Internet DRAFT - draft-ietf-mmusic-sctp-sdp
draft-ietf-mmusic-sctp-sdp
MMUSIC C. Holmberg
Internet-Draft Ericsson
Intended status: Standards Track R. Shpount
Expires: October 22, 2017 TurboBridge
S. Loreto
G. Camarillo
Ericsson
April 20, 2017
Session Description Protocol (SDP) Offer/Answer Procedures For Stream
Control Transmission Protocol (SCTP) over Datagram Transport Layer
Security (DTLS) Transport.
draft-ietf-mmusic-sctp-sdp-26
Abstract
The Stream Control Transmission Protocol (SCTP) is a transport
protocol used to establish associations between two endpoints.
draft-ietf-tsvwg-sctp-dtls-encaps-09 specifies how SCTP can be used
on top of the Datagram Transport Layer Security (DTLS) protocol,
referred to as SCTP-over-DTLS.
This specification defines the following new Session Description
Protocol (SDP) protocol identifiers (proto values):'UDP/DTLS/SCTP'
and 'TCP/DTLS/SCTP'. This specification also specifies how to use
the new proto values with the SDP Offer/Answer mechanism for
negotiating SCTP-over-DTLS associations.
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 October 22, 2017.
Holmberg, et al. Expires October 22, 2017 [Page 1]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. SCTP Terminology . . . . . . . . . . . . . . . . . . . . . . 4
4. SDP Media Descriptions . . . . . . . . . . . . . . . . . . . 4
4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. Protocol Identifiers . . . . . . . . . . . . . . . . . . 5
4.3. Media Format Management . . . . . . . . . . . . . . . . . 5
4.4. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.4.1. General . . . . . . . . . . . . . . . . . . . . . . . 6
4.4.2. SDP Media Description values . . . . . . . . . . . . 6
4.5. Example . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. SDP 'sctp-port' Attribute . . . . . . . . . . . . . . . . . . 6
5.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.3. Mux Category . . . . . . . . . . . . . . . . . . . . . . 7
6. SDP 'max-message-size' Attribute . . . . . . . . . . . . . . 8
6.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.2. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.3. Mux Category . . . . . . . . . . . . . . . . . . . . . . 9
7. UDP/DTLS/SCTP Transport Realization . . . . . . . . . . . . . 9
8. TCP/DTLS/SCTP Transport Realization . . . . . . . . . . . . . 10
9. Association And Connection Management . . . . . . . . . . . . 10
9.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.2. SDP sendrecv/sendonly/recvonly/inactive Attribute . . . . 10
9.3. SCTP Association . . . . . . . . . . . . . . . . . . . . 10
9.4. DTLS Association (UDP/DTLS/SCTP And TCP/DTLS/SCTP) . . . 11
9.5. TCP Connection (TCP/DTLS/SCTP) . . . . . . . . . . . . . 12
10. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 12
10.1. General . . . . . . . . . . . . . . . . . . . . . . . . 12
10.2. Generating the Initial SDP Offer . . . . . . . . . . . . 13
10.3. Generating the SDP Answer . . . . . . . . . . . . . . . 13
Holmberg, et al. Expires October 22, 2017 [Page 2]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
10.4. Offerer Processing of the SDP Answer . . . . . . . . . . 14
10.5. Modifying the Session . . . . . . . . . . . . . . . . . 15
11. Multihoming Considerations . . . . . . . . . . . . . . . . . 16
12. NAT Considerations . . . . . . . . . . . . . . . . . . . . . 16
12.1. General . . . . . . . . . . . . . . . . . . . . . . . . 16
12.2. ICE Considerations . . . . . . . . . . . . . . . . . . . 16
13. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 17
13.1. Establishment of UDP/DTLS/SCTP association . . . . . . . 17
14. Security Considerations . . . . . . . . . . . . . . . . . . . 18
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
15.1. New SDP proto values . . . . . . . . . . . . . . . . . . 19
15.2. New SDP Attributes . . . . . . . . . . . . . . . . . . . 19
15.2.1. sctp-port . . . . . . . . . . . . . . . . . . . . . 19
15.2.2. max-message-size . . . . . . . . . . . . . . . . . . 19
15.3. association-usage Name Registry . . . . . . . . . . . . 19
16. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20
17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
18. References . . . . . . . . . . . . . . . . . . . . . . . . . 23
18.1. Normative References . . . . . . . . . . . . . . . . . . 23
18.2. Informative References . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
1. Introduction
SDP (Session Description Protocol) [RFC4566] provides a general-
purpose format for describing multimedia sessions in announcements or
invitations. TCP-Based Media Transport in the Session Description
Protocol (SDP) [RFC4145] specifies a general mechanism for describing
and establishing TCP [RFC0793] streams. Connection-Oriented Media
Transport over the Transport Layer Security (TLS) Protocol in SDP
[RFC8122] extends RFC4145 [RFC4145] for describing TCP-based media
streams that are protected using TLS.
The Stream Control Transmission Protocol (SCTP) [RFC4960] is a
reliable transport protocol used to transport data between two
endpoints using SCTP associations.
[I-D.ietf-tsvwg-sctp-dtls-encaps] specifies how SCTP can be used on
top of the Datagram Transport Layer Security (DTLS) protocol,
referred to as SCTP-over-DTLS.
This specification defines the following new Session Description
Protocol (SDP) [RFC4566] protocol identifiers (proto
values):'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP'. This specification also
specifies how to use the new proto values with the SDP Offer/Answer
mechanism [RFC3264] for negotiating SCTP-over-DTLS associations.
Holmberg, et al. Expires October 22, 2017 [Page 3]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
NOTE: Due to the characteristics of TCP, while multiple SCTP streams
can still be used, usage of 'TCP/DTLS/SCTP' will always force ordered
and reliable delivery of the SCTP packets, which limits the usage of
the SCTP options. Therefore, it is RECOMMENDED that TCP is only used
in situations where UDP traffic is blocked.
2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. SCTP Terminology
SCTP Association: A protocol relationship between SCTP endpoints,
composed of the two SCTP endpoints and protocol state information
including Verification Tags and the currently active set of
Transmission Sequence Numbers (TSNs), etc. An association can be
uniquely identified by the transport addresses used by the endpoints
in the association.
SCTP Stream: A unidirectional logical channel established from one to
another associated SCTP endpoint, within which all user messages are
delivered in sequence except for those submitted to the unordered
delivery service.
SCTP-over-DTLS: SCTP used on top of DTLS, as specified in
[I-D.ietf-tsvwg-sctp-dtls-encaps].
4. SDP Media Descriptions
4.1. General
This section defines the following new SDP Media Description (m-
line) protocol identifiers (proto values) for describing an SCTP
association: 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP'. The section also
describes how an m- line, associated with the proto values, is
created.
The following is the format for an m- line, as specified in RFC4566
[RFC4566]:
m=<media> <port> <proto> <fmt> ...
The 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' proto values are similar to
both the 'UDP' and 'TCP' proto values in that they only describe the
transport-layer protocol and not the upper-layer protocol.
Holmberg, et al. Expires October 22, 2017 [Page 4]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
NOTE: When the 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' proto values are
used, the underlying transport protocol is respectively UDP and TCP;
SCTP is carried on top of DTLS which is on top of those transport-
layer protocols.
4.2. Protocol Identifiers
The new proto values are defined as below:
o The 'UDP/DTLS/SCTP' proto value describes an SCTP association on
top of a DTLS association on top of UDP, as defined in Section 7.
o The 'TCP/DTLS/SCTP' proto value describes an SCTP association on
top of a DTLS association on top of TCP, as defined in Section 8.
4.3. Media Format Management
[RFC4566] defines that specifications defining new proto values must
define the rules by which their media format (fmt) namespace is
managed.
An m- line with a proto value of 'UDP/DTLS/SCTP' or 'TCP/DTLS/SCTP'
always describes a single SCTP association.
In addition, such m- line MUST further indicate the application-layer
protocol using an 'fmt' identifier. There MUST be exactly one fmt
value per m- line associated with the proto values defined in this
specification. The 'fmt' namespace associated with those proto
values describes the generic application usage of the entire SCTP
association, including the associated SCTP streams.
When the 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' proto values, the m-
line fmt value, identifying the application-layer protocol, MUST be
registered by IANA. Section 15.3 defines the IANA registry for the
media format namespace.
NOTE: A mechanism on how to describe, and manage, individual SCTP
streams within an SCTP association, is outside the scope of this
specification. [I-D.ietf-mmusic-data-channel-sdpneg] defines a
mechanism for negotiating individual SCTP streams used to realize
WebRTC data channels [I-D.ietf-rtcweb-data-channel].
4.4. Syntax
Holmberg, et al. Expires October 22, 2017 [Page 5]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
4.4.1. General
This section defines the values that can be used within an SDP media
description ("m=" line) associated with an SCTP-over-DTLS
association.
This specification creates an IANA registry for 'association-usage'
values.
4.4.2. SDP Media Description values
m= line parameter parameter value(s)
------------------------------------------------------------------
<media>: 'application'
<proto>: 'UDP/DTLS/SCTP' or 'TCP/DTLS/SCTP'
<port>: UDP port number (for 'UDP/DTLS/SCTP')
TCP port number (for 'TCP/DTLS/SCTP')
<fmt>: a string denoting the association-usage,
limited to the syntax of a 'token' as
defined in RFC4566.
4.5. Example
m=application 12345 UDP/DTLS/SCTP webrtc-datachannel
a=sctp-port:5000
a=max-message-size:100000
NOTE: 'webrtc-datachannel' indicates the WebRTC Data Channel
Establishment Protocol defined in [I-D.ietf-rtcweb-data-protocol].
5. SDP 'sctp-port' Attribute
5.1. General
This section defines a new SDP media-level attribute, 'sctp-port'.
The attribute can be associated with an SDP media description (m-
line) with a 'UDP/DTLS/SCTP' or a 'TCP/DTLS/SCTP' proto value. In
that case the m- line port value indicates the port of the underlying
transport layer protocol (UDP or TCP), and the 'sctp-port' value
indicates the SCTP port.
No default value is defined for the SDP sctp-port attribute.
Therefore, if the attribute is not present, the associated m- line
MUST be considered invalid.
Holmberg, et al. Expires October 22, 2017 [Page 6]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
NOTE: This specification only defines the usage of the SDP 'sctp-
port' attribute when associated with an m- line containing one of the
following proto values: 'UDP/DTLS/SCTP' or 'TCP/DTLS/SCTP'. Usage of
the attribute with other proto values needs to be defined in a
separate specification.
5.2. Syntax
[RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this
document.]
The definition of the SDP 'sctp-port' attribute is:
Attribute name: sctp-port
Type of attribute: media
Mux category: CAUTION
Subject to charset: No
Purpose: Indicate the SCTP port value associated with
the SDP Media Description.
Appropriate values: Integer
Contact name: Christer Holmberg
Contact e-mail: christer.holmberg@ericsson.com
Reference: RFCXXXX
Syntax:
sctp-port-value = 1*5<DIGIT defined in RFC4566>
The SCTP port range is between 0 and 65535 (both included).
Leading zeroes MUST NOT be used.
Example:
a=sctp-port:5000
5.3. Mux Category
The mux category [I-D.ietf-mmusic-sdp-mux-attributes] for the SDP
'sctp-port' attribute is CAUTION.
As the usage of multiple SCTP associations on top of a single DTLS
association is outside the scope of this specification, no mux rules
are specified for the 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' proto
values. Future extensions, that define how to negotiate multiplexing
of multiple SCTP associations of top of a single DTLS association,
need to also define the mux rules for the attribute.
Holmberg, et al. Expires October 22, 2017 [Page 7]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
6. SDP 'max-message-size' Attribute
6.1. General
This section defines a new SDP media-level attribute, 'max-message-
size'. The attribute can be associated with an m- line to indicate
the maximum SCTP user message size (indicated in bytes) that an SCTP
endpoint is willing to receive on the SCTP association associated
with the m- line. Different attribute values can be used in each
direction.
An SCTP endpoint MUST NOT send a SCTP user message with a message
size that is larger than the maximum size indicated by the peer, as
it cannot be assumed that the peer would accept such message.
If the SDP 'max-message-size' attribute contains a maximum message
size value of zero, it indicates the SCTP endpoint will handle
messages of any size, subject to memory capacity etc.
If the SDP 'max-message-size' attribute is not present, the default
value is 64K.
NOTE: This specification only defines the usage of the SDP 'max-
message-size' attribute when associated with an m- line containing
one of the following proto values: 'UDP/DTLS/SCTP' or 'TCP/DTLS/
SCTP'. Usage of the attribute with other proto values needs to be
defined in a separate specification.
6.2. Syntax
[RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this
document.]
The definition of the SDP 'max-message-size' attribute is:
Holmberg, et al. Expires October 22, 2017 [Page 8]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
Attribute name: max-message-size
Type of attribute: media
Mux category: CAUTION
Subject to charset: No
Purpose: Indicate the maximum message size
(indicated in bytes) that an SCTP
endpoint is willing to receive on the
SCTP association associated with the SDP
Media Description.
Appropriate values: Integer
Contact name: Christer Holmberg
Contact e-mail: christer.holmberg@ericsson.com
Reference: RFCXXXX
Syntax:
max-message-size-value = 1*<DIGIT defined in RFC4566>
Leading zeroes MUST NOT be used.
Example:
a=max-message-size:100000
6.3. Mux Category
The mux category for the SDP 'max-message-size' attribute is CAUTION.
As the usage of multiple SCTP associations on top of a single DTLS
association is outside the scope of this specification, no mux rules
are specified for the 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' proto
values.
7. UDP/DTLS/SCTP Transport Realization
The UDP/DTLS/SCTP transport is realized as described below:
o SCTP on top of DTLS is realized according to the procedures
defined in [I-D.ietf-tsvwg-sctp-dtls-encaps]; and
o DTLS on top of UDP is realized according to the procedures in
defined in [RFC6347].
NOTE: While [I-D.ietf-tsvwg-sctp-dtls-encaps] allows multiple SCTP
associations on top of a single DTLS association, the procedures in
this specification only support the negotiation of a single SCTP
association on top of any given DTLS association.
Holmberg, et al. Expires October 22, 2017 [Page 9]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
8. TCP/DTLS/SCTP Transport Realization
The TCP/DTLS/SCTP transport is realized as described below:
o SCTP on top of DTLS is realized according to the procedures
defined in [I-D.ietf-tsvwg-sctp-dtls-encaps]; and
o DTLS on top of TCP is realized using the framing method defined in
[RFC4571], with DTLS packets being sent and received instead of
RTP/RTCP packets using the shim defined in [RFC4571], so that
length field defined in [RFC4571] precedes each DTLS message, and
SDP signaling according to the procedures defined in this
specification.
NOTE: TLS on top of TCP, without using the framing method defined in
[RFC4571] is outside the scope of this specification. A separate
proto value would need to be registered for such transport
realization.
9. Association And Connection Management
9.1. General
This section describes how to manage an SCTP association, DTLS
association and TCP connection using SDP attributes.
The SCTP association, the DTLS association and the TCP connection are
managed independently from each other. Each can be established and
closed without impacting others.
The detailed SDP Offer/Answer [RFC3264] procedures for the SDP
attributes are described in Section 10.
9.2. SDP sendrecv/sendonly/recvonly/inactive Attribute
This specification does not define semantics for the SDP direction
attributes [RFC4566]. Unless semantics of these attributes for an
SCTP association usage have been defined, SDP direction attributes
MUST be ignored if present.
9.3. SCTP Association
When an SCTP association is established, both SCTP endpoints MUST
initiate the SCTP association (i.e. both SCTP endpoints take the
'active' role), and MUST use the same SCTP port as client port and
server port (in order to prevent two separate SCTP associations from
being established).
Holmberg, et al. Expires October 22, 2017 [Page 10]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
As both SCTP endpoints take the 'active' role, the SDP 'setup'
attribute [RFC4145] does not apply to SCTP association establishment.
However the 'setup' attribute does apply to establishment of the
underlying DTLS association and TCP connection.
NOTE: The procedure above is different from TCP, where one endpoint
takes the 'active' role, the other endpoint takes the 'passive' role,
and only the 'active' endpoint initiates the TCP connection
[RFC4145].
NOTE: When the SCTP association is established it is assumed that any
NAT traversal procedures for the underlying transport protocol (UDP
or TCP) have successfully been performed.
The SDP 'connection' attribute [RFC4145] does not apply to the SCTP
association. In order to trigger the closure of an existing SCTP
association, and establishment of a new SCTP association, the SDP
'sctp-port' attribute [Section 5] is used to indicate a new
(different than the ones currently used) SCTP port. The existing
SCTP association is closed, and the new SCTP association is
established, if one or both endpoints signal a new SCTP port. The
'connection' attribute does apply to establishment of underlying TCP
connections.
Alternatively, an SCTP association can be closed using the SDP 'sctp-
port' attribute with a zero attribute value. Later, a new SCTP
association can be established using the procedures in this section
for establishing an SCTP association.
SCTP associations might be closed without SDP signalling, e.g, in
case of a failure. The procedures in this section MUST be followed
to establish a new SCTP association. This requires a new SDP Offer/
Answer exchange. New (different than the ones currently used) SCTP
ports MUST be used by both endpoints.
NOTE: Closing and establishing a new SCTP association using the SDP
'sctp-port' attribute will not affect the state of the underlying
DTLS association.
9.4. DTLS Association (UDP/DTLS/SCTP And TCP/DTLS/SCTP)
A DTLS association is managed according to the procedures in
[I-D.ietf-mmusic-dtls-sdp]. Hence, the SDP 'setup' attribute is used
to negotiate the (D)TLS roles ('client' and 'server') [RFC8122].
NOTE: The SDP 'setup' attribute is used to negotiate both the DTLS
roles and the TCP roles (Section 9.5).
Holmberg, et al. Expires October 22, 2017 [Page 11]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
NOTE: As described in [RFC5245], if the Interactive Connectivity
Establishment (ICE) mechanism [RFC5245] is used, all ICE candidates
associated with a DTLS association are considered part of the same
DTLS association. Thus, a switch from one candidate pair to another
candidate pair will not trigger the establishment of a new DTLS
association.
9.5. TCP Connection (TCP/DTLS/SCTP)
The TCP connection is managed according to the procedures in
[RFC4145]. Hence, the SDP 'setup' attribute is used to negotiate the
TCP roles ('active' and 'passive'), and the SDP 'connection'
attribute is used to indicate whether to use an existing TCP
connection, or create a new one. The SDP 'setup' attribute
'holdconn' value MUST NOT be used.
NOTE: A change of the TCP roles will also trigger a closure of the
DTLS association, and establishment of a new DTLS association,
according to the procedures in [I-D.ietf-mmusic-dtls-sdp].
NOTE: As specified in [I-D.ietf-mmusic-dtls-sdp], usage of the SDP
'setup' attribute 'holdconn' value is not allowed. Therefore this
specification also forbids usage of the attribute value for TCP, as
DTLS is transported on top of TCP.
10. SDP Offer/Answer Procedures
10.1. General
This section defines the SDP Offer/Answer [RFC3264] procedures for
negotiating and establishing an SCTP-over-DTLS association. Unless
explicitly stated, the procedures apply to both the 'UDP/DTLS/SCTP'
and 'TCP/DTLS/SCTP' m- line proto values.
Each endpoint MUST associate one or more certificate fingerprints,
using the SDP 'fingerprint' attribute with the m- line, following the
procedures in [RFC8122].
The authentication certificates are interpreted and validated as
defined in [RFC8122]. Self-signed certificates can be used securely,
provided that the integrity of the SDP description is assured as
defined in [RFC8122].
Each endpoint MUST associate an SDP 'tls-id' attribute with the m-
line, following the procedures in [I-D.ietf-mmusic-dtls-sdp].
Holmberg, et al. Expires October 22, 2017 [Page 12]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
10.2. Generating the Initial SDP Offer
When the offerer creates an initial offer, the offerer:
o MUST associate an SDP setup attribute with the m- line;
o MUST associate an SDP 'sctp-port' attribute with the m- line;
o MUST, in the case of TCP/DTLS/SCTP, associate an SDP 'connection'
attribute, with a 'new' attribute value, with the m- line; and
o MAY associate an SDP 'max-message-size' attribute [Section 6] with
the m- line.
10.3. Generating the SDP Answer
When the answerer receives an offer, which contains an m- line
describing an SCTP-over-DTLS association, if the answerer accepts the
association, the answerer:
o MUST insert a corresponding m- line in the answer, with an m- line
proto value [RFC3264] identical to the value in the offer;
o MUST associate an SDP 'setup' attribute with the m- line;
o MUST associate an SDP 'sctp-port' attribute with the m- line. If
the offer contained a new (different than the one currently used)
SCTP port value the answerer MUST also associate a new SCTP port
value. If the offer contained a zero SCTP port value, or if the
answerer does not accept the SCTP association, the answerer MUST
also associate a zero SCTP port value; and
o MAY associate an SDP 'max-message-size' attribute [Section 6] with
the m- line. The attribute value in the answer is independent
from the value (if present) in the corresponding m- line of the
offer.
Once the answerer has sent the answer the answerer:
o MUST, in the case of TCP/DTLS/SCTP, if a TCP connection has not
yet been established, or if an existing TCP connection is to be
closed and replaced by a new TCP connection, follow the procedures
in [RFC4145] for closing and establishing a TCP connection;
o MUST, if a DTLS association has not yet been established, or if an
existing DTLS association is to be closed and replaced by a new
DTLS association, follow the procedures in
Holmberg, et al. Expires October 22, 2017 [Page 13]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
[I-D.ietf-mmusic-dtls-sdp] for closing the currently used, and
establishing a new, DTLS association; and
o MUST, if an SCTP association has not yet been established, or if
an existing SCTP association is to be closed and replaced by a new
SCTP association, initiate the closing of the existing SCTP
association (if applicable) and establishment of the SCTP
association.
If the SDP 'sctp-port' attribute in the answer contains a zero
attribute value, the answerer MUST NOT establish an SCTP association.
If an SCTP association exists, the offerer MUST close it.
If the answerer does not accept the m- line in the offer, it MUST
assign a zero port value to the corresponding m- line in the answer,
following the procedures in [RFC3264]. In addition, the answerer
MUST NOT initiate the establishment of a TCP connection, a DTLS
association or a DTLS association associated with the m- line.
10.4. Offerer Processing of the SDP Answer
Once the offerer has received the answer the offerer:
o MUST, in the case of TCP/DTLS/SCTP, if a TCP connection has not
yet been established, or if an existing TCP connection is to be
closed and replaced by a new TCP connection, follow the procedures
in [RFC4145] for closing and establishing a TCP connection;
o MUST, if a DTLS association has not yet been established, or if an
existing DTLS association is to be closed and replaced by a new
DTLS association, follow the procedures in
[I-D.ietf-mmusic-dtls-sdp] for closing and establishing a DTLS
association; and
o MUST, if an SCTP association has not yet been established, or if
an existing SCTP association is to be closed and replaced by a new
SCTP association, initiate the closing of the existing SCTP
association (if applicable) and establishment of the SCTP
association.
If the SDP 'sctp-port' attribute in the answer contains a zero
attribute value, the offerer MUST NOT establish an SCTP association.
If an SCTP association exists in that case, the offerer MUST close
it.
If the m- line in the answer contains a zero port value, the offerer
MUST NOT initiate the establishment a TCP connection, a DTLS
association or an SCTP association associated with the m- line. If a
Holmberg, et al. Expires October 22, 2017 [Page 14]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
TCP connection, or a DTLS association or an SCTP association exists
in that case, the offerer MUST close it.
10.5. Modifying the Session
When an offerer sends an updated offer, in order to modify a
previously established SCTP association, it follows the procedures in
Section 10.2, with the following exceptions:
o If the offerer wants to close an SCTP association, and immediately
establish a new SCTP association, the offerer MUST associate an
SDP 'sctp-port' attribute with a new (different than the one
currently used) attribute value. This will not impact the
underlying DTLS association (and TCP connection in case of
TCP/DTLS/SCTP).
o If the offerer wants to close an SCTP association, without
immediately establishing a new SCTP association, the offerer MUST
associate an SDP 'sctp-port' attribute with a zero attribute
value. This will not impact the underlying DTLS association (and
TCP connection in case of TCP/DTLS/SCTP).
o If the offerer wants to establish an SCTP association, and another
SCTP association was previously closed, the offerer MUST associate
an SDP 'sctp-port' attribute with a new attribute value (different
than the value associated with the previous SCTP association). If
the previous SCTP association was closed successfully following
use of an SDP 'sctp-port' attribute with a zero attribute value,
the offerer MAY use the same attribute value for the new SCTP
association that was used with the previous SCTP association
before it was closed. This will not impact the underlying DTLS
association (and TCP connection in case of TCP/DTLS/SCTP).
o If the offerer wants to close an existing SCTP association, and
the underlying DTLS association (and the underlying TCP connection
in case of TCP/DTLS/SCTP) it MUST assign a zero port value to the
m- line associated with the SCTP and DTLS associations (and TCP
connection in case of TCP/DTLS/SCTP), following the procedures in
[RFC3264].
o NOTE: This specification does not define a mechanism for
explicitly closing a DTLS association while maintaining the
overlying SCTP association. However, if a DTLS association is
closed and replaced with a new DTLS association, as a result of
some other action [I-D.ietf-mmusic-dtls-sdp], the state of the
SCTP association is not affected.
Holmberg, et al. Expires October 22, 2017 [Page 15]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
The offer follows the procedures in [I-D.ietf-mmusic-dtls-sdp]
regarding the DTLS association impacts when modifying a session.
In the case of TCP/DTLS/SCTP, the offerer follows the procedures in
[RFC4145] regarding the TCP connection impacts when modifying a
session.
11. Multihoming Considerations
Multihoming is not supported when sending SCTP on top of DTLS, as
DTLS does not expose address management of the underlying transport
protocols (UDP or TCP) to its upper layer.
12. NAT Considerations
12.1. General
When SCTP-over-DTLS is used in NAT environment, it relies on the NAT
traversal procedures for the underlying transport protocol (UDP or
TCP).
12.2. ICE Considerations
When SCTP-over-DTLS is used with UDP based ICE candidates [RFC5245]
then the procedures for UDP/DTLS/SCTP [Section 7] are used.
When SCTP-over-DTLS is used with TCP based ICE candidates [RFC6544]
then the procedures for TCP/DTLS/SCTP [Section 8] are used.
In ICE environments, during the nomination process, endpoints go
through multiple ICE candidate pairs, until the most preferred
candidate pair is found. During the nomination process, data can be
sent as soon as the first working candidate pair is found, but the
nomination process still continues and selected candidate pairs can
still change while data is sent. Furthermore, if endpoints roam
between networks, for instance when mobile endpoint switches from
mobile connection to WiFi, endpoints will initiate an ICE restart,
which will trigger a new nomination process between the new set of
candidates and likely result in the new nominated candidate pair.
Implementations MUST treat all ICE candidate pairs associated with an
SCTP association on top of a DTLS association as part of the same
DTLS association. Thus, there will only be one SCTP handshake and
one DTLS handshake even if there are multiple valid candidate pairs,
and shifting from one candidate pair to another, including switching
between UDP to TCP candidate pairs, will not impact the SCTP or DTLS
associations. If new candidates are added, they will also be part of
the same SCTP and DTLS associations. When transitioning between
Holmberg, et al. Expires October 22, 2017 [Page 16]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
candidate pairs, different candidate pairs can be currently active in
different directions and implementations MUST be ready to receive
data on any of the candidates, even if this means sending and
receiving data using UDP/DTLS/SCTP and TCP/DTLS/SCTP at the same time
in different directions.
In order to maximize the likelihood of interoperability between the
endpoints, all ICE enabled SCTP-over-DTLS endpoints SHOULD implement
support for UDP/DTLS/SCTP.
When an SDP offer or answer is sent with multiple ICE candidates
during initial connection negotiation or after ICE restart, UDP based
candidates SHOULD be included and default candidate SHOULD be chosen
from one of those UDP candidates. The proto value MUST match the
transport protocol associated with the default candidate. If UDP
transport is used for the default candidate, then 'UDP/DTLS/SCTP'
proto value MUST be used. If TCP transport is used for the default
candidate, then 'TCP/DTLS/SCTP' proto value MUST be used. Note that
under normal circumstances the proto value for offers and answers
sent during ICE nomination SHOULD be 'UDP/DTLS/SCTP'.
When a subsequent SDP offer or answer is sent after ICE nomination is
complete, and does not initiate ICE restart, it will contain only the
nominated ICE candidate pair. In this case, the proto value MUST
match the transport protocol associated with the nominated ICE
candidate pair. If UDP transport is used for the nominated pair,
then 'UDP/DTLS/SCTP' proto value MUST be used. If TCP transport is
used for the nominated pair, then 'TCP/DTLS/SCTP' proto value MUST be
used. Please note that if an endpoint switches between TCP-based and
UDP-based candidates during the nomination process the endpoint is
not required to send an SDP offer for the sole purpose of keeping the
proto value of the associated m- line in sync.
NOTE: The text in the paragraph above only applies when the usage of
ICE has been negotiated. If ICE is not used, the proto value MUST
always reflect the transport protocol used at any given time.
13. Examples
13.1. Establishment of UDP/DTLS/SCTP association
Holmberg, et al. Expires October 22, 2017 [Page 17]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
SDP Offer:
m=application 54111 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP6 2001:DB8::A8FD
a=tls-id:abc3de65cddef001be82
a=setup:actpass
a=sctp-port:5000
a=max-message-size:100000
- The offerer indicates that the usage of the
UDP/DTLS/SCTP association will be as defined
for the 'webrtc-datachannel' format value.
- The offerer UDP port value is 54111.
- The offerer SCTP port value is 5000.
- The offerer indicates that it can take either the
client or the server DTLS role.
SDP Answer:
m=application 64300 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP6 2001:DB8::001D
a=tls-id:dbc8de77cddef001be90
a=setup:passive
a=sctp-port:6000
a=max-message-size:100000
- The answerer UDP port value is 64300.
- The answerer SCTP port value is 6000.
- The answerer takes the server DTLS role.
14. Security Considerations
[RFC4566] defines general SDP security considerations, while
[RFC3264], [RFC4145] and [RFC8122] define security considerations
when using the SDP offer/answer mechanism to negotiate media streams.
[RFC4960] defines general SCTP security considerations and
[I-D.ietf-tsvwg-sctp-dtls-encaps] defines security considerations
when using SCTP on top of DTLS.
This specification does not introduce new security considerations in
addition to those defined in the specifications listed above.
Holmberg, et al. Expires October 22, 2017 [Page 18]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
15. IANA Considerations
15.1. New SDP proto values
[RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this
document.]
This document updates the "Session Description Protocol (SDP)
Parameters" registry, following the procedures in [RFC4566], by
adding the following values to the table in the SDP "proto" field
registry:
+-------+---------------+-----------+
| Type | SDP Name | Reference |
+-------+---------------+-----------+
| proto | UDP/DTLS/SCTP | [RFCXXXX] |
| proto | TCP/DTLS/SCTP | [RFCXXXX] |
+-------+---------------+-----------+
Table 1: SDP "proto" field values
15.2. New SDP Attributes
15.2.1. sctp-port
This document defines a new SDP media-level attribute,'sctp-port'.
The details of the attribute are defined in Section 5.2.
15.2.2. max-message-size
This document defines a new SDP media-level attribute,'max-message-
size'. The details of the attribute are defined in Section 6.2.
15.3. association-usage Name Registry
[RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this
document.]
This specification creates a new IANA registry, following the
procedures in [RFC5226], for the namespace associated with the
'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' protocol identifiers. Each fmt
value describes the usage of an entire SCTP association, including
all SCTP streams associated with the SCTP association.
NOTE: Usage indication of individual SCTP streams is outside the
scope of this specification.
Holmberg, et al. Expires October 22, 2017 [Page 19]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
The fmt value, "association-usage", used with these "proto" values is
required. It is defined in Section 4.
As part of this registry, IANA maintains the following information:
association-usage name: The identifier of the subprotocol, as will
be used as the fmt value.
association-usage reference: A reference to the document in which
the association-usage is defined.
association-usage names are to be subject to the "First Come First
Served" IANA registration policy [RFC5226].
IANA is asked to add initial values to the registry.
|----------------------------------------------------------|
| name | Reference |
|----------------------------------------------------------|
| webrtc-datachannel | draft-ietf-rtcweb-data-protocol-xx, |
| | RFCXXX |
|----------------------------------------------------------|
[RFC EDITOR NOTE: Please hold the publication of this draft
until draft-ietf-rtcweb-data-protocol has been published as an RFC.
Then, replace the reference to draft-ietf-rtcweb-data-protocol
with the RFC number.]
[RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number
of this document.]
Figure 1
16. Acknowledgments
The authors wish to thank Harald Alvestrand, Randell Jesup, Paul
Kyzivat, Michael Tuexen, Juergen Stoetzer-Bradler, Flemming Andreasen
and Ari Keranen for their comments and useful feedback. Ben Campbell
provided comments as part of his AD review. Brian Carpenter
performed the Gen-ART review.
17.
[RFC EDITOR NOTE: Please remove this section when publishing]
Changes from draft-ietf-mmusic-sctp-sdp-25
Holmberg, et al. Expires October 22, 2017 [Page 20]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
o SDP 'dtls-id' attribute re-named to 'tls-id'.
Changes from draft-ietf-mmusic-sctp-sdp-24
o Minor editorial fix by Roman.
Changes from draft-ietf-mmusic-sctp-sdp-23
o Changes based on IESG review.
o - Proto value clarifications.
Changes from draft-ietf-mmusic-sctp-sdp-22
o Changes based on Gen-ART review by Brian Carpenter.
Changes from draft-ietf-mmusic-sctp-sdp-21
o Changes based on AD review by Ben Campbell.
Changes from draft-ietf-mmusic-sctp-sdp-20
o Informative reference to draft-ietf-rtcweb-data-protocol added.
Changes from draft-ietf-mmusic-sctp-sdp-19
o Changes based on WG chair comments from Flemming Andreasen.
Changes from draft-ietf-mmusic-sctp-sdp-18
o Changes based on WGLC comments from Paul Kyzivat.
Changes from draft-ietf-mmusic-sctp-sdp-17
o Removal of 'SCTP'.
o Document title changed.
o Disallow usage of SDP 'setup' attribute 'holdconn' value.
o Roman Shpount added as co-editor.
Changes from draft-ietf-mmusic-sctp-sdp-15
o Chapter about SCTP, DTLS and TCP association/connection management
modified.
o Removal of SCTP/DTLS.
Holmberg, et al. Expires October 22, 2017 [Page 21]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
Changes from draft-ietf-mmusic-sctp-sdp-14
o Changes based on WGLC comments from Magnus Westerlund.
o - ABNF clarification that token and port are defined in RFC4566.
o - Specify 40 as maximum digit character length for the SDP max-
message-size value.
o - Editorial clarification.
o Changes based on discussions at IETF#92.
o - Specify that all ICE candidate pairs belong to the same DTLS
association.
Changes from draft-ietf-mmusic-sctp-sdp-13
o Changes based on comments from Paul Kyzivat.
o - Text preventing usage of well-known ports removed.
o - Editorial clarification.
Changes from draft-ietf-mmusic-sctp-sdp-12
o Mux category rules added for new SDP attributes.
o Reference to draft-ietf-mmusic-sdp-mux-attributes added.
o Changes based on comments from Roman Shpount:
o - Specify that fingerprint or setup roles must not be modified,
unless underlying transport protocol is also modified.
o Changes based on comments from Ari Keranen:
o - Editorial corrections.
o Changes based on comments from Flemming Andreasen:
o - Clarify that, if UDP/DTLS/SCTP or TCP/DTLS/SCTP is used, the
DTLS association is established before the SCTP association.
o - Clarify that max-message-size value is given in bytes, and that
different values can be used per direction.
o - Section on fmtp attribute removed.
Holmberg, et al. Expires October 22, 2017 [Page 22]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
o - Editorial corrections.
Changes from draft-ietf-mmusic-sctp-sdp-11
o Example added.
Changes from draft-ietf-mmusic-sctp-sdp-10
o SDP max-message-size attribute added to IANA considerations.
o Changes based on comments from Paul Kyzivat:
o - Text about max message size removed from fmtp attribute section.
Changes from draft-ietf-mmusic-sctp-sdp-09
o 'DTLS/SCTP' split into 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP'
o Procedures for realizing UDP/DTLS/SCTP- and TCP/DTLS/SCTP
transports added.
Changes from draft-ietf-mmusic-sctp-sdp-08
o Default SCTP port removed:
o - Usage of SDP sctp-port attribute mandatory.
o SDP max-message-size attribute defined:
o - Attribute definition.
o - SDP Offer/Answer procedures.
o Text about SDP direction attributes added.
o Text about TLS role determination added.
18. References
18.1. Normative References
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<http://www.rfc-editor.org/info/rfc793>.
Holmberg, et al. Expires October 22, 2017 [Page 23]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
[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>.
[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>.
[RFC4571] Lazzaro, J., "Framing Real-time Transport Protocol (RTP)
and RTP Control Protocol (RTCP) Packets over Connection-
Oriented Transport", RFC 4571, DOI 10.17487/RFC4571, July
2006, <http://www.rfc-editor.org/info/rfc4571>.
[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, DOI 10.17487/RFC4960, September 2007,
<http://www.rfc-editor.org/info/rfc4960>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <http://www.rfc-editor.org/info/rfc6347>.
[RFC6544] Rosenberg, J., Keranen, A., Lowekamp, B., and A. Roach,
"TCP Candidates with Interactive Connectivity
Establishment (ICE)", RFC 6544, DOI 10.17487/RFC6544,
March 2012, <http://www.rfc-editor.org/info/rfc6544>.
[RFC8122] Lennox, J. and C. Holmberg, "Connection-Oriented Media
Transport over the Transport Layer Security (TLS) Protocol
in the Session Description Protocol (SDP)", RFC 8122,
DOI 10.17487/RFC8122, March 2017,
<http://www.rfc-editor.org/info/rfc8122>.
Holmberg, et al. Expires October 22, 2017 [Page 24]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
[I-D.ietf-mmusic-dtls-sdp]
Holmberg, C. and R. Shpount, "Using the SDP Offer/Answer
Mechanism for DTLS", draft-ietf-mmusic-dtls-sdp-24 (work
in progress), April 2017.
[I-D.ietf-tsvwg-sctp-dtls-encaps]
Tuexen, M., Stewart, R., Jesup, R., and S. Loreto, "DTLS
Encapsulation of SCTP Packets", draft-ietf-tsvwg-sctp-
dtls-encaps-09 (work in progress), January 2015.
[I-D.ietf-mmusic-sdp-mux-attributes]
Nandakumar, S., "A Framework for SDP Attributes when
Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-16
(work in progress), December 2016.
18.2. Informative References
[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>.
[I-D.ietf-rtcweb-data-channel]
Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data
Channels", draft-ietf-rtcweb-data-channel-13 (work in
progress), January 2015.
[I-D.ietf-mmusic-data-channel-sdpneg]
Drage, K., Makaraju, M., Stoetzer-Bradler, J., Ejzak, R.,
and J. Marcon, "SDP-based Data Channel Negotiation",
draft-ietf-mmusic-data-channel-sdpneg-12 (work in
progress), March 2017.
[I-D.ietf-rtcweb-data-protocol]
Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data Channel
Establishment Protocol", draft-ietf-rtcweb-data-
protocol-09 (work in progress), January 2015.
Authors' Addresses
Christer Holmberg
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: christer.holmberg@ericsson.com
Holmberg, et al. Expires October 22, 2017 [Page 25]
Internet-Draft SDP Offer/Answer For SCTP Over DTLS April 2017
Roman Shpount
TurboBridge
4905 Del Ray Avenue, Suite 300
Bethesda, MD 20814
USA
Phone: +1 (240) 292-6632
Email: rshpount@turbobridge.com
Salvatore Loreto
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: Salvatore.Loreto@ericsson.com
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: Gonzalo.Camarillo@ericsson.com
Holmberg, et al. Expires October 22, 2017 [Page 26]
