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Network Working Group                                        C. Jennings
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                             N. Modadugu
Expires: April 12, 2008                                     Google, Inc.
                                                        October 10, 2007


Session Initiation Protocol (SIP) over Datagram Transport Layer Security
                                 (DTLS)
                       draft-jennings-sip-dtls-05

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Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   This specification defines how to use Datagram Transport Layer
   Security (DTLS) as a transport for Session Initiation Protocol (SIP).
   DTLS is a protocol for providing Transport Layer Security (TLS)
   security over a datagram protocol.  This specification also specifies
   the IANA registrations for using SIP with Datagram Congestion Control
   Protocol (DCCP).  DTLS can be used with either UDP or the Datagram



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   Congestion Control Protocol (DCCP).  To accommodate this, this
   specification also defines how to use SIP directly over DCCP.


1.  Introduction

   Datagram Transport Layer Security (DTLS) [2] provides communication
   privacy similar to TLS [9] for datagram packets.  SIP can run over
   both stream and datagram transports, including UDP and TCP.  SIP [4]
   already defines how to use TLS with stream oriented transports.  This
   specification extends SIP to use DTLS with datagram oriented
   transports.  Since DTLS can be used with either UDP or the Datagram
   Congestion Control Protocol (DCCP) as the underlying transport this
   specification also defines the usage of SIP directly over DCCP.


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 RFC 2119 [5].


3.  VIA Codes

   Via header fields in SIP carry a transport protocol identifier.  This
   specification extends RFC 3261 to define the value "DTLS-UDP" for
   DTLS over UDP[2] and "DTLS-DCCP" for DTLS over DCCP[1] and "DCCP" for
   directly over DCCP[8].  The update to the ABNF[3] in RFC 3261 for
   this parameter is the following:
   transport         =/ "DCCP" / "DTLS-DCCP" / "DTLS-UDP"

   The following is an example Via header field:
   Via: SIP/2.0/DTLS-UDP atlanta.example.com:5060


4.  DTLS and DCCP Usage

   The normal rules for sending a request over UDP in RFC 3261 apply to
   sending over DTLS and directly over DCCP.  Note that the congestion
   safety rules for UDP do not apply to DTLS over DCCP and DCCP.  In
   addition, the normal rules for validating a TLS connection in RFC
   3261 apply to DTLS connections.  Requests with a SIPS URI can be sent
   over DTLS as well as TLS.

   Note that DCCP performs Path Maximum Transfer Unit (PMTU) discovery.
   Implementations of SIP over DTLS over DCCP and SIP over DCCP MUST use
   the PMTU discovered by DCCP when determining the maximum request size



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   for the connection.

4.1.  DCCP Option Usage

   The following considerations regarding the usage of DCCP options and
   features apply to the DCCP connections for DTLS and SIP directly over
   DCCP:

   o  Congestion Control ID (CCID) negotiation for both directions of
      the connection MUST include CCID 2 (TCP-like congestion control).
      CCID 2 optimizes for throughput over smooth rate changes and
      should be suitable for SIP applications.  Applications MAY choose
      to include other CCIDs, in any preference order.
   o  Connections MUST NOT use the Minimum Checksum Coverage Feature.


5.  Locating DTLS SIP Servers

   The normal rules from RFC 3263 [6] apply when locating a SIP server
   that supports DTLS.  The following new NAPTR[7] service values are
   defined: "SIPS+D2U" for UDP, and "SIPS+D2D" for DCCP[8].  In
   addition, the service value "SIP+D2D" should be used for SIP without
   DTLS directly over DCCP.

   The default port for DTLS over UDP or DCCP is 5061.  The default port
   for SIP directly over DCCP is 5060.


6.  Security Considerations

   The security issues with SIP using DTLS are equivalent to the issues
   of using SIP with TLS.  All the security considerations in RFC 3261
   relevant to TLS apply to DTLS.

   SIP over DCCP presents the same security issues as SIP over UDP, with
   the exception that DCCP enforces congestion control at the transport
   layer.


7.  IANA Considerations

   This document defines new NAPTR service field values for DTLS over
   DCCP and UDP as well as over DCCP with no DTLS.  IANA is requested to
   register these values under the "Registry for the SIP SRV Resource
   Record Services Field".  The resulting entries should be:






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    Services Field        Protocol  Reference
    --------------------  --------  ---------
    SIPS+D2U              UDP       [RFCXXXX]
    SIPS+D2D              DCCP      [RFCXXXX]
    SIP+D2D               DCCP      [RFCXXXX]

   [Note to RFC Editor: Please replace XXXX with the RFC number of this
   specification.]

   This document registers two new DCCP Service Codes registry as
   defined by RFC 4340.

   Service Code  ASCII  Description                         Reference
   ------------  -----  ----------------------------------  ---------
   1936289824    sip    SIP over DCCP                       [RFCXXXX]
   1936289907    sips   SIP over DCCP over DTLS             [RFCXXXX]

   This document defines to new ports in the DCCP Port Numbers Registry
   as defined by RFC 4340.

   Port Name       Port Number    Description                Reference
   --------------  -------------  -------------------------  ---------
   sip-dccp        5060/dccp      SIP over DCCP              [RFCXXXX]
   sip-dtls-dccp   5061/dccp      SIP over DTLS over DCCP    [RFCXXXX]


8.  Acknowledgments

   Much of text and outline for this specification came from RFC 4168
   authored by Jonathan Rosenberg, Henning Schulzrinne, and Gonzalo
   Camarillo.  Jakob Schlyter caught several typos.  Eric Rescorla
   provided helpful comments and text.  Tom Phelan provided much of the
   DCCP text.  Thanks also to Colin Perkins.


9.  References

9.1.  Normative References

   [1]  Phelan, T., "Datagram Transport Layer Security (DTLS) over the
        Datagram Congestion Control Protocol (DCCP)",
        draft-ietf-dccp-dtls (work in progress).

   [2]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
        Security", RFC 4347, April 2006.

   [3]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
        Specifications: ABNF", RFC 4234, October 2005.



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   [4]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
        Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
        Session Initiation Protocol", RFC 3261, June 2002.

   [5]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [6]  Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol
        (SIP): Locating SIP Servers", RFC 3263, June 2002.

   [7]  Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
        Three: The Domain Name System (DNS) Database", RFC 3403,
        October 2002.

   [8]  Kohler, E., Handley, M., and S. Floyd, "Datagram Congestion
        Control Protocol (DCCP)", RFC 4340, March 2006.

9.2.  Informative References

   [9]  Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS)
        Protocol Version 1.1", RFC 4346, April 2006.


Authors' Addresses

   Cullen Jennings
   Cisco Systems
   170 West Tasman Drive
   MS: SJC-21/2
   San Jose, CA  95134
   USA

   Phone: +1 408 902-3341
   Email: fluffy@cisco.com


   Nagendra Modadugu
   Google, Inc.
   1600 Ampitheatre Parkway
   Muntain View, CA  94043
   USA

   Email: ngm@google.com








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