Internet DRAFT - draft-thatcher-ice-network-cost
draft-thatcher-ice-network-cost
Network Working Group P. Thatcher
Internet-Draft H. Zhang
Intended status: Standards Track T. Brandstetter
Expires: March 23, 2017 Google
September 19, 2016
ICE Network Cost: Dynamically selecting ICE candidate pairs based on
relative cost of network interfaces
draft-thatcher-ice-network-cost-01
Abstract
This document describes an extension to the Interactive Connectivity
Establishment (ICE) that enables ICE agents to exchange information
about the relative cost of network interfaces and dynamically choose
the selected ICE candidate pair based on the cost of both the local
and remote network interfaces. For example, if a cellular network
interface has a higher cost than a Wi-Fi network interface, the ICE
agents can use that information to prefer candidate pairs with Wi-Fi
rather than cellular when possible, and only use cellular when
necessary.
This document additionally describes a second piece of information,
network ID, that goes along with the network cost and can be used to
know when a network interface has changed, even if two network
interfaces have the same network cost.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on March 23, 2017.
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Copyright Notice
Copyright (c) 2016 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Choosing a value for network cost and network ID . . . . . . 3
4. Signaling network cost and network ID . . . . . . . . . . . . 4
5. STUN attribute for network cost and network ID . . . . . . . 4
6. Interpreting network cost and network ID . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. Security Considerations . . . . . . . . . . . . . . . . . . . 5
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
10. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
In certain network conditions, ICE agents may prefer to use a network
interface with a lower cost (for a definition of cost chosen by the
ICE agent, which need not be directly related to monetary costs). If
the controlling side has such a preference, it can unilaterally
nominate a candidate pair with the network interface with lower cost,
but if either the controlling side has no such preference, or it
would like to take the controlled side's preference into account, it
cannot do so unless the controlled side provides information about
its network cost.
Additionally, if the network interface of the controlled side changes
(such as by using TURN mobility), the controlling side needs updated
information from the controlled side.
The controlling side may also wish to select candidate pairs not only
based on the relative cost between candidate pairs, but also the cost
relative to the quality of the network path. For example, if Wi-Fi
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has a much higher cost, but cellular is much higher quality, the
controlling side may select cellular even though it's higher cost.
To do so, the controlled side must provide information about the
network cost relative to the network quality. For example, if a
network cost 10 is equivalent to 100ms network RTT, a Wi-Fi with cost
0 and RTT 150ms will have equal preference to a cellular with cost 10
and RTT 50ms.
Although the controlled side already communicates an ICE candidate
priority, that candidate attribute doesn't meet the needs of this
situation for the following reasons:
o Candidate priority affects ICE check ordering as well as candidate
pair preference, which is undesirable in this situation, where the
ICE check order should be maintained, but the candidate pair
preference should be changed.
o Candidate priority cannot change when the network interface
changes (such as by using TURN mobility)
o Candidate priority is only defined relative to other priorities,
and can't be compared against network quality in a meaningful way.
2. Terminology
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 [RFC2119].
This specification makes use of all terminology defined by the
protocol for Interactive Connectivity Establishment in [RFC5245].
Network Cost A value indicating how much an ICE agent would prefer
to not use a given network interface. This may be, but need not
be related to monetary costs of using the network interface.
Network ID An ID that uniquely identifies a network interface.
3. Choosing a value for network cost and network ID
Network cost is an integer in the range 0-999, where larger values
indicate a stronger preference for not using that network interface.
Each network interface SHOULD have a unique network ID, in the range
of 0 to (2^16)-1.
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4. Signaling network cost and network ID
ICE agents MUST signal network cost on each ICE candidate if the cost
is non-zero. ICE agents MUST signal network ID on each ICE
candidate.
For example, in an SDP candidate line, the attributes could be
signaled as "network-cost 100 network-id 1".
5. STUN attribute for network cost and network ID
To communicate a change in network cost or to communicate network
cost for peer reflexive candidates, the following STUN attribute is
defined:
A 32-bit integer where the first 16 bits are the network ID and the
second 16 bits are network cost:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network ID | Network Cost |
In the initial ICE checks, ICE agents MUST communicate a network cost
and network ID if either is non-zero. The ICE agent MUST communicate
new values in subsequent ICE checks if the network cost or network ID
changes.
6. Interpreting network cost and network ID
If network cost is communicated via either signaling or STUN
attribute, the controlling side SHOULD use the network cost of the
controlled side as part of the criteria to determine which candidate
pair to select. It SHOULD use network cost before using candidate
priorities (network cost takes precedence over candidate priority),
and it SHOULD NOT change the ICE check order based on network cost.
If the controlling side chooses to balance network cost against
network quality, it is RECOMMENDED to treat a difference in network
cost of 10 as equivalent of a change in network RTT of 100ms.
Any time the controlling side sees a change in the network cost from
the controlled side, it MUST recalculate which candidate pair to
select and nominate the newly selected candidate pair, if it has
changed.
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7. IANA Considerations
This specification requests no actions from IANA.
8. Security Considerations
TODO
9. Acknowledgements
TODO
10. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245,
DOI 10.17487/RFC5245, April 2010,
<http://www.rfc-editor.org/info/rfc5245>.
Authors' Addresses
Peter Thatcher
Google
747 6th St S
Kirkland, WA 98033
USA
Email: pthatcher@google.com
Honghai Zhang
Google
747 6th St S
Kirkland, WA 98033
USA
Email: honghaiz@google.com
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Taylor Brandstetter
Google
747 6th St S
Kirkland, WA 98033
USA
Email: deadbeef@google.com
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