalam Cisco Systems 7200-12 Kit Creek Road Research Triangle Park, NC, NC 27709 US Email: carunach@cisco.com Dawes & Arunachalam Expires February 7, 2018 [Page 34]