Network Working Group R. Jesup
Internet-Draft Mozilla
Intended status: Standards Track S. Loreto
Expires: October 11, 2014 Ericsson
M. Tuexen
Muenster Univ. of Appl. Sciences
April 9, 2014
WebRTC Data Channel Establishment Protocol
draft-ietf-rtcweb-data-protocol-04.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 a simple protocol for establishing
symmetric data channels between the peers. It uses a two way
handshake and allows sending of user data without waiting for the
handshake to complete.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 11, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
Jesup, et al. Expires October 11, 2014 [Page 1]
Internet-Draft WebRTC Data Channel Establishment Protocol April 2014
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 3
5. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 4
5.1. DATA_CHANNEL_OPEN Message . . . . . . . . . . . . . . . . 4
5.2. DATA_CHANNEL_ACK Message . . . . . . . . . . . . . . . . 7
6. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8.1. SCTP Payload Protocol Identifier . . . . . . . . . . . . 9
8.2. New Message Type Registry . . . . . . . . . . . . . . . . 9
8.3. New Channel Type Registry . . . . . . . . . . . . . . . . 10
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
10.1. Normative References . . . . . . . . . . . . . . . . . . 11
10.2. Informational References . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
The Data Channel Establishment Protocol (DCEP) is designed to
provide, in the WebRTC data channel context
[I-D.ietf-rtcweb-data-channel], a simple in-band method to open
symmetric data channels. As discussed in
[I-D.ietf-rtcweb-data-channel], the protocol uses the Stream Control
Transmission Protocol (SCTP) [RFC4960] encapsulated in the 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].
Jesup, et al. Expires October 11, 2014 [Page 2]
Internet-Draft WebRTC Data Channel Establishment Protocol April 2014
3. Terminology
This document uses the following terms:
Association: An SCTP association.
Stream: A unidirectional stream of an SCTP association. It is
uniquely identified by an SCTP stream identifier (0-65534). Note:
the SCTP stream identifier 65535 is reserved due to SCTP INIT and
INIT-ACK chunks only allowing a maximum of 65535 streams to be
negotiated (0-65534).
Channel: Two Streams with the same SCTP stream identifier, one in
each direction, which 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.
The set of consistent properties includes
o whether the messages are transmitted reliable or unreliable. In
case of unreliable transmissions, the same level of unreliability
is used.
o whether the messages are delivered in-order or out-of order.
o the priority of the Channel.
o an optional label for the Channel.
o an optional protocol for the Channel.
o the SCTP streams.
The Data Channel Establishment Protocol uses a two way handshake to
open a data channel by combining two SCTP streams, one in each
direction, with the same SCTP stream identifier. The side wanting to
open a data channel selects an SCTP stream identifier for which the
corresponding incoming and outgoing SCTP stream is unused and sends a
DATA_CHANNEL_OPEN message on this outgoing SCTP stream. The peer
responds with a DATA_CHANNEL_ACK message on its corresponding
outgoing SCTP stream. Then the data channel is open. Please note
that the opening side can send user messages before the
DATA_CHANNEL_ACK is received. Data channel messages are sent on the
same Stream as the user messages belonging to the data channel. The
Jesup, et al. Expires October 11, 2014 [Page 3]
Internet-Draft WebRTC Data Channel Establishment Protocol April 2014
demultiplexing is based on the SCTP payload protocol identifier
(PPID), since the Data Channel Establishment Protocol uses a specific
PPID.
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 WebRTC, 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 labeled "x" at the same time, there will be two Channels
labeled "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 user data being passed with an
IANA-registered string ('WebSocket Subprotocol Name Registry' defined
in [RFC6455]), and may be useful for homogeneous applications which
may create more than one type of Channel. Please note that there is
also no attempt to resolve protocol glare.
5. Message Formats
Every Data Channel Establishment Protocol message starts with a one
byte field called "Message Type" which indicates the type of the
message. The corresponding values are managed by IANA (see
Section 8.2).
5.1. DATA_CHANNEL_OPEN Message
This message is sent initially on the stream used for user messages
using the channel.
Jesup, et al. Expires October 11, 2014 [Page 4]
Internet-Draft WebRTC Data Channel Establishment Protocol April 2014
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
DATA_CHANNEL_OPEN message. The suggested value of this field for
IANA is 0x03.
Channel Type: 1 byte (unsigned integer)
This field specifies the type of the channel to be opened and the
values are managed by IANA (see Section 8.3):
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
channel. User messages might not be transmitted or
retransmitted after a specified life-time given in milli-
Jesup, et al. Expires October 11, 2014 [Page 5]
Internet-Draft WebRTC Data Channel Establishment Protocol April 2014
seconds in the Reliability Parameter. This life-time starts
when providing the user message to the protocol stack.
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 protocol stack.
Priority: 2 bytes (integer)
The priority of the channel as described in
[I-D.ietf-rtcweb-data-channel]. The higher the number, the lower
the priority.
Reliability Parameter: 4 bytes (unsigned integer)
For reliable channels this field MUST be set to 0 on the sending
side and MUST be ignored on the receiving side. 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. The following
table summarizes this:
+------------------------------------------------+------------------+
| Channel Type | Reliability |
| | Parameter |
+------------------------------------------------+------------------+
| DATA_CHANNEL_RELIABLE | Ignored |
| DATA_CHANNEL_RELIABLE_UNORDERED | Ignored |
| DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT | Number of RTX |
| DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT_UNORDERED | Number of RTX |
| DATA_CHANNEL_PARTIAL_RELIABLE_TIMED | Lifetime in ms |
| DATA_CHANNEL_PARTIAL_RELIABLE_TIMED_UNORDERED | Lifetime in ms |
+------------------------------------------------+------------------+
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 as a UTF-8 encoded string. This may be an
empty string.
Protocol: Variable Length (sequence of characters)
Jesup, et al. Expires October 11, 2014 [Page 6]
Internet-Draft WebRTC Data Channel Establishment Protocol April 2014
The sub-protocol for the channel as a UTF-8 encoded string. If
this is an empty string the protocol is unspecified. If it is a
non-empty string, it specifies an protocol registered in the
'WebSocket Subprotocol Name Registry' created in [RFC6455].
5.2. DATA_CHANNEL_ACK Message
This message is sent in response to a DATA_CHANNEL_OPEN_RESPONSE
message on the stream used for user messages using the channel.
Reception of this message tells the opener that the channel setup
handshake is complete.
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 |
+-+-+-+-+-+-+-+-+
Message Type: 1 byte (unsigned integer)
This field holds the IANA defined message type for the
DATA_CHANNEL_ACK message. The suggested value of this field for
IANA is 0x02.
6. Procedures
All Data Channel Establishment Protocol messages MUST be sent using
ordered delivery and reliable transmission. They MUST be sent on the
same outgoing SCTP stream as the user messages belonging to the
corresponding data channel. Multiplexing and demultiplexing is done
by using the SCTP payload protocol identifier (PPID). Therefore Data
Channel Establishment Protocol message MUST be sent with the assigned
PPID for the Data Channel Establishment Protocol (see Section 8.1).
Other messages MUST NOT be sent using this PPID.
If one side wants to open a data channel, it chooses an SCTP stream
identifier for which the corresponding incoming and outgoing SCTP
streams are free. If the side is the DTLS client, it MUST choose an
even stream identifier, if the side is the DTLS server, it MUST
choose an odd one. It fills in the parameters of the
DATA_CHANNEL_OPEN message and sends it on the chosen SCTP stream.
After the DATA_CHANNEL_OPEN message has been sent, the sender of it
can start sending messages containing user data without waiting for
the reception of the corresponding DATA_CHANNEL_ACK message.
However, before the DATA_CHANNEL_ACK message or any other message has
been received on a data channel, all other messages containing user
data and belonging to this data channel MUST be sent ordered, no
matter whether the data channel is ordered or not. After the
Jesup, et al. Expires October 11, 2014 [Page 7]
Internet-Draft WebRTC Data Channel Establishment Protocol April 2014
DATA_CHANNEL_ACK or any other message has been received on the data
channel, messages containing user data MUST be send ordered on
ordered data channels and MUST be sent unordered on unordered data
channels. Therefore receiving a message containing user data on an
unused SCTP stream indicates an error. The corresponding channel
MUST be closed as described in [I-D.ietf-rtcweb-data-channel].
If a DATA_CHANNEL_OPEN message is received on an unused stream, the
stream identifier corresponds to the role of the peer and all
parameters in the DATA_CHANNEL_OPEN message are valid, then a
corresponding DATA_CHANNEL_ACK message is sent on the stream with the
same stream identifier as the one the DATA_CHANNEL_OPEN message was
received on.
If a DATA_CHANNEL_OPEN message is received on an already used SCTP
stream or there are any problems with parameters within the
DATA_CHANNEL_OPEN message or the DATA_CHANNEL_OPEN message itself is
not well-formed, the receiver MUST close the corresponding channel
using the procedure described in [I-D.ietf-rtcweb-data-channel] and
MUST NOT send a DATA_CHANNEL_ACK message in response to the received
message. Therefore, receiving an SCTP stream reset request for a
stream on which no DATA_CHANNEL_ACK message has been received
indicates to the sender of the corresponding DATA_CHANNEL_OPEN
message the failure of the data channel setup procedure. After also
successfully resetting the corresponding outgoing SCTP stream, which
concludes the channel closing initiated by the peer, a new
DATA_CHANNEL_OPEN message can be sent on the stream.
7. Security Considerations
This document does not add any additional considerations to the ones
given in [I-D.ietf-rtcweb-security] and
[I-D.ietf-rtcweb-security-arch].
8. IANA Considerations
[NOTE to RFC-Editor:
"RFCXXXX" is to be replaced by the RFC number you assign this
document.
]
IANA is asked to update the reference of an already existing SCTP
PPID assignment and to create two new registries for the Data Channel
Establishment Protocol.
Jesup, et al. Expires October 11, 2014 [Page 8]
Internet-Draft WebRTC Data Channel Establishment Protocol April 2014
8.1. SCTP Payload Protocol Identifier
This document uses one already registered SCTP Payload Protocol
Identifier (PPID) named "WebRTC Control". [RFC4960] creates the
registry "SCTP Payload Protocol Identifiers" from which this
identifier was assigned. IANA is requested to update the reference
of this assignment to point to this document and to update the name.
Therefore this assignment should be updated to read:
+-------------+-----------+-----------+
| Value | SCTP PPID | Reference |
+-------------+-----------+-----------+
| WebRTC DCEP | 50 | [RFCXXXX] |
+-------------+-----------+-----------+
8.2. New Message Type Registry
IANA is requested to create a new registration table "Message Type
Registry" for the Data Channel Establishment Protocol (DCEP) to
manage the one byte "Message Type" field in DCEP messages (see
Section 5).
The assignment of new message types is done through an RFC required
action, as defined in [RFC5226]. Documentation of the new message
type MUST contain the following information:
1. A name for the new message type;
2. A detailed procedural description of the use of messages with the
new type within the operation of the Data Channel Establishment
Protocol.
Initially the following values need to be registered:
+-------------------+-----------+-----------+
| Name | Type | Reference |
+-------------------+-----------+-----------+
| Reserved | 0x00 | [RFCXXXX] |
| Reserved | 0x01 | [RFCXXXX] |
| DATA_CHANNEL_ACK | 0x02 | [RFCXXXX] |
| DATA_CHANNEL_OPEN | 0x03 | [RFCXXXX] |
| Unassigned | 0x04-0xfe | |
| Reserved | 0xff | [RFCXXXX] |
+-------------------+-----------+-----------+
Please note that the values 0x00 and 0x01 are reserved to avoid
interoperability problems, since they have been used in earlier
Jesup, et al. Expires October 11, 2014 [Page 9]
Internet-Draft WebRTC Data Channel Establishment Protocol April 2014
versions of the document. The value 0xff has been reserved for
future extensibility.
8.3. New Channel Type Registry
IANA is requested to create a new registration table "Channel Type
Registry" for the Data Channel Establishment Protocol to manage the
one byte "Channel Type" field in DATA_CHANNEL_OPEN messages (see
Section 5.1).
The assignment of new message types is done through an RFC required
action, as defined in [RFC5226]. Documentation of the new channel
type MUST contain the following information:
1. A name for the new channel type;
2. A detailed procedural description of the user message handling
for data channels using this new channel type.
Please note that if new channel types support ordered and unordered
message delivery, the high order bit SHOULD be used to indicate
whether the message delivery is unordered or not.
Initially the following values need to be registered:
+------------------------------------------------+------+-----------+
| Name | Type | Reference |
+------------------------------------------------+------+-----------+
| DATA_CHANNEL_RELIABLE | 0x00 | [RFCXXXX] |
| DATA_CHANNEL_RELIABLE_UNORDERED | 0x80 | [RFCXXXX] |
| DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT | 0x01 | [RFCXXXX] |
| DATA_CHANNEL_PARTIAL_RELIABLE_REXMIT_UNORDERED | 0x81 | [RFCXXXX] |
| DATA_CHANNEL_PARTIAL_RELIABLE_TIMED | 0x02 | [RFCXXXX] |
| DATA_CHANNEL_PARTIAL_RELIABLE_TIMED_UNORDERED | 0x82 | [RFCXXXX] |
| Reserved | 0x7f | [RFCXXXX] |
| Reserved | 0xff | [RFCXXXX] |
| Unassigned | rest | |
+------------------------------------------------+------+-----------+
9. Acknowledgments
The authors wish to thank Harald Alvestrand, Adam Bergkvist, Barry
Dingle, Stefan Haekansson, Cullen Jennings, Paul Kyzivat, Irene
Ruengeler, Randall Stewart, Peter Thatcher, Martin Thompson, Justin
Uberti, and many others for their invaluable comments.
Jesup, et al. Expires October 11, 2014 [Page 10]
Internet-Draft WebRTC Data Channel Establishment Protocol April 2014
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC
4960, September 2007.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[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.
[I-D.ietf-tsvwg-sctp-dtls-encaps]
Tuexen, M., Stewart, R., Jesup, R., and S. Loreto, "DTLS
Encapsulation of SCTP Packets", draft-ietf-tsvwg-sctp-
dtls-encaps-03 (work in progress), February 2014.
10.2. Informational References
[RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol", RFC
6455, December 2011.
[I-D.ietf-rtcweb-data-channel]
Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data
Channels", draft-ietf-rtcweb-data-channel-07 (work in
progress), February 2014.
[I-D.ietf-rtcweb-security]
Rescorla, E., "Security Considerations for WebRTC", draft-
ietf-rtcweb-security-06 (work in progress), January 2014.
[I-D.ietf-rtcweb-security-arch]
Rescorla, E., "WebRTC Security Architecture", draft-ietf-
rtcweb-security-arch-09 (work in progress), February 2014.
Jesup, et al. Expires October 11, 2014 [Page 11]
Internet-Draft WebRTC Data Channel Establishment Protocol April 2014
Authors' Addresses
Randell Jesup
Mozilla
US
Email: randell-ietf@jesup.org
Salvatore Loreto
Ericsson
Hirsalantie 11
Jorvas 02420
FI
Email: salvatore.loreto@ericsson.com
Michael Tuexen
Muenster University of Applied Sciences
Stegerwaldstrasse 39
Steinfurt 48565
DE
Email: tuexen@fh-muenster.de
Jesup, et al. Expires October 11, 2014 [Page 12]
