Internet DRAFT - draft-thomson-tram-turn-bandwidth
draft-thomson-tram-turn-bandwidth
TRAM M. Thomson
Internet-Draft Mozilla
Intended status: Standards Track B. Aboba
Expires: January 5, 2015 Microsoft
A. Johnston
Avaya
O. Moskalenko
public project
rfc5766-turn-server
July 4, 2014
A Bandwidth Attribute for TURN
draft-thomson-tram-turn-bandwidth-01
Abstract
An attribute is defined for Session Traversal Utilities for NAT
(STUN) that allows for declarations of bandwidth limits on the
negotiated flow. The application of this attribute is the
negotiation of bandwidth between a Traversal Using Relays around NAT
(TURN) client and a TURN server.
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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This Internet-Draft will expire on January 5, 2015.
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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. The BANDWIDTH Attribute . . . . . . . . . . . . . . . . . . . . 4
4. Applications . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. STUN Usage . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. TURN Usage . . . . . . . . . . . . . . . . . . . . . . . . 5
4.3. ICE Usage . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Bandwidth Measurement Considerations . . . . . . . . . . . . . 5
5.1. Rate Enforcement . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
8. Implementation Status . . . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
This document defines a BANDWIDTH attribute that can be used to
request and allocate bandwidth at a Traversal Using Relays around NAT
(TURN) relay [RFC5766].
The operator of a TURN server will likely wish to provide fairness
between relayed sessions. A TURN server might also wish to limit the
use of service to audio-only sessions, or low bandwidth video and
audio sessions. In addition, the server may apply rate-limiting
policy depending on the credential used for authentication, or the
origin of the client. Without the BANDWIDTH attribute, there is no
way for a client to indicate the expected bandwidth utilization, or
for the server to indicate the maximum bandwidth utilization allowed
before rate limiting could be applied.
This attribute is used for indicating a bandwidth limit that is set
in policy. The sender is not advised or required to utilize
bandwidth up to this limit; limits are usually set well in excess of
application needs. Senders also limit their use of bandwidth in
reaction to path congestion and "circuit breakers".
Note that the BANDWIDTH attribute was originally in the TURN draft up
to version draft-ietf-behave-turn-07 where it was removed as "the
requirements for this feature were not clear and it was felt the
feature could be easily added later." This draft proposes adding
this attribute back into TURN. A related error code 507
"Insufficient Bandwidth Capacity" was also defined in the TURN
Internet-Draft, but is not proposed in this draft. This attribute
has also been proposed to be used by ICE to provide communication
consent [I-D.thomson-mmusic-rtcweb-bw-consent]. No use cases have
been identified where bandwidth information is useful for a STUN
server which is responding to STUN binding requests.
There have been discussions about what other media-related
information could be usefully exchanged between a TURN client and a
TURN server. One proposal was for the actual media type (voice,
video, data) to be exchanged. Other proposals include more
granularity over the bandwidth, including max, min, average, etc.
While these could be added, the authors do not feel the use cases for
these data have been sufficiently developed yet. Also, this
information is known in signaling through the SDP attributes and
parameters. In a particular implementation, it could be possible for
a signaling-aware entity to share this information with a TURN server
in order to apply policy for the media relay.
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2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in BCP 14, RFC 2119 [RFC2119] and indicate requirement
levels for compliant implementations.
The terms client, server, and peer are those used for TURN, as
defined in [RFC5766].
3. The BANDWIDTH Attribute
The BANDWIDTH attribute (identifier TBD) identifies the rate of
packet transmission in kilobits per second that is permitted for a
given transport flow. The BANDWIDTH attribute is a comprehension-
optional attribute (see Section 15 from [RFC5389]). Figure 1 shows
the format of this attribute.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Attribute Type (TBD) | Length (4) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bandwidth |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Bandwidth Attribute Format
The value of this attribute is an unsigned integer that represents
the maximum bandwidth for the flow in kilobits per second (1 kilobit
= 1024 bits). This is the original format of the Bandwidth
attribute. This format could include a maximum and average
bandwidth, as the BANDWIDTH-USAGE attribute proposed in
[I-D.martinsen-tram-discuss].
4. Applications
This section discusses the application of the BANDWIDTH attribute for
STUN, TURN, and ICE.
4.1. STUN Usage
Since the bandwidth of a communications session has no bearing on a
STUN server that simply responds to binding requests, this attribute
MUST NOT be used for client-server STUN requests or responses.
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4.2. TURN Usage
This attribute can be useful for communication between a TURN client
and a TURN server.
The BANDWIDTH attribute indicates a limit to available bandwidth for
TURN [RFC5766] allocation. The bandwidth limit is symmetric; the
value covers the bandwidth of data sent from a peer toward the TURN
server and the bandwidth of data sent from client to the TURN server.
A BANDWIDTH attribute MAY be present in an Allocate request. This
attribute indicates that the given bandwidth is requested. A
BANDWIDTH attribute MAY be present in an Allocate response. This
attribute in a response indicates the limit that will be applied by
the TURN server. The value a TURN server provides could be
influenced by the value that a TURN client requests at the discretion
of server policy. A client could use this bandwidth limitation of
the TURN server in choosing media types or in choosing codecs for a
media session.
4.3. ICE Usage
While [I-D.thomson-mmusic-rtcweb-bw-consent] proposed the use of the
BANDWIDTH attribute to provide bandwidth consent for ICE, this draft
does not do so. This attribute MUST NOT be used with ICE.
5. Bandwidth Measurement Considerations
Allocation messages (Binding and Allocate) sent to and from the TURN
server are exempt from any bandwidth measurement accounting.
In calculating bandwidth, the entire IP packet - including the header
- is measured. This is identical to the measurement performed by the
Real-time Transport Protocol (RTP) [RFC3550]. At a TURN server,
bandwidth measurement is performed on the packets arriving at or
leaving from the TURN server, prior to the encapsulation that occurs
between TURN server and TURN client.
Determining the rate requires that the bits be allocated to specific
intervals of time. How bits are allocated MAY vary between
implementations.
Measurement of bandwidth is imperfect and inconsistent. Packet
jitter can result in fluctuations in received packet rate so that a
receiver might see an instantaneous bandwidth that is different to
what the sender might have transmitted. Jitter can cause the
observed bandwidth of incoming packets to temporarily increase above
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the permitted rate. At a minimum, implementations SHOULD allow for
short periods of excessive bandwidth to allow for these temporary
increases.
5.1. Rate Enforcement
Enforcement of limits by the TURN server SHOULD provide an allowance
for application usages that temporarily exceed the limit. For
example, assessing observed bandwidth usage as an average over 10
seconds ensures that real-time video does not clip unnecessarily;
shorter durations could result in the enforcement affecting valuable
intra-frames.
6. Security Considerations
For STUN requests or responses that are not sent using TLS or DTLS
transport, the bandwidth information contained in the BANDWIDTH
attribute will be available to an eavesdropper who could use it to
learn about the nature of a session to be established. For example,
they might be able to deduce from the bandwidth requested that the
session is likely to be audio only, or audio and video. However, an
on-path attacker can likely learn this same information from either
the signaling channel or by inspecting the RTP packet headers, which
are in the clear for SRTP, or simply by measuring the media bandwidth
used.
If a STUN request or response is transported using TCP or UDP, the
BANDWIDTH attribute will have integrity protection from the MESSAGE-
INTEGRITY attribute if the request is authenticated using the STUN
short-term or long-term authentication method. Unauthenticated TCP
or UDP requests will not have integrity protection and could be
modified by a MitM attacker. The use of DTLS transport
[I-D.ietf-tram-stun-dtls] provides integrity protection for the
BANDWIDTH attribute regardless of the STUN authentication method
used.
7. IANA Considerations
The STUN BANDWIDTH attribute uses the TBD value in the comprehension-
optional range. This attribute is registered in the "STUN Attribute"
Registry following the procedures of Section 18.2 of [RFC5389].
8. Implementation Status
Note to RFC Editor: Please remove this entire section prior to
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publication, including the reference to RFC 6982.
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC6982].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
According to [RFC6982], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
A multiple realms capable advanced open source TURN server (named
'Coturn') has been created by Oleg Moskalenko and is freely licensed
under the New BSD license. This reference implementation and proof-
of-concept provides a clone (a spin-off) of the rfc5766-turn-server
project adding STUN BANDWIDTH attribute support, among other TRAM
Working Group STUN and TURN extensions.
'Coturn' is backward-compatible with rfc5766-turn-server project but
the code is more complex and it uses a different (also more complex)
database structure. It is the intent to add all IETF TRAM TURN
server related capabilities to this project as they mature. 'Coturn'
is publicly available and can be found at:
https://code.google.com/p/coturn/
9. References
9.1. Normative References
[I-D.ietf-tram-stun-dtls]
Petit-Huguenin, M. and G. Salgueiro, "Datagram Transport
Layer Security (DTLS) as Transport for Session Traversal
Utilities for NAT (STUN)", draft-ietf-tram-stun-dtls-05
(work in progress), June 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
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Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245,
April 2010.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389,
October 2008.
[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.
9.2. Informative References
[I-D.martinsen-tram-discuss]
Martinsen, P. and H. Wildfeuer, "Differentiated prIorities
and Status Code-points Using Stun Signalling (DISCUSS)",
draft-martinsen-tram-discuss-00 (work in progress),
February 2014.
[I-D.thomson-mmusic-rtcweb-bw-consent]
Thomson, M. and B. Aboba, "Bandwidth Constraints for
Session Traversal Utilities for NAT (STUN)",
draft-thomson-mmusic-rtcweb-bw-consent-00 (work in
progress), October 2012.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", RFC 6982,
July 2013.
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Authors' Addresses
Martin Thomson
Mozilla
331 E Evelyn Street
Mountain View, CA 94041
USA
Phone: +1 650-353-1925
Email: martin.thomson@gmail.com
Bernard Aboba
Microsoft
One Microsoft Way
Redmond, WA 98052
USA
Email: bernard_aboba@outlook.com
Alan Johnston
Avaya
St. Louis, MO
USA
Email: alan.b.johnston@gmail.com
Oleg Moskalenko
public project rfc5766-turn-server
Walnut Creek, CA
USA
Email: mom040267@gmail.com
URI: https://code.google.com/p/rfc5766-turn-server/
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