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Versions: (draft-jesup-rtcweb-data-protocol) 00 01 02 03 04 05 06 07 08 09 Draft is active
In: MissingRef
Network Working Group                                           R. Jesup
Internet-Draft                                                   Mozilla
Intended status: Standards Track                               S. Loreto
Expires: December 11, 2014                                      Ericsson
                                                               M. Tuexen
                                        Muenster Univ. of Appl. Sciences
                                                            June 9, 2014


               WebRTC Data Channel Establishment Protocol
                 draft-ietf-rtcweb-data-protocol-06.txt

Abstract

   The Real-Time Communication in WEB-browsers working group is charged
   to provide protocol 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 December 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
   carefully, as they describe your rights and restrictions with respect



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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 . . . . . . . . . . . . . . . . . . . . . . . . .   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 . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  SCTP Payload Protocol Identifier  . . . . . . . . . . . .   9
     8.2.  New Message Type Registry . . . . . . . . . . . . . . . .   9
     8.3.  New Channel Type Registry . . . . . . . . . . . . . . . .  10
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  11
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     10.2.  Informational References . . . . . . . . . . . . . . . .  12
   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].








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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

   The Data Channel Establishment 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  reliable or unreliable message transmission.  In case of
      unreliable transmissions, the same level of unreliability is used.

   o  in-order or out-of-order message delivery.

   o  the priority of the Channel.

   o  an optional label for the Channel.

   o  an optional protocol for the Channel.

   o  the SCTP streams.

   This protocol uses a two way handshake to open a data channel.  The
   handshake pairs one incoming and one outgoing SCTP stream, both
   having the same SCTP stream identifier, into a single bidirectional
   channel.  The side wanting to open a data channel selects an SCTP
   stream identifier for which the corresponding incoming and outgoing
   SCTP streams are unused and sends a DATA_CHANNEL_OPEN message on the
   outgoing SCTP stream.  The peer responds with a DATA_CHANNEL_ACK
   message on its corresponding outgoing SCTP stream.  Then the data
   channel is open.  Data channel messages are sent on the same Stream
   as the user messages belonging to the data channel.  The
   demultiplexing is based on the SCTP payload protocol identifier




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   (PPID), since the Data Channel Establishment Protocol uses a specific
   PPID.

   Note: The opening side can send user messages before the
   DATA_CHANNEL_ACK is received.

   To avoid glare in opening Channels, each side MUST use Streams with
   either even or odd SCTP stream identifiers when sending a
   DATA_CHANNEL_OPEN message.  When using SCTP over DTLS
   [I-D.ietf-tsvwg-sctp-dtls-encaps], the method used to determine which
   side uses odd or even is based on the underlying DTLS connection
   role: the side acting as the DTLS client MUST use Streams with even
   SCTP stream identifiers, the side acting as the DTLS server MUST use
   Streams with odd SCTP 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.














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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
      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-




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         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 (unsigned integer)
      The priority of the channel as described in
      [I-D.ietf-rtcweb-data-channel].

   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)
      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



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      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
   DATA_CHANNEL_ACK or any other message has been received on the data
   channel, messages containing user data MUST be send ordered on



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   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

   The DATA_CHANNEL_OPEN messages contains two variable length fields:
   the protocol and the label.  A receiver must be prepared to receive
   DATA_CHANNEL_OPEN messages where these field have the maximum length
   of 65535 bytes.  Error cases like the use of inconsistent lengths
   fields, unknown parameter values or violation the odd/even rule must
   also be handled by closing the corresponding channel.  An end-point
   must also be prepared that the peer open the maximum number of data
   channels.

   When using DCEP over SCTP encapsulated in DTLS as specified in
   [I-D.ietf-tsvwg-sctp-dtls-encaps], security properties like privacy,
   integrity, and source authentication can be provided by DTLS.  If
   DCEP is used without running over DTLS, this is not the case.

   For general considerations see [I-D.ietf-rtcweb-security] and
   [I-D.ietf-rtcweb-security-arch].







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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.

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:





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               +-------------------+-----------+-----------+
               | 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
   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:














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   +------------------------------------------------+------+-----------+
   | 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, Doug
   Leonard, Irene Ruengeler, Randall Stewart, Peter Thatcher, Martin
   Thompson, Justin Uberti, and many others for their invaluable
   comments.

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.

   [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-04 (work in progress), May 2014.








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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-09 (work in
              progress), May 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.

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








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