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Versions: (draft-holmberg-mmusic-sdp-dtls) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22

Network Working Group                                        C. Holmberg
Internet-Draft                                                  Ericsson
Updates: 5763,7345 (if approved)                              R. Shpount
Intended status: Standards Track                             TurboBridge
Expires: September 16, 2017                               March 15, 2017


             Using the SDP Offer/Answer Mechanism for DTLS
                   draft-ietf-mmusic-dtls-sdp-22.txt

Abstract

   This document defines the SDP offer/answer procedures for negotiating
   and establishing a DTLS association.  The document also defines the
   criteria for when a new DTLS association must be established.  The
   document updates RFC 5763 and RFC 7345, by replacing common SDP
   offer/answer procedures with a reference to this specification.

   This document defines a new SDP media-level attribute, 'dtls-id'.

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 September 16, 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



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Establishing a new DTLS Association . . . . . . . . . . . . .   3
     3.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.2.  Change of Local Transport Parameters  . . . . . . . . . .   4
     3.3.  Change of ICE ufrag value . . . . . . . . . . . . . . . .   4
   4.  SDP dtls-id Attribute . . . . . . . . . . . . . . . . . . . .   4
   5.  SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . .   6
     5.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.2.  Generating the Initial SDP Offer  . . . . . . . . . . . .   8
     5.3.  Generating the Answer . . . . . . . . . . . . . . . . . .   8
     5.4.  Offerer Processing of the SDP Answer  . . . . . . . . . .   9
     5.5.  Modifying the Session . . . . . . . . . . . . . . . . . .   9
   6.  ICE Considerations  . . . . . . . . . . . . . . . . . . . . .  10
   7.  Transport Protocol Considerations . . . . . . . . . . . . . .  11
     7.1.  Transport Re-Usage  . . . . . . . . . . . . . . . . . . .  11
   8.  SIP Considerations  . . . . . . . . . . . . . . . . . . . . .  11
   9.  RFC Updates . . . . . . . . . . . . . . . . . . . . . . . . .  11
     9.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .  11
     9.2.  Update to RFC 5763  . . . . . . . . . . . . . . . . . . .  11
     9.3.  Update to RFC 7345  . . . . . . . . . . . . . . . . . . .  16
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  20
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20
   12. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  20
   13. Change Log  . . . . . . . . . . . . . . . . . . . . . . . . .  20
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  24
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  24
     14.2.  Informative References . . . . . . . . . . . . . . . . .  25
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

1.  Introduction

   [RFC5763] defines SDP offer/answer procedures for SRTP-DTLS.
   [RFC7345] defines SDP offer/answer procedures for UDPTL-DTLS.  This
   specification defines general offer/answer procedures for DTLS, based
   on the procedures in [RFC5763].  Other specifications, defining
   specific DTLS usages, can then reference this specification, in order
   to ensure that the DTLS aspects are common among all usages.  Having
   common procedures is essential when multiple usages share the same
   DTLS association [I-D.ietf-mmusic-sdp-bundle-negotiation].  The
   document updates [RFC5763] and [RFC7345], by replacing common SDP
   offer/answer procedures with a reference to this specification.



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   NOTE: Since the publication of [RFC5763], [RFC4474] has been
   obsoleted by [I-D.ietf-stir-rfc4474bis].  The updating of the
   references (and the associated procedures) within [RFC5763] is
   outside the scope of this document.  However, implementers of
   [RFC5763] applications are encouraged to implement
   [I-D.ietf-stir-rfc4474bis] instead of [RFC4474].

   As defined in [RFC5763], a new DTLS association MUST be established
   when transport parameters are changed.  Transport parameter change is
   not well defined when Interactive Connectivity Establishment (ICE)
   [I-D.ietf-ice-rfc5245bis] is used.  One possible way to determine a
   transport change is based on ufrag change, but the ufrag value is
   changed both when ICE is negotiated and when ICE restart
   [I-D.ietf-ice-rfc5245bis] occurs.  These events do not always require
   a new DTLS association to be established, but currently there is no
   way to explicitly indicate in an SDP offer or answer whether a new
   DTLS association is required.  To solve that problem, this document
   defines a new SDP attribute, 'dtls-id'.  The pair of SDP 'dtls-id'
   attribute values (the attribute values of the offerer and the
   answerer) uniquely identifies the DTLS association.  Providing a new
   value of the 'dtls-id' attribute in an SDP offer or answers can be
   used to indicate whether a new DTLS association is to be established.

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 [RFC2119].

3.  Establishing a new DTLS Association

3.1.  General

   A new DTLS association must be established between two endpoints
   after a successful SDP offer/answer exchange in the following cases:

   o  The negotiated DTLS setup roles change; or

   o  One or more fingerprint values are modified, added or removed in
      either an SDP offer or answer; or

   o  The intent to establish a new DTLS association is explicitly
      signaled using SDP, by changing the value of the SDP 'dtls-id'
      attribute defined in this document;

   NOTE: The first two items above are based on the procedures in
   [RFC5763].  This specification adds the support for explicit
   signaling using the SDP 'dtls-id' attribute.



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   A new DTLS association can only be established as a result of the
   successful SDP offer/answer exchange.  Whenever an entity determines
   that a new DTLS association is required, the entity MUST initiate an
   SDP offer/answer exchange, following the procedures in Section 5.

   The sections below describe typical cases where a new DTLS
   association needs to be established.

   In this document, a "new DTLS association" between two endpoints
   refers to either an initial DTLS association (when no DTLS
   association is currently established between the endpoints) or an
   DTLS association replacing a previously established DTLS association.

3.2.  Change of Local Transport Parameters

   If an endpoint modifies its local transport parameters (address and/
   or port), and if the modification requires a new DTLS association,
   the endpoint must change its local SDP 'dtls-id' attribute value (see
   Section 4).

   If the underlying transport prohibits a DTLS association from
   spanning multiple transports, and if the transport is changed, the
   endpoint must change its local SDP 'dtls-id' attribute value (see
   Section 4).  An example of such a case is when DTLS is carried over
   SCTP, as described in [RFC6083].

3.3.  Change of ICE ufrag value

   If an endpoint uses ICE, and modifies a local ufrag value, and if the
   modification requires a new DTLS association, the endpoint MUST
   change its local SDP 'dtls-id' attribute value (see Section 4).

4.  SDP dtls-id Attribute

   The pair of SDP 'dtls-id' attribute values (the attribute values of
   the offerer and the answerer) uniquely identifies the DTLS
   association.














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          Name: dtls-id

          Value: dtls-id-value

          Usage Level: media

          Charset Dependent: no

          Default Value: N/A

          Syntax:

              dtls-id-value = 20*255(dtls-id-char)
              dtls-id-char = ALPHA / DIGIT / "+" / "/" / "-" / "_"

              <ALPHA and DIGIT defined in [RFC4566]>


          Example:

              a=dtls-id:abc3de65cddef001be82


   Every time an endpoint requests to establish a new DTLS association,
   the endpoint MUST generate a new local 'dtls-id' attribute value.  A
   non-changed local 'dtls-id' attribute value, in combination with non-
   changed fingerprints, indicates that the endpoint intends to reuse
   the existing DTLS association.

   The 'dtls-id' attribute value MUST be generated using a cryptographic
   random function and include at least 120 bits of randomness.

   No default value is defined for the SDP 'dtls-id' attribute.
   Implementations that wish to use the attribute MUST explicitly
   include it in SDP offers and answers.  If an offer or answer does not
   contain a 'dtls-id' attribute (this could happen if the offerer or
   answerer represents an existing implementation that has not been
   updated to support the 'dtls-id' attribute), unless there is another
   mechanism to explicitly indicate that a new DTLS association is to be
   established, a modification of one or more of the following
   characteristics MUST be treated as an indication that an endpoint
   wants to establish a new DTLS association:

   o  DTLS setup role; or

   o  fingerprint set; or

   o  local transport parameters; or



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   o  ICE ufrag value

   The mux category [I-D.ietf-mmusic-sdp-mux-attributes] for the 'dtls-
   id' attribute is 'IDENTICAL', which means that the attribute value
   must be identical across all media descriptions being multiplexed
   [I-D.ietf-mmusic-sdp-bundle-negotiation].

   For RTP-based media, the 'dtls-id' attribute applies to the whole
   associated media description.  The attribute MUST NOT be defined per
   source (using the SDP 'ssrc' attribute [RFC5576]).

   The SDP offer/answer [RFC3264] procedures associated with the
   attribute are defined in Section 5.

5.  SDP Offer/Answer Procedures

5.1.  General

   This section defines the generic SDP offer/answer procedures for
   negotiating a DTLS association.  Additional procedures (e.g.,
   regarding usage of specific SDP attributes etc.) for individual DTLS
   usages (e.g., SRTP-DTLS) are outside the scope of this specification,
   and need to be specified in a usage specific specification.

   NOTE: The procedures in this section are generalizations of
   procedures first specified in SRTP-DTLS [RFC5763], with the addition
   of usage of the SDP 'dtls-id' attribute.  That document is herein
   updated to make use of these new procedures.

   The procedures in this section apply to an SDP media description
   ("m=" line) associated with DTLS-protected media/data.

   When an offerer or answerer indicates that it wants to establish a
   new DTLS association, it needs to make sure that media packets in the
   existing DTLS association and new DTLS association can be de-
   multiplexed.  In case of an ordered transport (e.g., SCTP) this can
   be done simply by sending packets for the new DTLS association after
   all packets for the existing DTLS association have been sent.  In
   case of an unordered transport, such as UDP, packets for the old DTLS
   association can arrive after the answer SDP was received and after
   the first packets for the new DTLS association were received.  The
   only way to de-multiplex packets belonging to the old and new DTLS
   association is on the basis of transport 5-tuple.  Because of this,
   if an unordered transport is used for the DTLS association, a new
   transport (3-tuple) must be allocated by at least one of the
   endpoints so that DTLS packets can be de-multiplexed.





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   When an offerer needs to establish a new DTLS association, and if an
   unordered transport (e.g., UDP) is used, the offerer MUST allocate a
   new transport (3-tuple) for the offer in such a way that the offerer
   can disambiguate any packets associated with the new DTLS association
   from any packets associated with any other DTLS association.  This
   typically means using a local address and/or port, or a set of ICE
   candidates (see Section 6), which were not recently used for any
   other DTLS association.

   When an answerer needs to establish a new DTLS association, if an
   unordered transport is used, and if the offerer did not allocate a
   new transport, the answerer MUST allocate a new transport for the
   answer in such a way that it can disambiguate any packets associated
   with the new DTLS association from any packets associated with any
   other DTLS association.  This typically means using a local address
   and/or port, or a set of ICE candidates (see Section 6), which were
   not recently used for any other DTLS association.

   In order to negotiate a DTLS association, the following SDP
   attributes are used:

   o  The SDP 'setup' attribute, defined in [RFC4145], is used to
      negotiate the DTLS roles;

   o  The SDP 'fingerprint' attribute, defined in
      [I-D.ietf-mmusic-4572-update], is used to provide one or more
      fingerprint values; and

   o  The SDP 'dtls-id' attribute, defined in this specification, is
      used to identity the DTLS association.

   This specification does not define the usage of the SDP 'connection'
   attribute [RFC4145] for negotiating a DTLS association.  However, the
   attribute MAY be used if the DTLS association is used together with
   another protocol (e.g., SCTP or TCP) for which the usage of the
   attribute has been defined.

   Unlike for TCP and TLS connections, endpoints MUST NOT use the SDP
   'setup' attribute 'holdconn' value when negotiating a DTLS
   association.

   Endpoints MUST support the cipher suites as defined in
   [I-D.ietf-mmusic-4572-update].

   The certificate received during the DTLS handshake MUST match a
   certificate fingerprints received in SDP 'fingerprint' attributes
   according to the procedures defined in [I-D.ietf-mmusic-4572-update].
   If fingerprints do not match the hashed certificate, then an endpoint



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   MUST tear down the media session immediately (see
   [I-D.ietf-mmusic-4572-update]).  Note that it is permissible to wait
   until the other side's fingerprint(s) has been received before
   establishing the connection; however, this may have undesirable
   latency effects.

   SDP offerers and answerers might reuse certificates across multiple
   DTLS associations, and provide identical fingerprint values for each
   DTLS association.  The combination of the SDP 'dtls-id' attribute
   values of the SDP offerer and answerer identifies each individual
   DTLS association.

5.2.  Generating the Initial SDP Offer

   When an offerer sends the initial offer, the offerer MUST insert an
   SDP 'setup' attribute according to the procedures in [RFC4145], and
   one or more SDP 'fingerprint' attributes according to the procedures
   in [I-D.ietf-mmusic-4572-update].  In addition, the offerer MUST
   insert in the offer an SDP 'dtls-id' attribute with a unique value.

   If the offerer inserts the SDP 'setup' attribute with an 'actpass' or
   'passive' attribute value, the offerer MUST be prepared to receive a
   DTLS ClientHello message (if a new DTLS association is established by
   the answerer) from the answerer before the offerer receives the SDP
   answer.

5.3.  Generating the Answer

   When an answerer sends an answer, the answerer MUST insert in the
   answer an SDP 'setup' attribute according to the procedures in
   [RFC4145], and one or more SDP 'fingerprint' attributes according to
   the procedures in [I-D.ietf-mmusic-4572-update].  If the answerer
   determines, based on the criteria specified in Section 3.1, that a
   new DTLS association is to be established, the answerer MUST insert
   in the associated answer an SDP 'dtls-id' attribute with a new unique
   value.  Note that the offerer and answerer generate their own local
   'dtls-id' attribute values, and the combination of both values
   identify the DTLS association.

   If the answerer receives an offer that requires establishment of a
   new DTLS association, and if the answerer does not accept the
   establishment of a new DTLS association, the answerer MUST reject the
   "m=" lines associated with the suggested DTLS association [RFC3264].

   If an answerer receives an offer that does not require the
   establishment of a new DTLS association, and if the answerer
   determines that a new DTLS association is not to be established, the
   answerer MUST insert an SDP 'dtls-id' attribute with the previously



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   assigned value in the associated answer.  In addition, the answerer
   MUST insert an SDP 'setup' attribute with a value that does not
   change the previously negotiated DTLS roles, and one or more SDP
   'fingerprint' attributes values that do not change the previously
   sent fingerprint set, in the associated answer.

   If the answerer receives an offer that does not contain an SDP 'dtls-
   id' attribute, the answerer MUST NOT insert a 'dtls-id' attribute in
   the answer.

   If a new DTLS association is to be established, and if the answerer
   inserts an SDP 'setup' attribute with an 'active' value in the
   answer, the answerer MUST initiate a DTLS handshake by sending a DTLS
   ClientHello message towards the offerer.

5.4.  Offerer Processing of the SDP Answer

   When an offerer receives an answer that establishes a new DTLS
   association based on criteria defined in Section 3.1, and if the
   offerer becomes DTLS client (based on the value of the SDP 'setup'
   attribute value [RFC4145]), the offerer MUST establish a DTLS
   association.  If the offerer becomes DTLS server, it MUST wait for
   the answerer to establish the DTLS association.

   If the answer does not establish a new DTLS association, the offerer
   will continue using the previously established DTLS association.

   NOTE: A new DTLS association can be established based on changes in
   either an SDP offer or answer.  When communicating with legacy
   endpoints, an offerer can receive an answer that includes the same
   fingerprint set and setup role.  A new DTLS association MUST still be
   established if such an answer was received as a response to an offer
   which requested the establishment of a new DTLS association.

5.5.  Modifying the Session

   When the offerer sends a subsequent offer, and if the offerer wants
   to establish a new DTLS association, the offerer MUST insert an SDP
   'setup' attribute according to the procedures in [RFC4145], and one
   or more SDP 'fingerprint' attributes according to the procedures in
   [I-D.ietf-mmusic-4572-update].  In addition, the offerer MUST insert
   in the offer an SDP 'dtls-id' attribute with a new unique value.

   When the offerer sends a subsequent offer, and the offerer does not
   want to establish a new DTLS association, and if a previously
   established DTLS association exists, the offerer MUST insert an SDP
   'dtls-id' attribute with the previously assigned value in the offer.
   In addition, the offerer MUST insert an SDP 'setup' attribute, and



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   one or more SDP 'fingerprint' attributes with values that do not
   change the previously sent fingerprint set, in the offer.  The value
   of the 'setup' attribute SHOULD be set to 'actpass', in order to
   allow the answerer to establish a new DTLS association with a
   different role, but MAY be set to the current negotiated role
   ('active' or 'passive').  It MUST NOT be set to a value that changes
   the current negotiated role.

   NOTE: When a new DTLS association is being established, each endpoint
   needs to be prepared to receive data on both the new and old DTLS
   associations as long as both are alive.

6.  ICE Considerations

   When the Interactive Connectivity Establishment (ICE) mechanism
   [I-D.ietf-ice-rfc5245bis] is used, the ICE connectivity checks are
   performed before the DTLS handshake begins.  Note that if aggressive
   nomination mode is used, multiple candidate pairs may be marked valid
   before ICE finally converges on a single candidate pair.

   NOTE: Aggressive nomination has been deprecated from ICE, but must
   still be supported for backwards compatibility reasons
   [I-D.ietf-ice-rfc5245bis].

   When a new DTLS association is established over an unordered
   transport, in order to disambiguate any packets associated with the
   newly established DTLS association, at least one of the endpoints
   MUST allocate a completely new set of ICE candidates which were not
   recently used for any other DTLS association.  This means the
   answerer cannot initiate a new DTLS association unless the offerer
   initiated ICE restart [I-D.ietf-ice-rfc5245bis].  If the answerer
   wants to initiate a new DTLS association, it needs to initiate an ICE
   restart and a new offer/answer exchange on its own.  However, an ICE
   restart does not by default require a new DTLS association to be
   established.

   NOTE: Simple Traversal of the UDP Protocol through NAT (STUN) packets
   are sent directly over UDP, not over DTLS.  [RFC5764] describes how
   to demultiplex STUN packets from DTLS packets and SRTP packets.

   Each ICE candidate associated with a component is treated as being
   part of the same DTLS association.  Therefore, from a DTLS
   perspective it is not considered a change of local transport
   parameters when an endpoint switches between those ICE candidates.







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7.  Transport Protocol Considerations

7.1.  Transport Re-Usage

   If DTLS is transported on top of a connection-oriented transport
   protocol (e.g., TCP or SCTP), where all IP packets are acknowledged,
   all DTLS packets associated with a previous DTLS association MUST be
   acknowledged (or timed out) before a new DTLS association can be
   established on the same instance of that transport (5-tuple).

8.  SIP Considerations

   When the Session Initiation Protocol (SIP) [RFC3261] is used as the
   signal protocol for establishing a multimedia session, dialogs
   [RFC3261] might be established between the caller and multiple
   callees.  This is referred to as forking.  If forking occurs,
   separate DTLS associations will be established between the caller and
   each callee.

   It is possible to send an INVITE request which does not contain an
   SDP offer.  Such an INVITE request is often referred to as an 'empty
   INVITE', or an 'offer-less INVITE'.  The receiving endpoint will
   include the SDP offer in a response to the request.  When the
   endpoint generates such SDP offer, if a previously established DTLS
   association exists, the offerer MUST insert an SDP 'dtls-id'
   attribute, and one or more SDP 'fingerprint' attributes, with
   previously assigned attribute values.  If a previously established
   DTLS association did not exist, the offer MUST be generated based on
   the same rules as a new offer (see Section 5.2).  Regardless of the
   previous existence of a DTLS association, the SDP 'setup' attribute
   MUST be included according to the rules defined in [RFC4145] and if
   ICE is used, ICE restart MUST be initiated.

9.  RFC Updates

9.1.  General

   This section updates specifications that use DTLS-protected media, in
   order to reflect the procedures defined in this specification.

9.2.  Update to RFC 5763


Update to section 5:
--------------------

OLD TEXT:




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5.  Establishing a Secure Channel

   The two endpoints in the exchange present their identities as part of
   the DTLS handshake procedure using certificates. This document uses
   certificates in the same style as described in "Connection-Oriented
   Media Transport over the Transport Layer Security (TLS) Protocol in
   the Session Description Protocol (SDP)" [RFC4572].

   If self-signed certificates are used, the content of the
   subjectAltName attribute inside the certificate MAY use the uniform
   resource identifier (URI) of the user. This is useful for debugging
   purposes only and is not required to bind the certificate to one of
   the communication endpoints. The integrity of the certificate is
   ensured through the fingerprint attribute in the SDP. The
   subjectAltName is not an important component of the certificate
   verification.

   The generation of public/private key pairs is relatively expensive.
   Endpoints are not required to generate certificates for each session.

   The offer/answer model, defined in [RFC3264], is used by protocols
   like the Session Initiation Protocol (SIP) [RFC3261] to set up
   multimedia sessions. In addition to the usual contents of an SDP
   [RFC4566] message, each media description ("m=" line and associated
   parameters) will also contain several attributes as specified in
   [RFC5764], [RFC4145], and [RFC4572].

   When an endpoint wishes to set up a secure media session with another
   endpoint, it sends an offer in a SIP message to the other endpoint.
   This offer includes, as part of the SDP payload, the fingerprint of
   the certificate that the endpoint wants to use. The endpoint SHOULD
   send the SIP message containing the offer to the offerer's SIP proxy
   over an integrity protected channel. The proxy SHOULD add an
   Identity header field according to the procedures outlined in
   [RFC4474]. The SIP message containing the offer SHOULD be sent to
   the offerer's SIP proxy over an integrity protected channel. When
   the far endpoint receives the SIP message, it can verify the identity
   of the sender using the Identity header field. Since the Identity
   header field is a digital signature across several SIP header fields,
   in addition to the body of the SIP message, the receiver can also be
   certain that the message has not been tampered with after the digital
   signature was applied and added to the SIP message.

   The far endpoint (answerer) may now establish a DTLS association with
   the offerer. Alternately, it can indicate in its answer that the
   offerer is to initiate the TLS association. In either case, mutual
   DTLS certificate-based authentication will be used. After completing
   the DTLS handshake, information about the authenticated identities,



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   including the certificates, are made available to the endpoint
   application. The answerer is then able to verify that the offerer's
   certificate used for authentication in the DTLS handshake can be
   associated to the certificate fingerprint contained in the offer in
   the SDP. At this point, the answerer may indicate to the end user
   that the media is secured. The offerer may only tentatively accept
   the answerer's certificate since it may not yet have the answerer's
   certificate fingerprint.

   When the answerer accepts the offer, it provides an answer back to
   the offerer containing the answerer's certificate fingerprint. At
   this point, the offerer can accept or reject the peer's certificate
   and the offerer can indicate to the end user that the media is
   secured.

   Note that the entire authentication and key exchange for securing the
   media traffic is handled in the media path through DTLS. The
   signaling path is only used to verify the peers' certificate
   fingerprints.

   The offer and answer MUST conform to the following requirements.

   o  The endpoint MUST use the setup attribute defined in [RFC4145].
      The endpoint that is the offerer MUST use the setup attribute
      value of setup:actpass and be prepared to receive a client_hello
      before it receives the answer. The answerer MUST use either a
      setup attribute value of setup:active or setup:passive. Note that
      if the answerer uses setup:passive, then the DTLS handshake will
      not begin until the answerer is received, which adds additional
      latency. setup:active allows the answer and the DTLS handshake to
      occur in parallel. Thus, setup:active is RECOMMENDED. Whichever
      party is active MUST initiate a DTLS handshake by sending a
      ClientHello over each flow (host/port quartet).

   o  The endpoint MUST NOT use the connection attribute defined in
      [RFC4145].

   o  The endpoint MUST use the certificate fingerprint attribute as
      specified in [RFC4572].

   o  The certificate presented during the DTLS handshake MUST match the
      fingerprint exchanged via the signaling path in the SDP. The
      security properties of this mechanism are described in Section 8.

   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



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      may have undesirable latency effects.


NEW TEXT:

5.  Establishing a Secure Channel

   The two endpoints in the exchange present their identities as part of
   the DTLS handshake procedure using certificates. This document uses
   certificates in the same style as described in "Connection-Oriented
   Media Transport over the Transport Layer Security (TLS) Protocol in
   the Session Description Protocol (SDP)" [RFC4572].

   If self-signed certificates are used, the content of the
   subjectAltName attribute inside the certificate MAY use the uniform
   resource identifier (URI) of the user. This is useful for debugging
   purposes only and is not required to bind the certificate to one of
   the communication endpoints.  The integrity of the certificate is
   ensured through the fingerprint attribute in the SDP.

   The generation of public/private key pairs is relatively expensive.
   Endpoints are not required to generate certificates for each session.

   The offer/answer model, defined in [RFC3264], is used by protocols
   like the Session Initiation Protocol (SIP) [RFC3261] to set up
   multimedia sessions.

   When an endpoint wishes to set up a secure media session with another
   endpoint, it sends an offer in a SIP message to the other endpoint.
   This offer includes, as part of the SDP payload, a fingerprint of
   a certificate that the endpoint wants to use. The endpoint SHOULD
   send the SIP message containing the offer to the offerer's SIP proxy
   over an integrity protected channel. The proxy SHOULD add an
   Identity header field according to the procedures outlined in
   [RFC4474]. When the far endpoint receives the SIP message, it can
   verify the identity of the sender using the Identity header field.
   Since the Identity header field is a digital signature across several
   SIP header fields, in addition to the body of the SIP message, the
   receiver can also be certain that the message has not been tampered
   with after the digital signature was applied and added to the SIP
   message.

   The far endpoint (answerer) may now establish a DTLS association with
   the offerer. Alternately, it can indicate in its answer that the
   offerer is to initiate the DTLS association. In either case, mutual
   DTLS certificate-based authentication will be used. After completing
   the DTLS handshake, information about the authenticated identities,
   including the certificates, are made available to the endpoint



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   application. The answerer is then able to verify that the offerer's
   certificate used for authentication in the DTLS handshake can be
   associated to a certificate fingerprint contained in the offer in
   the SDP. At this point, the answerer may indicate to the end user
   that the media is secured. The offerer may only tentatively accept
   the answerer's certificate since it may not yet have the answerer's
   certificate fingerprint.

   When the answerer accepts the offer, it provides an answer back to
   the offerer containing the answerer's certificate fingerprint. At
   this point, the offerer can accept or reject the peer's certificate
   and the offerer can indicate to the end user that the media is
   secured.

   Note that the entire authentication and key exchange for securing
   the media traffic is handled in the media path through DTLS. The
   signaling path is only used to verify the peers' certificate
   fingerprints.

   The offerer and answerer MUST follow the SDP offer/answer procedures
   defined in [RFCXXXX].

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

Update to section 6.6:
----------------------

OLD TEXT:

6.6.  Session Modification

   Once an answer is provided to the offerer, either endpoint MAY
   request a session modification that MAY include an updated offer.
   This session modification can be carried in either an INVITE or
   UPDATE request. The peers can reuse the existing associations if
   they are compatible (i.e., they have the same key fingerprints and
   transport parameters), or establish a new one following the same
   rules are for initial exchanges, tearing down the existing
   association as soon as the offer/answer exchange is completed. Note
   that if the active/passive status of the endpoints changes, a new
   connection MUST be established.

NEW TEXT:

6.6.  Session Modification

   Once an answer is provided to the offerer, either endpoint MAY



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   request a session modification that MAY include an updated offer.
   This session modification can be carried in either an INVITE or
   UPDATE request. The peers can reuse an existing DTLS association,
   or establish a new one, following the procedures in [RFCXXXX].

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

Update to section 6.7.1:
------------------------

OLD TEXT:

6.7.1.  ICE Interaction

   Interactive Connectivity Establishment (ICE), as specified in
   [RFC5245], provides a methodology of allowing participants in
   multimedia sessions to verify mutual connectivity. When ICE is being
   used, the ICE connectivity checks are performed before the DTLS
   handshake begins. Note that if aggressive nomination mode is used,
   multiple candidate pairs may be marked valid before ICE finally
   converges on a single candidate pair. Implementations MUST treat all
   ICE candidate pairs associated with a single component as part of the
   same DTLS association. Thus, there will be only one DTLS handshake
   even if there are multiple valid candidate pairs. Note that this may
   mean adjusting the endpoint IP addresses if the selected candidate
   pair shifts, just as if the DTLS packets were an ordinary media
   stream.

   Note that Simple Traversal of the UDP Protocol through NAT (STUN)
   packets are sent directly over UDP, not over DTLS. [RFC5764]
   describes how to demultiplex STUN packets from DTLS packets and SRTP
   packets.

NEW TEXT:

6.7.1.  ICE Interaction

   The Interactive Connectivity Establishment (ICE)
   [I-D.ietf-ice-rfc5245bis] considerations for DTLS-protected media
   are described in [RFCXXXX].

9.3.  Update to RFC 7345


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




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Update to section 4:
--------------------

OLD TEXT:

4.  SDP Offerer/Answerer Procedures

4.1.  General

   An endpoint (i.e., both the offerer and the answerer) MUST create an
   SDP media description ("m=" line) for each UDPTL-over-DTLS media
   stream and MUST assign a UDP/TLS/UDPTL value (see Table 1) to the
   "proto" field of the "m=" line.

   The procedures in this section apply to an "m=" line associated with
   a UDPTL-over-DTLS media stream.

   In order to negotiate a UDPTL-over-DTLS media stream, the following
   SDP attributes are used:

   o  The SDP attributes defined for UDPTL over UDP, as described in
      [ITU.T38.2010]; and

   o  The SDP attributes, defined in [RFC4145] and [RFC4572], as
      described in this section.

   The endpoint MUST NOT use the SDP "connection" attribute [RFC4145].

   In order to negotiate the TLS roles for the UDPTL-over-DTLS transport
   connection, the endpoint MUST use the SDP "setup" attribute
   [RFC4145].

   If the endpoint supports, and is willing to use, a cipher suite with
   an associated certificate, the endpoint MUST include an SDP
   "fingerprint" attribute [RFC4572]. The endpoint MUST support SHA-256
   for generating and verifying the SDP "fingerprint" attribute value.
   The use of SHA-256 is preferred. UDPTL over DTLS, at a minimum, MUST
   support TLS_DHE_RSA_WITH_AES_128_GCM_SHA256 and MUST support
   TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256. UDPTL over DTLS MUST prefer
   TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 and any other Perfect Forward
   Secrecy (PFS) cipher suites over non-PFS cipher suites.
   Implementations SHOULD disable TLS-level compression.

   If a cipher suite with an associated certificate is selected during
   the DTLS handshake, the certificate received during the DTLS
   handshake MUST match the fingerprint received in the SDP
   "fingerprint" attribute. If the fingerprint does not match the
   hashed certificate, then the endpoint MUST tear down the media



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   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.

4.2.  Generating the Initial Offer

   The offerer SHOULD assign the SDP "setup" attribute with a value of
   "actpass", unless the offerer insists on being either the sender or
   receiver of the DTLS ClientHello message, in which case the offerer
   can use either a value of "active" (the offerer will be the sender of
   ClientHello) or "passive" (the offerer will be the receiver of
   ClientHello).  The offerer MUST NOT assign an SDP "setup" attribute
   with a "holdconn" value.

   If the offerer assigns the SDP "setup" attribute with a value of
   "actpass" or "passive", the offerer MUST be prepared to receive a
   DTLS ClientHello message before it receives the SDP answer.

4.3.  Generating the Answer

   If the answerer accepts the offered UDPTL-over-DTLS transport
   connection, in the associated SDP answer, the answerer MUST assign an
   SDP "setup" attribute with a value of either "active" or "passive",
   according to the procedures in [RFC4145]. The answerer MUST NOT
   assign an SDP "setup" attribute with a value of "holdconn".

   If the answerer assigns an SDP "setup" attribute with a value of
   "active" value, the answerer MUST initiate a DTLS handshake by
   sending a DTLS ClientHello message on the negotiated media stream,
   towards the IP address and port of the offerer.

4.4.  Offerer Processing of the Answer

   When the offerer receives an SDP answer, if the offerer ends up being
   active it MUST initiate a DTLS handshake by sending a DTLS
   ClientHello message on the negotiated media stream, towards the IP
   address and port of the answerer.

4.5.  Modifying the Session

   Once an offer/answer exchange has been completed, either endpoint MAY
   send a new offer in order to modify the session. The endpoints can
   reuse the existing DTLS association if the key fingerprint values and
   transport parameters indicated by each endpoint are unchanged.
   Otherwise, following the rules for the initial offer/answer exchange,
   the endpoints can negotiate and create a new DTLS association and,
   once created, delete the previous DTLS association, following the
   same rules for the initial offer/answer exchange. Each endpoint



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   needs to be prepared to receive data on both the new and old DTLS
   associations as long as both are alive.

NEW TEXT:

4.  SDP Offerer/Answerer Procedures

   An endpoint (i.e., both the offerer and the answerer) MUST create an
   SDP media description ("m=" line) for each UDPTL-over-DTLS media
   stream and MUST assign a UDP/TLS/UDPTL value (see Table 1) to the
   "proto" field of the "m=" line.

   The offerer and answerer MUST follow the SDP offer/answer procedures
   defined in [RFCXXXX] in order to negotiate the DTLS association
   associated with the UDPTL-over-DTLS media stream. In addition,
   the offerer and answerer MUST use the SDP attributes defined for
   UDPTL over UDP, as defined in [ITU.T38.2010].

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


Update to section 5.2.1:
------------------------

OLD TEXT:

5.2.1.  ICE Usage

   When Interactive Connectivity Establishment (ICE) [RFC5245] is being
   used, the ICE connectivity checks are performed before the DTLS
   handshake begins. Note that if aggressive nomination mode is used,
   multiple candidate pairs may be marked valid before ICE finally
   converges on a single candidate pair. User Agents (UAs) MUST treat
   all ICE candidate pairs associated with a single component as part
   of the same DTLS association. Thus, there will be only one DTLS
   handshake even if there are multiple valid candidate pairs. Note
   that this may mean adjusting the endpoint IP addresses if the
   selected candidate pair shifts, just as if the DTLS packets were an
   ordinary media stream. In the case of an ICE restart, the DTLS
   handshake procedure is repeated, and a new DTLS association is
   created. Once the DTLS handshake is completed and the new DTLS
   association has been created, the previous DTLS association is
   deleted.


NEW TEXT:




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5.2.1.  ICE Usage

   The Interactive Connectivity Establishment (ICE)
   [I-D.ietf-ice-rfc5245bis] considerations for DTLS-protected media
   are described in [RFCXXXX].

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


10.  Security Considerations

   This specification does not modify the security considerations
   associated with DTLS, or the SDP offer/answer mechanism.  In addition
   to the introduction of the SDP 'dtls-id' attribute, the specification
   simply clarifies the procedures for negotiating and establishing a
   DTLS association.

11.  IANA Considerations

   This document updates the "Session Description Protocol Parameters"
   registry as specified in Section 8.2.2 of [RFC4566].  Specifically,
   it adds the SDP 'dtls-id' attribute to the table for SDP media level
   attributes.


       Attribute name: dtls-id
       Type of attribute: media-level
       Subject to charset: no
       Purpose: Indicates whether a new DTLS association is to be
        established/re-established.
       Appropriate Values: see Section 4
       Contact name: Christer Holmberg
       Mux Category: IDENTICAL


12.  Acknowledgements

   Thanks to Justin Uberti, Martin Thomson, Paul Kyzivat, Jens Guballa,
   Charles Eckel, Gonzalo Salgueiro and Paul Jones for providing
   comments and suggestions on the document.  Ben Campbell performed an
   AD review.

13.  Change Log

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

   Changes from draft-ietf-mmusic-sdp-dtls-21



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   o  Changes based on AD review by Ben Campbell.

   o  (https://www.ietf.org/mail-archive/web/mmusic/current/
      msg17707.html)

   Changes from draft-ietf-mmusic-sdp-dtls-20

   o  Change to length and randomness of dtls-id attribute value.

   Changes from draft-ietf-mmusic-sdp-dtls-19

   o  Change based on comment from Roman.

   Changes from draft-ietf-mmusic-sdp-dtls-18

   o  Changes based on comments from Flemming.

   o  - Change in dtls-id value definition.

   o  - Editorial fixes.

   Changes from draft-ietf-mmusic-sdp-dtls-17

   o  Reference fix.

   Changes from draft-ietf-mmusic-sdp-dtls-16

   o  Editorial changes based on 2nd WGLC comments from Christian Groves
      and Nevenka Biondic.

   Changes from draft-ietf-mmusic-sdp-dtls-15

   o  dtls-id attribute value made globally unique

   Changes from draft-ietf-mmusic-sdp-dtls-14

   o  Changes based on comments from Flemming:

   o  - Additional dtls-is clarifiations

   o  - Editorial fixes

   Changes from draft-ietf-mmusic-sdp-dtls-13

   o  Text about the updated RFCs added to Abstract and Introduction

   o  Reference to RFC 5763 removed from section 6 (ICE Considerations)




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   o  Reference to RFC 5763 removed from section 8 (SIP Considerations)

   Changes from draft-ietf-mmusic-sdp-dtls-12

   o  "unreliable" changed to "unordered"

   Changes from draft-ietf-mmusic-sdp-dtls-11

   o  Attribute name changed to dtls-id

   o  Additional text based on comments from Roman Shpount.

   Changes from draft-ietf-mmusic-sdp-dtls-10

   o  Modified document to use dtls-id instead of dtls-connection

   o  Changes are based on comments from Eric Rescorla, Justin Uberti,
      and Paul Kyzivat.

   Changes from draft-ietf-mmusic-sdp-dtls-08

   o  Offer/Answer section modified in order to allow sending of
      multiple SDP 'fingerprint' attributes.

   o  Terminology made consistent: 'DTLS connection' replaced with 'DTLS
      association'.

   o  Editorial changes based on comments from Paul Kyzivat.

   Changes from draft-ietf-mmusic-sdp-dtls-07

   o  Reference to RFC 7315 replaced with reference to RFC 7345.

   Changes from draft-ietf-mmusic-sdp-dtls-06

   o  Text on restrictions regarding spanning a DTLS association over
      multiple transports added.

   o  Mux category added to IANA Considerations.

   o  Normative text regarding mux category and source-specific
      applicability added.

   o  Reference to RFC 7315 added.

   o  Clarified that offerer/answerer that has not been updated to
      support this specification will not include the dtls-id attribute
      in offers and answers.



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   o  Editorial corrections based on WGLC comments from Charles Eckel.

   Changes from draft-ietf-mmusic-sdp-dtls-05

   o  Text on handling offer/answer error conditions added.

   Changes from draft-ietf-mmusic-sdp-dtls-04

   o  Editorial nits fixed based on comments from Paul Kyzivat:

   Changes from draft-ietf-mmusic-sdp-dtls-03

   o  Changes based on comments from Paul Kyzivat:

   o  - Modification of dtls-id attribute section.

   o  - Removal of IANA considerations subsection.

   o  - Making note into normative text in o/a section.

   o  Changes based on comments from Martin Thompson:

   o  - Abbreviations section removed.

   o  - Clarify that a new DTLS association requires a new o/a
      transaction.

   Changes from draft-ietf-mmusic-sdp-dtls-02

   o  - Updated RFCs added to boilerplate.

   Changes from draft-ietf-mmusic-sdp-dtls-01

   o  - Annex regarding 'dtls-id-id' attribute removed.

   o  - Additional SDP offer/answer procedures, related to certificates,
      added.

   o  - Updates to RFC 5763 and RFC 7345 added.

   o  - Transport protocol considerations added.

   Changes from draft-ietf-mmusic-sdp-dtls-00

   o  - SDP 'connection' attribute replaced with new 'dtls-id'
      attribute.

   o  - IANA Considerations added.



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   o  - E-mail regarding 'dtls-id-id' attribute added as Annex.

   Changes from draft-holmberg-mmusic-sdp-dtls-01

   o  - draft-ietf-mmusic version of draft submitted.

   o  - Draft file name change (sdp-dtls -> dtls-sdp) due to collision
      with another expired draft.

   o  - Clarify that if ufrag in offer is unchanged, it must be
      unchanged in associated answer.

   o  - SIP Considerations section added.

   o  - Section about multiple SDP fingerprint attributes added.

   Changes from draft-holmberg-mmusic-sdp-dtls-00

   o  - Editorial changes and clarifications.

14.  References

14.1.  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,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,
              <http://www.rfc-editor.org/info/rfc3261>.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              DOI 10.17487/RFC3264, June 2002,
              <http://www.rfc-editor.org/info/rfc3264>.

   [RFC4145]  Yon, D. and G. Camarillo, "TCP-Based Media Transport in
              the Session Description Protocol (SDP)", RFC 4145,
              DOI 10.17487/RFC4145, September 2005,
              <http://www.rfc-editor.org/info/rfc4145>.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
              July 2006, <http://www.rfc-editor.org/info/rfc4566>.



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   [RFC4572]  Lennox, J., "Connection-Oriented Media Transport over the
              Transport Layer Security (TLS) Protocol in the Session
              Description Protocol (SDP)", RFC 4572,
              DOI 10.17487/RFC4572, July 2006,
              <http://www.rfc-editor.org/info/rfc4572>.

   [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, DOI 10.17487/RFC5763, May
              2010, <http://www.rfc-editor.org/info/rfc5763>.

   [RFC7345]  Holmberg, C., Sedlacek, I., and G. Salgueiro, "UDP
              Transport Layer (UDPTL) over Datagram Transport Layer
              Security (DTLS)", RFC 7345, DOI 10.17487/RFC7345, August
              2014, <http://www.rfc-editor.org/info/rfc7345>.

   [I-D.ietf-ice-rfc5245bis]
              Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive
              Connectivity Establishment (ICE): A Protocol for Network
              Address Translator (NAT) Traversal", draft-ietf-ice-
              rfc5245bis-08 (work in progress), December 2016.

   [I-D.ietf-mmusic-4572-update]
              Lennox, J. and C. Holmberg, "Connection-Oriented Media
              Transport over TLS in SDP", draft-ietf-mmusic-
              4572-update-13 (work in progress), February 2017.

   [I-D.ietf-mmusic-sdp-mux-attributes]
              Nandakumar, S., "A Framework for SDP Attributes when
              Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-16
              (work in progress), December 2016.

   [I-D.ietf-mmusic-sdp-bundle-negotiation]
              Holmberg, C., Alvestrand, H., and C. Jennings,
              "Negotiating Media Multiplexing Using the Session
              Description Protocol (SDP)", draft-ietf-mmusic-sdp-bundle-
              negotiation-36 (work in progress), October 2016.

14.2.  Informative References

   [RFC4474]  Peterson, J. and C. Jennings, "Enhancements for
              Authenticated Identity Management in the Session
              Initiation Protocol (SIP)", RFC 4474,
              DOI 10.17487/RFC4474, August 2006,
              <http://www.rfc-editor.org/info/rfc4474>.





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   [RFC5245]  Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Protocol for Network Address Translator (NAT)
              Traversal for Offer/Answer Protocols", RFC 5245,
              DOI 10.17487/RFC5245, April 2010,
              <http://www.rfc-editor.org/info/rfc5245>.

   [RFC5576]  Lennox, J., Ott, J., and T. Schierl, "Source-Specific
              Media Attributes in the Session Description Protocol
              (SDP)", RFC 5576, DOI 10.17487/RFC5576, June 2009,
              <http://www.rfc-editor.org/info/rfc5576>.

   [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,
              DOI 10.17487/RFC5764, May 2010,
              <http://www.rfc-editor.org/info/rfc5764>.

   [RFC6083]  Tuexen, M., Seggelmann, R., and E. Rescorla, "Datagram
              Transport Layer Security (DTLS) for Stream Control
              Transmission Protocol (SCTP)", RFC 6083,
              DOI 10.17487/RFC6083, January 2011,
              <http://www.rfc-editor.org/info/rfc6083>.

   [I-D.ietf-stir-rfc4474bis]
              Peterson, J., Jennings, C., Rescorla, E., and C. Wendt,
              "Authenticated Identity Management in the Session
              Initiation Protocol (SIP)", draft-ietf-stir-rfc4474bis-16
              (work in progress), February 2017.

   [ITU.T38.2010]
              International Telecommunications Union, "Procedures for
              real-time Group 3 facsimile communication over IP
              networks", ITU-T Recommendation T.38, September 2010.

Authors' Addresses

   Christer Holmberg
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: christer.holmberg@ericsson.com








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Internet-DraftUsing the SDP Offer/Answer Mechanism for DTLS   March 2017


   Roman Shpount
   TurboBridge
   4905 Del Ray Avenue, Suite 300
   Bethesda, MD  20814
   USA

   Phone: +1 (240) 292-6632
   Email: rshpount@turbobridge.com











































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