MMUSIC T. Reddy
Internet-Draft P. Patil
Intended status: Standards Track D. Wing
Expires: April 7, 2013 Cisco
October 4, 2012
Happy Eyeballs Extension for ICE
draft-reddy-mmusic-ice-happy-eyeballs-00
Abstract
This document specifies requirements for algorithms that make ICE
connectivity checks more aggressive to reduce delays in dual stack
host connectivity checks when there is a path failure for the address
family preferred by the application or by the operating system. As
IPv6 is usually preferred, the procedures in this document helps
avoid user-noticable delays wheen the IPv6 path is broken or
excessively slow.
Status of this Memo
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This Internet-Draft will expire on April 7, 2013.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3
3. Candidates Priority . . . . . . . . . . . . . . . . . . . . . . 3
4. Algorithm overview . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Processing the Results . . . . . . . . . . . . . . . . . . 5
5. Relayed Candidates . . . . . . . . . . . . . . . . . . . . . . 7
6. Setting Te, Tr and MAX_PAIRS_HAPPYEYE_STAGE . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
In situations where there are many IPv6 addresses, ICE [RFC5245] will
prefer IPv6 [RFC6724] and will attempt connectivity checks on all the
IPv6 candidates before trying an IPv4 candidate. If the IPv6 path is
broken, this fallback to IPv4 can consume a lot of time, harming user
satisfaction of dual stack devices.
This document describes an algorithm that makes ICE connectivity
checks more responsive to failures of an address family by performing
connectivity checks with both IPv6 and IPv4 candidates in parallel if
IPv6 connectivity checks have not yet succeeded. This document
specifies requirements for any such algorithm, with the goals that
the ICE agent need not be inordinately harmed with a simple
parallelisation of IPv6 and IPv4 connectivity checks and ensuring
that the priority of precedence defined in [RFC6724] be honored.
For either of the address families, there is also a very realistic
chance that connectivity checks for relayed candidates will always
work. There are scenarios where firewalls block connectivity checks
for Host/Server Reflexive candidates or for IPv4 or for IPv6. This
document also proposes an optimization where connectivity checks with
relayed checks are performed earlier than usual if connectivity
checks using other candidates do not succeed.
2. Notational Conventions
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 note uses terminology defined in [RFC5245].
3. Candidates Priority
A prioritization formula is used by ICE [RFC5245] so that most
preferred address pairs are tested first, and if a sufficiently good
pair is discovered, the tests can be stopped. With IPv6, addresses
obtained from local network interfaces, called host candidates, are
recommended as high-priority ones to be tested first since if they
work, they provide usually the best path between the two hosts. The
ICE specification recommends to use the rules defined in [RFC6724] as
part of the prioritization formula for IPv6 host candidates and
[I-D.keranen-mmusic-ice-address-selection] updates the ICE rules on
how IPv6 host candidates are selected.
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For dual stack hosts the preference for IPv6 host candidates is
higher than IPv4 host candidates based on precedence value of IP
addresses described in [RFC6724]. IPv6 server reflexive candidates
have higher precedence than IPv4 server reflexive candidate since
NPTv6 is stateless and transport-agnostic.
(highest) IPv6 Host Candidate
IPv4 Host Candidate
IPv6 Server Reflexive Candidate
IPv4 Server Reflexive Candidate
IPv6 Relayed Transport Candidate
(lowest) IPv4 Relayed Transport Candidate
Figure 1: Candidate Preferences in decreasing order
By using the technique in Section 4 IPv6 candidate pairs will be
tested first as usual, but if connectivity checks are not successful
after a certain period of time, the algorithm will become more
aggressive and connectivity checks using IPv6/IPv4 host/
server-reflexive candidates will be performed simultaneously. If
connectivity checks with IPv6 candidate pairs do not yield any
successful result then ICE endpoints can immediately start sending
media using IPv4 host/server-reflexive candidates.
Note: [RFC6724] permits administrator to change the policy table to
prefer IPv4 addresses over IPv6 addresses in which case the algorithm
described in the next section is reversed.
4. Algorithm overview
The Happy Eyeballs Extension for ICE is governed by a timer (Te) that
is started just before carrying out the ICE connectivity checks for
each check list under the following conditions:
1. when the candidates pairs include IPv6 and IPv4 addresses
2. list of IPv6 candidate pairs is higher than a configured
threshold (MAX_PAIRS_HAPPYEYE_STAGE_I). [RFC5245] recommends a
limit of 100 for the candidate pairs.
When the timer (Te) fires, if the connectivity check using IPv6
candidate pairs are not yet successful and if the number of IPv6
candidate pairs with remote candidates of type host in the check list
that are in Waiting and Frozen state are non-zero, the ICE agent
performs the following Happy Eyeball steps in parallel with the
regular ICE Ordinary checks:
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o Find the highest priority pair in the checklist that is in the
Waiting state with candidate address family being IPv4 and remote
candidate of type host. If there are no remote IPv6 candidates of
type server-reflexive then IPv4 remote candidates of type server-
reflexive will be added to the search.
1. If there is such a pair then perform ICE connectivity check on
this pair and set the state of the candidate pair to In-
Progress.
2. If there is no such pair find the highest priority pair in the
checklist that is in the Frozen state with candidate address
family being IPv4 and remote candidate of type host candidate.
If there are no remote IPv6 candidates of type server-
reflexive then IPv4 remote candidates of type server-reflexive
will be added to the search. If there is such pair in Frozen
state then unfreeze the pair, perform connectivity check on
this pair and set the state of the candidate pair to In-
Progress.
o The above mentioned steps will be followed every Ta milliseconds
and stopped when any of the below conditions are met:
1. All IPv6 candidate pairs with remote candidates of type host
in the check list are in any of the following states
Succeeded, In-Progress or Failed states. The parallel
activity is not required beyond this point because the regular
ICE algorithm will itself pick up IPv4 candidate pairs not yet
tested.
2. All IPv4 candidate pairs with remote candidates of type host/
server reflexive are in any of the following states Succeeded,
In-Progress or Failed states.
4.1. Processing the Results
If ICE connectivity checks using an IPv4 candidate is successful then
ICE Agent will performs as usual "Discovering Peer Reflexive
Candidates" (Section 7.1.3.2.1 of [RFC5245]), "Constructing a Valid
Pair" (Section 7.1.3.2.2 of [RFC5245]), "Updating Pair States"
(Section 7.1.3.2.3 of [RFC5245]), "Updating the Nominated Flag"
(Section 7.1.3.2.4 of [RFC5245]).
If ICE connectivity checks using an IPv4 candidate is successful for
each component of the media stream and connectivity checks using IPv6
candidates is not yet successful, the ICE endpoint will declare
victory, conclude ICE for the media stream and start sending media
using IPv4. However, it is also possible that ICE endpoint continues
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to perform ICE connectivity checks with IPv6 candidate pairs and if
checks using higher-priority IPv6 candidate pair is successful then
media stream can be moved to the IPv6 candidate pair. Continuing to
perform connectivity checks can be useful for subsequent connections,
to optimize which connectivity checks are tried first. Such
optimization is out of scope of this document.
The following diagram shows the behaviour during the connectivity
check when Alice calls Bob and Agent Alice is the controlling agent
and uses the aggressive nomination algorithm. "USE-CAND" implies the
presence of the USE-CANDIDATE attribute.
Alice Bob
| |
| Bind Req USE-CAND Bind Req |
| using IPv6 using IPv6 |
|------------------>X X<-----------------------|
| Bind Req USE-CAND Bind Req |
| using IPv6 after Ta using IPv6 |
|------------------>X X<-----------------------|
| Bind Req USE-CAND |
| using IPv6 after Ta Bind Req |
|------------------>X using IPv6 |
| X<-----------------------|
| |
[Timer Te fires, try IPv4 in parallel] |
| |
| Bind Req USE-CAND |
| using IPv4 |
|------------------------------------------------------------>|
| Bind Req USE-CAND |
| using IPv6 after Ta |
|------------------> X |
| Bind Resp |
| using IPv4 |
|<----------------------------------------------------------- |
| RTP |
|============================================================>|
| Bind Req |
| using IPv4 |
|<------------------------------------------------------------|
| Bind Response |
| using IPv4 |
|------------------------------------------------------------>|
| RTP |
|<===========================================================>|
Figure 2: Happy Eyeballs Extension for ICE
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5. Relayed Candidates
The optimization proposes doing connectivity checks with relayed
candidates in parallel with other candidates. The algorithm does not
make a distinction between IPv6/IPv4 relayed candidates and will
choose the existing order among relayed candidate pair defined by
ICE. If ICE connectivity check is successful using a relayed
candidate from either of the IP address families, the ICE agent can
stop connectivity checks for other relayed candidates.
This part of the Happy Eyeballs Extension for ICE is governed by a
timer (Tr) that is started just before carrying out the ICE
connectivity checks for each check list under the following
conditions:
1. when the candidates pairs include IPv6 and IPv4 relayed addresses
2. list of candidate pairs is higher than a configured threshold
(MAX_PAIRS_HAPPYEYE_STAGE_I).
When the timer (Tr) fires, If no ICE connectivity checks are
successful as yet and if ICE Connectivity checks using IPv6 and IPv4
local relayed candidates have not yet been attempted then the
following steps will be started by the ICE agent in parallel with
other connectivity checks:
o Find the highest priority pair in the checklist that is in the
Waiting state with local candidate of type relayed.
1. If there is such a pair then perform ICE connectivity check on
this pair and set the state of the candidate pair to In-Progress.
2. If there is no such pair find the highest priority pair in the
checklist that is in the Frozen state with local candidate of
type relayed. If there is such pair in Frozen state then
unfreeze the pair, perform connectivity check on this pair and
set the state of the candidate pair to In-Progress.
If ICE connectivity checks using relayed candidate is successful then
ICE Agent will performs as usual "Constructing a Valid Pair" (Section
7.1.3.2.2 of [RFC5245]), "Updating Pair States" (Section 7.1.3.2.3 of
[RFC5245]), "Updating the Nominated Flag" (Section 7.1.3.2.4 of
[RFC5245]). If ICE connectivity checks using local relayed
candidates is successful for each component of the media stream and
connectivity checks using higher priority candidate pairs has not yet
succeeded then conclude ICE for the media stream and proceed to send
media using local relayed candidate.
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However ICE connectivity checks MUST be continued and if the check
succeeds for a pair whose priority is higher than the previously
selected candidate pair then media session will be moved to this
pair. Hence media will only be sent briefly on TURN relays.
Additional TURN server load is created due to this recommendations,
especially when connectivity check using IPv6/IPv4 host/
server-reflexive candidates are not completing quickly and the side
affect could be that RTP receivers will receive packets out of order
during switchover.
6. Setting Te, Tr and MAX_PAIRS_HAPPYEYE_STAGE
The value of Ta, Tr, MAX_PAIRS_HAPPYEYE_STAGE_I,
MAX_PAIRS_HAPPYEYE_STAGE_II and SHOULD be configurable, and SHOULD
have a default of:
Te : 150ms
Tr : 500ms
MAX_PAIRS_HAPPYEYE_STAGE_I : 12
MAX_PAIRS_HAPPYEYE_STAGE_II : 6
Figure 3: Default Values
7. IANA Considerations
None.
8. Security Considerations
STUN connectivity check using MAC computed during key exchanged in
the signaling channel provides message integrity and data origin
authentication as described in section 2.5 of [RFC5245] apply to this
use.
9. References
9.1. Normative References
[I-D.keranen-mmusic-ice-address-selection]
Keranen, A. and J. Arkko, "Update on Candidate Address
Selection for Interactive Connectivity Establishment
(ICE)", draft-keranen-mmusic-ice-address-selection-01
(work in progress), July 2012.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245,
April 2010.
[RFC6724] Thaler, D., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, September 2012.
9.2. Informative References
[RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address
Translator (NAT) Terminology and Considerations",
RFC 2663, August 1999.
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
Prashanth Patil
Cisco Systems, Inc.
Cessna Business Park, Varthur Hobli
Sarjapur Marthalli Outer Ring Road
Bangalore, Karnataka 560103
India
Email: praspati@cisco.com
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Dan Wing
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, California 95134
USA
Email: dwing@cisco.com
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