rfc8873
Internet Engineering Task Force (IETF) JM. Recio, Ed.
Request for Comments: 8873 Unaffiliated
Updates: 4975 C. Holmberg
Category: Standards Track Ericsson
ISSN: 2070-1721 January 2021
Message Session Relay Protocol (MSRP) over Data Channels
Abstract
This document specifies how a Web Real-Time Communication (WebRTC)
data channel can be used as a transport mechanism for the Message
Session Relay Protocol (MSRP) and how the Session Description
Protocol (SDP) offer/answer mechanism can be used to negotiate such a
data channel, referred to as an MSRP data channel. Two network
configurations are supported: the connection of two MSRP data channel
endpoints; and a gateway configuration, which connects an MSRP data
channel endpoint with an MSRP endpoint that uses either TCP or TLS.
This document updates RFC 4975.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8873.
Copyright Notice
Copyright (c) 2021 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
(https://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
2. Conventions
3. WebRTC Data Channel Considerations
3.1. MSRP Data Channel
4. SDP Considerations
4.1. MSRP URI
4.2. MSRP URI msrp-scheme
4.3. Use of the 'dcmap' Attribute
4.4. Use of the 'dcsa' Attribute
4.5. Use of the DCSA-Embedded 'setup' Attribute
4.6. Session Closing
4.7. Support for MSRP File Transfer Function
4.8. Example
5. MSRP Considerations
5.1. Session Mapping
5.2. Session Opening
5.3. Session Closing
5.4. Data Framing
5.5. Data Sending, Receiving, and Reporting
5.6. Support for MSRP File Transfer Function
6. Gateway Considerations
7. Updates to RFC 4975
8. Security Considerations
9. IANA Considerations
9.1. "msrps" URI scheme
9.2. Subprotocol Identifier "msrp"
9.3. SDP Attributes
10. References
10.1. Normative References
10.2. Informative References
Acknowledgments
Authors' Addresses
1. Introduction
The Message Session Relay Protocol (MSRP) [RFC4975] is a protocol for
transmitting a series of related instant messages in the context of a
session. In addition to instant messaging, MSRP can also be used for
image sharing or file transfer. MSRP was initially defined in
[RFC4975] to work over TCP and TLS connections, and over a WebSocket
subprotocol specified by [RFC7977].
This document specifies how a Web Real-Time Communication (WebRTC)
data channel [RFC8831] can be used as a transport mechanism for MSRP
without the TCP and TLS layers, and how the Session Description
Protocol (SDP) offer/answer mechanism for data channels [RFC8864] can
be used to negotiate such a data channel.
In this document, an MSRP data channel refers to a WebRTC data
channel for which the instantiated subprotocol is "msrp" and the data
channel is negotiated using the SDP offer/answer mechanism [RFC8864].
Defining MSRP as a data channel subprotocol has many benefits:
* provides to applications a proven protocol enabling instant
messaging, file transfer, image sharing
* integrates those features with other WebRTC voice, video, and data
features
* leverages the SDP-based negotiation already defined for MSRP
* allows the interworking with MSRP endpoints running on a TCP or
TLS connection
Compared to the WebSocket protocol, which provides a message-passing
protocol to applications with no direct access to TCP or TLS sockets,
data channels provide a low-latency transport and leverage NAT-aware
connectivity and the security features of WebRTC.
This document defines an MSRP data channel endpoint as an MSRP
application that uses a WebRTC data channel for MSRP transport. This
document describes configurations for connecting such endpoint to
another MSRP data channel endpoint, or to an MSRP endpoint that uses
either TCP or TLS transport.
This document updates [RFC4975] as described in Section 7.
2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. WebRTC Data Channel Considerations
3.1. MSRP Data Channel
The following WebRTC data channel property values [RFC8831] apply to
an MSRP data channel:
+==========================+=================+
| Property | Value |
+==========================+=================+
| Subprotocol Identifier | msrp |
+--------------------------+-----------------+
| Transmission reliability | reliable |
+--------------------------+-----------------+
| Transmission order | in-order |
+--------------------------+-----------------+
| Label | See Section 4.3 |
+--------------------------+-----------------+
Table 1
4. SDP Considerations
The generic SDP considerations, including the SDP offer/answer
procedures [RFC3264], for negotiating a WebRTC data channel are
defined in [RFC8864]. This section and its subsections define the
SDP considerations that are specific to an MSRP data channel,
identified by the "subprotocol" attribute parameter, with an "msrp"
parameter value in the 'dcmap' attribute.
4.1. MSRP URI
This document extends the MSRP URI syntax [RFC4975] by defining the
new transport parameter value "dc" (an abbreviation of data channel):
transport /= "dc"
; Add "dc" to existing transports per Section 9 of [RFC4975]
MSRP design provides for new transport bindings (see Section 6 of
[RFC4975]). MSRP implementations are expected to allow unrecognized
transports for which there is no need to establish a connection to
the resource described by the URI, as is the case of data channels
(Section 4.4).
4.2. MSRP URI msrp-scheme
The msrp-scheme portion of the MSRP URI that represents an MSRP data
channel endpoint (used in the SDP 'path' attribute and in the MSRP
message headers) is always "msrps", which indicates that the MSRP
data channel is always secured using DTLS as described in [RFC8831].
4.3. Use of the 'dcmap' Attribute
An offerer and answerer SHALL, in each offer and answer, include a
'dcmap' attribute [RFC8864] in the SDP media description ("m="
section) [RFC4566] describing the SCTP association [RFC4960] used to
realize the MSRP data channel.
The attribute includes the following data channel parameters:
* "label=" labelstring
* "subprotocol=" "msrp"
The labelstring is set by the MSRP application according to
[RFC8864].
The offerer and answerer SHALL NOT include the "max-retr" and the
"max-time" attribute parameters in the 'dcmap' attribute.
The offerer and answerer MAY include the "ordered" attribute
parameter in the 'dcmap' attribute. If included, the attribute
parameter value SHALL be set to "true".
Below is an example of a 'dcmap' attribute for an MSRP session to be
negotiated with the "dcmap-stream-id" parameter set to 2 and the
"label" parameter set to "chat":
a=dcmap:2 label="chat";subprotocol="msrp"
4.4. Use of the 'dcsa' Attribute
An offerer and answerer can, in each offer and answer, include one or
more data channel subprotocol attributes ('dcsa' attributes)
[RFC8864] in the "m=" section describing the SCTP association used to
realize the MSRP data channel. An SDP attribute included in a 'dcsa'
attribute is referred to as a DCSA-embedded attribute.
If an offerer or answerer receives a 'dcsa' attribute that contains
an SDP attribute for which usage has not been defined for an MSRP
data channel, the offerer or answerer should ignore the 'dcsa'
attribute, following the rules in Section 6.7 of [RFC8864].
An offerer and answerer SHALL include a 'dcsa' attribute for each of
the following MSRP-specific SDP attributes:
* defined in [RFC4975]: 'path'.
* defined in [RFC6714]: 'msrp-cema'.
* defined in [RFC6135]: 'setup'. See Section 4.5.
It is considered a protocol error if one or more of the DCSA-embedded
attributes listed above are not included in an offer or answer.
An offerer and answerer MAY include a 'dcsa' attribute for any of the
following MSRP-specific SDP attributes, following the procedures
defined for each attribute:
* defined in [RFC4975]: 'accept-types', 'accept-wrapped-types', and
'max-size'.
* defined in [RFC4566]: 'sendonly', 'recvonly', 'inactive', and
'sendrecv'.
* defined in [RFC5547]: all the parameters related to MSRP file
transfer. See Section 4.7.
A subsequent offer or answer MAY update the previously negotiated
MSRP subprotocol attributes while keeping the 'dcmap' attribute
associated with the MSRP data channel unchanged. The semantics for
newly negotiated MSRP subprotocol attributes are per [RFC4975].
When MSRP messages are transported on a data channel, the 'path'
attribute is not used for the routing of the messages. The MSRP data
channel is established using the SDP offer/answer procedures defined
in [RFC8864], and the MSRP messages are then transported on that data
channel. This is different from legacy MSRP [RFC4975] but similar to
MSRP Connection Establishment for Media Anchoring (MSRP CEMA)
[RFC6714]. Because of this, a DCSA-embedded 'msrp-cema' attribute is
mandated for MSRP sessions over data channels. However, when an
endpoint receives an MSRP message over a data channel, it MUST still
perform the MSRP URI comparison procedures defined in [RFC4975].
4.5. Use of the DCSA-Embedded 'setup' Attribute
As described in Section 4.4, the usage of a DCSA-embedded 'setup'
attribute is mandated for MSRP sessions over data channels. It is
used to negotiate which MSRP data channel endpoint assumes the active
role as per Section 4.2.2 of [RFC6135] and Section 5.4 of [RFC4975].
It has no relationship with the DTLS connection establishment roles
[RFC8841].
The DCSA-embedded 'setup' attribute is of the form "a=dcsa:x
setup:<role>", with x being the data channel's SCTP stream
identifier, so that the 'setup' attribute is explicitly associated
with an MSRP session over a specific data channel.
4.6. Session Closing
An MSRP session is closed by closing the associated data channel
following the procedures in [RFC8864].
The port value for the "m=" line SHOULD NOT be changed (e.g., to
zero) when closing an MSRP session (unless all data channels are
being closed and the SCTP association is no longer needed) since this
would close the SCTP association and impact all of the data channels.
In all cases in [RFC4975] where the procedure calls for setting the
port to zero in the MSRP "m=" line in an SDP offer for TCP transport,
the SDP offerer of an MSRP session with data channel transport SHALL
remove the corresponding 'dcmap' and 'dcsa' attributes.
4.7. Support for MSRP File Transfer Function
SDP attributes specified in [RFC5547] for a file transfer "m=" line
are embedded as subprotocol-specific attributes using the syntax
defined in [RFC8864].
4.8. Example
Below is an example of an offer and an answer that include the
attributes needed to establish two MSRP sessions: one for chat and
one for file transfer. The example is derived from a combination of
examples in [RFC4975] and [RFC5547].
Offer:
m=application 54111 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP6 2001:db8::3
a=max-message-size:100000
a=sctp-port:5000
a=setup:actpass
a=fingerprint:SHA-256 12:DF:3E:5D:49:6B:19:E5:7C:AB:4A:AD:B9:B1:\
3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB:4A:AD
a=tls-id:4a756565cddef001be82
a=dcmap:0 label="chat";subprotocol="msrp"
a=dcsa:0 msrp-cema
a=dcsa:0 setup:active
a=dcsa:0 accept-types:message/cpim text/plain
a=dcsa:0 path:msrps://2001:db8::3:54111/si438dsaodes;dc
a=dcmap:2 label="file transfer";subprotocol="msrp"
a=dcsa:2 sendonly
a=dcsa:2 msrp-cema
a=dcsa:2 setup:active
a=dcsa:2 accept-types:message/cpim
a=dcsa:2 accept-wrapped-types:*
a=dcsa:2 path:msrps://2001:db8::3:54111/jshA7we;dc
a=dcsa:2 file-selector:name:"picture1.jpg" type:image/jpeg \
size:1463440 hash:sha-256:7C:DF:3E:5D:49:6B:19:E5:12:AB:4A:AD:\
4A:B1:3F:82:3E:3B:54:12:02:5D:18:DF:49:6B:19:E5:7C:AB:B9:AD
a=dcsa:2 file-transfer-id:rjEtHAcYVZ7xKwGYpGGwyn5gqsSaU7Ep
a=dcsa:2 file-disposition:attachment
a=dcsa:2 file-date:creation:"Tue, 11 Aug 2020 19:05:30 +0200"
a=dcsa:2 file-icon:cid:id2@bob.example.com
a=dcsa:2 file-range:1-1463440
Answer:
m=application 51444 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP6 IP6 2001:db8::1
a=max-message-size:100000
a=sctp-port:6000
a=setup:passive
a=fingerprint:SHA-256 5D:02:3E:AD:49:6B:19:E5:7C:AB:4A:AD:B9:\
B1:3F:82:18:3B:54:DF:12:6B:3E:5D:49:DF:19:E5:7C:AB:4A:5D
a=tls-id:65cd4a7565debe82f100
a=dcmap:0 label="chat";subprotocol="msrp"
a=dcsa:0 msrp-cema
a=dcsa:0 setup:passive
a=dcsa:0 accept-types:message/cpim text/plain
a=dcsa:0 path:msrps://2001:db8::1:51444/di551fsaodes;dc
a=dcmap:2 label="file transfer";subprotocol="msrp"
a=dcsa:2 recvonly
a=dcsa:2 msrp-cema
a=dcsa:2 setup:passive
a=dcsa:2 accept-types:message/cpim
a=dcsa:2 accept-wrapped-types:*
a=dcsa:2 path:msrps://2001:db8::1:51444/jksh7Bwc;dc
a=dcsa:2 file-selector:name:"picture1.jpg" type:image/jpeg \
size:1463440
a=dcsa:2 file-transfer-id:rjEtHAcYVZ7xKwGYpGGwyn5gqsSaU7Ep
a=dcsa:2 file-range:1-1463440
Note that due to RFC formatting conventions, this document splits SDP
content that exceeds 72 characters across lines, marking this line
folding with a backslash character. This backslash and its trailing
CRLF and whitespace would not appear in actual SDP content.
5. MSRP Considerations
The procedures specified in [RFC4975] apply except when this document
specifies otherwise. This section describes the MSRP considerations
specific to an MSRP data channel.
5.1. Session Mapping
In this document, each MSRP session maps to one data channel exactly.
5.2. Session Opening
Section 4.5 describes how the active MSRP data channel endpoint role
is negotiated. The active MSRP data channel endpoint uses the data
channel established for this MSRP session by the generic data channel
opening procedure defined in [RFC8864].
As soon as the WebRTC data channel is opened, the MSRP session is
actually opened by the active MSRP data channel endpoint. In order
to do this, the active MSRP data channel endpoint sends an MSRP SEND
message (empty or not) to the peer (passive) MSRP data channel
endpoint.
5.3. Session Closing
The closure of an MSRP session SHALL be signaled via SDP following
the requirements in Section 4.6.
If the data channel used to transport the MSRP session fails and is
torn down, the MSRP data channel endpoints SHALL consider the MSRP
session failed. An MSRP data channel endpoint MAY, based on local
policy, try to negotiate a new MSRP data channel.
5.4. Data Framing
Each text-based MSRP message is sent on the corresponding data
channel using standard MSRP framing and chunking procedures, as
defined in [RFC4975], with each MSRP chunk delivered in a single SCTP
user message. Therefore all sent MSRP chunks SHALL have lengths of
less than or equal to the value of the peer's 'max-message-size'
attribute [RFC8841] associated with the SCTP association.
5.5. Data Sending, Receiving, and Reporting
Data sending, receiving, and reporting procedures SHALL conform to
[RFC4975].
5.6. Support for MSRP File Transfer Function
[RFC5547] defines an end-to-end file transfer method based on MSRP
and the SDP offer/answer mechanism. This file transfer method is
also usable by MSRP data channel endpoints with the following
considerations:
* As an MSRP session maps to one data channel, a file transfer
session maps also to one data channel.
* SDP attributes are negotiated as specified in Section 4.7.
* Once the file transfer is complete, the same data channel MAY be
reused for another file transfer.
6. Gateway Considerations
This section describes the network configuration where one MSRP
endpoint uses an MSRP data channel as MSRP transport, the other MSRP
endpoint uses TLS/TCP connections as MSRP transport, and the two MSRP
endpoints interwork via a gateway.
Specifically, a gateway can be configured to interwork an MSRP
session over a data channel with a peer that does not support data
channel transport in one of two ways.
In one model, the gateway performs as an MSRP Back-to-Back User Agent
(B2BUA) to interwork all the procedures as necessary between the
endpoints. No further specification is needed for this model.
Alternately, the gateway can provide transport-level interworking
between MSRP endpoints using different transport protocols. In
accordance with Section 4.4, 'path' attributes SHALL NOT be used for
transport-level interworking.
When the gateway performs transport-level interworking between MSRP
endpoints, all of the procedures in Section 4 and Section 5 apply to
each peer, with the following additions:
* The gateway SHALL use the MSRP CEMA mechanism [RFC6714] towards
the non-data channel endpoint.
* If the non-data channel endpoint does not support MSRP CEMA,
transport-level interworking mode is not possible, and the gateway
needs to act as an MSRP B2BUA.
* The gateway SHALL NOT modify the 'path' attribute received from
data channel or from non-data channel endpoints.
* The gateway SHALL NOT modify the 'setup' value received from data
channel or from non-data channel endpoints.
* The endpoint establishing an MSRP session using data channel
transport SHALL NOT request inclusion of any relays, although it
MAY interoperate with a peer that signals the use of relays.
7. Updates to RFC 4975
This document updates [RFC4975] by allowing the usage of the "msrps"
scheme when the underlying connection is protected with DTLS.
8. Security Considerations
MSRP traffic over data channels, including confidentiality,
integrity, and source authentication, is secured as specified by
[RFC8831]. However, [RFC4975] allows transport of MSRP traffic over
nonsecured TCP connections and does not provide a mechanism to
guarantee usage of TLS end to end. As described in [RFC4975], even
if TLS is used between some hops, TCP might still be used between
other hops. Operators need to establish proper policies in order to
ensure that the MSRP traffic is protected between endpoints.
[RFC5547] specifies security considerations related to the usage of
MSRP for file transfer.
[RFC7092] specifies security considerations related to B2BUAs.
Note that the discussion in Section 14.5 of [RFC4975] on MSRP message
attribution to remote identities applies to data channel transport.
If the Session Initiation Protocol (SIP) [RFC3261] is used to
implement the offer/answer transactions for establishing the MSRP
data channel, the SIP security considerations specified in [RFC3261]
apply.
9. IANA Considerations
9.1. "msrps" URI scheme
This document modifies the usage of the "msrps" URI scheme,
registered by [RFC4975], by adding DTLS as a protected transport
indicated by the URI scheme.
A reference to RFC 8873 has been added to the URI scheme "msrps" in
the "Uniform Resource Identifier (URI) Schemes" registry.
9.2. Subprotocol Identifier "msrp"
A reference to RFC 8873 has been added to the subprotocol identifier
"msrp" in the "WebSocket Subprotocol Name Registry".
9.3. SDP Attributes
This document modifies the usage of a set of SDP attributes if any of
those attributes is included in an SDP 'dcsa' attribute associated
with an MSRP data channel. The modified usage of the SDP 'setup'
attribute is described in Section 4.5. The usage of the other SDP
attributes is described in Section 4.4.
* 'accept-types'
* 'accept-wrapped-types'
* 'file-date'
* 'file-disposition'
* 'file-icon'
* 'file-range'
* 'file-selector'
* 'file-transfer-id'
* 'inactive'
* 'max-size'
* 'msrp-cema'
* 'path'
* 'recvonly'
* 'sendonly'
* 'sendrecv'
The usage level "dcsa (msrp)" has been added to the registration of
the SDP 'accept-types' attribute in the Session Description Protocol
(SDP) Parameters "att-field" subregistry as follows:
Contact name: IESG
Contact email: iesg@ietf.org
Attribute name: accept-types
Usage level: dcsa (msrp)
Purpose: Contain the list of media types that the endpoint
is willing to receive.
Reference: RFC 8873
The usage level "dcsa (msrp)" has been added to the registration of
the SDP 'accept-wrapped-types' attribute in the Session Description
Protocol (SDP) Parameters "att-field" subregistry as follows:
Contact name: IESG
Contact email: iesg@ietf.org
Attribute name: accept-wrapped-types
Usage level: dcsa (msrp)
Purpose: Contain the list of media types that the endpoint
is willing to receive in an MSRP message with
multipart content.
Reference: RFC 8873
The usage level "dcsa (msrp)" has been added to the registration of
the SDP 'file-date' attribute in the Session Description Protocol
(SDP) Parameters "att-field" subregistry as follows:
Contact name: IESG
Contact email: iesg@ietf.org
Attribute name: file-date
Usage level: dcsa (msrp)
Purpose: Indicate one or more dates related to the file in
an MSRP file transfer negotiation.
Reference: RFC 8873
The usage level "dcsa (msrp)" has been added to the registration of
the SDP 'file-disposition' attribute in the Session Description
Protocol (SDP) Parameters "att-field" subregistry as follows:
Contact name: IESG
Contact email: iesg@ietf.org
Attribute name: file-disposition
Usage level: dcsa (msrp)
Purpose: Provide a suggestion to the other endpoint about
the intended disposition of the file in an MSRP
file transfer negotiation.
Reference: RFC 8873
The usage level "dcsa (msrp)" has been added to the registration of
the SDP 'file-icon' attribute in the Session Description Protocol
(SDP) Parameters "att-field" subregistry as follows:
Contact name: IESG
Contact email: iesg@ietf.org
Attribute name: file-icon
Usage level: dcsa (msrp)
Purpose: Contain a pointer to a small preview icon
representing the contents of the file in an MSRP
file transfer negotiation.
Reference: RFC 8873
The usage level "dcsa (msrp)" has been added to the registration of
the SDP 'file-range' attribute in the Session Description Protocol
(SDP) Parameters "att-field" subregistry as follows:
Contact name: IESG
Contact email: iesg@ietf.org
Attribute name: file-range
Usage level: dcsa (msrp)
Purpose: Contain the range of transferred octets of the file
in an MSRP file transfer negotiation.
Reference: RFC 8873
The usage level "dcsa (msrp)" has been added to the registration of
the SDP 'file-selector' attribute in the Session Description Protocol
(SDP) Parameters "att-field" subregistry as follows:
Contact name: IESG
Contact email: iesg@ietf.org
Attribute name: file-selector
Usage level: dcsa (msrp)
Purpose: Indicate a file in an MSRP file transfer
negotiation.
Reference: RFC 8873
The usage level "dcsa (msrp)" has been added to the registration of
the SDP 'file-transfer-id' attribute in the Session Description
Protocol (SDP) Parameters "att-field" subregistry as follows:
Contact name: IESG
Contact email: iesg@ietf.org
Attribute name: file-transfer-id
Usage level: dcsa (msrp)
Purpose: Indicate a unique identifier of the file transfer
operation in an MSRP file transfer negotiation.
Reference: RFC 8873
The usage level "dcsa (msrp)" has been added to the registration of
the SDP 'inactive' attribute in the Session Description Protocol
(SDP) Parameters "att-field" subregistry as follows:
Contact name: IESG
Contact email: iesg@ietf.org
Attribute name: inactive
Usage level: dcsa (msrp)
Purpose: Negotiate the direction of the media flow on an
MSRP data channel.
Reference: RFC 8873
The usage level "dcsa (msrp)" has been added to the registration of
the SDP 'max-size' attribute in the Session Description Protocol
(SDP) Parameters "att-field" subregistry as follows:
Contact name: IESG
Contact email: iesg@ietf.org
Attribute name: max-size
Usage level: dcsa (msrp)
Purpose: Indicate the largest message an MSRP endpoint
wishes to accept.
Reference: RFC 8873
The usage level "dcsa (msrp)" has been added to the registration of
the SDP 'msrp-cema' attribute in the Session Description Protocol
(SDP) Parameters "att-field" subregistry as follows:
Contact name: IESG
Contact email: iesg@ietf.org
Attribute name: msrp-cema
Usage level: dcsa (msrp)
Purpose: Indicate that the routing of MSRP messages
transported on a data channel is more similar to
the MSRP CEMA mechanism than the legacy MSRP
routing mechanism.
Reference: RFC 8873
The usage level "dcsa (msrp)" has been added to the registration of
the SDP 'path' attribute in the Session Description Protocol (SDP)
Parameters "att-field" subregistry as follows:
Contact name: IESG
Contact email: iesg@ietf.org
Attribute name: path
Usage level: dcsa (msrp)
Purpose: Indicate an endpoint, but not used for routing, as
described in Section 4.4.
Reference: RFC 8873
The usage level "dcsa (msrp)" has been added to the registration of
the SDP 'recvonly' attribute in the Session Description Protocol
(SDP) Parameters "att-field" subregistry as follows:
Contact name: IESG
Contact email: iesg@ietf.org
Attribute name: recvonly
Usage level: dcsa (msrp)
Purpose: Negotiate the direction of the media flow on an
MSRP data channel.
Reference: RFC 8873
The usage level "dcsa (msrp)" has been added to the registration of
the SDP 'sendonly' attribute in the Session Description Protocol
(SDP) Parameters "att-field" subregistry as follows:
Contact name: IESG
Contact email: iesg@ietf.org
Attribute name: sendonly
Usage level: dcsa (msrp)
Purpose: Negotiate the direction of the media flow on an
MSRP data channel.
Reference: RFC 8873
The usage level "dcsa (msrp)" has been added to the registration of
the SDP 'setup' attribute in the "att-field" subregistry as follows:
Contact name: IESG
Contact email: iesg@ietf.org
Attribute name: setup
Usage level: dcsa (msrp)
Purpose: Negotiate the active role of an MSRP session over a
data channel as per Section 4.5.
Reference: RFC 8873
The usage level "dcsa (msrp)" has been added to the registration of
the SDP 'sendrecv' attribute in the Session Description Protocol
(SDP) Parameters "att-field" subregistry as follows:
Contact name: IESG
Contact email: iesg@ietf.org
Attribute name: sendrecv
Usage level: dcsa (msrp)
Purpose: Negotiate the direction of the media flow on an
MSRP data channel.
Reference: RFC 8873
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://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,
<https://www.rfc-editor.org/info/rfc3264>.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
July 2006, <https://www.rfc-editor.org/info/rfc4566>.
[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, DOI 10.17487/RFC4960, September 2007,
<https://www.rfc-editor.org/info/rfc4960>.
[RFC4975] Campbell, B., Ed., Mahy, R., Ed., and C. Jennings, Ed.,
"The Message Session Relay Protocol (MSRP)", RFC 4975,
DOI 10.17487/RFC4975, September 2007,
<https://www.rfc-editor.org/info/rfc4975>.
[RFC5547] Garcia-Martin, M., Isomaki, M., Camarillo, G., Loreto, S.,
and P. Kyzivat, "A Session Description Protocol (SDP)
Offer/Answer Mechanism to Enable File Transfer", RFC 5547,
DOI 10.17487/RFC5547, May 2009,
<https://www.rfc-editor.org/info/rfc5547>.
[RFC6135] Holmberg, C. and S. Blau, "An Alternative Connection Model
for the Message Session Relay Protocol (MSRP)", RFC 6135,
DOI 10.17487/RFC6135, February 2011,
<https://www.rfc-editor.org/info/rfc6135>.
[RFC6714] Holmberg, C., Blau, S., and E. Burger, "Connection
Establishment for Media Anchoring (CEMA) for the Message
Session Relay Protocol (MSRP)", RFC 6714,
DOI 10.17487/RFC6714, August 2012,
<https://www.rfc-editor.org/info/rfc6714>.
[RFC7977] Dunkley, P., Llewellyn, G., Pascual, V., Salgueiro, G.,
and R. Ravindranath, "The WebSocket Protocol as a
Transport for the Message Session Relay Protocol (MSRP)",
RFC 7977, DOI 10.17487/RFC7977, September 2016,
<https://www.rfc-editor.org/info/rfc7977>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8831] Jesup, R., Loreto, S., and M. Tüxen, "WebRTC Data
Channels", RFC 8831, DOI 10.17487/RFC8831, January 2021,
<https://www.rfc-editor.org/info/rfc8831>.
[RFC8841] Holmberg, C., Shpount, R., Loreto, S., and G. Camarillo,
"Session Description Protocol (SDP) Offer/Answer
Procedures for Stream Control Transmission Protocol (SCTP)
over Datagram Transport Layer Security (DTLS) Transport",
RFC 8841, DOI 10.17487/RFC8841, January 2021,
<https://www.rfc-editor.org/info/rfc8841>.
[RFC8864] Drage, K., Makaraju, M., Ejzak, R., Marcon, J., and R.
Even, Ed., "Negotiation Data Channels Using the Session
Description Protocol (SDP)", RFC 8864,
DOI 10.17487/RFC8864, January 2021,
<https://www.rfc-editor.org/info/rfc8864>.
10.2. Informative References
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<https://www.rfc-editor.org/info/rfc3261>.
[RFC7092] Kaplan, H. and V. Pascual, "A Taxonomy of Session
Initiation Protocol (SIP) Back-to-Back User Agents",
RFC 7092, DOI 10.17487/RFC7092, December 2013,
<https://www.rfc-editor.org/info/rfc7092>.
Acknowledgments
The authors wish to acknowledge the borrowing of ideas from another
Internet-Draft by Peter Dunkley and Gavin Llewellyn, and to thank
Flemming Andreasen, Christian Groves, Paul Kyzivat, Jonathan Lennox,
Uwe Rauschenbach, Albrecht Schwarz, and Keith Drage for their
invaluable comments.
Richard Ejzak, Keith Drage, and Juergen Stoetzer-Bradler contributed
to an earlier draft version of this document before the draft was
readopted.
Julien Maisonneuve helped with the readoption of this document, and
Maridi R. Makaraju (Raju) contributed valuable comments after the
document was readopted.
Authors' Addresses
Jose M. Recio (editor)
Unaffiliated
Email: jose@ch3m4.com
Christer Holmberg
Ericsson
Hirsalantie 11
FI-02420 Jorvas
Finland
Email: christer.holmberg@ericsson.com
ERRATA
