Transports for RTCWEB
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harald@alvestrand.no
This document describes the data transport protocols used by RTCWEB,
including the protocols used for interaction with intermediate boxes
such as firewalls, relays and NAT boxes.
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 RFC 2119.
The IETF RTCWEB effort, part of the WebRTC effort carried out in
cooperation between the IETF and the W3C, is aimed at specifying a
protocol suite that is useful for real time multimedia exchange between
browsers.
The overall effort is described in the RTCWEB overview document,
. This document focuses
on the data transport protocos that are used by conforming
implementations.
This protocol suite is designed for WebRTC, and intends to satisfy
the security considerations described in the WebRTC security documents,
and .
The protocol specifications used here assume that the following
protocols are available to the implementations of the RTCWEB
protocols:
UDP. This is the protocol assumed by most protocol elements
described.
TCP. This is used for HTTP/WebSockets, as well as for TURN/SSL
and ICE-TCP.
For both protocols, this specification assumes the ability to
set the DSCP code point of the sockets opened. It does not assume that
the DSCP codepoints will be honored, and does assume that they may be
zeroed or changed, since this is a local configuration issue.
This specification does not assume that the implementation will
have access to ICMP or raw IP.
The primary mechanism to deal with middle boxes is ICE, which is an
appropriate way to deal with NAT boxes and firewalls that accept
traffic from the inside, but only from the outside if it's in response
to inside traffic (simple stateful firewalls).
In order to deal with symmetric NATs, TURN MUST be supported.
In order to deal with firewalls that block all UDP traffic, TURN
over TCP MUST be supported. (QUESTION: What about ICE-TCP?)
The following specifications MUST be supported:
ICE
TURN, including TURN over TCP [[QUESTION: and TURN over TLS]],
.
For referring to STUN and TURN servers, this specification
depends on the STUN URI, .
For data transport over the RTCWEB data channel , RTCWEB implementations
support SCTP over DTLS over ICE. This is specified in . Negotiation of this
transport in SCTP is defined in .
The setup protocol for RTCWEB data channels is described in .
For transport of media, secure RTP is used. The details of the
profile of RTP used are described in "RTP Usage" .
RTCWEB implementations MUST support multiplexing of SCTP/DTLS and
RTP over the same port pair, as described in the DTLS_SRTP
specification , section 5.1.2.
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
Security considerations are enumerated in .
This document is based on earlier versions embedded in , which were the results of
contributions from many RTCWEB WG members.