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Versions: 00 draft-ietf-mmusic-udptl-dtls

DISPATCH Working Group                                       C. Holmberg
Internet-Draft                                               I. Sedlacek
Intended status: Standards Track                                Ericsson
Expires: December 22, 2013                                 June 20, 2013


   UDP Transport Layer (UDPTL) over Datagram Transport Layer Security
                                 (DTLS)
                 draft-holmberg-dispatch-udptl-dtls-00

Abstract

   This document specifies how the UDP Transport Layer (UDPTL) protocol
   can be transported over the Datagram Transport Layer Security (DTLS)
   protocol, how the usage of UDPTL over DTLS is indicated in the
   Session Description Protocol (SDP), and how UDPTL over DTLS is
   negotiated in a session established using the Session Initiation
   Protocol (SIP).

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 December 22, 2013.

Copyright Notice

   Copyright (c) 2013 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



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Secure Channel  . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Secure Channel Establishment  . . . . . . . . . . . . . .   4
     3.2.  Secure Channel Usage  . . . . . . . . . . . . . . . . . .   5
   4.  Miscellaneous Considerations  . . . . . . . . . . . . . . . .   5
     4.1.  Anonymous Calls . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  Middlebox Interaction . . . . . . . . . . . . . . . . . .   5
     4.3.  Rekeying  . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   7
   8.  Change Log  . . . . . . . . . . . . . . . . . . . . . . . . .   7
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Appendix A.  Example  . . . . . . . . . . . . . . . . . . . . . .   8
     A.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   8
     A.2.  Basic Message Flow with Identity  . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   UDPTL [ITU.T38.1998] is the predominant protocol for fax transport in
   IP networks.  The protocol stack for fax transport using UDPTL is
   shown in Table 1.

                      +-----------------------------+
                      |           Protocol          |
                      +-----------------------------+
                      | Internet facsimile protocol |
                      +-----------------------------+
                      |            UDPTL            |
                      +-----------------------------+
                      |             UDP             |
                      +-----------------------------+
                      |              IP             |
                      +-----------------------------+

                Table 1: Protocol stack for UDPTL over UDP

   UDPTL does not offer integrity and confidentiality protection.  To
   enable integrity and confidentiality protection, [ITU.T38.2004]



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   specifies fax transport over RTP/SAVP.  However, fax transport over
   RTP/SAVP is not widely supported.

   The mechanism in this document provides integrity and confidentiality
   protection for fax by specifying fax transport using UDPTL over DTLS
   [RFC6347].  The protocol stack for integrity and confidentiality
   protected fax transport using UDPTL over DTLS is shown in Table 2.

                      +-----------------------------+
                      |           Protocol          |
                      +-----------------------------+
                      | Internet facsimile protocol |
                      +-----------------------------+
                      |            UDPTL            |
                      +-----------------------------+
                      |             DTLS            |
                      +-----------------------------+
                      |             UDP             |
                      +-----------------------------+
                      |              IP             |
                      +-----------------------------+

                Table 2: Protocol stack for UDPTL over UDP

   The mechanism in this document is motivated as follows:

   o  The design of DTLS [RFC6347] is well-known and implementations are
      widely available.
   o  No DTLS extensions are required in order to enable UDPTL transport
      over DTLS.
   o  Fax transport using UDPTL over DTLS only requires insertion of the
      DTLS layer between the UDPTL layer and the UDP layer, as shown in
      Table 2.

   This document specifies the transport of UDPTL over DTLS using the
   DTLS record layer "application_data" packets [RFC6347].

   Since the DTLS record layer "application_data" packet does not
   indicate whether it carries UDPTL, or some other protocol, the usage
   of a dedicated DTLS association for transport of UDPTL needs to be
   negotiated, e.g. using the Session Description Protocol (SDP)
   [RFC4566] and the SDP offer/answer mechanism [RFC3264].

   Therefore, this document specifies a new <proto> value [RFC4566] for
   the SDP "m=" line [RFC3264], in order to indicate UDPTL over DTLS in
   SDP messages [RFC4566].





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2.  Conventions

   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 BCP 14, RFC 2119
   [RFC2119].

   The DTLS uses the term "session" to refer to a long-lived set of
   keying material that spans DTLS associations.  In this document, in
   order to be consistent with SIP/SDP usage of "session" terminology,
   we use it to refer to a multimedia session and use the term "DTLS
   session" to refer to the DTLS construct.  We use the term "DTLS
   association" to refer to a particular DTLS cipher suite and keying
   material set that is associated with a single host/ port quartet.
   The same DTLS session can be used to establish the keying material
   for multiple DTLS associations.  For consistency with other SIP/SDP
   usage, we use the term "connection" when what's being referred to is
   a multimedia stream that is not specifically DTLS.

3.  Secure Channel

3.1.  Secure Channel Establishment

   The SDP offer/answer mechanism [RFC3264] is used by other protocols,
   e.g.  the Session Initiation Protocol (SIP) [RFC3261] to negotiate
   and establish multimedia sessions.

   In addition to the usual contents of an SDP media description ("m="
   line) specified for UDPTL over the UDP, each SDP media description
   for UDPTL over DTLS over the UDP will also contain several SDP
   attributes, as specified in [RFC4145] and [RFC4572].

   The SDP offer and SDP answer MUST conform to the following
   requirements:

   o  The endpoint MUST set the "proto" field of the "m=" line to the
      token specified in Table 3.
   o  The endpoint MUST use the SDP setup attribute [RFC4145].  The
      offerer MUST assign the SDP setup attribute with setup:actpass
      value, and MUST be prepared to receive a DTLS client_hello message
      before it receives the SDP answer.  The answerer MUST assign the
      SDP setup attribute with either setup:active value or
      setup:passive value.  The answerer SHOULD assign the SDP setup
      attribute with the setup:active value.  Whichever party is active
      MUST initiate a DTLS handshake by sending a ClientHello over each
      flow (host/port quartet).
   o  The endpoint MUST use the SDP certificate fingerprint attribute
      [RFC4572].



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   o  The certificate presented during the DTLS handshake MUST match the
      fingerprint exchanged via the signaling path in the SDP.
   o  If the fingerprint does not match the hashed certificate, then the
      endpoint MUST tear down the media session immediately.  Note that
      it is permissible to wait until the other side's fingerprint has
      been received before establishing the connection; however, this
      may have undesirable latency effects.

   Editor's note: FFS if connection attribute defined in RFC4145 is
   needed.

3.2.  Secure Channel Usage

   The DTLS is used as specified in [RFC6347].  Once the DTLS handshake
   is completed, the UDPTL packets SHALL be transported in DTLS record
   layer "application_data" packets.

4.  Miscellaneous Considerations

4.1.  Anonymous Calls

   When making anonymous calls, a new self-signed certificate SHOULD be
   used for each call and the content of the subjectAltName attribute
   inside the certificate MUST NOT contain information that either
   allows correlation or identification of the user making anonymous
   calls.

4.2.  Middlebox Interaction

   The procedures defined for SRTP-DTLS in [RFC5763] section 6.7 for
   interaction with middleboxes also apply to UPPTL over DTLS.

   The procedures defined for SRTP-DTLS in [RFC5764] section 5.1.2 for
   distinguishing DTLS and STUN packets also apply to UDPTL over DTLS.

   Editor's note: The complete SRTP-DTLS implementation is not needed.
   Only the parts for interaction with middleboxes in RFC5763 and for
   distinguishing DTLS and STUN packets in RFC5764 are needed.  Should
   those be copied into this document?

4.3.  Rekeying










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   After the DTLS handshake caused by rekeying has completed, because of
   possible packet reordering on the wire, packets protected by the
   previous set of keys can arrive.  To compensate for this fact,
   receivers SHOULD maintain both sets of keys for some time in order to
   be able to decrypt and verify older packets.  The duration of
   maintaining the previous set of keys after the finish of the DTLS
   handshake is out of scope of this document.

5.  Security Considerations

   DTLS media signaled with SIP requires a way to ensure that the
   communicating peers' certificates are correct.

   The standard DTLS strategy for authenticating the communicating
   parties is to give the server (and optionally the client) a PKIX
   [RFC5280] certificate.  The client then verifies the certificate and
   checks that the name in the certificate matches the server's domain
   name.  This works because there are a relatively small number of
   servers with well-defined names; a situation that does not usually
   occur in the VoIP context.

   The design described in this document is intended to leverage the
   authenticity of the signaling channel (while not requiring
   confidentiality).  As long as each side of the connection can verify
   the integrity of the SDP received from the other side, then the DTLS
   handshake cannot be hijacked via a man-in-the-middle attack.  This
   integrity protection is easily provided by the caller to the callee
   (see Alice to Bob in Section 7) via the SIP Identity [RFC4474]
   mechanism.  Other mechanisms, such as the S/MIME mechanism [RFC3261],
   or perhaps future mechanisms yet to be specified could also serve
   this purpose.

   While this mechanism can still be used without such integrity
   mechanisms, the security provided is limited to defense against
   passive attack by intermediaries.  An active attack on the signaling
   plus an active attack on the media plane can allow an attacker to
   attack the connection (R-SIG-MEDIA in the notation of [RFC5479]).

6.  IANA Considerations

   This document updates the "Session Description Protocol (SDP)
   Parameters" registry as specified in Section 8.2.2 of [RFC4566].
   Specifically, it adds the values in the Table 3 to the table for the
   "proto" field.

                  +-------+---------------+------------+
                  |  Type |    SDP Name   | Reference  |
                  +-------+---------------+------------+



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                  | proto | UDP/TLS/UDPTL | [RFC-XXXX] |
                  +-------+---------------+------------+

                     Table 3: SDP "proto" field values

   [RFC EDITOR NOTE: Please replace RFC-XXXX with the RFC number of this
   document.]

7.  Acknowledgments

   Special thanks to Peter Dawes who provided comments to this draft.

8.  Change Log

   [RFC EDITOR NOTE: Please remove this section when publishing]

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.

   [RFC3261]  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.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264, June
              2002.

   [RFC4145]  Yon, D. and G. Camarillo, "TCP-Based Media Transport in
              the Session Description Protocol (SDP)", RFC 4145,
              September 2005.

   [RFC4474]  Peterson, J. and C. Jennings, "Enhancements for
              Authenticated Identity Management in the Session
              Initiation Protocol (SIP)", RFC 4474, August 2006.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.

   [RFC4572]  Lennox, J., "Connection-Oriented Media Transport over the
              Transport Layer Security (TLS) Protocol in the Session
              Description Protocol (SDP)", RFC 4572, July 2006.





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   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC5763]  Fischl, J., Tschofenig, H., and E. Rescorla, "Framework
              for Establishing a Secure Real-time Transport Protocol
              (SRTP) Security Context Using Datagram Transport Layer
              Security (DTLS)", RFC 5763, May 2010.

   [RFC5764]  McGrew, D. and E. Rescorla, "Datagram Transport Layer
              Security (DTLS) Extension to Establish Keys for the Secure
              Real-time Transport Protocol (SRTP)", RFC 5764, May 2010.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, January 2012.

   [ITU.T38.1998]
              International Telecommunications Union, "Procedures for
              real time Group 3 facsimile communication between
              terminals using IP Networks", ITU-T Recommendation T.38,
              1998.

   [ITU.T38.2004]
              International Telecommunications Union, "Procedures for
              real-time Group 3 facsimile communication over IP
              networks", ITU-T Recommendation T.38, 2004.

9.2.  Informative References

   [RFC5479]  Wing, D., Fries, S., Tschofenig, H., and F. Audet,
              "Requirements and Analysis of Media Security Management
              Protocols", RFC 5479, April 2009.

Appendix A.  Example

A.1.  General

   Prior to establishing the session, both Alice and Bob generate self-
   signed certificates which are used for a single session or, more
   likely, reused for multiple sessions.

   The SIP signaling from Alice to her proxy is transported over TLS to
   ensure an integrity protected channel between Alice and her identity
   service.  Transport between proxies should also be protected somehow.

   Only one element is shown for Alice's and Bob's proxies for the
   purposes of simplification.



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   Only the mandatory SDP T.38 attributes are shown for simplification.

A.2.  Basic Message Flow with Identity

   Figure 1 shows an example message flow of session establishment for
   T.38 fax securely transported using UDPTL over DTLS.

   In this example flow, Alice acts as the passive endpoint of DTLS
   association and Bob acts as the active endpoint of DTLS association.

   Alice                    Proxies                   Bob
     | (1) SIP INVITE         |                        |
     |----------------------->|                        |
     |                        | (2) SIP INVITE         |
     |                        |----------------------->|
     |                        |   (3) DTLS ClientHello |
     |<------------------------------------------------|
     |    (4) remaining messages of DTLS handshake     |
     |<----------------------------------------------->|
     |                        |                        |
     |                        |                        |
     |                        |         (5) SIP 200 OK |
     |                        |<-----------------------|
     |         (6) SIP 200 OK |                        |
     |<-----------------------|                        |
     | (7) SIP ACK            |                        |
     |------------------------------------------------>|
     |      (8) T.38 message using UDPTL over DTLS     |
     |<----------------------------------------------->|
     |                        |                        |

                Figure 1: Basic message flow with Identity

   Message (1):

      Figure 2 shows the initial INVITE request sent by Alice to Alice's
      proxy.  The initial INVITE request contains an SDP offer.


      The "m=" line in the SDP Offer indicates T.38 fax using UDPTL over
      DTLS.


      The SDP setup:actpass attribute in the SDP Offer indicates that
      Alice has requested to be either the active or passive endpoint.






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      The SDP fingerprint attribute in the SDP Offer indicates the
      certificate fingerprint computed from Alice's self-signed
      certificate.





   INVITE sip:bob@example.com SIP/2.0
   To: <sip:bob@example.com>
   From: "Alice"<sip:alice@example.com>;tag=843c7b0b
   Via: SIP/2.0/TLS ua1.example.com;branch=z9hG4bK-0e53sadfkasldkfj
   Contact: <sip:alice@ua1.example.com>
   Call-ID: 6076913b1c39c212@REVMTEpG
   CSeq: 1 INVITE
   Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, UPDATE
   Max-Forwards: 70
   Content-Type: application/sdp
   Content-Length: xxxx
   Supported: from-change

   v=0
   o=- 1181923068 1181923196 IN IP4 ua1.example.com
   s=example1
   c=IN IP4 ua1.example.com
   t=0 0
   m=image 6056 UDP/TLS/UDPTL t38
   a=setup:actpass
   a=fingerprint: SHA-1 \
     4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
   a=T38FaxRateManagement:transferredTCF

                           Figure 2: Message (1)

   Message (2):

      Figure 3 shows the SIP INVITE request sent by Bob's proxy to Bob.


      The SIP INVITE request contains an Identity header field and an
      Identity-Info header fields inserted by Alice's proxy.


      When received, Bob verifies the identity provided in the SIP
      INVITE request.






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   INVITE sip:bob@ua2.example.com SIP/2.0
   To: <sip:bob@example.com>
   From: "Alice"<sip:alice@example.com>;tag=843c7b0b
   Via: SIP/2.0/TLS proxy.example.com;branch=z9hG4bK-0e53sadfkasldk
   Via: SIP/2.0/TLS ua1.example.com;branch=z9hG4bK-0e53sadfkasldkfj
   Record-Route: <sip:proxy.example.com;lr>
   Contact: <sip:alice@ua1.example.com>
   Call-ID: 6076913b1c39c212@REVMTEpG
   CSeq: 1 INVITE
   Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, UPDATE
   Max-Forwards: 69
   Identity: CyI4+nAkHrH3ntmaxgr01TMxTmtjP7MASwliNRdupRI1vpkXRvZXx1ja9k
             3W+v1PDsy32MaqZi0M5WfEkXxbgTnPYW0jIoK8HMyY1VT7egt0kk4XrKFC
             HYWGCl0nB2sNsM9CG4hq+YJZTMaSROoMUBhikVIjnQ8ykeD6UXNOyfI=
   Identity-Info: https://example.com/cert
   Content-Type: application/sdp
   Content-Length: xxxx
   Supported: from-change

   v=0
   o=- 1181923068 1181923196 IN IP4 ua1.example.com
   s=example1
   c=IN IP4 ua1.example.com
   t=0 0
   m=image 6056 UDP/TLS/UDPTL t38
   a=setup:actpass
   a=fingerprint: SHA-1 \
     4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
   a=T38FaxRateManagement:transferredTCF

                           Figure 3: Message (2)

   Message (3):

      Assuming that Alice's identity is valid, Bob sends a DTLS
      ClientHello directly to Alice.

   Message (4):

      Alice and Bob exchange further messages of DTLS handshake
      (HelloVerifyRequest, ClientHello, ServerHello, Certificate,
      ServerKeyExchange, CertificateRequest, ServerHelloDone,
      Certificate, ClientKeyExchange, CertificateVerify,
      ChangeCipherSpec, Finished).


      When Bob receives the certificate of Alice via DTLS, Bob checks
      whether the certificate fingerprint calculated from the Alice's



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      certificate received via DTLS matches the certificate fingerprint
      received in the a=fingerprint SDP attribute of Figure 3.  In this
      message flow, the check is successful and thus session setup
      continues.

   Message (5):

      Figure 4 shows a 200 (OK) response to the initial SIP INVITE
      request, sent by Bob to Bob's proxy.  The 200 (OK) response
      contains an SDP answer.


      The "m=" line in the SDP Answer indicates T.38 fax using UDPTL
      over DTLS.


      The SDP setup:active attribute in the SDP Answer indicates that
      Bob has requested to be the active endpoint.


      The SDP fingerprint attribute in the SDP Answer indicates the
      certificate fingerprint computed from Bob's self-signed
      certificate.





   SIP/2.0 200 OK
   To: <sip:bob@example.com>;tag=6418913922105372816
   From: "Alice" <sip:alice@example.com>;tag=843c7b0b
   Via: SIP/2.0/TLS proxy.example.com:5061;branch=z9hG4bK-0e53sadfkasldk
   Via: SIP/2.0/TLS ua1.example.com;branch=z9hG4bK-0e53sadfkasldkfj
   Record-Route: <sip:proxy.example.com;lr>
   Call-ID: 6076913b1c39c212@REVMTEpG
   CSeq: 1 INVITE
   Contact: <sip:bob@ua2.example.com>
   Content-Type: application/sdp
   Content-Length: xxxx
   Supported: from-change

   v=0
   o=- 6418913922105372816 2105372818 IN IP4 ua2.example.com
   s=example2
   c=IN IP4 ua2.example.com
   t=0 0
   m=image 12000 UDP/TLS/UDPTL t38
   a=setup:active



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   a=fingerprint: SHA-1 \
     FF:FF:FF:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
   a=T38FaxRateManagement:transferredTCF

                           Figure 4: Message (6)

   Message (6):

      Figure 5 shows a 200 (OK) response to the initial SIP INVITE
      request, sent by Alice's proxy to Alice.  Alice checks if the
      certificate fingerprint calculated from the Bob's certificate
      received via DTLS is the same as the certificate fingerprint
      received in the a=fingerprint SDP attribute of Figure 5.  In this
      message flow, the check is successful and thus session setup
      continues.



   SIP/2.0 200 OK
   To: <sip:bob@example.com>;tag=6418913922105372816
   From: "Alice" <sip:alice@example.com>;tag=843c7b0b
   Via: SIP/2.0/TLS ua1.example.com;branch=z9hG4bK-0e53sadfkasldkfj
   Record-Route: <sip:proxy.example.com;lr>
   Call-ID: 6076913b1c39c212@REVMTEpG
   CSeq: 1 INVITE
   Contact: <sip:bob@ua2.example.com>
   Content-Type: application/sdp
   Content-Length: xxxx
   Supported: from-change

   v=0
   o=- 6418913922105372816 2105372818 IN IP4 ua2.example.com
   s=example2
   c=IN IP4 ua2.example.com
   t=0 0
   m=image 12000 UDP/TLS/UDPTL t38
   a=setup:active
   a=fingerprint: SHA-1 \
     FF:FF:FF:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB
   a=T38FaxRateManagement:transferredTCF

                           Figure 5: Message (7)

   Message (7):

      Alice sends the SIP ACK request to Bob.

   Message (8):



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Internet-Draft               UDPTL over DTLS                   June 2013


      At this point, Bob and Alice can exchange T.38 fax securely
      transported using UDPTL over DTLS.


Authors' Addresses

   Christer Holmberg
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: christer.holmberg@ericsson.com


   Ivo Sedlacek
   Ericsson
   Sokolovska 79
   Praha  18600
   Czech Republic

   Email: ivo.sedlacek@ericsson.com





























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