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In: MissingRef
Network Working Group                                        C. Holmberg
Internet-Draft                                                  Ericsson
Intended status: Standards Track                              R. Shpount
Expires: April 21, 2016                                      TurboBridge
                                                        October 19, 2015


             Using the SDP Offer/Answer Mechanism for DTLS
                   draft-ietf-mmusic-dtls-sdp-01.txt

Abstract

   This draft defines the SDP offer/answer procedures for negotiating
   and establishing a DTLS association.  The draft also defines the
   criteria for when a new DTLS association must be established.

   This draft defines a new SDP media-level attribute, 'dtls-
   connection'.

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 April 21, 2016.

Copyright Notice

   Copyright (c) 2015 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
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   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.  Abbreviations . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Establishing a new DTLS Association . . . . . . . . . . . . .   3
     4.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   3
     4.2.  Change of Local Transport Parameters  . . . . . . . . . .   3
     4.3.  Change of ICE ufrag value . . . . . . . . . . . . . . . .   4
     4.4.  Multiple SDP fingerprint attributes . . . . . . . . . . .   4
   5.  SDP DTLS-Connection Attribute . . . . . . . . . . . . . . . .   4
     5.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.2.  ABNF  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . .   5
     6.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   5
     6.2.  Generating the Initial SDP Offer  . . . . . . . . . . . .   5
     6.3.  Generating the Answer . . . . . . . . . . . . . . . . . .   5
     6.4.  Offerer Processing of the SDP Answer  . . . . . . . . . .   6
     6.5.  Modifying the Session . . . . . . . . . . . . . . . . . .   6
   7.  ICE Considerations  . . . . . . . . . . . . . . . . . . . . .   7
   8.  SIP Considerations  . . . . . . . . . . . . . . . . . . . . .   7
   9.  RFC Updates . . . . . . . . . . . . . . . . . . . . . . . . .   7
   10. Security Considerations . . . . . . . . . . . . . . . . . . .   7
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     11.1.  Registration of New SDP Attribute  . . . . . . . . . . .   7
   12. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   13. Change Log  . . . . . . . . . . . . . . . . . . . . . . . . .   8
   14. Normative References  . . . . . . . . . . . . . . . . . . . .   9
   Appendix A.  Design Considerations  . . . . . . . . . . . . . . .  10
     A.1.  dtls-connection versus dtls-connection-id . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   [RFC5763] defines SDP Offer/Answer procedures for SRTP-DTLS.  This
   draft defines the SDP Offer/Answer [RFC3264] procedures for
   negotiation DTLS in general, based on the procedures in [RFC5763].

   This draft also defines a new SDP attribute, 'dtls-connection'.  The
   attribute is used in SDP offers and answers to explicitly indicate
   whether a new DTLS association is to be established.

   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)



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   [RFC5245] 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 [RFC5245] 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 draft defines a new SDP attribute, 'dtls-
   connection'.  The attribute is used in SDP offers and answers to
   explicitly indicate whether a new DTLS association is to be
   established/re-established.  The attribute can be used both with and
   without ICE.

2.  Abbreviations

   TBD

3.  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].

4.  Establishing a new DTLS Association

4.1.  General

   A new DTLS association MUST be established in the following cases:

   o  The DTLS roles change;

   o  The fingerprint (certificate) value changes; or

   o  The establishment of a new DTLS association is explicitly
      signaled;

   NOTE: The first two items list above are based on the procedures in
   [RFC5763].  This draft adds the support for explicit signaling.

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

4.2.  Change of Local Transport Parameters

   If an endpoint modifies its local transport parameters (IP address
   and/or port), and if the modification requires a new DTLS
   association, the endpoint MUST either change its DTLS role, its
   fingerprint value and/or use the SDP 'dtls-connection' attribute with
   a 'new' value Section 5.



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4.3.  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
   either change its DTLS role, its fingerprint value and/or use the SDP
   'dtls-connection' attribute with a 'new' value Section 5.

4.4.  Multiple SDP fingerprint attributes

   It is possible to associate multiple SDP fingerprint attribute values
   to an 'm-' line.  If any of the attribute values associated with an
   'm-' line are removed, or if any new attribute values are added, it
   is considered a fingerprint value change.

5.  SDP DTLS-Connection Attribute

5.1.  General

   The SDP 'connection' attribute [RFC4145] was originally defined for
   connection-oriented protocols, e.g.  TCP and TLS.  This section
   defines a similar attribute, 'dtls-connection', to be used with DTLS.

   A 'dtls-connection' attribute value of 'new' indicates that a new
   DTLS association MUST be established.  A 'dtls-connection' attribute
   value of 'existing' indicates that a new DTLS association MUST NOT be
   established.

   Unlike the SDP 'connection' attribute for TLS, there is no default
   value defined for the 'dtls-connection' 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 an
   attribute, other means needs to be used in order for endpoints to
   determine whether an offer or answer is associated with an event that
   requires the DTLS association to be re-established.

   The SDP Offer/Answer [RFC3264] procedures associated with the
   attribute are defined in Section 6

5.2.  ABNF

   The ABNF [RFC5234] grammar for the SDP 'dtls-connection' attributes
   is:


       dtls-connection-attr   = "a=dtls-connection:" conn-value
       conn-value             = "new" / "existing"





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6.  SDP Offer/Answer Procedures

6.1.  General

   This section defines the SDP offer/answer procedures for using the
   SDP 'dtls-connection' attribute for DTLS.  The section also describes
   how the usage of the SDP 'setup' attribute and the SDP 'fingerprint'
   attribute [RFC4572] is affected.

   The procedures in this section are based on the procedures for SRTP-
   DTLS [RFC5763], with the addition of usage of the SDP 'dtls-
   connection' attribute.

6.2.  Generating the Initial SDP Offer

   When the offerer sends the initial offer, and the offerer wants to
   establish a DTLS association, it MUST insert an SDP 'dtls-connection'
   attribute with a 'new' value in the offer.  In addition, the offerer
   MUST insert an SDP 'setup' attribute according to the procedures in
   [RFC4145], and an SDP 'fingerprint' attribute according to the
   procedures in [RFC4572], in the offer.

   Unlike for TCP and TLS connections, in case of DTLS associations the
   SDP 'setup' attribute 'holdconn' value MUST NOT be used.

6.3.  Generating the Answer

   If an answerer receives an offer that contains an SDP 'dtls-
   connection' attribute with a 'new' value, the answerer MUST insert a
   'new' value in the associated answer.  The same applies if the
   answerer receives an offer that contains an SDP 'dtls-connection'
   attribute with a 'new' value, but the answerer determines (based on
   the criteria for establishing a new DTLS association) that a new DTLS
   association is to be established.  In addition, the answerer MUST
   insert an SDP 'setup' attribute according to the procedures in
   [RFC4145], and an SDP 'fingerprint' attribute according to the
   procedures in [RFC4572], in the answer.

   If the answerer does not accept the establishment of the DTLS
   association, it MUST reject the "m=" lines associated with the
   suggested DTLS association [RFC3264].

   If an answerer receives an offer that contains a 'dtls-connection'
   attribute with an 'existing' value, and if the answerer determines
   that a new DTLS association does not need to be established, it MUST
   insert a connection attribute with an 'existing' value in the
   associated answer.  In addition, the answerer MUST insert an SDP
   'setup' attribute with a value that does not change the previously



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   negotiated DTLS roles, and an SDP 'fingerprint' attribute with a
   value that does not change the fingerprint, in the answer.

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

   If a new DTLS association is to be established, and if the answerer
   becomes DTLS client, the answerer MUST initiate the procedures for
   establishing the DTLS association.  If the answerer becomes DTLS
   server, it MUST wait for the offerer to establish the DTLS
   association.

6.4.  Offerer Processing of the SDP Answer

   When an offerer receives an answer that contains an SDP 'dtls-
   connection' attribute with a 'new' value, and if the offerer becomes
   DTLS client, 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 contains an SDP 'dtls-connection' attribute with an
   'existing' value, the offerer will continue using the previously
   established DTLS association.  It is considered an error case if the
   answer contains a 'dtls-connection' attribute with an 'existing'
   value, and a DTLS association does not exist.

6.5.  Modifying the Session

   When the offerer sends a subsequent offer, and the offerer wants to
   establish a new DTLS association, the offerer MUST insert an SDP
   'dtls-connection' attribute with a 'new' value in the offer.  In
   addition, the offerer MUST insert an SDP 'setup' attribute according
   to the procedures in [RFC4145], and an SDP 'fingerprint' attribute
   according to the procedures in [RFC4572], in the offer.

   when the offerer sends a subsequent offer, and the offerer does not
   want to establish a new DTLS association, if a previously established
   DTLS association exists, the offerer MUST insert an SDP 'dtls-
   connection' attribute with an 'existing' value in the offer.  In
   addition, the offerer MUST insert an SDP 'setup' attribute with a
   value that does not change the previously negotiated DTLS roles, and
   an SDP 'fingerprint' attribute with a value that does not change the
   fingerprint, in the offer.







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7.  ICE Considerations

   An ICE restart [RFC5245] does not by default require a new DTLS
   association to be established.

   As defined in [RFC5763], 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.

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 MUST be established between the caller and
   each callee.

   It is possible to send an INVITE request which does not contain an
   SDP offer.  Such INVITE request is often referred to as an 'empty
   INVITE', or an 'offerless INVITE'.  The receiving endpoint will
   include the SDP offer in a response associated with the response.
   When the endpoint generates such SDP offer, it MUST assign an SDP
   connection attribute, with a 'new' value, to each 'm-' line that
   describes DTLS protected media.  If ICE is used, the endpoint MUST
   allocate a new set of ICE candidates, in order to ensure that two
   DTLS association would not be running over the same transport.

9.  RFC Updates

   Here we will add the RFC updates that are needed.

10.  Security Considerations

   This draft does not modify the security considerations associated
   with DTLS, or the SDP offer/answer mechanism.  The draft simply
   clarifies the procedures for negotiating and establishing a DTLS
   association.

11.  IANA Considerations

11.1.  Registration of New SDP Attribute

   This document updates the "Session Description Protocol Parameters"
   registry as specified in Section 8.2.2 of [RFC4566].  Specifically,




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   it adds the SDP attributes in Section 11.1 to the table for SDP media
   level attributes.


       Attribute name: dtls-connection
       Type of attribute: media-level
       Subject to charset: no
       Purpose: TBD
       Appropriate Values: see Section X
       Contact name: Christer Holmberg


12.  Acknowledgements

   Thanks to Justin Uberti, Martin Thomson, Paul Kyzivat and Jens
   Guballa for providing comments and suggestions on the draft.

13.  Change Log

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

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

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

   o  - IANA Considerations added.

   o  - E-mail regarding 'dtls-connection-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.




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14.  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>.

   [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>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <http://www.rfc-editor.org/info/rfc5234>.

   [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>.








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   [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>.

Appendix A.  Design Considerations

A.1.  dtls-connection versus dtls-connection-id

   The text below is from an e-mail sent by Roman to the MMUSIC mailing
   list, 1st October 2015.  It is intended to serve as background
   reading when discussing the way forward regarding the SDP attribute.


   The "dtls-ufrag" has little to do with ICE and exists
   in a completely different layer. We can call this
   attribute "dtls-connection-id" if this will makes it
   less spooky. The problem that I am trying to resolve
   with new attribute is related to when new DTLS association
   needs to be established. I would argue that original
   intent was, that new DTLS association needs to be
   established on change of one of the end points or
   DTLS association setup attributes (setup role or
   fingerprint).

   Originally, end point change was detected based on
   transport 5-tuple change. This, of cause, does not
   work for ICE, where 5-tuple is not known in advance
   and all 5-tuples associated with the same ICE component
   should be treated as the same connection. One option was
   to detect end point change when ICE is used based on
   ICE ufrag change, but this does not work either since
   ufrag can change due to ICE restart, but the same
   endpoints will continue to communicate.

   I would also argue that setting up new DTLS association
   on 5-tuple change does not always work for non-ICE case
   either, since we can have an end point which can initiate
   a re-INVITE when it detects the local IP changes due to
   DHCP lease expiration or any other reason. This transport
   change does not necessarily require DTLS association
   change, and new DTLS handshake is undesirable since it
   will delay the media flow re-establishment but several
   network round trips.

   So, we need to detect when two new end-points are
   communicating and new DTLS association needs to be



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   setup. What we originally proposed is that end point
   will simply tell that it is setting up a new session
   by using SDP connection attribute or some renamed
   version of it.

   What I am saying here is that end point cannot always
   identify if it needs to setup a new DTLS association.
   The problem arises when new offer is generated in
   response to an offerless INVITE. In such case, an end
   point does not know if it is continuing to communicate
   with the same end-point or if this offer is intended
   to be sent to a new end point.

   There are two solution possible to this:

   1. We specify that if an end points generates an offer in
   response to an offer-less INVITE it should always assume
   it is communicating with a new end point, it MUST add
   "connection:new" and MUST make sure that none of the
   existing transports can be possibly reused for this new
   DTLS association by allocating new IP:port for non ICE
   or a complete new set of ICE candidates in case of ICE.
   This will work, but it is wasteful when offer-less INVITE
   re-establishes connection between two existing end points.
   In such cases additional ports will be consumed, TURN
   tunnels will be allocated, and time spent on creating a
   DTLS session when all of this can be simply reused.

   2. Instead of asking the end point which generates the
   offer to determine if it is establishing a new DTLS
   association, we will ask the end point to identify itself.
   So, instead of SDP connection attribute, an end point
   will provide some sort of randomly generated end point
   identifier in the new attribute (dtls-ufrag or
   dtls-connection-id). When the connection ID pair stays
   the same, the existing DTLS association continues to run
   over the negotiated transport. If one of the connection
   IDs changes, this would mean new DTLS association would
   need to be established. This nicely uncouples end point
   change identification from transport and makes negotiation
   follow the original intent.

   In case of response to an offer-less INVITE, an offer with
   the existing connection ID will be generated. If this offer
   is sent to a new end point, both end points will detect
   that new DTLS association is required due to connection ID
   change of the answering end point. If this offer will be
   sent to an end point which is already a part of the existing



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   DTLS association, no new DTLS association will be necessary,
   since both connection IDs will stay the same.

   This also gives us path to a more "strategic" solution in the
   future. DTLS handshake can be extended to include the
   connection ID. Each DTLS handshake can negotiate a association
   identifier similar to SSRC which can be used in the all
   subsequent DTLS messages for this association. This way
   multiple DTLS associations can be multiplexed over the single
   transport and each of them can be tied to an m= line in
   offer/answer. This, of cause, is not part of the current
   draft and is outside of MMUSIC chapter, but does provide a
   natural extension path for DTLS in the future.

   In general Christer and I are trying to understand if there
   is interest in formalizing the dtls-connection-id option
   (more complex) or if we should stick with SDP
   connection:new/existing attribute and force new DTLS association
   always be established in response to offer-less INVITE (simpler
   option but can waste resources).

   Please let us know if these options need further clarification
   or if you have any additional questions or opinions.


Authors' Addresses

   Christer Holmberg
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: christer.holmberg@ericsson.com


   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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