Network Working Group H. Alvestrand
Internet-Draft Google
Intended status: Experimental November 10, 2010
Expires: May 14, 2011
A Datagram Transport for the RTC-Web profile
draft-alvestrand-dispatch-rtcweb-datagram-00
Abstract
This document describes a combination and profiling of existing IETF
protocols to provide a datagram service that is suitable as a generic
transport substrate for the RTC-Web family of real-time audio/video
applications.
Requirements Language
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 [RFC2119].
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
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Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference
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This Internet-Draft will expire on May 14, 2011.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
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publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Service model . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Channel types . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. UDP channel . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. TCP channel . . . . . . . . . . . . . . . . . . . . . . . . 4
4.3. TLS channel . . . . . . . . . . . . . . . . . . . . . . . . 4
4.4. DTLS channel . . . . . . . . . . . . . . . . . . . . . . . 4
4.5. Channels with relay . . . . . . . . . . . . . . . . . . . . 4
5. Channel setup, teardown and usage . . . . . . . . . . . . . . . 5
6. An URI scheme for datagram channels . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
10.1. Normative References . . . . . . . . . . . . . . . . . . . 6
10.2. Informative References . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
When transporting audio / video data between participants on the
current Internet, there are a number of obstacles to be faced.
Among them are NAT boxes, firewalls, connection interruptions, the
availability of multiple paths between participants, and capacity
issues.
This memo describes a combination of existing protocols that can be
used to achieve a seamless datagram transport service across this
very heterogenous environment.
An overview of the effort of which this is a part can be found in the
overview document, [overview].
2. Terminology
This draft uses a couple of commonly used terms in quite specific
ways. The reader is advised to study these definitions carefully.
(TODO: Agree on terminology to use)
Session An association with two endpoints, between which datagrams
flow.
Datagram A sequence of octets, of a given length. In this
specification, a datagram does not carry addressing information.
Channel One means of transporting a datagram over a session. A
session may have multiple channels at any time.
Endpoint One end of a session. This document does not distinguish
between an initiator and a responder endpoint.
Control channel A means of communication between the endpoints of a
session that does not require a transport to be active.
Typically, authentication, authorization and negotiation is
carried out over the control channel. The specification of the
control channel is out of scope for this specification.
3. Service model
The basic model presented is a datagram model. On top of this one
can layer various services, such as pseudoTCP (REF), RTP[RFC3550] or
any other higher layer protocol that is capable of running across a
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datagram service.
The addressing model departs from the traditional Internet model in
that end point addresses are not used for endpoint identification,
only for channel establisment; instead, an initial packet exchange,
using ICE [RFC5245], is used to bind a channel to a prenegotiated
session.
The datagram service is not completely transparent; in particular, it
is not possible to carry a datagram where the two highest bits of the
first octet are zero and octet 5 to 8 contain the value 0x2112A442,
since these datagrams are reserved for use of the STUN protocol (RFC
5389 section 6).
4. Channel types
4.1. UDP channel
An UDP channel is negotiated using ICE. Each datagram is simply
carried as the content of an UDP packet.
4.2. TCP channel
A TCP channel consists of a TCP connection, over which are sent
datagrams packaged according to (REF). The binding of a TCP channel
is done by executing an ICE negotiation over the first few packets
passed across the TCP channel.
4.3. TLS channel
A TLS channel consists of a standard TLS negotiation, followed by
passing datagrams over the TLS record layer; the length fields of
(REF) are not used. A TLS channel is bound to its session by <insert
process description>.
4.4. DTLS channel
A DTLS channel is created by executing a DTLS connection negotiation,
followed by datagram exchange, where the datagrams are protected by
DTLS mechanisms. The DTLS channel is bound to its session by <insert
process>.
4.5. Channels with relay
If there is no possibility of setting up a direct connection, a relay
must be used. The specification from TURN [RFC5766]is used.
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5. Channel setup, teardown and usage
The service model envisioned here is that all datagrams arriving on a
session are considered equally valid. The session gives no
guarantees against duplication, loss or reordering; such concerns are
left to the higher protocol layers.
The expected normal usage is that two endpoints will exchange
addressing information that can be used for a series of potential
channels, that the endpoints will probe for working channels using
ICE (RFC 5245), and use the "best" candidate, while using the STUN
probing facilities to keep some number of "second best" candidates
alive if the "best" candidate stops working.
A data-sending endpoint may unilaterally decide to start or stop
using an established channel at any time. No negotiation is
necessary.
A receiving endpoint will learn that a channel has been removed by
not seeing any more STUN keepalive messages on that channel within
<timeout>.
A session is considered closed when all channels that have been
successfully established have timed out.
6. An URI scheme for datagram channels
This URI scheme is mainly included in order to make it easy for APIs
that normally use URIs as what they use to refer to objects.
The DGSESSION URI scheme specifies the information required for a
session; it consists of two parts:
o An absolute reference, which includes the user name and password
used to establish the connection.
o A series of addressing hints, which include the data necessary to
establish a channel.
<TODO: Fill out an URI registration template for the scheme>
Example:
dgsession:username:password?ipv4:12.34.56:udp:12345&
ipv6:2002::dead:beef:tcp:80&ipv4:12.34.56.78:tls:443
The sequence of addressing hints is an indication of the preference
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of the URL constructor for the sequence in which to try these
candidates; the most preferred address is the one to the left.
Note that a DGSESSION URI is a capability; anyone with the URI will
be able to connect to the entity. They should therefore be handled
in the same way as (short-term) passwords, and never passed in the
clear.
7. IANA Considerations
This document registers the URI scheme from section Paragraph 1.
Note to RFC Editor: this section may be removed on publication as an
RFC.
8. Security Considerations
As with all layered protocols, it is a matter for the application to
decide which level security should be provided at. For instance, an
RTP session protected using SRTP <ref> can be considered to not need
any further safeguards against interception, modification or replay,
so can be passed "in the clear" across any channel type here. For
data without such protection, adequate measures need to be taken; in
particular, it is trivially easy for someone with the ability to
snoop and insert packets to insert fake packets into an established
UDP channel.
The main defense against denial-of-service attacks is the fact that
the ICE mechanisms were designed for low cost refusal of unauthorized
connections.
9. Acknowledgements
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.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
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[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245,
April 2010.
[RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using
Relays around NAT (TURN): Relay Extensions to Session
Traversal Utilities for NAT (STUN)", RFC 5766, April 2010.
10.2. Informative References
[overview]
Alvestrand, H., "Overview: Real Time Protocols for Brower-
based Applications", November 2010.
Author's Address
Harald Tveit Alvestrand
Google
Kungsbron 2
Stockholm, 11122
Sweden
Email: harald@alvestrand.no
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