MMUSIC T. Reddy
Internet-Draft D. Wing
Intended status: Informational B. VerSteeg
Expires: April 13, 2014 R. Penno
Cisco
V. Singh
Aalto University
October 10, 2013
Improving ICE Interface Selection Using Port Control Protocol (PCP) Flow
Extension
draft-reddy-mmusic-ice-best-interface-pcp-00
Abstract
A host with multiple interfaces needs to choose the best interface
for communication. Oftentimes, this decision is based on a static
configuration and does not consider the link characteristics of that
interface, which may affect the user experience.
This document describes a mechanism for an endpoint to query the link
characteristics from the access router (the router at the other end
of the endpoint's access link) using a Port Control Protocol (PCP)
Flow Extension. This information influences endpoint's Interactive
Connectivity Establishment (ICE) candidate selection algorithm.
Status of this Memo
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This Internet-Draft will expire on April 13, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3
3. Algorithm overview . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Changed Link Quality . . . . . . . . . . . . . . . . . . . 4
4. Multiple Interfaces . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Multiple Interfaces for media streams . . . . . . . . . . . 5
4.2. Availability of New Interfaces . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . . 6
Appendix A. . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
A.1. Delay Factor in Discovering the Link Characteristics . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
ICE [RFC5245] uses a prioritization formula to perform connectivity
checks, in which the most preferred address pairs are tested first
and when a sufficiently good pair is discovered, the ICE connectivity
tests are stopped. ICE prefers address pairs in the following order:
transport address directly attached to the endpoint's network
interface (host candidate), transport address on the public side of a
NAT (server reflexive candidate), and finally, transport address that
are allocated on a media relay (relayed candidate). This approach
works well for an endpoint with a single interface, but is too
simplistic for endpoints with multiple interfaces. The network
interfaces may have different link characteristics, but that will not
be known without the awareness of the upstream and downstream
characteristics of the access link.
In this document, an ICE agent [RFC5245] uses PCP Flow Extension
[I-D.wing-pcp-flowdata] to determine the link characteristics of the
host's interfaces, which influence the ICE candidate priority.
As this document explains the interworking of ICE and Port Control
Protocol (PCP) Flow Extensions, it is beneficial to first read the
Overview of ICE (Section 2 of ICE [RFC5245]) and PCP Flowdata Option
[I-D.wing-pcp-flowdata]. Additionally, PCP for WebRTC
[I-D.penno-rtcweb-pcp] describes the problems with traversing NATs
and firewalls, current techniques used to solve them and the PCP
solution in these scenarios.
2. Notational Conventions
This note uses terminology defined in ICE [RFC5245] and PCP
[RFC6887].
3. Algorithm overview
The proposed algorithm is backward compatible with existing
implementations, and does not require any changes other than to the
selection of candidate priority.
When an endpoint first joins a network, it determines if the network
supports PCP Flow Extensions by following the procedures described in
[I-D.wing-pcp-flowdata]. Basically, the endpoint sends a PCP Flow
Extension probe packet, the response to which provides coarse
information on the link capabilities. After confirming that PCP Flow
Extensions are supported on that network interface, the ICE agent can
use PCP Flow Extensions on that interface (rather than STUN).
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When a media session needs to be established, and the user and
operator controlled policies on an endpoint permit more than one
interface for a media session, the ICE agent uses PCP Flow Extensions
to (a) obtain a mapping from its NAT or firewall and (b) determine
the characteristics of the link. After receiving the PCP Flow
Extension responses from its various interfaces, the ICE agent sorts
the ICE candidates according to the link capacity characteristics.
ICE candidates from the interface which best fulfills the desired
flow characteristics is assigned the highest priority and the best
suited interface should be used to communicate with the TURN server
to learn the relayed candidate address.
The ICE agent calculates the priorities of host and server-reflexive
candidates based on the above steps and signals these candidates in
offer or answer to the remote peer. After the offer and answer are
exchanged, the participating ICE agents begin pairing the candidates,
ordering them into check lists to start the ICE connectivity check
phase and eventually select the pair of candidates that will be used
for real-time communication.
3.1. Changed Link Quality
It is possible that the characteristics of a link may change over
time, and therefore the ICE agent may want to move the media to a
different interface. For example, if a competing high-bandwidth flow
starts or finishes its data transmission; the DSL line rate might
have improved (or degraded); the link capacity may have been
dynamically increased (or decreased). When link quality changes in
such a fashion, the PCP Flow Extensions sends a PCP message to the
endpoint. Upon receiving the message, the ICE agent may decide to
move the active flow to a more suitable interface and performs ICE
restart to trigger the switch over of the media streams to the new
interface.
For ICE local relayed candidates, the ICE agent can switch to the
more suitable interface by refreshing its allocation with the TURN
server using the procedures explained in section 5 of Mobility using
TURN [I-D.wing-mmusic-ice-mobility]. Thus reusing the local relayed
candidate on a different interface even if the endpoint IP address
changes. Therefore, the ICE agent can switch over local relayed
candidate to the most suited interface that meets the requirements of
the media stream. This way, even without informing the SIP server
and remote peer, ICE agent can switch over a local relayed candidate
to the most suited interface which meets the requested flow
characteristics.
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4. Multiple Interfaces
If multiple interfaces are available, the ICE agent can use PCP Flow
Extensions [I-D.wing-pcp-flowdata] to determine the best path. The
advantage is PCP can be used to select the most suitable interface
for the media streams. When an endpoint has multiple interfaces (for
example 3G, 4G, WiFi, VPN, etc.), an ICE agent can choose the
interfaces for media streams according to the path characteristics,
as discussed in the previous section.
4.1. Multiple Interfaces for media streams
If the requested flow characteristics for the media streams cannot be
handled by a single interface but by multiple interfaces then the ICE
agent performs the following steps:
o ICE agent based on the ICE connectivity results could select
multiple interfaces for the media session. For example, the ICE
agent selects to send the audio stream over the WiFi access point
because it offers (via PCP Flow Extensions) low delay, low packet
loss and average capacity of 120 Kbps, but for the video stream it
selects the 3G interface because it offers medium delay, medium
packet loss and average capacity of 500Kbps.
o Alternatively, the ICE agent on a mobile device may also want to
select the best suited interface among all the available
interfaces even if it does not serve the requested flow
characteristics for all the media streams, so that other
interfaces can be turned off to increase the battery life of
cellular connected devices such as smartphones or tablets.
4.2. Availability of New Interfaces
If the available interfaces do not meet the requested flow
characteristics then ICE agent can either proceed as usual using the
"Recommended Formula" explained in Section 4.1.2.1 of [RFC5245] to
prioritize the candidates or use the Happy Eyeballs Extension for ICE
algorithm proposed in [I-D.reddy-mmusic-ice-happy-eyeballs] for dual-
stack endpoint. When new interfaces become available then ICE agent
can use PCP Flow Extension to find if the newly available interfaces
meet the flow characteristics. When a PCP response is received from
at least one of the new interfaces and if it meets the requirements,
the endpoint can re-connect to the SIP proxy using the new interface.
The endpoint uses the candidates indicated in the previous PCP
response, it exchanges updated offer/answer to trigger ICE restart.
Once the ICE processing reaches the "Completed state", the ICE
endpoint can successfully switch the media session over to the new
interface. The interface initially used for communication can now be
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turned off without disrupting communications.
5. IANA Considerations
None.
6. Security Considerations
Security considerations discussed in [RFC6887] are to be taken into
account.
7. Acknowledgements
Authors would like to thank Anca Zamfir for comments and review.
8. References
8.1. Normative References
[I-D.wing-pcp-flowdata]
Wing, D., Penno, R., and T. Reddy, "PCP Flowdata Option",
draft-wing-pcp-flowdata-00 (work in progress), July 2013.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245,
April 2010.
[RFC6887] Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
Selkirk, "Port Control Protocol (PCP)", RFC 6887,
April 2013.
8.2. Informative References
[I-D.penno-rtcweb-pcp]
Penno, R., Reddy, T., Wing, D., and M. Boucadair, "PCP
Considerations for WebRTC Usage",
draft-penno-rtcweb-pcp-00 (work in progress), May 2013.
[I-D.reddy-mmusic-ice-happy-eyeballs]
Reddy, T., Patil, P., and D. Wing, "Happy Eyeballs
Extension for ICE",
draft-reddy-mmusic-ice-happy-eyeballs-03 (work in
progress), October 2013.
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[I-D.wing-mmusic-ice-mobility]
Wing, D., Reddy, T., Patil, P., and P. Martinsen,
"Mobility with ICE (MICE)",
draft-wing-mmusic-ice-mobility-05 (work in progress),
September 2013.
Appendix A.
A.1. Delay Factor in Discovering the Link Characteristics
Some concern has been expressed, that discovering the link
characteristics may consume more time than using STUN. However, STUN
will actually take more time than learning link characteristics,
because a STUN request/response traverses across more routers than a
PCP Flow Extension request.
Authors' Addresses
Tirumaleswar Reddy
Cisco Systems, Inc.
Cessna Business Park, Varthur Hobli
Sarjapur Marathalli Outer Ring Road
Bangalore, Karnataka 560103
India
Email: tireddy@cisco.com
Dan Wing
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, California 95134
USA
Email: dwing@cisco.com
Bill VerSteeg
Cisco Systems, Inc.
5030 Sugarloaf Parkway
Lawrenceville 30044
USA
Email: billvs@cisco.com
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Reinaldo Penno
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, 95134
USA
Phone:
Email: repenno@cisco.com
URI:
Varun Singh
Aalto University
School of Electrical Engineering
Otakaari 5 A
Espoo, FIN 02150
Finland
Email: varun.singh@iki.fi
URI: http://www.netlab.tkk.fi/~varun/
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