RTCWeb Working Group R. Jesup
Internet-Draft Mozilla
Intended status: Standards Track S. Loreto
Expires: January 16, 2014 Ericsson
M. Tuexen
Muenster Univ. of Appl. Sciences
July 15, 2013
WebRTC Data Channel Protocol
draft-ietf-rtcweb-data-protocol-00.txt
Abstract
The Web Real-Time Communication (WebRTC) working group is charged to
provide protocols to support for direct interactive rich
communication using audio, video, and data between two peers' web-
browsers. This document specifies an actual (minor) protocol for how
the JS-layer DataChannel objects provide the data channels between
the peers.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 16, 2014.
Copyright Notice
Copyright (c) 2013 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
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publication of this document. Please review these documents
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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
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 3
5. Opening Handshake . . . . . . . . . . . . . . . . . . . . . . 4
6. Control Messages . . . . . . . . . . . . . . . . . . . . . . 4
6.1. DATA_CHANNEL_OPEN Message . . . . . . . . . . . . . . . . 4
7. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Adding a Channel (in-band open) . . . . . . . . . . . . . 6
7.2. Adding a Channel (external negotiation) . . . . . . . . . 7
7.3. Closing a Channel . . . . . . . . . . . . . . . . . . . . 7
7.4. Sending and Receiving Data . . . . . . . . . . . . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
11.1. Normative References . . . . . . . . . . . . . . . . . . 9
11.2. Informational References . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
The DataChannel Protocol is designed to provide, in the WebRTC
context [I-D.ietf-rtcweb-overview], a generic transport service
allowing a Web Browser to exchange generic data in a bidirectional
peer to peer fashion. As discussed in [I-D.ietf-rtcweb-data-channel]
the protocol uses Stream Control Transmission Protocol (SCTP)
[RFC4960] encapsulated on Datagram Transport Layer Security (DTLS)
[RFC6347] as described in [I-D.ietf-tsvwg-sctp-dtls-encaps] to
benefit from their already standardized transport and security
features.
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. Terminology
This document uses the following terms:
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Association: An SCTP association.
Stream: A unidirectional stream of an SCTP association. It is
uniquely identified by a stream identifier (0-65535).
Channel: Two Streams with the same identifier, one in each
direction, that are managed together.
4. Protocol Overview
This protocol is a simple, low-overhead way to establish
bidirectional Channels over an SCTP association with a consistent set
of properties.
Channels are created by sending an optional DATA_CHANNEL_OPEN message
on an unused Stream. There is no handshake, and the channel is
available to send on as soon as the DATA_CHANNEL_OPEN has been sent.
Alternatively, both sides make externally agree to a set of
parameters for a Channel, in which case no DATA_CHANNEL_OPEN message
is required.
To avoid glare in opening Channels, each side must use either even or
odd Streams when sending a DATA_CHANNEL_OPEN message. The method
used to determine which side uses odd or even is based on the
underlying DTLS connection role when used in rtcweb, with the side
acting as the DTLS client using even stream identifiers.
Note: There is no attempt to resolve label glare; if both sides open
a Channel labelled "x" at the same time, there will be two Channels
labelled "x" - one on an even Stream pair, one on an odd pair.
The protocol field is to ease cross-application interoperation
("federation") by identifying the data being passed with an IANA-
registered string, and may also be useful for homogenous applications
which may create more than one type of Channel.
Data that arrives which on an unused Stream MUST be held for a period
TBD until a DATA_CHANNEL_OPEN arrived for that Channel, or until the
protocol stack has been told to expect data on that Stream (via
external negotiation), or until [TBD - report error]. This allows
for external negotiation of streams (or assumption of negotiation by
cooperating applications). If a later DATA_CHANNEL_OPEN arrives that
conflicts with the pre-set properties of the Channel, an error should
be signaled to higher levels.
Channels are closed by an SCTP reset of the Stream.
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5. Opening Handshake
The opening handshake is based on the multimedia session description
exchange that happens between the browsers, typically through a Web
Server acting as the signaling service.
[I-D.ietf-mmusic-sctp-sdp] defines the protocol identifier, 'DTLS/
SCTP', and defines how to establish an SCTP association over DTLS
using the Session Description Protocol (SDP).
The SCTP association is created with the number of streams specified
by the application, and if not specified, then it SHOULD default to
16 streams.
It is recommended that additional streams be available dynamically
based on [RFC6525].
6. Control Messages
Control Messages are sent to manage opening bidirectional channels.
A DATA_CHANNEL_OPEN message is sent on the Stream that is intended to
be used for a new Channel, and this creates a bidirectional Channel
that may be used by both sides to send data.
6.1. DATA_CHANNEL_OPEN Message
This message is sent initially on the stream used for user messages
using the channel. All DATA_CHANNEL_OPEN messages MUST be sent using
SCTP options for reliable in-order delivery.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Type | Channel Type | Priority |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reliability Parameter |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Length | Protocol Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ /
| Label |
/ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ /
| Protocol |
/ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Message Type: 1 byte (unsigned integer)
This field holds the IANA defined message type for the the
DATA_CHANNEL_OPEN message. The suggested value of this field for
IANA is 0x03. NOTE: values 0x00-0x02 were used in an older draft
with incompatible structures. Any future incompatible message
changes should define new message types.
Channel Type: 1 byte (unsigned integer)
This field specifies the type of the channel to be opened:
DATA_CHANNEL_RELIABLE (0x00): The channel provides a reliable in-
order bi-directional communication channel.
DATA_CHANNEL_RELIABLE_UNORDERED (0x80): The channel provides a
reliable unordered bi-directional communication channel.
DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT (0x01): The channel provides
a partially-reliable in-order bi-directional Communication
channel. User messages will not be retransmitted more times
than specified in the Reliability Parameter.
DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT_UNORDERED (0x81): The
channel provides a partial reliable unordered bi-directional
Communication channel. User messages will not be
retransmitted more times than specified in the Reliability
Parameter.
DATA_CHANNEL_PARTIAL_RELIABLE_TIMED (0x02): The channel provides
a partial reliable in-order bi-directional Communication
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channel. User messages might not be transmitted or
retransmitted after a specified life-time given in milli-
seconds in the Reliability Parameter. This life-time starts
when providing the user message to the Javascript engine.
DATA_CHANNEL_PARTIAL_RELIABLE_TIMED_UNORDERED (0x82): The channel
provides a partial reliable unordered bi-directional
Communication channel. User messages might not be
transmitted or retransmitted after a specified life-time
given in milli-seconds in the Reliability Parameter. This
life-time starts when providing the user message to the
Javascript engine.
Priority: 2 bytes (integer)
The priority of the channel.
Reliability Parameter: 4 bytes (unsigned integer)
This field is ignored if a reliable channel is used.
If a partial reliable channel with limited number of
retransmissions is used, this field specifies the number of
retransmissions. If a partial reliable channel with limited
lifetime is used, this field specifies the maximum lifetime in
milliseconds.
Label Length: 2 bytes (unsigned integer)
The length of the label field in bytes.
Protocol Length: 2 bytes (unsigned integer)
The length of the protocol field in bytes.
Label: Variable Length (sequence of characters)
The name of the channel. This may be an empty string.
Protocol: Variable Length (sequence of characters)
The protocol for the channel. This may be an empty string. If
used, it SHOULD be an IANA-registered protocol.
7. Procedures
7.1. Adding a Channel (in-band open)
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When one side wants to add a channel using in-band declaration, it
picks an unused outgoing Stream (even stream identifier for DTLS
clients, or odd for DTLS servers); if no unused streams are available
a negotiation to increase the number is done via [RFC6525], or
failure is returned. It should also check that the other side has
the same channel available, and if not then initiate an increase in
the number of streams. It then sends a DATA_CHANNEL_OPEN control
message on the outgoing stream.
When an DATA_CHANNEL_OPEN is received on an incoming Stream, the
Stream is associated with a newly-created Channel (unless the Stream
was already part of an externally-negotiated Channel). If any data
had arrived on the Stream before the Open arrives and had been
buffered, it is now delivered on the new Channel.
The channel_type and reliability_parameters fields of the
DATA_CHANNEL_OPEN message MUST be used to set up the reverse side of
the Channel so that both directions use the same options by default.
7.2. Adding a Channel (external negotiation)
When one side wants to add a channel using external negotiation, it
picks a Stream. This can be done by asking the protocol to select an
unused Stream (of the approriate even or odd type), or by simply
telling the protocol what Stream to use. In the latter case, 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. Note that
there is no requirement for both sides to have the same options for
an externally-negotiated stream, though typically this will be the
case.
The application must now 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.
7.3. Closing a Channel
Channels MUST be closed by and SCTP reset of the outgoing Stream. If
an incoming Stream is reset by the peer, an corresponding outgoing
stream reset SHOULD be issued. If the streams in both directions of
a Channel are reset, the Channel is considered fully closed and the
Streams are available for reuse for new channel opens.
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7.4. Sending and Receiving Data
Data shall be sent using PPID's other than the Data Channel Control
PPID. These PPID's should be registered with IANA via (TBD). The
meaning of these data PPIDs and the format of the data shall be
specific to the usage of this protocol, and typically shall be
provided to the higher layers to allow proper decoding of the data.
It is RECOMMENDED that higher layers wishing to transfer large
messages fragment them using PPIDs or other mechanisms to avoid
monopolization of the SCTP association by the transfer of a single
large message, unless a future SCTP draft relaxes this concern. If
fragmented solely with PPID values, then transmission MUST occur on a
reliable in-order channel. If in-band application framing is used,
then other options may be possible.
For WebRTC, data PPID's for DOMStrings and binary data (and
fragmentation thereof) shall be created.
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.
Data may be sent immediately after sending or receiving a
DATA_CHANNEL_OPEN message, or after creating an externally-negotiated
Channel.
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.
8. Security Considerations
To be done.
9. IANA Considerations
[NOTE to RFC-Editor:
"RFCXXXX" is to be replaced by the RFC number you assign this
document.
]
[NOTE to RFC-Editor:
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The suggested values for the Payload Protocol Identifiers are
tentative and to be confirmed by IANA.
]
This document defines five new SCTP Payload Protocol Identifiers
(PPIDs). [RFC4960] creates the registry "SCTP Payload Protocol
Identifiers" from which these identifiers need to be assigned. The
following values are suggested:
+---------------------+-----------+-----------+
| Value | SCTP PPID | Reference |
+---------------------+-----------+-----------+
| WebRTC Control | 50 | [RFCXXXX] |
| DOMString Last | 51 | [RFCXXXX] |
| Binary Data Partial | 52 | [RFCXXXX] |
| Binary Data Last | 53 | [RFCXXXX] |
| DOMString Partial | 54 | [RFCXXXX] |
+---------------------+-----------+-----------+
10. Acknowledgments
The authors wish to thank Martin Thompson, Cullen Jennings, Harald
Alvestrand, Peter Thatcher, Adam Bergkvist, Justin Uberti, Randall
Stewart, Stefan Haekansson and many others for their invaluable
comments.
11. References
11.1. Normative 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.
Conrad, "Stream Control Transmission Protocol (SCTP)
Partial Reliability Extension", RFC 3758, May 2004.
[RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC
4960, September 2007.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, January 2012.
[RFC6525] Stewart, R., Tuexen, M., and P. Lei, "Stream Control
Transmission Protocol (SCTP) Stream Reconfiguration", RFC
6525, February 2012.
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[I-D.ietf-mmusic-sctp-sdp]
Loreto, S. and G. Camarillo, "Stream Control Transmission
Protocol (SCTP)-Based Media Transport in the Session
Description Protocol (SDP)", draft-ietf-mmusic-sctp-sdp-04
(work in progress), June 2013.
[I-D.ietf-tsvwg-sctp-dtls-encaps]
Jesup, R., Loreto, S., Stewart, R., and M. Tuexen, "DTLS
Encapsulation of SCTP Packets for RTCWEB", draft-ietf-
tsvwg-sctp-dtls-encaps-00 (work in progress), February
2013.
11.2. Informational References
[I-D.ietf-rtcweb-overview]
Alvestrand, H., "Overview: Real Time Protocols for Brower-
based Applications", draft-ietf-rtcweb-overview-06 (work
in progress), February 2013.
[I-D.ietf-rtcweb-data-channel]
Jesup, R., Loreto, S., and M. Tuexen, "RTCWeb Data
Channels", draft-ietf-rtcweb-data-channel-04 (work in
progress), February 2013.
Authors' Addresses
Randell Jesup
Mozilla
US
Email: randell-ietf@jesup.org
Salvatore Loreto
Ericsson
Hirsalantie 11
Jorvas 02420
FI
Email: salvatore.loreto@ericsson.com
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Michael Tuexen
Muenster University of Applied Sciences
Stegerwaldstrasse 39
Steinfurt 48565
DE
Email: tuexen@fh-muenster.de
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