draft-ietf-mmusic-dtls-sdp-18.txt   draft-ietf-mmusic-dtls-sdp-19.txt 
Network Working Group C. Holmberg Network Working Group C. Holmberg
Internet-Draft Ericsson Internet-Draft Ericsson
Updates: 5763,7345 (if approved) R. Shpount Updates: 5763,7345 (if approved) R. Shpount
Intended status: Standards Track TurboBridge Intended status: Standards Track TurboBridge
Expires: August 1, 2017 January 28, 2017 Expires: August 17, 2017 February 13, 2017
Using the SDP Offer/Answer Mechanism for DTLS Using the SDP Offer/Answer Mechanism for DTLS
draft-ietf-mmusic-dtls-sdp-18.txt draft-ietf-mmusic-dtls-sdp-19.txt
Abstract Abstract
This document defines the SDP offer/answer procedures for negotiating This document defines the SDP offer/answer procedures for negotiating
and establishing a DTLS association. The document also defines the and establishing a DTLS association. The document also defines the
criteria for when a new DTLS association must be established. The criteria for when a new DTLS association must be established. The
document updates RFC 5763 and RFC 7345, by replacing common SDP document updates RFC 5763 and RFC 7345, by replacing common SDP
offer/answer procedures with a reference to this specification. offer/answer procedures with a reference to this specification.
This document defines a new SDP media-level attribute, 'dtls-id'. This document defines a new SDP media-level attribute, 'dtls-id'.
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This Internet-Draft will expire on August 1, 2017. This Internet-Draft will expire on August 17, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Establishing a new DTLS Association . . . . . . . . . . . . . 3 3. Establishing a new DTLS Association . . . . . . . . . . . . . 3
3.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.2. Change of Local Transport Parameters . . . . . . . . . . 4 3.2. Change of Local Transport Parameters . . . . . . . . . . 4
3.3. Change of ICE ufrag value . . . . . . . . . . . . . . . . 4 3.3. Change of ICE ufrag value . . . . . . . . . . . . . . . . 4
4. SDP dtls-id Attribute . . . . . . . . . . . . . . . . . . . . 4 4. SDP dtls-id Attribute . . . . . . . . . . . . . . . . . . . . 4
5. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 5 5. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 6
5.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. Generating the Initial SDP Offer . . . . . . . . . . . . 7 5.2. Generating the Initial SDP Offer . . . . . . . . . . . . 8
5.3. Generating the Answer . . . . . . . . . . . . . . . . . . 8 5.3. Generating the Answer . . . . . . . . . . . . . . . . . . 8
5.4. Offerer Processing of the SDP Answer . . . . . . . . . . 8 5.4. Offerer Processing of the SDP Answer . . . . . . . . . . 9
5.5. Modifying the Session . . . . . . . . . . . . . . . . . . 9 5.5. Modifying the Session . . . . . . . . . . . . . . . . . . 9
6. ICE Considerations . . . . . . . . . . . . . . . . . . . . . 9 6. ICE Considerations . . . . . . . . . . . . . . . . . . . . . 10
7. Transport Protocol Considerations . . . . . . . . . . . . . . 10 7. Transport Protocol Considerations . . . . . . . . . . . . . . 11
7.1. Transport Re-Usage . . . . . . . . . . . . . . . . . . . 10 7.1. Transport Re-Usage . . . . . . . . . . . . . . . . . . . 11
8. SIP Considerations . . . . . . . . . . . . . . . . . . . . . 10 8. SIP Considerations . . . . . . . . . . . . . . . . . . . . . 11
9. RFC Updates . . . . . . . . . . . . . . . . . . . . . . . . . 11 9. RFC Updates . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 11 9.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.2. Update to RFC 5763 . . . . . . . . . . . . . . . . . . . 11 9.2. Update to RFC 5763 . . . . . . . . . . . . . . . . . . . 11
9.3. Update to RFC 7345 . . . . . . . . . . . . . . . . . . . 16 9.3. Update to RFC 7345 . . . . . . . . . . . . . . . . . . . 16
10. Security Considerations . . . . . . . . . . . . . . . . . . . 19 10. Security Considerations . . . . . . . . . . . . . . . . . . . 20
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20
13. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 20 13. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 20
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 23 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
14.1. Normative References . . . . . . . . . . . . . . . . . . 23 14.1. Normative References . . . . . . . . . . . . . . . . . . 24
14.2. Informative References . . . . . . . . . . . . . . . . . 24 14.2. Informative References . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26
1. Introduction 1. Introduction
[RFC5763] defines SDP Offer/Answer procedures for SRTP-DTLS. [RFC5763] defines SDP offer/answer procedures for SRTP-DTLS.
[RFC7345] defines SDP offer/answer procedures for UDPTL-DTLS. This [RFC7345] defines SDP offer/answer procedures for UDPTL-DTLS. This
specification defines general offer/answer procedures for DTLS, based specification defines general offer/answer procedures for DTLS, based
on the procedures in [RFC5763]. Other specifications, defining on the procedures in [RFC5763]. Other specifications, defining
specific DTLS usages, can then reference this specification, in order specific DTLS usages, can then reference this specification, in order
to ensure that the DTLS aspects are common among all usages. Having to ensure that the DTLS aspects are common among all usages. Having
common procedures is essential when multiple usages share the same common procedures is essential when multiple usages share the same
DTLS association [I-D.ietf-mmusic-sdp-bundle-negotiation]. The DTLS association [I-D.ietf-mmusic-sdp-bundle-negotiation]. The
document updates [RFC5763] and [RFC7345], by replacing common SDP document updates [RFC5763] and [RFC7345], by replacing common SDP
offer/answer procedures with a reference to this specification. offer/answer procedures with a reference to this specification.
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[I-D.ietf-ice-rfc5245bis] is used. One possible way to determine a [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 transport change is based on ufrag change, but the ufrag value is
changed both when ICE is negotiated and when ICE restart changed both when ICE is negotiated and when ICE restart
[I-D.ietf-ice-rfc5245bis] occurs. These events do not always require [I-D.ietf-ice-rfc5245bis] occurs. These events do not always require
a new DTLS association to be established, but currently there is no 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 way to explicitly indicate in an SDP offer or answer whether a new
DTLS association is required. To solve that problem, this document DTLS association is required. To solve that problem, this document
defines a new SDP attribute, 'dtls-id'. The pair of SDP 'dtls-id' defines a new SDP attribute, 'dtls-id'. The pair of SDP 'dtls-id'
attribute values (the attribute values of the offerer and the attribute values (the attribute values of the offerer and the
answerer) uniquely identifies the DTLS association. Providing a new answerer) uniquely identifies the DTLS association. Providing a new
value of 'dtls-id' attribute in an SDP offer or answers can be used value of the 'dtls-id' attribute in an SDP offer or answers can be
to indicate whether a new DTLS association is to be established. used to indicate whether a new DTLS association is to be established.
2. Conventions 2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Establishing a new DTLS Association 3. Establishing a new DTLS Association
3.1. General 3.1. General
A new DTLS association MUST be established after a successful SDP A new DTLS association MUST be established after a successful SDP
offer/answer transaction in the following cases: offer/answer exchange in the following cases:
o The negotiated DTLS setup roles change; or o The negotiated DTLS setup roles change; or
o One or more fingerprint values are modified, added or removed in o One or more fingerprint values are modified, added or removed in
either an SDP offer or answer; or either an SDP offer or answer; or
o The intent to establish a new DTLS association is explicitly o The intent to establish a new DTLS association is explicitly
signaled by changing the value of the SDP 'dtls-id' attribute signaled by changing the value of the SDP 'dtls-id' attribute
defined in this document; defined in this document;
NOTE: The first two items list above are based on the procedures in NOTE: The first two items above are based on the procedures in
[RFC5763]. This specification adds the support for explicit [RFC5763]. This specification adds the support for explicit
signaling using the SDP 'dtls-id' attribute. signaling using the SDP 'dtls-id' attribute.
A new DTLS association can only established as a result of the A new DTLS association can only be established as a result of the
successful SDP offer/answer transaction. Whenever an entity successful SDP offer/answer exchange. Whenever an entity determines
determines that a new DTLS association is required, the entity MUST that a new DTLS association is required, the entity MUST initiate an
initiate an SDP offer/answer transaction, following the procedures in SDP offer/answer exchange, following the procedures in Section 5.
Section 5.
The sections below describe typical cases where a new DTLS The sections below describe typical cases where a new DTLS
association needs to be established. association needs to be established.
3.2. Change of Local Transport Parameters 3.2. Change of Local Transport Parameters
If an endpoint modifies its local transport parameters (address and/ If an endpoint modifies its local transport parameters (address and/
or port), and if the modification requires a new DTLS association, or port), and if the modification requires a new DTLS association,
the endpoint MUST change its local SDP 'dtls-id' attribute value the endpoint MUST change its local SDP 'dtls-id' attribute value (see
Section 4. Section 4).
If the underlying transport explicitly prohibits a DTLS association If the underlying transport explicitly prohibits a DTLS association
to span multiple transports, and if the transport is changed, the to span multiple transports, and if the transport is changed, the
endpoint MUST change its local SDP 'dtls-id' attribute value endpoint MUST change its local SDP 'dtls-id' attribute value (see
Section 4. An example of such case is when DTLS is carried over Section 4). An example of such a case is when DTLS is carried over
SCTP, as described in [RFC6083]. SCTP, as described in [RFC6083].
3.3. Change of ICE ufrag value 3.3. Change of ICE ufrag value
If an endpoint uses ICE, and modifies a local ufrag value, and if the If an endpoint uses ICE, and modifies a local ufrag value, and if the
modification requires a new DTLS association, the endpoint MUST modification requires a new DTLS association, the endpoint MUST
change its local SDP 'dtls-id' attribute value Section 4. change its local SDP 'dtls-id' attribute value (see Section 4).
4. SDP dtls-id Attribute 4. SDP dtls-id Attribute
The pair of SDP 'dtls-id' attribute values (the attribute values of The pair of SDP 'dtls-id' attribute values (the attribute values of
the offerer and the answerer) uniquely identifies the DTLS the offerer and the answerer) uniquely identifies the DTLS
association. association.
Name: dtls-id Name: dtls-id
Value: dtls-id-value Value: dtls-id-value
Usage Level: media Usage Level: media
Charset Dependent: no Charset Dependent: no
Default Value: N/A Default Value: N/A
Syntax: Syntax:
dtls-id-value = 0*256 <alpha-numeric defined in [RFC4566]> dtls-id-value = 6*256(dtls-id-char)
dtls-id-char = ALPHA / DIGIT / "+" / "/" / "-" / "_"
<ALPHA and DIGIT defined in [RFC4566]>
Example: Example:
a=dtls-id:abc3dl a=dtls-id:abc3de65cddef001
Every time an endpoint requests to establish a new DTLS association, Every time an endpoint requests to establish a new DTLS association,
the endpoint MUST generate a new unique local 'dtls-id' attribute the endpoint MUST generate a new local 'dtls-id' attribute value. A
value. A non-changed local 'dtls-id' attribute value, in combination non-changed local 'dtls-id' attribute value, in combination with non-
with non-changed fingerprints, indicates that the endpoint intends to changed fingerprints, indicates that the endpoint intends to reuse
reuse the existing DTLS association. the existing DTLS association.
The mechanism to generate the unique local 'dtls-id' attribute value The 'dtls-id' attribute value MUST contain at least 32 bits of
MUST guarantee global uniqueness of the value for the lifetime of the randomness.
DTLS association associated with the attribute value.
No default value is defined for the SDP 'dtls-id' attribute. No default value is defined for the SDP 'dtls-id' attribute.
Implementations that wish to use the attribute MUST explicitly Implementations that wish to use the attribute MUST explicitly
include it in SDP offers and answers. If an offer or answer does not include it in SDP offers and answers. If an offer or answer does not
contain an attribute (this could happen if the offerer or answerer contain a 'dtls-id' attribute (this could happen if the offerer or
represents an existing implementation that has not been updated to answerer represents an existing implementation that has not been
support the 'dtls-id' attribute), the offer or answer MUST be treated updated to support the 'dtls-id' attribute), the offer or answer MUST
as if no 'dtls-id' attribute is included. Unless there is another be treated as if no 'dtls-id' attribute is included. Unless there is
mechanism to explicitly indicate that a new DTLS association is to be another mechanism to explicitly indicate that a new DTLS association
established, a modification of one or more of the following is to be established, a modification of one or more of the following
characteristics MUST be treated as an indication that an endpoint characteristics MUST be treated as an indication that an endpoint
wants to establish a new DTLS association: wants to establish a new DTLS association:
o DTLS setup role; or o DTLS setup role; or
o fingerprint set; or o fingerprint set; or
o local transport parameters; or o local transport parameters; or
o ICE ufrag value o ICE ufrag value
The mux category [I-D.ietf-mmusic-sdp-mux-attributes] for the 'dtls- The mux category [I-D.ietf-mmusic-sdp-mux-attributes] for the 'dtls-
id' attribute is 'IDENTICAL', which means that the attribute value id' attribute is 'IDENTICAL', which means that the attribute value
must be identical across all media descriptions being multiplexed must be identical across all media descriptions being multiplexed
[I-D.ietf-mmusic-sdp-bundle-negotiation]. [I-D.ietf-mmusic-sdp-bundle-negotiation].
For RTP-based media, the 'dtls-id' attribute apply to whole For RTP-based media, the 'dtls-id' attribute applies to the whole
associated media description. The attribute MUST NOT be defined per associated media description. The attribute MUST NOT be defined per
source (using the SDP 'ssrc' attribute [RFC5576]). source (using the SDP 'ssrc' attribute [RFC5576]).
The SDP offer/answer [RFC3264] procedures associated with the The SDP offer/answer [RFC3264] procedures associated with the
attribute are defined in Section 5 attribute are defined in Section 5.
5. SDP Offer/Answer Procedures 5. SDP Offer/Answer Procedures
5.1. General 5.1. General
This section defines the generic SDP offer/answer procedures for This section defines the generic SDP offer/answer procedures for
negotiating a DTLS association. Additional procedures (e.g., negotiating a DTLS association. Additional procedures (e.g.,
regarding usage of specific SDP attributes etc.) for individual DTLS regarding usage of specific SDP attributes etc.) for individual DTLS
usages (e.g., SRTP-DTLS) are outside the scope of this specification, usages (e.g., SRTP-DTLS) are outside the scope of this specification,
and need to be specified in a usage specific specification. and need to be specified in a usage specific specification.
NOTE: The procedures in this section are generalizations of NOTE: The procedures in this section are generalizations of
procedures first specified in SRTP-DTLS [RFC5763], with the addition procedures first specified in SRTP-DTLS [RFC5763], with the addition
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procedures first specified in SRTP-DTLS [RFC5763], with the addition procedures first specified in SRTP-DTLS [RFC5763], with the addition
of usage of the SDP 'dtls-id' attribute. That document is herein of usage of the SDP 'dtls-id' attribute. That document is herein
updated to make use of these new procedures. updated to make use of these new procedures.
The procedures in this section apply to an SDP media description The procedures in this section apply to an SDP media description
("m=" line) associated with DTLS-protected media/data. ("m=" line) associated with DTLS-protected media/data.
When an offerer or answerer indicates that it wants to establish a 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 new DTLS association, it needs to make sure that media packets in the
existing DTLS association and new DTLS association can be de- existing DTLS association and new DTLS association can be de-
multiplexed. In case of ordered transport (e.g., SCTP) this can be multiplexed. In case of an ordered transport (e.g., SCTP) this can
done simply by sending packets for new DTLS association after all be done simply by sending packets for the new DTLS association after
packets for existing DTLS association have been sent. In case of all packets for the existing DTLS association have been sent. In
unordered transport, such as UDP, packets for the old DTLS case of an unordered transport, such as UDP, packets for the old DTLS
association can arrive after the answer SDP was received and after association can arrive after the answer SDP was received and after
first packets for the new DTLS association were received. The only the first packets for the new DTLS association were received. The
way to de-multiplex packets belonging to old and new DTLS association only way to de-multiplex packets belonging to the old and new DTLS
is on the basis of transport 5-tuple. Because of this, if unordered association is on the basis of transport 5-tuple. Because of this,
transport is used for DTLS association, new transport (3-tuple) MUST if an unordered transport is used for the DTLS association, a new
be allocated by at least one of the end points so that DTLS packets transport (3-tuple) MUST be allocated by at least one of the end
can be de-multiplexed. points so that DTLS packets can be de-multiplexed.
When an offerer needs to establish a new DTLS association, and if an 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 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 new transport (3-tuple) for the offer in such a way that the offerer
can disambiguate any packets associated with the new DTLS association can disambiguate any packets associated with the new DTLS association
from any packets associated with any other DTLS association. This from any packets associated with any other DTLS association. This
typically means using a local address and/or port, or a set of ICE 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 candidates (see Section 6), which were not recently used for any
other DTLS association. other DTLS association.
When an answerer needs to establish a new DTLS association, if an When an answerer needs to establish a new DTLS association, if an
unordered transport is used, and if the offerer did not allocate a unordered transport is used, and if the offerer did not allocate a
new transport, the answerer MUST allocate a new transport for the new transport, the answerer MUST allocate a new transport for the
answer in such a way that it can disambiguate any packets associated answer in such a way that it can disambiguate any packets associated
with new DTLS association from any packets associated with any other with the new DTLS association from any packets associated with any
DTLS association. This typically means using a local address and/or other DTLS association. This typically means using a local address
port, or a set of ICE candidates (see Section 6), which were not and/or port, or a set of ICE candidates (see Section 6), which were
recently used for any other DTLS association. not recently used for any other DTLS association.
In order to negotiate a DTLS association, the following SDP In order to negotiate a DTLS association, the following SDP
attributes are used: attributes are used:
o The SDP 'setup' attribute, defined in [RFC4145], is used to o The SDP 'setup' attribute, defined in [RFC4145], is used to
negotiate the DTLS roles; negotiate the DTLS roles;
o The SDP 'fingerprint' attribute, defined in o The SDP 'fingerprint' attribute, defined in
[I-D.ietf-mmusic-4572-update], is used to provide one or more [I-D.ietf-mmusic-4572-update], is used to provide one or more
fingerprint values; and fingerprint values; and
o The SDP 'dtls-id' attribute, defined in this specification. 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' This specification does not define the usage of the SDP 'connection'
attribute [RFC4145] for negotiating a DTLS connection. However, the attribute [RFC4145] for negotiating a DTLS association. However, the
attribute MAY be used if the DTLS association is used together with 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 another protocol (e.g., SCTP or TCP) for which the usage of the
attribute has been defined. attribute has been defined.
Unlike for TCP and TLS connections, endpoints MUST NOT use the SDP Unlike for TCP and TLS connections, endpoints MUST NOT use the SDP
'setup' attribute 'holdconn' value when negotiating a DTLS 'setup' attribute 'holdconn' value when negotiating a DTLS
association. association.
Endpoints MUST support the cipher suites as defined in Endpoints MUST support the cipher suites as defined in
[I-D.ietf-mmusic-4572-update]. [I-D.ietf-mmusic-4572-update].
The certificate received during the DTLS handshake MUST match the The certificate received during the DTLS handshake MUST match a
certificate fingerprints received in SDP 'fingerprint' attributes certificate fingerprints received in SDP 'fingerprint' attributes
according to procedures defined in [I-D.ietf-mmusic-4572-update]. If according to the procedures defined in [I-D.ietf-mmusic-4572-update].
fingerprints do not match the hashed certificate, then an endpoint If fingerprints do not match the hashed certificate, then an endpoint
MUST tear down the media session immediately. Note that it is MUST tear down the media session immediately (see
permissible to wait until the other side's fingerprint has been [I-D.ietf-mmusic-4572-update]). Note that it is permissible to wait
received before establishing the connection; however, this may have until the other side's fingerprint(s) has been received before
undesirable latency effects. establishing the connection; however, this may have undesirable
latency effects.
SDP offerers and answerers might reuse certificates across multiple SDP offerers and answerers might reuse certificates across multiple
DTLS associations, and provide identical fingerprint values for each DTLS associations, and provide identical fingerprint values for each
DTLS association. It MUST be ensured that the combination of SDP the DTLS association. The combination of the SDP 'dtls-id' attribute
'dtls-id' attribute values of the SDP offerer and answerer is unique values of the SDP offerer and answerer identifies each individual
across all DTLS associations that might be handled by the SDP offerer DTLS association.
and answerer.
5.2. Generating the Initial SDP Offer 5.2. Generating the Initial SDP Offer
When an offerer sends the initial offer, the offerer MUST insert an When an offerer sends the initial offer, the offerer MUST insert an
SDP 'setup' attribute according to the procedures in [RFC4145], and SDP 'setup' attribute according to the procedures in [RFC4145], and
one or more SDP 'fingerprint' attributes according to the procedures one or more SDP 'fingerprint' attributes according to the procedures
in [I-D.ietf-mmusic-4572-update]. In addition, the offerer MUST 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. 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 If the offerer inserts the SDP 'setup' attribute with an 'actpass' or
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When the Interactive Connectivity Establishment (ICE) mechanism When the Interactive Connectivity Establishment (ICE) mechanism
[I-D.ietf-ice-rfc5245bis] is used, the ICE connectivity checks are [I-D.ietf-ice-rfc5245bis] is used, the ICE connectivity checks are
performed before the DTLS handshake begins. Note that if aggressive performed before the DTLS handshake begins. Note that if aggressive
nomination mode is used, multiple candidate pairs may be marked valid nomination mode is used, multiple candidate pairs may be marked valid
before ICE finally converges on a single candidate pair. before ICE finally converges on a single candidate pair.
NOTE: Aggressive nomination has been deprecated from ICE, but must NOTE: Aggressive nomination has been deprecated from ICE, but must
still be supported for backwards compatibility reasons. still be supported for backwards compatibility reasons.
When new DTLS association is established over an unordered transport, When a new DTLS association is established over an unordered
in order to disambiguate any packets associated with the newly transport, in order to disambiguate any packets associated with the
established DTLS association, at least one of the endpoints MUST newly established DTLS association, at least one of the endpoints
allocate a completely new set of ICE candidates which were not MUST allocate a completely new set of ICE candidates which were not
recently used for any other DTLS association. This means the recently used for any other DTLS association. This means the
answerer cannot initiate a new DTLS association unless the offerer answerer cannot initiate a new DTLS association unless the offerer
initiated ICE restart [I-D.ietf-ice-rfc5245bis]. If the answerer initiated ICE restart [I-D.ietf-ice-rfc5245bis]. If the answerer
wants to initiate a new DTLS association, it needs to initiate an ICE 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 and a new offer/answer exchange on its own. However, an ICE
restart does not by default require a new DTLS association to be restart does not by default require a new DTLS association to be
established. established.
NOTE: Simple Traversal of the UDP Protocol through NAT (STUN) packets NOTE: Simple Traversal of the UDP Protocol through NAT (STUN) packets
are sent directly over UDP, not over DTLS. [RFC5764] describes how are sent directly over UDP, not over DTLS. [RFC5764] describes how
skipping to change at page 10, line 37 skipping to change at page 11, line 13
parameters when an endpoint switches between those ICE candidates. parameters when an endpoint switches between those ICE candidates.
7. Transport Protocol Considerations 7. Transport Protocol Considerations
7.1. Transport Re-Usage 7.1. Transport Re-Usage
If DTLS is transported on top of a connection-oriented transport If DTLS is transported on top of a connection-oriented transport
protocol (e.g., TCP or SCTP), where all IP packets are acknowledged, protocol (e.g., TCP or SCTP), where all IP packets are acknowledged,
all DTLS packets associated with a previous DTLS association MUST be all DTLS packets associated with a previous DTLS association MUST be
acknowledged (or timed out) before a new DTLS association can be acknowledged (or timed out) before a new DTLS association can be
established on the same transport. established on the same instance of that transport (5-tuple).
8. SIP Considerations 8. SIP Considerations
When the Session Initiation Protocol (SIP) [RFC3261] is used as the When the Session Initiation Protocol (SIP) [RFC3261] is used as the
signal protocol for establishing a multimedia session, dialogs signal protocol for establishing a multimedia session, dialogs
[RFC3261] might be established between the caller and multiple [RFC3261] might be established between the caller and multiple
callees. This is referred to as forking. If forking occurs, callees. This is referred to as forking. If forking occurs,
separate DTLS associations MUST be established between the caller and separate DTLS associations MUST be established between the caller and
each callee. each callee.
It is possible to send an INVITE request which does not contain an 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 SDP offer. Such an INVITE request is often referred to as an 'empty
INVITE', or an 'offer-less INVITE'. The receiving endpoint will INVITE', or an 'offer-less INVITE'. The receiving endpoint will
include the SDP offer in a response to the request. When the include the SDP offer in a response to the request. When the
endpoint generates such SDP offer, if a previously established DTLS endpoint generates such SDP offer, if a previously established DTLS
association exists, the offerer SHOULD insert an SDP 'dtls-id' association exists, the offerer SHOULD insert an SDP 'dtls-id'
attribute, and one or more SDP 'fingerprint' attributes, with attribute, and one or more SDP 'fingerprint' attributes, with
previously assigned attribute values. If a previously established previously assigned attribute values. If a previously established
DTLS association did not exists, the offer SHOULD be generated based DTLS association did not exist, the offer SHOULD be generated based
on the same rules as a new offer Section 5.2. Regardless of the on the same rules as a new offer (see Section 5.2). Regardless of
previous existence of a DTLS association, the SDP 'setup' attribute the previous existence of a DTLS association, the SDP 'setup'
MUST be included according to the rules defined in [RFC4145] and if attribute MUST be included according to the rules defined in
ICE is used, ICE restart MUST be initiated. [RFC4145] and if ICE is used, ICE restart MUST be initiated.
9. RFC Updates 9. RFC Updates
9.1. General 9.1. General
This section updates specifications that use DTLS-protected media, in This section updates specifications that use DTLS-protected media, in
order to reflect the procedures defined in this specification. order to reflect the procedures defined in this specification.
9.2. Update to RFC 5763 9.2. Update to RFC 5763
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12. Acknowledgements 12. Acknowledgements
Thanks to Justin Uberti, Martin Thomson, Paul Kyzivat, Jens Guballa, Thanks to Justin Uberti, Martin Thomson, Paul Kyzivat, Jens Guballa,
Charles Eckel and Gonzalo Salgueiro for providing comments and Charles Eckel and Gonzalo Salgueiro for providing comments and
suggestions on the document. suggestions on the document.
13. 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-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 Changes from draft-ietf-mmusic-sdp-dtls-17
o Reference fix. o Reference fix.
Changes from draft-ietf-mmusic-sdp-dtls-16 Changes from draft-ietf-mmusic-sdp-dtls-16
o Editorial changes based on 2nd WGLC comments from Christian Groves o Editorial changes based on 2nd WGLC comments from Christian Groves
and Nevenka Biondic. and Nevenka Biondic.
Changes from draft-ietf-mmusic-sdp-dtls-15 Changes from draft-ietf-mmusic-sdp-dtls-15
 End of changes. 38 change blocks. 
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