draft-ietf-rtcweb-data-channel-01.txt   draft-ietf-rtcweb-data-channel-02.txt 
RTCWeb Working Group R. Jesup Network Working Group R. Jesup
Internet-Draft Mozilla Internet-Draft Mozilla
Intended status: Informational S. Loreto Intended status: Standards Track S. Loreto
Expires: March 11, 2013 Ericsson Expires: April 26, 2013 Ericsson
M. Tuexen M. Tuexen
Muenster Univ. of Appl. Sciences Muenster Univ. of Appl. Sciences
September 7, 2012 October 23, 2012
RTCWeb Datagram Connection RTCWeb Datagram Connection
draft-ietf-rtcweb-data-channel-01.txt draft-ietf-rtcweb-data-channel-02.txt
Abstract Abstract
The Web Real-Time Communication (WebRTC) working group is charged to The Web Real-Time Communication (WebRTC) working group is charged to
provide protocol support for direct interactive rich communication provide protocol support for direct interactive rich communication
using audio, video, and data between two peers' web-browsers. This using audio, video, and data between two peers' web-browsers. This
document describes the non-media data transport aspects of the WebRTC document describes the non-media data transport aspects of the WebRTC
framework. It provides an architectural overview of how the Stream framework. It provides an architectural overview of how the Stream
Control Transmission Protocol (SCTP) is used in the WebRTC context as Control Transmission Protocol (SCTP) is used in the WebRTC context as
a generic transport service allowing Web Browser to exchange generic a generic transport service allowing Web Browser to exchange generic
skipping to change at page 1, line 40 skipping to change at page 1, line 40
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 March 11, 2013. This Internet-Draft will expire on April 26, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 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
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Use Cases for Unreliable Datagram Based Channels . . . . . 5 4. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Use Cases for Reliable Channels (Datagram or Stream 4.1. Use Cases for Unreliable Datagram Based Channels . . . . . 5
4.2. Use Cases for Reliable Channels (Datagram or Stream
Based) . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Based) . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Datagrams over SCTP over DTLS over UDP . . . . . . . . . . . . 6 5. SCTP over DTLS over UDP Considerations . . . . . . . . . . . . 6
5. The Envisioned Usage of SCTP in the RTCWeb Context . . . . . . 8 6. The Usage of SCTP in the RTCWeb Context . . . . . . . . . . . 8
5.1. Association Setup . . . . . . . . . . . . . . . . . . . . 8 6.1. Association Setup . . . . . . . . . . . . . . . . . . . . 9
5.2. SCTP Streams . . . . . . . . . . . . . . . . . . . . . . . 9 6.2. SCTP Streams . . . . . . . . . . . . . . . . . . . . . . . 9
5.3. Channel Definition . . . . . . . . . . . . . . . . . . . . 9 6.3. Channel Definition . . . . . . . . . . . . . . . . . . . . 9
5.4. Usage of Payload Protocol Identifier . . . . . . . . . . . 9 6.4. Usage of Payload Protocol Identifier . . . . . . . . . . . 10
6. Minor Protocol and Message Format . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10 7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
10. Informative References . . . . . . . . . . . . . . . . . . . . 10 10. Informative References . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction 1. Introduction
The issue of how best to handle non-media data types in the context Non-media data types in the context of RTCWEB are handled by using
of RTCWEB has reached a general consensus on the usage of SCTP SCTP [RFC4960] encapsulated in DTLS [RFC6347].
[RFC4960] encapsulated on DTLS [RFC6347]:
+----------+ +----------+
| SCTP | | SCTP |
+----------+ +----------+
| DTLS | | DTLS |
+----------+ +----------+
| ICE/UDP | | ICE/UDP |
+----------+ +----------+
Figure 1: Basic stack diagram Figure 1: Basic stack diagram
The encapsulation of SCTP over DTLS over ICE/UDP provides a NAT The encapsulation of SCTP over DTLS over ICE/UDP provides a NAT
traversal solution together with confidentiality, source traversal solution together with confidentiality, source
authenticated, integrity protected transfers. This data transport authenticated, integrity protected transfers. This data transport
service operates in parallel to the media transports, and all of them service operates in parallel to the media transports, and all of them
can eventually share a single transport-layer port number. can eventually share a single transport-layer port number.
SCTP provides multiple streams natively with reliable, unreliable and SCTP as specified in [RFC4960] with the extension defined in
[RFC3758] provides multiple streams natively with reliable, and
partially-reliable delivery modes. partially-reliable delivery modes.
The remainder of this document is organized as follows: Section 2 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 requirements and use cases for both unreliable and
reliable peer to peer datagram base channel; Section 4 arguments SCTP reliable peer to peer datagram base channel; Section 5 arguments SCTP
over DTLS over UDP; Section 5 provides an overview of how SCTP should over DTLS over UDP; Section 6 provides an overview of how SCTP should
be used by the RTCWeb protocol framework for transporting non-media be used by the RTCWeb protocol framework for transporting non-media
data between browsers. data between browsers.
2. Requirements 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. Requirements
This section lists the requirements for P2P data connections between This section lists the requirements for P2P data connections between
two browsers. two browsers.
Req. 1 Multiple simultaneous datagram streams must be supported. Req. 1 Multiple simultaneous datagram streams MUST be supported.
Note that there may 0 or more media streams in parallel with Note that there may 0 or more media streams in parallel with
the data streams, and the number and state (active/inactive) the data streams, and the number and state (active/inactive)
of the media streams may change at any time. of the media streams may change at any time.
Req. 2 Both reliable and unreliable datagram streams must be Req. 2 Both reliable and unreliable datagram streams MUST be
supported. supported.
Req. 3 Data streams must be congestion controlled; either Req. 3 Data streams 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 datagram exchanges don't cause streams, to ensure that datagram exchanges don't cause
congestion problems for the media streams, and that the congestion problems for the media streams, and that the
rtcweb PeerConnection as a whole is fair with competing rtcweb PeerConnection as a whole is fair with competing
streams such as TCP. streams 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 the
relative priority of each datagram stream relative to each relative priority of each datagram stream relative to each
other, and relative to the media streams. [ TBD: how this is other, and relative to the media streams. [ TBD: how this is
encoded and what the impact of this is. ] This will interact encoded and what the impact of this is. ] This will interact
with the congestion control algorithms. with the congestion control algorithms.
Req. 5 Datagram streams must be encrypted; allowing for Req. 5 Datagram streams MUST be encrypted; allowing for
confidentiality, integrity and source authentication. See confidentiality, integrity and source authentication. See
[I-D.ietf-rtcweb-security] and [I-D.ietf-rtcweb-security] and
[I-D.ietf-rtcweb-security-arch] for detailed info. [I-D.ietf-rtcweb-security-arch] for detailed info.
Req. 6 Consent and NAT traversal mechanism: These are handled by Req. 6 Consent and NAT traversal mechanism: These are handled by
the PeerConnection's ICE [RFC5245] connectivity checks and the PeerConnection's ICE [RFC5245] connectivity checks and
optional TURN servers. optional TURN servers.
Req. 7 Data streams must provide message fragmentation support such Req. 7 Data streams MUST provide message fragmentation support such
that IP-layer fragmentation does not occur no matter how that IP-layer fragmentation does not occur no matter how
large a message the Javascript application passes to be large a message the Javascript application passes to be
sent. sent.
Req. 8 The data stream transport protocol must not encode local IP Req. 8 The data stream transport protocol MUST not encode local IP
addresses inside its protocol fields; doing so reveals addresses inside its protocol fields; doing so reveals
potentially private information, and leads to failure if the potentially private information, and leads to failure if the
address is depended upon. address is depended upon.
Req. 9 The data stream protocol should support unbounded-length Req. 9 The data stream protocol SHOULD support unbounded-length
"messages" (i.e., a virtual socket stream) at the "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;
or else it must support at least a maximum application-layer or it MUST support a maximum application-layer message size
message size of 2GB. of at least 2GB.
Req. 10 The data stream packet format/encoding must be such that it Req. 10 The data stream packet format/encoding MUST be such that it
is impossible for a malicious Javascript to generate an is impossible for a malicious Javascript to generate an
application message crafted such that it could be application message crafted such that it could be
interpreted as a native protocol over UDP - such as UPnP, interpreted as a native protocol over UDP - such as UPnP,
RTP, SNMP, STUN, etc. RTP, SNMP, STUN, etc.
Req. 11 The data stream transport protocol must start with the Req. 11 The data stream transport protocol MUST start with the
assumption of a PMTU of 1280 [ *** need justification ***] assumption of a PMTU of 1280 [ *** need justification ***]
bytes until measured otherwise. bytes until measured otherwise.
Req. 12 The data stream transport protocol must not rely on ICMP or Req. 12 The data stream transport protocol MUST NOT rely on ICMP or
ICMPv6 being generated or being passed back, such as for ICMPv6 being generated or being passed back, such as for
PMTU discovery. PMTU discovery.
Req. 13 It must be possible to implement the protocol stack in the Req. 13 It MUST be possible to implement the protocol stack in the
user application space. user application space.
3. Use Cases 4. Use Cases
3.1. Use Cases for Unreliable Datagram Based Channels 4.1. Use Cases for Unreliable Datagram Based 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 is sent via one or more unreliable data channels. Note that
at any time there may be no media channels, or all media at any time there may be no media channels, or all media
channels may be inactive, and that there may also be reliable channels may be inactive, and that there may also be reliable
data channels in use. data channels in use.
U-C 2 Non-critical state updates about a user in a video chat or U-C 2 Non-critical state updates about a user in a video chat or
conference, such as Mute state. conference, such as Mute state.
3.2. Use Cases for Reliable Channels (Datagram or Stream Based) 4.2. Use Cases for Reliable Channels (Datagram or Stream Based)
Note that either reliable datagrams or streams are possible; reliable Note that either reliable datagrams or streams are possible; reliable
streams would be fairly simple to layer on top of SCTP reliable streams would be fairly simple to layer on top of SCTP reliable
datagrams with in-order delivery. datagrams with in-order delivery.
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. Typically this transferred, such as control information. Typically this
would be datagrams. Such a game may have no media channels, would be datagrams. Such a game may have no media channels,
or they may be inactive at any given time, or may only be or they may be inactive at any given time, or may only be
added due to in-game actions. added due to in-game actions.
skipping to change at page 6, line 10 skipping to change at page 6, line 17
datagrams. datagrams.
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. Typically this would be datagrams. PeerConnection. Typically this would be datagrams.
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 PeerConnection to send and receive HTTP/HTTPS requests and
data, for example to avoid local internet filtering or data, for example to avoid local internet filtering or
monitoring. Typically this would be streams. monitoring. Typically this would be streams.
4. Datagrams over SCTP over DTLS over UDP 5. SCTP over DTLS over UDP Considerations
The encapsulation of SCTP over DTLS as defined in The encapsulation of SCTP over DTLS as defined in
[I-D.tuexen-tsvwg-sctp-dtls-encaps] provides a NAT traversal solution [I-D.tuexen-tsvwg-sctp-dtls-encaps] provides a NAT traversal solution
together with confidentiality, source authenticated, integrity together with confidentiality, source authenticated, integrity
protected transfers. SCTP provides also natively several interesting protected transfers. SCTP as specified in [RFC4960] MUST be used in
features for transporting non-media data between browsers: combination with the extension defined in [RFC3758] and provides the
following interesting features for transporting non-media data
between browsers:
o Support of multiple streams. o Support of multiple streams.
o Ordered and unordered delivery of user messages. o Ordered and unordered delivery of user messages.
o Reliable and partial-reliable transport of user messages. o Reliable and partial-reliable transport of user messages.
Each SCTP user message contains a so called Payload Protocol Each SCTP user message contains a so called Payload Protocol
Identifier (PPID) that is passed to SCTP by its upper layer and sent Identifier (PPID) that is passed to SCTP by its upper layer and sent
to its peer. This value represents an application (or upper layer) to its peer. This value represents an application (or upper layer)
specified protocol identifier and be used to transport multiple specified protocol identifier and be used to transport multiple
protocols over a single SCTP association. The sender provides for protocols over a single SCTP association. The sender provides for
each protocol a specific PPID and the receiver demultiplexes the each protocol a specific PPID and the receiver MAY demultiplex the
messages based on the received PPID. messages based on the received PPID.
The encapsulation of SCTP over DTLS, together with the SCTP features The encapsulation of SCTP over DTLS, together with the SCTP features
listed above satisfies all the requirements listed in in Section 2. listed above satisfies all the requirements listed in Section 3.
The layering of protocols for WebRTC is shown in the following The layering of protocols for WebRTC is shown in the following
Figure 2. Figure 2.
+------+ +------+
|RTCWEB| |RTCWEB|
| DATA | | DATA |
+------+ +------+
| SCTP | | SCTP |
+--------------------+ +--------------------+
| STUN | SRTP | DTLS | | STUN | SRTP | DTLS |
+--------------------+ +--------------------+
| ICE | | ICE |
+--------------------+ +--------------------+
| UDP1 | UDP2 | ... | | UDP1 | UDP2 | ... |
+--------------------+ +--------------------+
Figure 2: WebRTC protocol layers Figure 2: WebRTC protocol layers
This stack (especially in contrast to DTLS over SCTP [RFC6083]) has This stack (especially in contrast to DTLS over SCTP [RFC6083]) has
been chosen because it been chosen because it
o supports the transmission of arbitrary large user messages. o supports the transmission of arbitrary large user messages.
o shares the DTLS connection with the media channels. o shares the DTLS connection with the media channels.
o provides privacy for the SCTP control information. o provides privacy for the SCTP control information.
Considering the protocol stack of Figure 2 the usage of DTLS over UDP Considering the protocol stack of Figure 2 the usage of DTLS over UDP
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.tuexen-tsvwg-sctp-dtls-encaps]. specified in [I-D.tuexen-tsvwg-sctp-dtls-encaps].
Since DTLS is typically implemented in user-land, an SCTP user-land Since DTLS is typically implemented in user-land, the SCTP stack also
implementation must also be used. 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 can be used, since DTLS does not expose any address associations SHOULD 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 must 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. This IPv4 and the Differentiated Services Code Point (DSCP) field required
is required for performing path MTU discovery. The DTLS for supporting [I-D.ietf-rtcweb-qos]. Being able to set the (DF)-bit
implementation must also support sending user messages exceeding the in case of IPv4 is required for performing path MTU discovery. The
path MTU. DTLS implementation SHOULD also support sending user messages
exceeding the path MTU.
When supporting multiple SCTP associations over a single DTLS Incoming ICMP or ICMPv6 messages can't be processed by the SCTP
connection, incoming ICMP or ICMPv6 messages can't be processed by layer, since there is no way to identify the corresponding
the SCTP layer, since there is no way to identify the corresponding association. Therefore SCTP MUST support performing Path MTU
association. Therefore the number of SCTP associations should be discovery without relying on ICMP or ICMPv6. In general, the lower
limited to one or ICMP and ICMPv6 messages should be ignored. In layer interface of an SCTP implementation SHOULD be adapted to
general, the lower layer interface of an SCTP implementation has to address the differences between IPv4 or IPv6 (being connection-less)
be adapted to address the differences between IPv4 or IPv6 (being or DTLS (being connection-oriented).
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 supports the usage of multiple SCTP streams. A This protocol stack MUST support the usage of multiple SCTP streams.
user message can be sent ordered or unordered and, if the SCTP A user message can be sent ordered or unordered and with partial or
implementations support [RFC3758], with partial reliability. When full reliability. The partial reliability extension MUST support
using partial reliability, it might make sense to use a policy policies to limit
limiting the number of retransmissions by time or number. Limiting
the number of retransmissions to zero provides a UDP-like service o the transmission and retransmission by time.
where each user message is sent exactly once.
o the number of retransmissions.
Limiting the number of retransmissions to zero combined with
unordered delivery provides a UDP-like service where each user
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. Due to the typical parallel
SRTP media streams, it will be advantageous to select a delay- SRTP media streams, a delay-sensitive congestion control algorithm
sensitive congestion control algorithm or to at least coordinate MUST be supported and the congestion control MAY be coordinated
congestion control between the data channels and the media streams to between the data channels and the media streams to avoid a data
avoid a data channel transfer ending up with most or all the channel channel transfer ending up with most or all the channel bandwidth.
bandwidth. Since SCTP does not have an internal negotiaton mechanism
for selecting a congestion control algorithm, the algorithm should be
negotiated before establishment of the SCTP associaton.
5. The Envisioned Usage of SCTP in the RTCWeb Context 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.
The appealing features of SCTP in the RTCWeb context are: 6. The Usage of SCTP in the RTCWeb Context
The important features of SCTP in the RTCWeb context are:
o TCP-friendly congestion control. o 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 for multiple channels with different characteristics.
o Support for out-of-order delivery. o Support for out-of-order delivery.
o Support for large datagrams and PMTU-discovery and fragmentation. o Support for large datagrams and PMTU-discovery and fragmentation.
o Reliable or partial reliability support. o Reliable or partial reliability support.
o Support of multiple streams. o Support of multiple streams.
Multihoming will not be used in this scenario. The SCTP layer would 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) would expose. unreliable datagram service) exposes.
5.1. Association Setup 6.1. Association Setup
The SCTP association would 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 would use the DTLS connection created at the start of selection. It will use the DTLS connection selected via SDP;
the PeerConnection connection. typically this will be shared via BUNDLE with DTLS connections used
to key the DTLS-SRTP media streams.
The application should indicate the number of simultaneous 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 a default, with a suggested value the implementation SHOULD provide a default, with a suggested value
of 16. If more simultaneous streams are needed, [RFC6525] allows of 16. If more simultaneous streams are needed, [RFC6525] allows
adding additional (but not removing) streams to an existing adding additional (but not removing) streams to an existing
association. There can be up to 65535 SCTP streams per SCTP association. Note there can be up to 65536 SCTP streams per SCTP
association in each direction. association in each direction.
5.2. SCTP Streams 6.2. SCTP Streams
SCTP defines a stream as an unidirectional logical channel existing SCTP defines a stream as an 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. Each user are used to provide the notion of in-sequence delivery and for
message is sent on a particular stream, either order or unordered. multiplexing. Each user message is sent on a particular stream,
Ordering is preserved only for all ordered messages sent on the same either order or unordered. Ordering is preserved only for all
stream. ordered messages sent on the same stream.
5.3. Channel Definition 6.3. 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 un-reliable 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.
A possible realization of a bidirectional Data Channel is a pair of The realization of a bidirectional Data Channel is a pair of one
one incoming stream and one outcoming 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 and used to provide this functionality is stream values are selected is protocol and implementation dependent.
up to the protocol.
Closing of a Data Channel can be signalled resetting the Closing of a Data Channel MUST be signalled by resetting the
corresponding streams [RFC6525]. Resetting a stream set the Stream corresponding streams [RFC6525]. Resetting a stream set the Stream
Sequence Numbers (SSNs) of the stream back to 'zero' with a 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. Closed streams are available to reuse. has been performed. Closed streams are available to reuse.
[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. expired) before resetting the stream.
5.4. Usage of Payload Protocol Identifier 6.4. Usage of Payload Protocol Identifier
The SCTP Payload Protocol Identifiers (PPIDs) can be used to signal
the interpretation of the "Payload data", like a string, ASCII or
binary data.
RFC 4960 [RFC4960] creates the registry from which these identifiers
have been assigned. Eventual PPIDs defined within the RTCWeb Context
have to be registered with IANA.
6. Minor Protocol and Message Format
A separate draft (draft-jesup-rtcweb-data-protocol) proposes the
minor protocol to set up and manage the bidirectional data channels
needed to satisify the requirements in this document for WebRTC.
Masking of the protocol is not needed if the lower layer always The SCTP Payload Protocol Identifiers (PPIDs) MUST used to signal the
encrypts with DTLS. 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 array or a a Javascript blob.
7. Security Considerations 7. Security Considerations
To be done. To be done.
8. IANA Considerations 8. IANA Considerations
This document does not require any actions by the IANA. This document does not require any actions by the IANA.
9. Acknowledgments 9. Acknowledgments
Many thanks for comments, ideas, and text from Cullen Jennings, Eric Many thanks for comments, ideas, and text from Harald Alvestrand,
Rescorla, Randall Stewart, Justin Uberti, Adam Bergkvist and Harald Adam Bergkvist, Cullen Jennings, Eric Rescorla, Randall Stewart, and
Alvestrand. Justin Uberti.
10. Informative References 10. Informative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3758] Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P. [RFC3758] Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P.
Conrad, "Stream Control Transmission Protocol (SCTP) Conrad, "Stream Control Transmission Protocol (SCTP)
Partial Reliability Extension", RFC 3758, May 2004. Partial Reliability Extension", RFC 3758, May 2004.
[RFC4960] Stewart, R., "Stream Control Transmission Protocol", [RFC4960] Stewart, R., "Stream Control Transmission Protocol",
RFC 4960, September 2007. RFC 4960, September 2007.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT) (ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245, Traversal for Offer/Answer Protocols", RFC 5245,
skipping to change at page 11, line 23 skipping to change at page 11, line 40
Transmission Protocol (SCTP) Stream Reconfiguration", Transmission Protocol (SCTP) Stream Reconfiguration",
RFC 6525, February 2012. RFC 6525, February 2012.
[I-D.ietf-rtcweb-security] [I-D.ietf-rtcweb-security]
Rescorla, E., "Security Considerations for RTC-Web", Rescorla, E., "Security Considerations for RTC-Web",
draft-ietf-rtcweb-security-03 (work in progress), draft-ietf-rtcweb-security-03 (work in progress),
June 2012. June 2012.
[I-D.ietf-rtcweb-security-arch] [I-D.ietf-rtcweb-security-arch]
Rescorla, E., "RTCWEB Security Architecture", Rescorla, E., "RTCWEB Security Architecture",
draft-ietf-rtcweb-security-arch-03 (work in progress), draft-ietf-rtcweb-security-arch-05 (work in progress),
July 2012. October 2012.
[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-01 (work Establishment Protocol", draft-ietf-rtcweb-jsep-01 (work
in progress), June 2012. in progress), June 2012.
[I-D.ietf-rtcweb-qos]
Dhesikan, S., Druta, D., Jones, P., and J. Polk, "DSCP and
other packet markings for RTCWeb QoS",
draft-ietf-rtcweb-qos-00 (work in progress), October 2012.
[I-D.ietf-tsvwg-sctp-udp-encaps] [I-D.ietf-tsvwg-sctp-udp-encaps]
Tuexen, M. and R. Stewart, "UDP Encapsulation of SCTP Tuexen, M. and R. Stewart, "UDP Encapsulation of SCTP
Packets", draft-ietf-tsvwg-sctp-udp-encaps-04 (work in Packets", draft-ietf-tsvwg-sctp-udp-encaps-06 (work in
progress), July 2012. progress), October 2012.
[I-D.jesup-rtcweb-data-protocol]
Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data Channel
Protocol", draft-jesup-rtcweb-data-protocol-03 (work in
progress), September 2012.
[I-D.tuexen-tsvwg-sctp-dtls-encaps] [I-D.tuexen-tsvwg-sctp-dtls-encaps]
Jesup, R., Loreto, S., Stewart, R., and M. Tuexen, "DTLS Jesup, R., Loreto, S., Stewart, R., and M. Tuexen, "DTLS
Encapsulation of SCTP Packets for RTCWEB", Encapsulation of SCTP Packets for RTCWEB",
draft-tuexen-tsvwg-sctp-dtls-encaps-01 (work in progress), draft-tuexen-tsvwg-sctp-dtls-encaps-01 (work in progress),
July 2012. July 2012.
Authors' Addresses Authors' Addresses
Randell Jesup Randell Jesup
 End of changes. 63 change blocks. 
139 lines changed or deleted 159 lines changed or added

This html diff was produced by rfcdiff 1.41. The latest version is available from http://tools.ietf.org/tools/rfcdiff/