Internet Engineering Task Force (IETF)
Request for Comments: 7355
Updates: 6873
Category: Informational
ISSN: 2070-1721

G. Salgueiro
Cisco
V. Pascual
A. Roman
S. Garcia
Quobis
September 2014

Indicating WebSocket Protocol as a Transport

in the Session Initiation Protocol (SIP) Common Log Format (CLF)

Abstract

RFC 7118 specifies a WebSocket subprotocol as a reliable real-time transport mechanism between Session Initiation Protocol (SIP) entities to enable usage of SIP in web-oriented deployments. This document updates the SIP Common Log Format (CLF), defined in RFC 6873, with a new "Transport Flag" for such SIP WebSocket transport.

Status of This Memo

This document is not an Internet Standards Track specification; it is published for informational purposes.

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 5741.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7355.

Copyright Notice

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.

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Document Conventions  . . . . . . . . . . . . . . . . . . . .   3
   4.  Usage of the WebSocket Transport Flag . . . . . . . . . . . .   3
   5.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  SIP over WebSocket (WS) . . . . . . . . . . . . . . . . .   4
     5.2.  SIP over Secure WebSocket (WSS) . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   8

1. Introduction

The WebSocket protocol [RFC6455] enables bidirectional message exchange between clients and servers on top of a persistent TCP connection (optionally secured with TLS [RFC5246]). The initial protocol handshake makes use of HTTP [RFC7230] semantics, allowing the WebSocket protocol to reuse existing transport connections.

RFC 7118 [RFC7118] defines a WebSocket subprotocol for transporting SIP messages between a WebSocket client and server.

SIP messages can be logged using the Common Log Format defined in RFC 6873 [RFC6873]. In order to make such SIP CLF logging possible for SIP messages transported over the WebSocket protocol, a new WebSocket "Transport Flag" ('W') must be added to the "Transport Flags" already defined in RFC 6873 [RFC6873] (i.e., UDP, TCP, and SCTP).

This document updates RFC 6873 [RFC6873] by defining a new SIP CLF "Transport Flag" value for WebSocket.

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

3. Document Conventions

This document contains several examples of SIP CLF records showing messages over plain and secure WebSocket connections. The formatting described in this document does not permit the examples to be unambiguously rendered due to the constraints imposed by the formatting rules for RFCs. To avoid ambiguity and to meet the RFC layout requirements, this document uses the <allOneLine/> markup convention established in [RFC4475]. This markup convention is described in detail in Section 3 of RFC 6873 [RFC6873] and used throughout that document for representing the syntax of SIP CLF records.

4. Usage of the WebSocket Transport Flag

Section 4.2 of RFC6873 [RFC6873] specifies the mandatory fields in a SIP CLF record. The fourth and fifth bytes of the five-byte "Flags Field" are the "Transport Flag" and the "Encryption Flag", respectively. SIP messages transported over both a plain and secure WebSocket connection can be clearly distinguished by appropriately setting these two flag fields.

The currently registered values of the "Transport Flag" (Section 9.2 of RFC 6873) are UDP ('U'), TCP ('T'), and SCTP ('S'). This document defines and registers a new "Transport Flag" value 'W' for WebSocket transport of SIP messages and consequently updates RFC 6873 [RFC6873] and the IANA "SIP CLF Transport Flag Values" registry.

SIP CLF records of messages transported over a plain WebSocket connection (WS) MUST set the "Transport Flag" to this new 'W' value and the "Encryption Flag" value to 'U' (Unencrypted). SIP CLF records of messages transported over a secure WebSocket (WSS) connection (i.e., WS over TLS) MUST set the "Transport Flag" to this new 'W' value and the "Encryption Flag" value to 'E' (Encrypted).

5. Examples

The following examples show sample SIP CLF records logged for SIP messages transported over both plain and secure WebSocket connections.

5.1. SIP over WebSocket (WS)

The following example represents a SIP INVITE request sent over a plain WebSocket connection. For the sake of brevity, the Session Description Protocol (SDP) [RFC4566] body is omitted.

   INVITE sip:bob@example.com SIP/2.0
   Via: SIP/2.0/WS df7jal23ls0d.invalid;branch=z9hG4bK56sdasks
   From: sip:alice@example.com;tag=asdyka899
   To: sip:bob@example.com
   Call-ID: asidkj3ss
   CSeq: 1 INVITE
   Max-Forwards: 70
   Date: Thu, 6 Feb 2014 15:02:03 GMT
   Supported: path, outbound, gruu
   Route: <sip:proxy.example.com:80;transport=ws;lr>
   Contact: <sip:alice@example.com;gr=urn:uuid:f81-7dec-14a06cf1;ob>
   Content-Type: application/sdp
   Content-Length: 418

Shown below is approximately how this message would appear as a single record in a SIP CLF logging file if encoded according to the syntax described in [RFC6873]. Due to RFC conventions, this log entry has been split into five lines, instead of the two lines that actually appear in a log file; and the tab characters have been padded out using spaces to simulate their appearance in a text terminal.

   A0000E7,0053005C005E00720080009200A600A800BE00C800D200DE00E7
   <allOneLine>
   1328821153.010    RORWU    1 INVITE    -    sip:bob@example.com
   192.0.2.10:80    192.0.2.200:56485    sip:bob@example.com    -
   sip:alice@example.com    asdyka899    asidkj3ss    S1781761-88
   C67651-11
   </allOneLine>

A bit-exact version of the actual log entry is provided here, Base64 encoded [RFC4648], using the uuencode utility.

   begin-base64 644 clf_ws_record
   QTAwMDBFNywwMDUzMDA1QzAwNUUwMDcyMDA4MDAwOTIwMEE2MDBBODAwQkUwMEM4MDBE
   MjAwREUwMEU3CjEzMjg4MjExNTMuMDEwCVJPUldVCTEgSU5WSVRFCS0Jc2lwOmJvYkBl
   eGFtcGxlLmNvbQkxOTIuMC4yLjEwOjgwCTE5Mi4wLjIuMjAwOjU2NDg1CXNpcDpib2JA
   ZXhhbXBsZS5jb20JLQlzaXA6YWxpY2VAZXhhbXBsZS5jb20JYXNkeWthODk5CWFzaWRr
   ajNzcwlTMTc4MTc2MS04OAlDNjc2NTEtMTEKCg==
   ====

The original SIP CLF format can be obtained by reversing the effects of uuencode by simply applying the uudecode transform. Additionally, to recover the unencoded file, the Base64 text above may be passed as input to the following perl script (the output should be redirected to a file).

   <CODE BEGINS>
   
   #!/usr/bin/perl
   use strict;
   my $bdata = "";
   use MIME::Base64;
   while(<>)
   {
         if (/begin-base64 644 clf_ws_record/ .. /-- ==== --/)
         {
             if ( m/^\s*[^\s]+\s*$/)
             {
               $bdata = $bdata . $_;
             }
          }
   }
   print decode_base64($bdata);
   
   <CODE ENDS>

5.2. SIP over Secure WebSocket (WSS)

The following example represents a SIP INVITE request sent over a secure WebSocket connection (i.e., WebSocket over TLS [RFC5246]). For the sake of brevity, the SDP body is omitted.

   INVITE sip:bob@example.com SIP/2.0
   Via: SIP/2.0/WSS df7jal23ls0d.invalid;branch=z9hG4bK56sdasks
   From: sip:alice@example.com;tag=asdyka899
   To: sip:bob@example.com
   Call-ID: asidkj3ss
   CSeq: 1 INVITE
   Max-Forwards: 70
   Date: Thu, 6 Feb 2014 15:02:03 GMT
   Supported: path, outbound, gruu
   Route: <sip:proxy.example.com:443;transport=ws;lr>
   Contact: <sip:alice@example.com;gr=urn:uuid:f81-7dec-14a06cf1;ob>
   Content-Type: application/sdp
   Content-Length: 439

   A0000E8,0053005C005E00720081009300A700A900BF00C900D300DF00E8
   <allOneLine>
   1328821153.010    RORWE    1 INVITE    -    sip:bob@example.com
   192.0.2.10:443    192.0.2.200:56485    sip:bob@example.com    -
   sip:alice@example.com:5060    asdyka899    asidkj3ss    S1781761-88
   C67651-11
   </allOneLine>

A bit-exact version of the actual log entry is provided here, Base64 encoded.

   begin-base64 644 clf_ws_record
   QTAwMDBFOCwwMDUzMDA1QzAwNUUwMDcyMDA4MTAwOTMwMEE3MDBBOTAwQkYwMEM5MDBE
   MzAwREYwMEU4CjEzMjg4MjExNTMuMDEwCVJPUldVCTEgSU5WSVRFCS0Jc2lwOmJvYkBl
   eGFtcGxlLmNvbQkxOTIuMC4yLjEwOjQ0MwkxOTIuMC4yLjIwMDo1NjQ4NQlzaXA6Ym9i
   QGV4YW1wbGUuY29tCS0Jc2lwOmFsaWNlQGV4YW1wbGUuY29tCWFzZHlrYTg5OQlhc2lk
   a2ozc3MJUzE3ODE3NjEtODgJQzY3NjUxLTExCgo=
   ====

6. Security Considerations

This document merely adds a new "Transport Flag" value for the WebSocket protocol. This value may be set in a SIP CLF record, but its use does not intrinsically introduce any new security considerations. When logging protocol information, such as with SIP CLF, there are a myriad of security, privacy, and data protection issues to consider. These are exhaustively described in RFC 6872 [RFC6872] and RFC 6873 [RFC6873].

Any security considerations specific to the WebSocket protocol or its application as a transport for SIP are detailed in the relevant specifications (the WebSocket protocol [RFC6455] and SIP over WebSockets [RFC7118]) and are considered outside the scope of this document.

7. IANA Considerations

This document defines a new value ('W') for SIP CLF "Transport Flag". IANA has registered this value in the "SIP CLF Transport Flag Values" registry, as shown in Table 1 below.

            +-------+--------------------+--------------------+
            | Value | Transport Protocol |     Reference      |
            +-------+--------------------+--------------------+
            |   W   |     WebSocket      | RFC 7118, RFC 7355 |
            +-------+--------------------+--------------------+

Table 1: IANA-Registered SIP CLF Transport Flag

8. Acknowledgements

The authors would like to thank Vijay Gurbani for shepherding this document and Area Director Richard Barnes for his sponsorship. This work benefitted from the thorough review and constructive comments of Richard Barnes, Barry Leiba, Benoit Claise, Pete Resnick, Stephen Farrel, and Vijay Gurbani.

9. References

9.1. Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.
   
   [RFC6455]  Fette, I. and A. Melnikov, "The WebSocket Protocol", RFC
              6455, December 2011.
   
   [RFC6872]  Gurbani, V., Burger, E., Anjali, T., Abdelnur, H., and O.
              Festor, "The Common Log Format (CLF) for the Session
              Initiation Protocol (SIP): Framework and Information
              Model", RFC 6872, February 2013.
   
   [RFC6873]  Salgueiro, G., Gurbani, V., and A. Roach, "Format for the
              Session Initiation Protocol (SIP) Common Log Format
              (CLF)", RFC 6873, February 2013.
   
   [RFC7118]  Baz Castillo, I., Millan Villegas, J., and V. Pascual,
              "The WebSocket Protocol as a Transport for the Session
              Initiation Protocol (SIP)", RFC 7118, January 2014.

9.2. Informative References

   [RFC4475]  Sparks, R., Hawrylyshen, A., Johnston, A., Rosenberg, J.,
              and H. Schulzrinne, "Session Initiation Protocol (SIP)
              Torture Test Messages", RFC 4475, May 2006.
   
   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.
   
   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, October 2006.
   
   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.
   
   [RFC7230]  Fielding, R. and J. Reschke, "Hypertext Transfer Protocol
              (HTTP/1.1): Message Syntax and Routing", RFC 7230, June
              2014.

Authors' Addresses

   Gonzalo Salgueiro
   Cisco Systems, Inc.
   7200-12 Kit Creek Road
   Research Triangle Park, NC  27709
   US

EMail:

          gsalguei@cisco.com

Victor Pascual
Quobis

   EMail: victor.pascual@quobis.com

Anton Roman
Quobis

   EMail: anton.roman@quobis.com

Sergio Garcia Ramos
Quobis

   EMail: sergio.garcia@quobis.com