draft-ietf-rtcweb-data-channel-05.txt   draft-ietf-rtcweb-data-channel-06.txt 
Network Working Group R. Jesup RTCWeb Working Group R. Jesup
Internet-Draft Mozilla Internet-Draft Mozilla
Intended status: Standards Track S. Loreto Intended status: Standards Track S. Loreto
Expires: January 16, 2014 Ericsson Expires: April 24, 2014 Ericsson
M. Tuexen M. Tuexen
Muenster Univ. of Appl. Sciences Muenster Univ. of Appl. Sciences
July 15, 2013 October 21, 2013
RTCWeb Data Channels RTCWeb Data Channels
draft-ietf-rtcweb-data-channel-05.txt draft-ietf-rtcweb-data-channel-06.txt
Abstract Abstract
The Web Real-Time Communication (WebRTC) working group is charged to The Real-Time Communication in WEB-browsers (RTCWeb) working group is
provide protocol support for direct interactive rich communication charged to provide protocol support for direct interactive rich
using audio, video, and data between two peers' web-browsers. This communication using audio, video, and data between two peers' web-
document specifies the non-media data transport aspects of the WebRTC browsers. This document specifies the non-media data transport
framework. It provides an architectural overview of how the Stream aspects of the RTCWeb framework. It provides an architectural
Control Transmission Protocol (SCTP) is used in the WebRTC context as overview of how the Stream Control Transmission Protocol (SCTP) is
a generic transport service allowing Web Browser to exchange generic used in the RTCWeb context as a generic transport service allowing
data from peer to peer. WEB-browsers to exchange generic data from peer to peer.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 16, 2014. This Internet-Draft will expire on April 24, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2013 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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2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Use Cases for Unreliable Data Channels . . . . . . . . . 3 3.1. Use Cases for Unreliable Data Channels . . . . . . . . . 3
3.2. Use Cases for Reliable Data Channels . . . . . . . . . . 3 3.2. Use Cases for Reliable Data Channels . . . . . . . . . . 3
4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 4
5. SCTP over DTLS over UDP Considerations . . . . . . . . . . . 5 5. SCTP over DTLS over UDP Considerations . . . . . . . . . . . 5
6. The Usage of SCTP in the RTCWeb Context . . . . . . . . . . . 8 6. The Usage of SCTP in the RTCWeb Context . . . . . . . . . . . 8
6.1. SCTP Protocol Considerations . . . . . . . . . . . . . . 8 6.1. SCTP Protocol Considerations . . . . . . . . . . . . . . 8
6.2. Association Setup . . . . . . . . . . . . . . . . . . . . 9 6.2. Association Setup . . . . . . . . . . . . . . . . . . . . 9
6.3. SCTP Streams . . . . . . . . . . . . . . . . . . . . . . 9 6.3. SCTP Streams . . . . . . . . . . . . . . . . . . . . . . 9
6.4. Channel Definition . . . . . . . . . . . . . . . . . . . 9 6.4. Channel Definition . . . . . . . . . . . . . . . . . . . 10
6.5. Usage of Payload Protocol Identifier . . . . . . . . . . 10 6.5. Opening a Channel . . . . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10 6.6. Transferring User Data on a Channel . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 6.7. Closing a Channel . . . . . . . . . . . . . . . . . . . . 11
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
10.1. Normative References . . . . . . . . . . . . . . . . . . 10 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
10.2. Informative References . . . . . . . . . . . . . . . . . 12 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 10.1. Normative References . . . . . . . . . . . . . . . . . . 12
10.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction 1. Introduction
Non-media data types in the context of RTCWeb are handled by using Non-media data types in the context of RTCWeb are handled by using
SCTP [RFC4960] encapsulated in DTLS [RFC6347]. SCTP [RFC4960] encapsulated in DTLS [RFC6347].
+----------+ +----------+
| SCTP | | SCTP |
+----------+ +----------+
| DTLS | | DTLS |
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The encapsulation of SCTP over DTLS (see The encapsulation of SCTP over DTLS (see
[I-D.ietf-tsvwg-sctp-dtls-encaps]) over ICE/UDP (see [RFC5245]) [I-D.ietf-tsvwg-sctp-dtls-encaps]) over ICE/UDP (see [RFC5245])
provides a NAT traversal solution together with confidentiality, provides a NAT traversal solution together with confidentiality,
source authentication, and integrity protected transfers. This data source authentication, and integrity protected transfers. This data
transport service operates in parallel to the media transports, and transport service operates in parallel to the media transports, and
all of them can eventually share a single transport-layer port all of them can eventually share a single transport-layer port
number. number.
SCTP as specified in [RFC4960] with the partial reliability extension SCTP as specified in [RFC4960] with the partial reliability extension
defined in [RFC3758] provides multiple streams natively with defined in [RFC3758] provides multiple streams natively with
reliable, and partially-reliable delivery modes. reliable, and partially-reliable delivery modes for user messages.
Using the reconfiguration extension defined in [RFC6525] allows to
increase the number of streams during the lifetime of an SCTP
association and to reset individual SCTP streams.
The remainder of this document is organized as follows: Section 4 and The remainder of this document is organized as follows: Section 3 and
Section 3 provide requirements and use cases for both unreliable and Section 4 provide use cases and requirements for both unreliable and
reliable peer to peer datagram base channel; Section 5 arguments SCTP reliable peer to peer data channels; Section 5 arguments SCTP over
over DTLS over UDP; Section 6 provides an specification of how SCTP DTLS over UDP; Section 6 provides the specification of how SCTP
should be used by the RTCWeb protocol framework for transporting non- should be used by the RTCWeb protocol framework for transporting non-
media data between browsers. media data between WEB-browsers.
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. Use Cases 3. Use Cases
This section defined use cases specific to data channels. For This section defined use cases specific to data channels. For
general use cases see [I-D.ietf-rtcweb-use-cases-and-requirements]. general use cases see [I-D.ietf-rtcweb-use-cases-and-requirements].
3.1. Use Cases for Unreliable Data Channels 3.1. Use Cases for Unreliable Data Channels
U-C 1 A real-time game where position and object state information U-C 1: A real-time game where position and object state information
is sent via one or more unreliable data channels. Note that at is sent via one or more unreliable data channels. Note that at
any time there may be no media channels, or all media channels may any time there may be no media channels, or all media channels may
be inactive, and that there may also be reliable data channels in be inactive, and that there may also be reliable data channels in
use. use.
U-C 2 Providing non-critical information to a user about the reason U-C 2: Providing non-critical information to a user about the reason
for a state update in a video chat or conference, such as Mute for a state update in a video chat or conference, such as mute
state. state.
3.2. Use Cases for Reliable Data Channels 3.2. Use Cases for Reliable Data Channels
U-C 3: A real-time game where critical state information needs to be
U-C 3 A real-time game where critical state information needs to be
transferred, such as control information. Such a game may have no transferred, such as control information. Such a game may have no
media channels, or they may be inactive at any given time, or may media channels, or they may be inactive at any given time, or may
only be added due to in-game actions. only be added due to in-game actions.
U-C 4 Non-realtime file transfers between people chatting. Note U-C 4: Non-realtime file transfers between people chatting. Note
that this may involve a large number of files to transfer that this may involve a large number of files to transfer
sequentially or in parallel, such as when sharing a folder of sequentially or in parallel, such as when sharing a folder of
images or a directory of files. images or a directory of files.
U-C 5 Realtime text chat while talking with an individual or with U-C 5: Realtime text chat during an audio and/or video call with an
multiple people in a conference. individual or with multiple people in a conference.
U-C 6 Renegotiation of the set of media streams in the U-C 6: Renegotiation of the set of media streams in the
PeerConnection. PeerConnection.
U-C 7 Proxy browsing, where a browser uses data channels of a U-C 7: Proxy browsing, where a browser uses data channels of a
PeerConnection to send and receive HTTP/HTTPS requests and data, PeerConnection to send and receive HTTP/HTTPS requests and data,
for example to avoid local internet filtering or monitoring. for example to avoid local internet filtering or monitoring.
4. Requirements 4. Requirements
This section lists the requirements for P2P data channels between two This section lists the requirements for P2P data channels between two
browsers. browsers.
Req. 1 Multiple simultaneous data channels MUST be supported. Note Req. 1: Multiple simultaneous data channels MUST be supported.
that there may 0 or more media streams in parallel with the data Note that there may 0 or more media streams in parallel with the
channels, and the number and state (active/inactive) of the media data channels, and the number and state (active/inactive) of the
streams may change at any time. media streams may change at any time.
Req. 2 Both reliable and unreliable data channels MUST be Req. 2: Both reliable and unreliable data channels MUST be
supported. supported.
Req. 3 Data channels MUST be congestion controlled; either Req. 3: Data channels MUST be congestion controlled; either
individually, as a class, or in conjunction with the media individually, as a class, or in conjunction with the media
streams, to ensure that data channels don't cause congestion streams, to ensure that data channels don't cause congestion
problems for the media streams, and that the RTCWeb PeerConnection problems for the media streams, and that the RTCWeb PeerConnection
as a whole is fair with competing traffic such as TCP. as a whole is fair with competing traffic such as TCP.
Req. 4 The application SHOULD be able to provide guidance as to the Req. 4: The application SHOULD be able to provide guidance as to
relative priority of each data channel relative to each other, and the relative priority of each data channel relative to each other,
relative to the media streams. [ TBD: how this is encoded and and relative to the media streams. [ TBD: how this is encoded and
what the impact of this is. ] This will interact with the what the impact of this is. ] This will interact with the
congestion control algorithms. congestion control algorithms.
Req. 5 Data channels MUST be secured; allowing for confidentiality, Req. 5: Data channels MUST be secured; allowing for
integrity and source authentication. See confidentiality, integrity and source authentication. See
[I-D.ietf-rtcweb-security] and [I-D.ietf-rtcweb-security-arch] for [I-D.ietf-rtcweb-security] and [I-D.ietf-rtcweb-security-arch] for
detailed info. detailed info.
Req. 6 Data channels MUST provide message fragmentation support Req. 6: Data channels MUST provide message fragmentation support
such that IP-layer fragmentation can be avoided no matter how such that IP-layer fragmentation can be avoided no matter how
large a message the Javascript application passes to be sent. It large a message the JavaScript application passes to be sent. It
also MUST ensure that large data channel transfers don't unduely also MUST ensure that large data channel transfers don't unduly
delay traffic on other data channels. delay traffic on other data channels.
Req. 7 The data channel transport protocol MUST NOT encode local IP Req. 7: The data channel transport protocol MUST NOT encode local
addresses inside its protocol fields; doing so reveals potentially IP addresses inside its protocol fields; doing so reveals
private information, and leads to failure if the address is potentially private information, and leads to failure if the
depended upon. address is depended upon.
Req. 8 The data channel transport protocol SHOULD support Req. 8: The data channel transport protocol SHOULD support
unbounded-length "messages" (i.e., a virtual socket stream) at the unbounded-length "messages" (i.e., a virtual socket stream) at the
application layer, for such things as image-file-transfer; application layer, for such things as image-file-transfer;
Implementations might enforce a reasonable message size limit. Implementations might enforce a reasonable message size limit.
Req. 9 The data channel transport protocol SHOULD avoid IP Req. 9: The data channel transport protocol SHOULD avoid IP
fragmentation. It MUST support PMTU discovery and MUST NOT rely fragmentation. It MUST support PMTU (Path MTU) discovery and MUST
on ICMP or ICMPv6 being generated or being passed back, especially NOT rely on ICMP or ICMPv6 being generated or being passed back,
for PMTU discovery. especially for PMTU discovery.
Req. 10 It MUST be possible to implement the protocol stack in the Req. 10: It MUST be possible to implement the protocol stack in the
user application space. user application space.
5. SCTP over DTLS over UDP Considerations 5. SCTP over DTLS over UDP Considerations
The important features of SCTP in the RTCWeb context are: The important features of SCTP in the RTCWeb context are:
o TCP-friendly congestion control. o Usage of a TCP-friendly congestion control.
o The congestion control is modifiable for integration with media o The congestion control is modifiable for integration with media
stream congestion control. stream congestion control.
o Support for multiple channels with different characteristics. o Support of multiple unidirectional streams, each providing its own
notion of ordered message delivery.
o Support for out-of-order delivery. o Support of ordered and out-of-order message delivery.
o Support for large datagrams and PMTU-discovery and fragmentation. o Supporting arbitrary large user message by providing fragmentation
and reassembly.
o Reliable or partial reliability support. o Support of PMTU-discovery.
o Support of multiple streams. o Support of reliable or partially reliable message transport.
SCTP multihoming will not be used in RTCWeb. The SCTP layer will SCTP multihoming will not be used in RTCWeb. The SCTP layer will
simply act as if it were running on a single-homed host, since that simply act as if it were running on a single-homed host, since that
is the abstraction that the lower layer (a connection oriented, is the abstraction that the lower layer (a connection oriented,
unreliable datagram service) exposes. unreliable datagram service) exposes.
The encapsulation of SCTP over DTLS defined in The encapsulation of SCTP over DTLS defined in
[I-D.ietf-tsvwg-sctp-dtls-encaps] provides confidentiality, source [I-D.ietf-tsvwg-sctp-dtls-encaps] provides confidentiality, source
authenticated, and integrity protected transfers. Using DTLS over authenticated, and integrity protected transfers. Using DTLS over
UDP in combination with ICE enables NAT traversal in IPv4 based UDP in combination with ICE enables NAT traversal in IPv4 based
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is specified in [RFC6347], while the usage of SCTP on top of DTLS is is specified in [RFC6347], while the usage of SCTP on top of DTLS is
specified in [I-D.ietf-tsvwg-sctp-dtls-encaps]. specified in [I-D.ietf-tsvwg-sctp-dtls-encaps].
Since DTLS is typically implemented in user-land, the SCTP stack also Since DTLS is typically implemented in user-land, the SCTP stack also
needs to be a user-land stack. needs to be a user-land stack.
When using DTLS as the lower layer, only single homed SCTP When using DTLS as the lower layer, only single homed SCTP
associations MUST be used, since DTLS does not expose any address associations MUST be used, since DTLS does not expose any address
management to its upper layer. The ICE/UDP layer can handle IP management to its upper layer. The ICE/UDP layer can handle IP
address changes during a session without needing to notify the DTLS address changes during a session without needing to notify the DTLS
and SCTP layers, though it would be advantageous to retest path MTU and SCTP layers, though it would be advantageous to retest Path MTU
on an IP address change. on an IP address change.
DTLS implementations used for this stack SHOULD support controlling DTLS implementations used for this stack SHOULD support controlling
fields of the IP layer like the Don't fragment (DF)-bit in case of fields of the IP layer like the Don't Fragment (DF)-bit in case of
IPv4 and the Differentiated Services Code Point (DSCP) field required IPv4 and the Differentiated Services Code Point (DSCP) field required
for supporting [I-D.ietf-rtcweb-qos]. Being able to set the (DF)-bit for supporting [I-D.ietf-rtcweb-qos]. Being able to set the (DF)-bit
in case of IPv4 is required for performing path MTU discovery. The in case of IPv4 is required for performing path MTU discovery. The
DTLS implementation SHOULD also support sending user messages DTLS implementation SHOULD also support sending user messages
exceeding the path MTU. exceeding the Path MTU.
Incoming ICMP or ICMPv6 messages can't be processed by the SCTP Incoming ICMP or ICMPv6 messages can't be processed by the SCTP
layer, since there is no way to identify the corresponding layer, since there is no way to identify the corresponding
association. Therefore SCTP MUST support performing Path MTU association. Therefore SCTP MUST support performing Path MTU
discovery without relying on ICMP or ICMPv6 as specified in [RFC4821] discovery without relying on ICMP or ICMPv6 as specified in [RFC4821]
using probing messages specified in [RFC4820]. The initial Path MTU using probing messages specified in [RFC4820]. The initial Path MTU
MUST NOT exceed 1280 [ *** need justification ***] bytes until at the IP layer MUST NOT exceed 1200 bytes for IPv4 and 1280 for
measured otherwise. IPv6. Taking an overhead of 20 bytes for IPv4, 40 bytes for IPv6, 8
bytes for UDP, 13 + X for DTLS and 28 bytes for SCTP into account,
this results in an SCTP payload of 1131 - X when IPv4 is used and
1192 - X bytes when IPv6 is used.
In general, the lower layer interface of an SCTP implementation In general, the lower layer interface of an SCTP implementation
SHOULD be adapted to address the differences between IPv4 or IPv6 SHOULD be adapted to address the differences between IPv4 and IPv6
(being connection-less) or DTLS (being connection-oriented). (being connection-less) or DTLS (being connection-oriented).
When protocol stack of Figure 2 is used, DTLS protects the complete When protocol stack of Figure 2 is used, DTLS protects the complete
SCTP packet, so it provides confidentiality, integrity and source SCTP packet, so it provides confidentiality, integrity and source
authentication of the complete SCTP packet. authentication of the complete SCTP packet.
This protocol stack MUST support the usage of multiple SCTP streams. This protocol stack MUST support the usage of multiple SCTP streams.
A user message can be sent ordered or unordered and with partial or A user message can be sent ordered or unordered and with partial or
full reliability. The partial reliability extension MUST support full reliability. The partial reliability extension MUST support
policies to limit policies to limit
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o the number of retransmissions. o the number of retransmissions.
Limiting the number of retransmissions to zero combined with Limiting the number of retransmissions to zero combined with
unordered delivery provides a UDP-like service where each user unordered delivery provides a UDP-like service where each user
message is sent exactly once and delivered in the order received. message is sent exactly once and delivered in the order received.
SCTP provides congestion control on a per-association base. This SCTP provides congestion control on a per-association base. This
means that all SCTP streams within a single SCTP association share means that all SCTP streams within a single SCTP association share
the same congestion window. Traffic not being sent over SCTP is not the same congestion window. Traffic not being sent over SCTP is not
covered by the SCTP congestion control. Due to the typical parallel covered by the SCTP congestion control. Using a congestion control
SRTP media streams, a delay-sensitive congestion control algorithm different from the standard one might improve the impact on the
MUST be supported and the congestion control MAY be coordinated parallel SRTP media streams. Since SCTP does not support the
between the data channels and the media streams to avoid a data negotiation of a congestion control algorithm, alternate congestion
channel transfer ending up with most or all the channel bandwidth. controls SHOULD only require a different sender side behavior using
Since SCTP does not support the negotiation of a congestion control
algorithm, the algorithm either MUST be negotiated before
establishment of the SCTP association or MUST NOT require any
negotiation because it only requires sender side behavior using
existing information carried in the association. existing information carried in the association.
6. The Usage of SCTP in the RTCWeb Context 6. The Usage of SCTP in the RTCWeb Context
6.1. SCTP Protocol Considerations 6.1. SCTP Protocol Considerations
The DTLS encapsulation of SCTP packets as described in The DTLS encapsulation of SCTP packets as described in
[I-D.ietf-tsvwg-sctp-dtls-encaps] MUST be used. The following SCTP [I-D.ietf-tsvwg-sctp-dtls-encaps] MUST be used.
protocol extensions are required:
The following SCTP protocol extensions are required:
o The stream reset extension defined in [RFC6525] MUST be supported. o The stream reset extension defined in [RFC6525] MUST be supported.
It is used for closing channels. It is used for closing channels.
o The dynamic address reconfiguration extension defined in [RFC5061] o The dynamic address reconfiguration extension defined in [RFC5061]
MUST be used to signal the support of the stream reset extension MUST be used to signal the support of the stream reset extension
defined in [RFC6525], other features of [RFC5061] MUST NOT be defined in [RFC6525], other features of [RFC5061] MUST NOT be
used. used.
o The partial reliability extension defined in [RFC3758] MUST be o The partial reliability extension defined in [RFC3758] MUST be
supported. In addition to the timed reliability PR-SCTP policy supported. In addition to the timed reliability PR-SCTP policy
defined in [RFC3758], the limited retransmission policy defined in defined in [RFC3758], the limited retransmission policy defined in
[I-D.tuexen-tsvwg-sctp-prpolicies] MUST be supported. [I-D.tuexen-tsvwg-sctp-prpolicies] MUST be supported.
o The message interleaving extension defined in Once support for message interleaving as currently being discussed in
[I-D.stewart-tsvwg-sctp-ndata] MUST be supported. [I-D.stewart-tsvwg-sctp-ndata] is available, it SHOULD be supported.
6.2. Association Setup 6.2. Association Setup
The SCTP association will be set up when the two endpoints of the The SCTP association will be set up when the two endpoints of the
WebRTC PeerConnection agree on opening it, as negotiated by JSEP WebRTC PeerConnection agree on opening it, as negotiated by JSEP
(typically an exchange of SDP) [I-D.ietf-rtcweb-jsep]. Additionally, (typically an exchange of SDP) [I-D.ietf-rtcweb-jsep]. Additionally,
the negotiation SHOULD include some type of congestion control the negotiation SHOULD include some type of congestion control
selection. It will use the DTLS connection selected via SDP; selection. It will use the DTLS connection selected via SDP;
typically this will be shared via BUNDLE or equivalent with DTLS typically this will be shared via BUNDLE or equivalent with DTLS
connections used to key the DTLS-SRTP media streams. connections used to key the DTLS-SRTP media streams.
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The application SHOULD indicate the initial number of streams The application SHOULD indicate the initial number of streams
required when opening the association, and if no value is supplied, required when opening the association, and if no value is supplied,
the implementation SHOULD provide an appropriate default. If more the implementation SHOULD provide an appropriate default. If more
simultaneous streams are needed, [RFC6525] allows adding additional simultaneous streams are needed, [RFC6525] allows adding additional
(but not removing) streams to an existing association. Note there (but not removing) streams to an existing association. Note there
can be up to 65536 SCTP streams per SCTP association in each can be up to 65536 SCTP streams per SCTP association in each
direction. direction.
6.3. SCTP Streams 6.3. SCTP Streams
SCTP defines a stream as an unidirectional logical channel existing SCTP defines a stream as a unidirectional logical channel existing
within an SCTP association one to another SCTP endpoint. The streams within an SCTP association one to another SCTP endpoint. The streams
are used to provide the notion of in-sequence delivery and for are used to provide the notion of in-sequence delivery and for
multiplexing. Each user message is sent on a particular stream, multiplexing. Each user message is sent on a particular stream,
either order or unordered. Ordering is preserved only for ordered either order or unordered. Ordering is preserved only for ordered
messages sent on the same stream. messages sent on the same stream.
6.4. Channel Definition 6.4. Channel Definition
The W3C has consensus on defining the application API for WebRTC The W3C has consensus on defining the application API for WebRTC
dataChannels to be bidirectional. They also consider the notions of DataChannels to be bidirectional. They also consider the notions of
in-sequence, out-of-sequence, reliable and un-reliable as properties in-sequence, out-of-sequence, reliable and unreliable as properties
of Channels. One strong wish is for the application-level API to be of Channels. One strong wish is for the application-level API to be
close to the API for WebSockets, which implies bidirectional streams close to the API for WebSockets, which implies bidirectional streams
of data and waiting for onopen to fire before sending, a textual of data and waiting for onopen to fire before sending, a textual
label used to identify the meaning of the stream, among other things. label used to identify the meaning of the stream, among other things.
Each data channel also has a priority. These priorities MUST NOT be
strict priorities.
The realization of a bidirectional Data Channel is a pair of one The realization of a bidirectional Data Channel is a pair of one
incoming stream and one outgoing SCTP stream. incoming stream and one outgoing SCTP stream.
The simple protocol specified in [I-D.jesup-rtcweb-data-protocol]
MUST be used to set up and manage the bidirectional data channels.
Note that there's no requirement for the SCTP streams used to create Note that there's no requirement for the SCTP streams used to create
a bidirectional channel have the same number in each direction. How a bidirectional channel have the same number in each direction. How
stream values are selected is protocol and implementation dependent. stream values are selected is protocol and implementation dependent.
6.5. Opening a Channel
Data channels can be opened by using internal or external
negotiation. The details are out of scope of this document.
A simple protocol for internal negotiation is specified in
[I-D.ietf-rtcweb-data-protocol] and MUST be supported.
When one side wants to open a channel using external negotiation, it
picks a Stream. This can be based on the DTLS role (the client picks
even stream identifiers, the server odd stream identifiers) or done
in a different way. However, the application is responsible for
avoiding collisions with existing Streams. If it attempts to re-use
a Stream which is part of an existing Channel, the addition SHOULD
fail. In addition to choosing a Stream, the application SHOULD also
inform the protocol of the options to use for sending messages. The
application MUST ensure in an application-specific manner that the
other side will also inform the protocol that the selected Stream is
to be used, and the parameters for sending data from that side.
6.6. Transferring User Data on a Channel
All data sent on a Channel in both directions MUST be sent over the
underlying Stream using the reliability defined when the Channel was
opened unless the options are changed, or per-message options are
specified by a higher level.
No more than one message should be put into an SCTP user message.
The SCTP Payload Protocol Identifiers (PPIDs) are used to signal the
interpretation of the "Payload data". For identifying a JavaScript
string the PPID "DOMString Last" MUST be used, for JavaScript binary
data (ArrayBuffer or Blob) the PPID "Binary Data Last" MUST be used
(see Section 8).
The SCTP base protocol specified in [RFC4960] does not support the
interleaving of user messages. Therefore sending a large user
message can monopolize the SCTP association. To overcome this
limitation, [I-D.stewart-tsvwg-sctp-ndata] defines an extension to
support message interleaving. Once such an extension is available,
it SHOULD be used.
As long as message interleaving is not supported, the sending
application SHOULD fragment large user messages for reliable and
ordered data channels. For sending large JavaScript strings, it uses
the PPID "DOMString Partial" for all but the last fragments and the
PPID "DOMString Last" for the last one. For JavaScript binary data
the PPIDs "Binary Data Partial" and "Binary Data Last" are used. The
reassembly based on the PPID MUST be supported. For data channel
which are not reliable and ordered, the sender MAY limit the maximum
message size to avoid monopolization.
It is recommended that message size be kept within certain size
bounds (TBD) as applications will not be able to support arbitrarily-
large single messages.
The sender MAY disable the Nagle algorithm to minimize the latency.
6.7. Closing a Channel
Closing of a Data Channel MUST be signaled by resetting the Closing of a Data Channel MUST be signaled by resetting the
corresponding streams [RFC6525]. Resetting a stream set the Stream corresponding outgoing streams [RFC6525]. Resetting a stream set the
Sequence Numbers (SSNs) of the stream back to 'zero' with a Stream Sequence Numbers (SSNs) of the stream back to 'zero' with a
corresponding notification to the application layer that the reset corresponding notification to the application layer that the reset
has been performed. Streams are available to reuse after a reset has has been performed. Streams are available to reuse after a reset has
been performed. been performed.
[RFC6525] also guarantees that all the messages are delivered (or [RFC6525] also guarantees that all the messages are delivered (or
expired) before resetting the stream. abandoned) before resetting the stream.
6.5. Usage of Payload Protocol Identifier
The SCTP Payload Protocol Identifiers (PPIDs) can be used to signal
the interpretation of the "Payload data", like the protocol specified
in [I-D.jesup-rtcweb-data-protocol] uses them to identify a
Javascript string, a Javascript binary data (ArrayBuffer or Blob) and
to provide fragmentation support for large messages that may cause
the message to monopolize the SCTP association.
7. Security Considerations 7. Security Considerations
This document does not add any additional considerations to the ones This document does not add any additional considerations to the ones
given in [I-D.ietf-rtcweb-security] and given in [I-D.ietf-rtcweb-security] and
[I-D.ietf-rtcweb-security-arch]. [I-D.ietf-rtcweb-security-arch].
8. IANA Considerations 8. IANA Considerations
This document does not require any actions by the IANA. [NOTE to RFC-Editor:
"RFCXXXX" is to be replaced by the RFC number you assign this
document.
]
This document uses four already registered SCTP Payload Protocol
Identifiers (PPIDs). [RFC4960] creates the registry "SCTP Payload
Protocol Identifiers" from which these identifiers were assigned.
IANA is requested to update the reference of these four assignments
to point to this document. Therefore these four assignments should
be updated to read:
+---------------------+-----------+-----------+
| Value | SCTP PPID | Reference |
+---------------------+-----------+-----------+
| DOMString Last | 51 | [RFCXXXX] |
| Binary Data Partial | 52 | [RFCXXXX] |
| Binary Data Last | 53 | [RFCXXXX] |
| DOMString Partial | 54 | [RFCXXXX] |
+---------------------+-----------+-----------+
9. Acknowledgments 9. Acknowledgments
Many thanks for comments, ideas, and text from Harald Alvestrand, Many thanks for comments, ideas, and text from Harald Alvestrand,
Adam Bergkvist, Cullen Jennings, Eric Rescorla, Randall Stewart, Adam Bergkvist, Cullen Jennings, Eric Rescorla, Randall Stewart,
Justin Uberti, and Magnus Westerlund. Justin Uberti, and Magnus Westerlund.
10. References 10. References
10.1. Normative References 10.1. Normative References
skipping to change at page 11, line 33 skipping to change at page 13, line 29
2010. 2010.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, January 2012. Security Version 1.2", RFC 6347, January 2012.
[RFC6525] Stewart, R., Tuexen, M., and P. Lei, "Stream Control [RFC6525] Stewart, R., Tuexen, M., and P. Lei, "Stream Control
Transmission Protocol (SCTP) Stream Reconfiguration", RFC Transmission Protocol (SCTP) Stream Reconfiguration", RFC
6525, February 2012. 6525, February 2012.
[I-D.stewart-tsvwg-sctp-ndata] [I-D.stewart-tsvwg-sctp-ndata]
Stewart, R., Tuexen, M., and S. Loreto, "A New Data Chunk Stewart, R., Tuexen, M., Loreto, S., and R. Seggelmann, "A
for Stream Control Transmission Protocol", draft-stewart- New Data Chunk for Stream Control Transmission Protocol",
tsvwg-sctp-ndata-01 (work in progress), February 2013. draft-stewart-tsvwg-sctp-ndata-03 (work in progress),
October 2013.
[I-D.jesup-rtcweb-data-protocol] [I-D.ietf-rtcweb-data-protocol]
Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data Channel Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data Channel
Protocol", draft-jesup-rtcweb-data-protocol-04 (work in Protocol", draft-ietf-rtcweb-data-protocol-00 (work in
progress), February 2013. progress), July 2013.
[I-D.ietf-tsvwg-sctp-dtls-encaps] [I-D.ietf-tsvwg-sctp-dtls-encaps]
Jesup, R., Loreto, S., Stewart, R., and M. Tuexen, "DTLS Tuexen, M., Stewart, R., Jesup, R., and S. Loreto, "DTLS
Encapsulation of SCTP Packets for RTCWEB", draft-ietf- Encapsulation of SCTP Packets", draft-ietf-tsvwg-sctp-
tsvwg-sctp-dtls-encaps-00 (work in progress), February dtls-encaps-02 (work in progress), October 2013.
2013.
[I-D.ietf-rtcweb-security] [I-D.ietf-rtcweb-security]
Rescorla, E., "Security Considerations for RTC-Web", Rescorla, E., "Security Considerations for WebRTC", draft-
draft-ietf-rtcweb-security-04 (work in progress), January ietf-rtcweb-security-05 (work in progress), July 2013.
2013.
[I-D.ietf-rtcweb-security-arch] [I-D.ietf-rtcweb-security-arch]
Rescorla, E., "RTCWEB Security Architecture", draft-ietf- Rescorla, E., "WebRTC Security Architecture", draft-ietf-
rtcweb-security-arch-06 (work in progress), January 2013. rtcweb-security-arch-07 (work in progress), July 2013.
[I-D.ietf-rtcweb-jsep] [I-D.ietf-rtcweb-jsep]
Uberti, J. and C. Jennings, "Javascript Session Uberti, J. and C. Jennings, "Javascript Session
Establishment Protocol", draft-ietf-rtcweb-jsep-03 (work Establishment Protocol", draft-ietf-rtcweb-jsep-04 (work
in progress), February 2013. in progress), September 2013.
[I-D.ietf-rtcweb-qos] [I-D.ietf-rtcweb-qos]
Dhesikan, S., Druta, D., Jones, P., and J. Polk, "DSCP and Dhesikan, S., Druta, D., Jones, P., and J. Polk, "DSCP and
other packet markings for RTCWeb QoS", draft-ietf-rtcweb- other packet markings for RTCWeb QoS", draft-ietf-rtcweb-
qos-00 (work in progress), October 2012. qos-00 (work in progress), October 2012.
10.2. Informative References 10.2. Informative References
[RFC6083] Tuexen, M., Seggelmann, R., and E. Rescorla, "Datagram [RFC6083] Tuexen, M., Seggelmann, R., and E. Rescorla, "Datagram
Transport Layer Security (DTLS) for Stream Control Transport Layer Security (DTLS) for Stream Control
Transmission Protocol (SCTP)", RFC 6083, January 2011. Transmission Protocol (SCTP)", RFC 6083, January 2011.
[RFC6951] Tuexen, M. and R. Stewart, "UDP Encapsulation of Stream [RFC6951] Tuexen, M. and R. Stewart, "UDP Encapsulation of Stream
Control Transmission Protocol (SCTP) Packets for End-Host Control Transmission Protocol (SCTP) Packets for End-Host
to End-Host Communication", RFC 6951, May 2013. to End-Host Communication", RFC 6951, May 2013.
[I-D.ietf-rtcweb-use-cases-and-requirements] [I-D.ietf-rtcweb-use-cases-and-requirements]
Holmberg, C., Hakansson, S., and G. Eriksson, "Web Real- Holmberg, C., Hakansson, S., and G. Eriksson, "Web Real-
Time Communication Use-cases and Requirements", draft- Time Communication Use-cases and Requirements", draft-
ietf-rtcweb-use-cases-and-requirements-11 (work in ietf-rtcweb-use-cases-and-requirements-12 (work in
progress), June 2013. progress), October 2013.
[I-D.tuexen-tsvwg-sctp-prpolicies] [I-D.tuexen-tsvwg-sctp-prpolicies]
Loreto, S., Seggelmann, R., Stewart, R., and M. Tuexen, Tuexen, M., Seggelmann, R., Stewart, R., and S. Loreto,
"Additional Policies for the Partial Delivery Extension of "Additional Policies for the Partial Delivery Extension of
the Stream Control Transmission Protocol", draft-tuexen- the Stream Control Transmission Protocol", draft-tuexen-
tsvwg-sctp-prpolicies-02 (work in progress), July 2013. tsvwg-sctp-prpolicies-03 (work in progress), October 2013.
Authors' Addresses Authors' Addresses
Randell Jesup Randell Jesup
Mozilla Mozilla
US US
Email: randell-ietf@jesup.org Email: randell-ietf@jesup.org
Salvatore Loreto Salvatore Loreto
Ericsson Ericsson
Hirsalantie 11 Hirsalantie 11
Jorvas 02420 Jorvas 02420
FI FI
Email: salvatore.loreto@ericsson.com Email: salvatore.loreto@ericsson.com
Michael Tuexen Michael Tuexen
Muenster University of Applied Sciences Muenster University of Applied Sciences
Stegerwaldstrasse 39 Stegerwaldstrasse 39
Steinfurt 48565 Steinfurt 48565
DE DE
Email: tuexen@fh-muenster.de Email: tuexen@fh-muenster.de
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