Network Working Group R. Jesup Internet-Draft Mozilla Intended status: Standards Track S. Loreto Expires: August 15, 2014 Ericsson M. Tuexen Muenster Univ. of Appl. Sciences February 11, 2014 WebRTC Data Channel Establishment Protocol draft-ietf-rtcweb-data-protocol-03.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 August 15, 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 August 15, 2014 [Page 1] Internet-Draft WebRTC Data Channel Establishment Protocol February 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 . . . . . . . . . . . . . . . . 6 6. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . 8 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 8.1. SCTP Payload Protocol Identifier . . . . . . . . . . . . 8 8.2. New Message Type Registry . . . . . . . . . . . . . . . . 8 8.3. New Channel Type Registry . . . . . . . . . . . . . . . . 9 8.4. New Protocol Registry . . . . . . . . . . . . . . . . . . 10 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 10.1. Normative References . . . . . . . . . . . . . . . . . . 10 10.2. Informational References . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 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 August 15, 2014 [Page 2] Internet-Draft WebRTC Data Channel Establishment Protocol February 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 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 demultiplexing is based on the SCTP payload protocol identifier Jesup, et al. Expires August 15, 2014 [Page 3] Internet-Draft WebRTC Data Channel Establishment Protocol February 2014 (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 (see Section 8.4), and may be useful for homogenous applications which may create more than one type of Channel. 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. 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 | / \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Jesup, et al. Expires August 15, 2014 [Page 4] Internet-Draft WebRTC Data Channel Establishment Protocol February 2014 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. 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- 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 as described in [I-D.ietf-rtcweb-data-channel]. The higher the number, the lower the priority. 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 Jesup, et al. Expires August 15, 2014 [Page 5] Internet-Draft WebRTC Data Channel Establishment Protocol February 2014 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. This may be an empty string. Protocol: Variable Length (sequence of characters) The protocol for the channel. If this is an empty string the protocol us unspecified. If it is an non-empty string, it specifies an IANA-registered protocol (see Section 8.4). 5.2. DATA_CHANNEL_ACK Message This message is sent in response to an 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 the DATA_CHANNEL_ACK message. The suggested value of this field for IANA is 0x02. Jesup, et al. Expires August 15, 2014 [Page 6] Internet-Draft WebRTC Data Channel Establishment Protocol February 2014 6. Procedures All Data Channel Establishment Protocol messages MUST be sent requesting ordered delivery and using 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 message MUST NOT be sent using this PPID. If one sides 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 the data channel, all other messages containing user data and belonging to the data channel MUST be sent ordered, not 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 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 outgoing SCTP stream MUST be reset using [RFC6525]. 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 reset the corresponding outgoing SCTP stream using [RFC6525] 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 Jesup, et al. Expires August 15, 2014 [Page 7] Internet-Draft WebRTC Data Channel Establishment Protocol February 2014 corresponding DATA_CHANNEL_OPEN message the failure of the data channel setup procedure. After also successfully resetting the corresponding outgoing SCTP stream, 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 three 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). Jesup, et al. Expires August 15, 2014 [Page 8] Internet-Draft WebRTC Data Channel Establishment Protocol February 2014 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 versions of the document. 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 indicated whether the message delivery is unordered or not. Initially the following values need to be registered: Jesup, et al. Expires August 15, 2014 [Page 9] Internet-Draft WebRTC Data Channel Establishment Protocol February 2014 +------------------------------------------------+------+-----------+ | 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 | | +------------------------------------------------+------+-----------+ 8.4. New Protocol Registry IANA is requested to create a new registration table "Protocol Registry" for the Data Channel Establishment Protocol to manage the "Protocol" field of type string in DATA_CHANNEL_OPEN messages (see Section 5.1). The assignment of new message types is done through an First Come First Served action, as defined in [RFC5226]. Documentation of the new protocol MUST contain the following information: 1. A name for the protocol; 2. A reference for the protocol indicated by the registered string. Initially this registry is empty. 9. Acknowledgments The authors wish to thank Harald Alvestrand, Adam Bergkvist, Barry Dingle, Stefan Haekansson, Cullen Jennings, 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. Jesup, et al. Expires August 15, 2014 [Page 10] Internet-Draft WebRTC Data Channel Establishment Protocol February 2014 [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 [I-D.ietf-rtcweb-data-channel] Jesup, R., Loreto, S., and M. Tuexen, "RTCWeb Data Channels", draft-ietf-rtcweb-data-channel-06 (work in progress), October 2013. [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-08 (work in progress), January 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 Jesup, et al. Expires August 15, 2014 [Page 11] Internet-Draft WebRTC Data Channel Establishment Protocol February 2014 Michael Tuexen Muenster University of Applied Sciences Stegerwaldstrasse 39 Steinfurt 48565 DE Email: tuexen@fh-muenster.de Jesup, et al. Expires August 15, 2014 [Page 12]