draft-ietf-rtcweb-data-channel-08.txt   draft-ietf-rtcweb-data-channel-09.txt 
Network Working Group R. Jesup Network Working Group R. Jesup
Internet-Draft Mozilla Internet-Draft Mozilla
Intended status: Standards Track S. Loreto Intended status: Standards Track S. Loreto
Expires: October 11, 2014 Ericsson Expires: November 16, 2014 Ericsson
M. Tuexen M. Tuexen
Muenster Univ. of Appl. Sciences Muenster Univ. of Appl. Sciences
April 9, 2014 May 15, 2014
WebRTC Data Channels WebRTC Data Channels
draft-ietf-rtcweb-data-channel-08.txt draft-ietf-rtcweb-data-channel-09.txt
Abstract Abstract
The Real-Time Communication in WEB-browsers working group is charged The Real-Time Communication in WEB-browsers working group is charged
to provide protocol support for direct interactive rich communication to 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 specifies the non-(S)RTP media data transport aspects of the document specifies the non-SRTP media data transport aspects of the
WebRTC framework. It provides an architectural overview of how the WebRTC framework. It provides an architectural overview of how the
Stream Control Transmission Protocol (SCTP) is used in the WebRTC Stream Control Transmission Protocol (SCTP) is used in the WebRTC
context as a generic transport service allowing WEB-browsers to context as a generic transport service allowing WEB-browsers to
exchange generic data from peer to peer. exchange generic data from peer to peer.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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 October 11, 2014. This Internet-Draft will expire on November 16, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 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
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7. Security Considerations . . . . . . . . . . . . . . . . . . . 11 7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
10.1. Normative References . . . . . . . . . . . . . . . . . . 12 10.1. Normative References . . . . . . . . . . . . . . . . . . 12
10.2. Informative References . . . . . . . . . . . . . . . . . 14 10.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction 1. Introduction
Non-(S)RTP media data types in the context of WebRTC are handled by Non-SRTP media data types in the context of WebRTC are handled by
using SCTP [RFC4960] encapsulated in DTLS [RFC6347]. using SCTP [RFC4960] encapsulated in 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 (see The encapsulation of SCTP over DTLS (see
[I-D.ietf-tsvwg-sctp-dtls-encaps]) over ICE/UDP (see [RFC5245]) [I-D.ietf-tsvwg-sctp-dtls-encaps]) over ICE/UDP (see [RFC5245])
provides a NAT traversal solution together with confidentiality, provides a NAT traversal solution together with confidentiality,
source authentication, and integrity protected transfers. This data source authentication, and integrity protected transfers. This data
transport service operates in parallel to the (S)RTP media transport service operates in parallel to the SRTP media transports,
transports, and all of them can eventually share a single transport- and all of them can eventually share a single transport-layer port
layer port number. number.
SCTP as specified in [RFC4960] with the partial reliability extension SCTP as specified in [RFC4960] with the partial reliability extension
defined in [RFC3758] and the additional policies defined in defined in [RFC3758] and the additional policies defined in
[I-D.ietf-tsvwg-sctp-prpolicies] provides multiple streams natively [I-D.ietf-tsvwg-sctp-prpolicies] provides multiple streams natively
with reliable, and the relevant partially-reliable delivery modes for with reliable, and the relevant partially-reliable delivery modes for
user messages. Using the reconfiguration extension defined in user messages. Using the reconfiguration extension defined in
[RFC6525] allows to increase the number of streams during the [RFC6525] allows to increase the number of streams during the
lifetime of an SCTP association and to reset individual SCTP streams. lifetime of an SCTP association and to reset individual SCTP streams.
Using [I-D.ietf-tsvwg-sctp-ndata] allows to interleave large messages Using [I-D.ietf-tsvwg-sctp-ndata] allows to interleave large messages
to avoid the monopolization and adds the support of prioritizing of to avoid the monopolization and adds the support of prioritizing of
SCTP streams. SCTP streams.
The remainder of this document is organized as follows: Section 3 and The remainder of this document is organized as follows: Section 3 and
Section 4 provide use cases and requirements for both unreliable and Section 4 provide use cases and requirements for both unreliable and
reliable peer to peer data channels; Section 5 discusses SCTP over reliable peer to peer data channels; Section 5 discusses SCTP over
DTLS over UDP; Section 6 provides the specification of how SCTP DTLS over UDP; Section 6 provides the specification of how SCTP
should be used by the WebRTC protocol framework for transporting should be used by the WebRTC protocol framework for transporting non-
non-(S)RTP media data between WEB-browsers. SRTP media data between WEB-browsers.
2. Conventions 2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Use Cases 3. Use Cases
This section defines use cases specific to data channels. For This section defines use cases specific to data channels. For
general use cases see [I-D.ietf-rtcweb-use-cases-and-requirements]. general use cases see [I-D.ietf-rtcweb-use-cases-and-requirements].
3.1. Use Cases for Unreliable Data Channels 3.1. Use Cases for Unreliable Data 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 (S)RTP media channels, or all at any time there may be no SRTP media channels, or all SRTP
(S)RTP media channels may be inactive, and that there may media channels may be inactive, and that there may also be
also be reliable data channels in use. reliable data channels in use.
U-C 2: Providing non-critical information to a user about the reason U-C 2: Providing non-critical information to a user about the reason
for a state update in a video chat or conference, such as for a state update in a video chat or conference, such as
mute state. mute state.
3.2. Use Cases for Reliable Data Channels 3.2. Use Cases for Reliable Data Channels
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. Such a game may transferred, such as control information. Such a game may
have no (S)RTP media channels, or they may be inactive at any have no SRTP media channels, or they may be inactive at any
given time, or may only be added due to in-game actions. given time, or may only be added due to in-game actions.
U-C 4: Non-realtime file transfers between people chatting. Note U-C 4: Non-realtime file transfers between people chatting. Note
that this may involve a large number of files to transfer that this may involve a large number of files to transfer
sequentially or in parallel, such as when sharing a folder of sequentially or in parallel, such as when sharing a folder of
images or a directory of files. images or a directory of files.
U-C 5: Realtime text chat during an audio and/or video call with an U-C 5: Realtime text chat during an audio and/or video call with an
individual or with multiple people in a conference. individual or with multiple people in a conference.
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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. monitoring.
4. Requirements 4. Requirements
This section lists the requirements for P2P data channels between two This section lists the requirements for P2P data channels between two
browsers. browsers.
Req. 1: Multiple simultaneous data channels MUST be supported. Req. 1: Multiple simultaneous data channels MUST be supported.
Note that there may be 0 or more (S)RTP media streams in Note that there may be 0 or more SRTP media streams in
parallel with the data channels in the same PeerConnection, parallel with the data channels in the same PeerConnection,
and the number and state (active/inactive) of these (S)RTP and the number and state (active/inactive) of these SRTP
media streams may change at any time. media streams may change at any time.
Req. 2: Both reliable and unreliable data channels MUST be Req. 2: Both reliable and unreliable data channels MUST be
supported. supported.
Req. 3: Data channels of a PeerConnection MUST be congestion Req. 3: Data channels of a PeerConnection MUST be congestion
controlled; either individually, as a class, or in controlled; either individually, as a class, or in
conjunction with the (S)RTP media streams of the conjunction with the SRTP media streams of the
PeerConnection, to ensure that data channels don't cause PeerConnection, to ensure that data channels don't cause
congestion problems for these (S)RTP media streams, and congestion problems for these SRTP media streams, and that
that the WebRTC PeerConnection as a whole is fair with the WebRTC PeerConnection as a whole is fair with competing
competing traffic such as TCP. traffic such as TCP.
Req. 4: The application SHOULD be able to provide guidance as to Req. 4: The application SHOULD be able to provide guidance as to
the relative priority of each data channel relative to each the relative priority of each data channel relative to each
other, and relative to the (S)RTP media streams. This will other, and relative to the SRTP media streams. This will
interact with the congestion control algorithms. interact with the congestion control algorithms.
Req. 5: Data channels MUST be secured; allowing for Req. 5: Data channels MUST be secured; 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: Data channels MUST provide message fragmentation support Req. 6: Data channels MUST provide message fragmentation support
such that IP-layer fragmentation can be avoided no matter such that IP-layer fragmentation can be avoided no matter
how large a message the JavaScript application passes to be how large a message the JavaScript application passes to be
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Req. 10: It MUST be possible to implement the protocol stack in the Req. 10: It MUST be possible to implement the protocol stack in the
user application space. user application space.
5. SCTP over DTLS over UDP Considerations 5. SCTP over DTLS over UDP Considerations
The important features of SCTP in the WebRTC context are: The important features of SCTP in the WebRTC context are:
o Usage of a TCP-friendly congestion control. o Usage of a TCP-friendly congestion control.
o The congestion control is modifiable for integration with the o The congestion control is modifiable for integration with the SRTP
(S)RTP media stream congestion control. media stream congestion control.
o Support of multiple unidirectional streams, each providing its own o Support of multiple unidirectional streams, each providing its own
notion of ordered message delivery. notion of ordered message delivery.
o Support of ordered and out-of-order message delivery. o Support of ordered and out-of-order message delivery.
o Supporting arbitrary large user messages by providing o Supporting arbitrary large user messages by providing
fragmentation and reassembly. fragmentation and reassembly.
o Support of PMTU-discovery. o Support of PMTU-discovery.
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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) exposes. unreliable datagram service) exposes.
The encapsulation of SCTP over DTLS defined in The encapsulation of SCTP over DTLS defined in
[I-D.ietf-tsvwg-sctp-dtls-encaps] provides confidentiality, source [I-D.ietf-tsvwg-sctp-dtls-encaps] provides confidentiality, source
authenticated, and integrity protected transfers. Using DTLS over authenticated, and integrity protected transfers. Using DTLS over
UDP in combination with ICE enables middlebox traversal in IPv4 and UDP in combination with ICE enables middlebox traversal in IPv4 and
IPv6 based networks. SCTP as specified in [RFC4960] MUST be used in IPv6 based networks. SCTP as specified in [RFC4960] MUST be used in
combination with the extension defined in [RFC3758] and provides the combination with the extension defined in [RFC3758] and provides the
following features for transporting non-(S)RTP media data between following features for transporting non-SRTP media data between
browsers: browsers:
o Support of multiple unidirectional streams. o Support of multiple unidirectional 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 Payload Protocol Identifier (PPID) Each SCTP user message contains a Payload Protocol Identifier (PPID)
that is passed to SCTP by its upper layer on the sending side and that is passed to SCTP by its upper layer on the sending side and
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| UDP1 | UDP2 | ... | | UDP1 | UDP2 | ... |
+----------------------------------+ +----------------------------------+
Figure 2: WebRTC protocol layers Figure 2: WebRTC protocol layers
This stack (especially in contrast to DTLS over SCTP [RFC6083] in This stack (especially in contrast to DTLS over SCTP [RFC6083] in
combination with SCTP over UDP [RFC6951]) has been chosen because it combination with SCTP over UDP [RFC6951]) has 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 (S)RTP media channels of the o shares the DTLS connection with the SRTP media channels of the
PeerConnection. PeerConnection.
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.ietf-tsvwg-sctp-dtls-encaps]. Please note that the specified in [I-D.ietf-tsvwg-sctp-dtls-encaps]. Please note that the
demultiplexing STUN vs. (S)RTP vs. DTLS is done as described in demultiplexing STUN vs. SRTP vs. DTLS is done as described in
Section 5.1.2 of [RFC5764] and SCTP is the only payload of DTLS. Section 5.1.2 of [RFC5764] and SCTP is the only payload of DTLS.
Since DTLS is typically implemented in user-land, the SCTP stack also Since DTLS is typically implemented in user-land, the SCTP stack also
needs to be a user-land stack. 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 are supported, since DTLS does not expose any address associations are supported, 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 interaction with the address changes during a session without needing interaction with the
DTLS and SCTP layers. However, SCTP SHOULD be notified when an DTLS and SCTP layers. However, SCTP SHOULD be notified when an
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Limiting the number of retransmissions to zero combined with Limiting the number of retransmissions to zero combined with
unordered delivery provides a UDP-like service where each user unordered delivery provides a UDP-like service where each user
message is sent exactly once and delivered in the order received. 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. Using a congestion control covered by the SCTP congestion control. Using a congestion control
different from than the standard one might improve the impact on the different from than the standard one might improve the impact on the
parallel (S)RTP media streams. parallel SRTP media streams.
6. The Usage of SCTP for Data Channels 6. The Usage of SCTP for Data Channels
6.1. SCTP Protocol Considerations 6.1. SCTP Protocol Considerations
The DTLS encapsulation of SCTP packets as described in The DTLS encapsulation of SCTP packets as described in
[I-D.ietf-tsvwg-sctp-dtls-encaps] MUST be used. [I-D.ietf-tsvwg-sctp-dtls-encaps] MUST be used.
The following SCTP protocol extensions are required: The following SCTP protocol extensions are required:
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The support for message interleaving as defined in The support for message interleaving as defined in
[I-D.ietf-tsvwg-sctp-ndata] SHOULD be used. [I-D.ietf-tsvwg-sctp-ndata] SHOULD be used.
6.2. Association Setup 6.2. Association Setup
The SCTP association will 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]. It will use (typically an exchange of SDP) [I-D.ietf-rtcweb-jsep]. It will use
the DTLS connection selected via ICE; typically this will be shared the DTLS connection selected via ICE; typically this will be shared
via BUNDLE or equivalent with DTLS connections used to key the (S)RTP via BUNDLE or equivalent with DTLS connections used to key the SRTP
media streams. media streams.
The number of streams negotiated during SCTP association setup SHOULD The number of streams negotiated during SCTP association setup SHOULD
be 65535, which is the maximum number of streams that can negotiated be 65535, which is the maximum number of streams that can negotiated
during the association setup. during the association setup.
6.3. SCTP Streams 6.3. SCTP Streams
SCTP defines a stream as a unidirectional logical channel existing SCTP defines a stream as a unidirectional logical channel existing
within an SCTP association to another SCTP endpoint. The streams are within an SCTP association to another SCTP endpoint. The streams are
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[I-D.ietf-tsvwg-sctp-ndata] [I-D.ietf-tsvwg-sctp-ndata]
Stewart, R., Tuexen, M., Loreto, S., and R. Seggelmann, "A Stewart, R., Tuexen, M., Loreto, S., and R. Seggelmann, "A
New Data Chunk for Stream Control Transmission Protocol", New Data Chunk for Stream Control Transmission Protocol",
draft-ietf-tsvwg-sctp-ndata-00 (work in progress), draft-ietf-tsvwg-sctp-ndata-00 (work in progress),
February 2014. February 2014.
[I-D.ietf-rtcweb-data-protocol] [I-D.ietf-rtcweb-data-protocol]
Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data Channel Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data Channel
Establishment Protocol", draft-ietf-rtcweb-data- Establishment Protocol", draft-ietf-rtcweb-data-
protocol-03 (work in progress), February 2014. protocol-04 (work in progress), April 2014.
[I-D.ietf-tsvwg-sctp-dtls-encaps] [I-D.ietf-tsvwg-sctp-dtls-encaps]
Tuexen, M., Stewart, R., Jesup, R., and S. Loreto, "DTLS Tuexen, M., Stewart, R., Jesup, R., and S. Loreto, "DTLS
Encapsulation of SCTP Packets", draft-ietf-tsvwg-sctp- Encapsulation of SCTP Packets", draft-ietf-tsvwg-sctp-
dtls-encaps-03 (work in progress), February 2014. dtls-encaps-04 (work in progress), May 2014.
[I-D.ietf-rtcweb-security] [I-D.ietf-rtcweb-security]
Rescorla, E., "Security Considerations for WebRTC", draft- Rescorla, E., "Security Considerations for WebRTC", draft-
ietf-rtcweb-security-06 (work in progress), January 2014. ietf-rtcweb-security-06 (work in progress), January 2014.
[I-D.ietf-rtcweb-security-arch] [I-D.ietf-rtcweb-security-arch]
Rescorla, E., "WebRTC Security Architecture", draft-ietf- Rescorla, E., "WebRTC Security Architecture", draft-ietf-
rtcweb-security-arch-09 (work in progress), February 2014. rtcweb-security-arch-09 (work in progress), February 2014.
[I-D.ietf-rtcweb-jsep] [I-D.ietf-rtcweb-jsep]
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