draft-ietf-mmusic-dtls-sdp-00.txt   draft-ietf-mmusic-dtls-sdp-01.txt 
Network Working Group C. Holmberg Network Working Group C. Holmberg
Internet-Draft Ericsson Internet-Draft Ericsson
Intended status: Standards Track R. Shpount Intended status: Standards Track R. Shpount
Expires: March 10, 2016 TurboBridge Expires: April 21, 2016 TurboBridge
September 7, 2015 October 19, 2015
Using the SDP Offer/Answer Mechanism for DTLS Using the SDP Offer/Answer Mechanism for DTLS
draft-ietf-mmusic-dtls-sdp-00.txt draft-ietf-mmusic-dtls-sdp-01.txt
Abstract Abstract
This draft defines the SDP offer/answer procedures for negotiating This draft defines the SDP offer/answer procedures for negotiating
and establishing a DTLS association. The draft also defines the and establishing a DTLS association. The draft also defines the
criteria for when a new DTLS association must be established. 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 Status of This Memo
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provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Establishing a new DTLS Association . . . . . . . . . . . . . 3 2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. ICE Considerations . . . . . . . . . . . . . . . . . . . 3 4. Establishing a new DTLS Association . . . . . . . . . . . . . 3
2.3. SIP Considerations . . . . . . . . . . . . . . . . . . . 3 4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . 4 4.2. Change of Local Transport Parameters . . . . . . . . . . 3
4. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4 4.3. Change of ICE ufrag value . . . . . . . . . . . . . . . . 4
5. SDP Connection Attribute for DTLS . . . . . . . . . . . . . . 4 4.4. Multiple SDP fingerprint attributes . . . . . . . . . . . 4
5. SDP DTLS-Connection Attribute . . . . . . . . . . . . . . . . 4
5.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 4 5.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 4
6. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 4 5.2. ABNF . . . . . . . . . . . . . . . . . . . . . . . . . . 4
6.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 4 6. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 5
6.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.2. Generating the Initial SDP Offer . . . . . . . . . . . . 5 6.2. Generating the Initial SDP Offer . . . . . . . . . . . . 5
6.3. Generating the Answer . . . . . . . . . . . . . . . . . . 5 6.3. Generating the Answer . . . . . . . . . . . . . . . . . . 5
6.4. Offerer Processing of the SDP Answer . . . . . . . . . . 6 6.4. Offerer Processing of the SDP Answer . . . . . . . . . . 6
6.5. Modifying the Session . . . . . . . . . . . . . . . . . . 6 6.5. Modifying the Session . . . . . . . . . . . . . . . . . . 6
7. RFC Updates . . . . . . . . . . . . . . . . . . . . . . . . . 6 7. ICE Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. Security Considerations . . . . . . . . . . . . . . . . . . . 7 8. SIP Considerations . . . . . . . . . . . . . . . . . . . . . 7
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 9. RFC Updates . . . . . . . . . . . . . . . . . . . . . . . . . 7
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 10. Security Considerations . . . . . . . . . . . . . . . . . . . 7
11. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 7 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
12. Normative References . . . . . . . . . . . . . . . . . . . . 7 11.1. Registration of New SDP Attribute . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 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 1. Introduction
[RFC5763] defines SDP Offer/Answer procedures for SRTP-DTLS. This [RFC5763] defines SDP Offer/Answer procedures for SRTP-DTLS. This
draft defines the SDP Offer/Answer [RFC3264] procedures for draft defines the SDP Offer/Answer [RFC3264] procedures for
negotiation DTLS in general, based on the procedures in [RFC5763]. negotiation DTLS in general, based on the procedures in [RFC5763].
This draft also defines the usage of the SDP 'connection' attribute This draft also defines a new SDP attribute, 'dtls-connection'. The
with DTLS. The attribute is used in SDP offers and answers to attribute is used in SDP offers and answers to explicitly indicate
explicitly indicate whether a new DTLS association is to be whether a new DTLS association is to be established.
established.
As defined in [RFC5245], when Interactive Connectivity Establishment As defined in [RFC5763], a new DTLS association MUST be established
(ICE) [RFC5245] is used, the ufrag value is changed both when ICE is when transport parameters are changed. Transport parameter change is
negotiated, and when ICE restart [RFC5245] occurs. These events do not well defined when Interactive Connectivity Establishment (ICE)
not always require a new DTLS association to be established, but
currently there is no way to explicitly indicate in an SDP offer or [RFC5245] is used. One possible way to determine a transport change
answer whether a new DTLS association is required. To solve that is based on ufrag change, but the ufrag value is changed both when
problem, this draft defines the usage of the SDP 'connection' ICE is negotiated and when ICE restart [RFC5245] occurs. These
attribute with DTLS. The attribute is used in SDP offers and answers events do not always require a new DTLS association to be
to explicitly indicate whether a new DTLS association is 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 established/re-established. The attribute can be used both with and
without ICE. without ICE.
2. Establishing a new DTLS Association 2. Abbreviations
2.1. General TBD
As defined in [RFC5763], an endpoint MUST indicate (in an offer or 3. Conventions
answer) that a new DTLS association to established in the following
cases:
o The DTLS roles change; 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].
o The fingerprint (certificate) value changes; 4. Establishing a new DTLS Association
o The local transport parameters (IP address and/or port) of at 4.1. General
least one endpoint change; or
o If ICE is used and the ufrag value changes, and there is no A new DTLS association MUST be established in the following cases:
explicit indication (SDP 'connection' attribute) that a new DTLS
association shall not be established;
When a new DTLS association is established, an endpoint MUST use a o The DTLS roles change;
new set of transport parameters (IP address and port combination).
2.2. ICE Considerations o The fingerprint (certificate) value changes; or
An ICE restart [RFC5245] does not by default require a new DTLS o The establishment of a new DTLS association is explicitly
association to be established. A new DTLS association needs to be signaled;
established only if or more of the criteria listed in Section 2.1 is
fulfilled (e.g. if the local transport paramters change).
As defined in [RFC5763], each ICE candidate associated with a NOTE: The first two items list above are based on the procedures in
component is treated as being part of the same DTLS association. [RFC5763]. This draft adds the support for explicit signaling.
Therefore, from a DTLS perspective it is not considered a change of
local transport parameters when an endpoint switches between those
ICE candidates.
2.3. SIP Considerations The sections below describe typical cases where a new DTLS
association needs to be established.
When the Session Initiation Protocol (SIP) [RFC3261] is used as the 4.2. Change of Local Transport Parameters
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.
3. Abbreviations 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.
TBD 4.3. Change of ICE ufrag value
4. Conventions 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.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 4.4. Multiple SDP fingerprint attributes
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
5. SDP Connection Attribute for DTLS 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 5.1. General
The SDP 'connection' attribute [RFC4145] was originally defined for The SDP 'connection' attribute [RFC4145] was originally defined for
connection-oriented protocols, e.g. TCP and TLS. This section connection-oriented protocols, e.g. TCP and TLS. This section
defines how the attribute is used with DTLS. defines a similar attribute, 'dtls-connection', to be used with DTLS.
A 'connection' attribute value of 'new' indicates that a new DTLS A 'dtls-connection' attribute value of 'new' indicates that a new
association MUST be established. A 'connection' attribute value of DTLS association MUST be established. A 'dtls-connection' attribute
'existing' indicates that a new DTLS association MUST NOT be value of 'existing' indicates that a new DTLS association MUST NOT be
established. established.
When used with DTLS, there is no default value defined for the Unlike the SDP 'connection' attribute for TLS, there is no default
attribute. Implementations that wish to use the attribute MUST value defined for the 'dtls-connection' attribute. Implementations
explicitly include it in SDP offers and answers. If an offer or that wish to use the attribute MUST explicitly include it in SDP
answer does not contain an attribute, other means needs to be used in offers and answers. If an offer or answer does not contain an
order for endpoints to determine whether an offer or answer is attribute, other means needs to be used in order for endpoints to
associated with an event that requires the DTLS association to be re- determine whether an offer or answer is associated with an event that
established. 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"
6. SDP Offer/Answer Procedures 6. SDP Offer/Answer Procedures
6.1. General 6.1. General
This section defines the SDP offer/answer procedures for using the This section defines the SDP offer/answer procedures for using the
SDP 'connection' attribute for DTLS. The section also describes how SDP 'dtls-connection' attribute for DTLS. The section also describes
the usage of the SDP 'setup' attribute and the SDP 'fingerprint' how the usage of the SDP 'setup' attribute and the SDP 'fingerprint'
attribute [RFC4572] is affected. attribute [RFC4572] is affected.
The procedures in this section are based on the procedures for SRTP- The procedures in this section are based on the procedures for SRTP-
DTLS [RFC5763], with the addition of usage of the SDP 'connection' DTLS [RFC5763], with the addition of usage of the SDP 'dtls-
attribute. connection' attribute.
6.2. Generating the Initial SDP Offer 6.2. Generating the Initial SDP Offer
When the offerer sends the initial offer, and the offerer wants to When the offerer sends the initial offer, and the offerer wants to
establish a DTLS association, it MUST insert an SDP 'connection' establish a DTLS association, it MUST insert an SDP 'dtls-connection'
attribute with a 'new' value in the offer. In addition, the offerer attribute with a 'new' value in the offer. In addition, the offerer
MUST insert an SDP 'setup' attribute according to the procedures in MUST insert an SDP 'setup' attribute according to the procedures in
[RFC4572], and an SDP 'fingerprint' attribute according to the [RFC4145], and an SDP 'fingerprint' attribute according to the
procedures in [RFC4572], in the offer. procedures in [RFC4572], in the offer.
If ICE is used, the offerer MUST insert the SDP 'ice-ufrag' and 'ice- Unlike for TCP and TLS connections, in case of DTLS associations the
pwd' attributes according to the procedures in [RFC5245] in the SDP 'setup' attribute 'holdconn' value MUST NOT be used.
offer.
6.3. Generating the Answer 6.3. Generating the Answer
If an answerer receives an offer that contains an SDP 'connection' If an answerer receives an offer that contains an SDP 'dtls-
attribute with a 'new' value, the answerer MUST insert a 'new' value connection' attribute with a 'new' value, the answerer MUST insert a
in the associated answer. The same applies if the answerer receives 'new' value in the associated answer. The same applies if the
an offer that contains an SDP 'connection' attribute with a 'new' answerer receives an offer that contains an SDP 'dtls-connection'
value, but the answerer determines (based on the criteria for attribute with a 'new' value, but the answerer determines (based on
establishing a new DTLS association) that a new DTLS association is the criteria for establishing a new DTLS association) that a new DTLS
to be established. In addition, the answerer MUST insert an SDP association is to be established. In addition, the answerer MUST
'setup' attribute according to the procedures in [RFC4572], and an insert an SDP 'setup' attribute according to the procedures in
SDP 'fingerprint' attribute according to the procedures in [RFC4572], [RFC4145], and an SDP 'fingerprint' attribute according to the
in the answer. procedures in [RFC4572], in the answer.
If the answerer does not accept the establishment of the DTLS If the answerer does not accept the establishment of the DTLS
association, it MUST reject the "m=" lines associated with the association, it MUST reject the "m=" lines associated with the
suggested DTLS association [RFC3264]. suggested DTLS association [RFC3264].
If an answerer receives an offer that contains a 'connection' If an answerer receives an offer that contains a 'dtls-connection'
attribute with an 'existing' value, and if the answerer determines attribute with an 'existing' value, and if the answerer determines
that a new DTLS association does not need to be established, it MUST that a new DTLS association does not need to be established, it MUST
insert a connection attribute with an 'existing' value in the insert a connection attribute with an 'existing' value in the
associated answer. In addition, the answerer MUST insert an SDP associated answer. In addition, the answerer MUST insert an SDP
'setup' attribute with a value that does not change the previously 'setup' attribute with a value that does not change the previously
negotiated DTLS roles, and an SDP 'fingerprint' attribute with a negotiated DTLS roles, and an SDP 'fingerprint' attribute with a
value that does not change the fingerprint, in the answer. value that does not change the fingerprint, in the answer.
If the answerer receives an offer that does not contain an SDP If the answerer receives an offer that does not contain an SDP 'dtls-
'connection' attribute, the answerer MUST NOT insert a 'connection' connection' attribute, the answerer MUST NOT insert a 'dtls-
attribute in the answer. connection' attribute in the answer.
If ICE is used, the answerer MUST insert the SDP 'ice-ufrag' and
'ice-pwd' attributes according to the procedures in [RFC5245] in the
answer.
If a new DTLS association is to be established, and if the answerer If a new DTLS association is to be established, and if the answerer
becomes DTLS client, the answerer MUST initiate the procedures for becomes DTLS client, the answerer MUST initiate the procedures for
establishing the DTLS association. If the answerer becomes DTLS establishing the DTLS association. If the answerer becomes DTLS
server, it MUST wait for the offerer to establish the DTLS server, it MUST wait for the offerer to establish the DTLS
association. association.
6.4. Offerer Processing of the SDP Answer 6.4. Offerer Processing of the SDP Answer
When an offerer receives an answer that contains an SDP 'connection' When an offerer receives an answer that contains an SDP 'dtls-
attribute with a 'new' value, and if the offerer becomes DTLS client, connection' attribute with a 'new' value, and if the offerer becomes
the offerer MUST establish a DTLS association. If the offerer DTLS client, the offerer MUST establish a DTLS association. If the
becomes DTLS server, it MUST wait for the answerer to establish the offerer becomes DTLS server, it MUST wait for the answerer to
DTLS association. establish the DTLS association.
If the answer contains an SDP 'connection' attribute with an If the answer contains an SDP 'dtls-connection' attribute with an
'existing' value, the offerer will continue using the previously 'existing' value, the offerer will continue using the previously
established DTLS association. It is considered an error case if the established DTLS association. It is considered an error case if the
answer contains a 'connection' attribute with an 'existing' value, answer contains a 'dtls-connection' attribute with an 'existing'
and a DTLS association does not exist. value, and a DTLS association does not exist.
6.5. Modifying the Session 6.5. Modifying the Session
When the offerer sends a subsequent offer, and the offerer wants to When the offerer sends a subsequent offer, and the offerer wants to
establish a new DTLS association, the offerer MUST insert an SDP establish a new DTLS association, the offerer MUST insert an SDP
'connection' attribute with a 'new' value in the offer. In addition, 'dtls-connection' attribute with a 'new' value in the offer. In
the offerer MUST insert an SDP 'setup' attribute according to the addition, the offerer MUST insert an SDP 'setup' attribute according
procedures in [RFC4572], and an SDP 'fingerprint' attribute according to the procedures in [RFC4145], and an SDP 'fingerprint' attribute
to the procedures in [RFC4572], in the offer. according to the procedures in [RFC4572], in the offer.
when the offerer sends a subsequent offer, and the offerer does not when the offerer sends a subsequent offer, and the offerer does not
want to establish a new DTLS association, if a previously established want to establish a new DTLS association, if a previously established
DTLS association exists, the offerer MUST insert an SDP 'connection' DTLS association exists, the offerer MUST insert an SDP 'dtls-
attribute with an 'existing' value in the offer. In addition, the connection' attribute with an 'existing' value in the offer. In
offerer MUST insert an SDP 'setup' attribute with a value that does addition, the offerer MUST insert an SDP 'setup' attribute with a
not change the previously negotiated DTLS roles, and an SDP value that does not change the previously negotiated DTLS roles, and
'fingerprint' attribute with a value that does not change the an SDP 'fingerprint' attribute with a value that does not change the
fingerprint, in the offer. fingerprint, in the offer.
If ICE is used, the offerer MUST insert the SDP 'ice-ufrag' and 'ice- 7. ICE Considerations
pwd' attributes according to the procedures in [RFC5245] in the
subsequent offer.
7. RFC Updates 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. Here we will add the RFC updates that are needed.
8. Security Considerations 10. Security Considerations
This draft does not modify the security considerations associated This draft does not modify the security considerations associated
with DTLS, or the SDP offer/answer mechanism. The draft simply with DTLS, or the SDP offer/answer mechanism. The draft simply
clarifies the procedures for negotiating and establishing a DTLS clarifies the procedures for negotiating and establishing a DTLS
association. association.
9. IANA Considerations 11. IANA Considerations
TBD 11.1. Registration of New SDP Attribute
10. Acknowledgements This document updates the "Session Description Protocol Parameters"
registry as specified in Section 8.2.2 of [RFC4566]. Specifically,
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 Thanks to Justin Uberti, Martin Thomson, Paul Kyzivat and Jens
Guballa for providing comments and suggestions on the draft. Guballa for providing comments and suggestions on the draft.
11. Change Log 13. Change Log
[RFC EDITOR NOTE: Please remove this section when publishing] [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 Changes from draft-holmberg-mmusic-sdp-dtls-01
o - draft-ietf-mmusic version of draft submitted. o - draft-ietf-mmusic version of draft submitted.
o - Draft file name change (sdp-dtls -> dtls-sdp) due to collision o - Draft file name change (sdp-dtls -> dtls-sdp) due to collision
with another expired draft. 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 Changes from draft-holmberg-mmusic-sdp-dtls-00
o - Editorial changes and clarifications. o - Editorial changes and clarifications.
12. Normative References 14. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E. A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261, Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002, DOI 10.17487/RFC3261, June 2002,
skipping to change at page 8, line 10 skipping to change at page 9, line 28
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264, with Session Description Protocol (SDP)", RFC 3264,
DOI 10.17487/RFC3264, June 2002, DOI 10.17487/RFC3264, June 2002,
<http://www.rfc-editor.org/info/rfc3264>. <http://www.rfc-editor.org/info/rfc3264>.
[RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in [RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in
the Session Description Protocol (SDP)", RFC 4145, the Session Description Protocol (SDP)", RFC 4145,
DOI 10.17487/RFC4145, September 2005, DOI 10.17487/RFC4145, September 2005,
<http://www.rfc-editor.org/info/rfc4145>. <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 [RFC4572] Lennox, J., "Connection-Oriented Media Transport over the
Transport Layer Security (TLS) Protocol in the Session Transport Layer Security (TLS) Protocol in the Session
Description Protocol (SDP)", RFC 4572, Description Protocol (SDP)", RFC 4572,
DOI 10.17487/RFC4572, July 2006, DOI 10.17487/RFC4572, July 2006,
<http://www.rfc-editor.org/info/rfc4572>. <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 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT) (ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245, Traversal for Offer/Answer Protocols", RFC 5245,
DOI 10.17487/RFC5245, April 2010, DOI 10.17487/RFC5245, April 2010,
<http://www.rfc-editor.org/info/rfc5245>. <http://www.rfc-editor.org/info/rfc5245>.
[RFC5763] Fischl, J., Tschofenig, H., and E. Rescorla, "Framework [RFC5763] Fischl, J., Tschofenig, H., and E. Rescorla, "Framework
for Establishing a Secure Real-time Transport Protocol for Establishing a Secure Real-time Transport Protocol
(SRTP) Security Context Using Datagram Transport Layer (SRTP) Security Context Using Datagram Transport Layer
Security (DTLS)", RFC 5763, DOI 10.17487/RFC5763, May Security (DTLS)", RFC 5763, DOI 10.17487/RFC5763, May
2010, <http://www.rfc-editor.org/info/rfc5763>. 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
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
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 Authors' Addresses
Christer Holmberg Christer Holmberg
Ericsson Ericsson
Hirsalantie 11 Hirsalantie 11
Jorvas 02420 Jorvas 02420
Finland Finland
Email: christer.holmberg@ericsson.com Email: christer.holmberg@ericsson.com
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