Network Working Group M. Boucadair
Internet-Draft Y. Noisette
Intended status: Standards Track France Telecom
Expires: January 28, 2010 A. Allen
Research in Motion (RIM)
July 27, 2009
The atypes media feature tag for Session Initiation Protocol (SIP)
draft-boucadair-dispatch-ipv6-atypes-00
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Abstract
This specification defines a new media feature tag called atypes.
This new media feature tag indicates the IP address type capabilities
of the UA (User Agent) and can aid the routing process and ease the
invocation of required functions when heterogeneous (i.e. IPv4 and
IPv6) parties are involved in a given SIP session.
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].
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Justification for atypes . . . . . . . . . . . . . . . . . . . 5
3. Relationship of atypes to ANAT/ICE . . . . . . . . . . . . . . 5
4. sip.atypes Media Feature Tag . . . . . . . . . . . . . . . . . 7
5. Session Routing Considerations . . . . . . . . . . . . . . . . 9
6. Examples of atypes tag usages . . . . . . . . . . . . . . . . 9
6.1. IPv4-only UA . . . . . . . . . . . . . . . . . . . . . . . 9
6.2. IPv6-only UA . . . . . . . . . . . . . . . . . . . . . . . 10
6.3. Dual Stack REGISTER with one IP address in Contact
header field . . . . . . . . . . . . . . . . . . . . . . . 11
6.4. Dual Stack REGISTER with two IP addresses in Contact
header field . . . . . . . . . . . . . . . . . . . . . . . 12
6.5. Dual Stack REGISTER with one IPv4-mapped IPv6 address
in the Contact header field . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
8. Security Considerations . . . . . . . . . . . . . . . . . . . 14
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
10.1. Normative References . . . . . . . . . . . . . . . . . . . 15
10.2. Informative References . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
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1. Introduction
Due to IPv4 address exhaustion problem, IPv6 deployment should be
accelerated. In this context and especially from a SIP perspective,
the IPv4-IPv6 co-existence introduces heterogeneous scenarios with
combinations of IPv4 and IPv6 nodes some of which are capable of
supporting both IPv4 and IPv6 dual stack (DS) and some of which are
capable of supporting only IPv4 or only IPv6. Additionally, some UAs
that are dual stack capable are unable to use both interfaces
natively at the same time which can mean for example that if a UA has
to use IPv6 for signaling it cannot use IPv4 for media even though
the UA supports an IPv4 stack. This mainly motivated by restrictions
due to available resources such the need to maintain one PDP (packet
data protocol) context in case of mobile networks.
Draft-ietf-sipping-ipv6-transition [I-D.ietf-sipping-v6-transition]
provides recommendations to solve this issue including recommending
Dual Stack (DS) nodes in the core service platform having the
signalling and media path traverse these DS elements. While this is
viable for big service providers it not viable for smaller ones
especially at the earlier stages of IPv6 deployment. Upgrading
existing networks to follow all these recommendations requires a
large investment.
An interim alternative is to use a SIP Application Level Gateway
(ALG) and a Network Address Translation - Protocol
Translation(NAT-PT) node to convert between IPv4 and IPv6 addressing.
However an ALG and a NAT-PT/NAT64 introduce additional nodes into the
signaling and media paths and can result in the so called "trombone"
effect with signaling and even more importantly media being
unnecessarily routed via an ALG/NAT-PT/NAT64 in a network located at
a significant distance from both of the UAs involved in the session.
This is particularly significant in mobile networks in roaming
scenarios where potentially media then has be routed via multiple
hops over international links when a roaming user establishes a
session with a user located in the roamed to country. This situation
is potentially unavoidable when an ALG/NAT-PT/NAT64 is needed to be
inserted in the signaling and the media path because of incompatible
IP versions between UAs that require IP address translation. It is
highly undesirable to redundantly include ALG/NAT-PT/NAT64 nodes in
the path when the UAs can establish sessions without requiring ALG/
NAT-PT nodes in the path.
In order to avoid redundant inclusion of ALG/ NAT-PT/NAT64 nodes in
the path, it is necessary for network nodes to be able to determine
the connectivity types supported by UAs prior to forwarding session
establishment requests. Without such a capability, SIP Proxy Servers
have no way to predict a session failure without a ALG/NAT-PT/NAT64
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being included in the path even when the ANAT [RFC4091] [RFC4092] or
ICE [I-D.ietf-mmusic-ice] mechanisms are also used.
Additionally, when multiple UAs are registered with the same Address
of Record (AoR) it is useful to be able to have a UA indicate a
preference to contact a UA using the mechanism defined in RFC 3841
[RFC3841] that supports the same IP version in order to avoid the
need for NAT-PT/NAT64.
This specification also addresses call routing and optimization
mechanisms using the atypes Media Feature Tag to avoid as much as
possible invoking SIP ALGs and NAT-PT/NAT64 when establishing a
multimedia session between UAs.
2. Justification for atypes
SIP service platforms should be aware of the type of the involved
peers before forwarding session establishment requests. If these
means are not supported, SIP Proxy Servers have no way to predict a
session failure, even if ANAT [RFC4091] or ICE [I-D.ietf-mmusic-ice]
procedures are adopted, and also to optimise the invocation of
adaptation functions.
The first alternative to notify the service platform about the type
of the UA is to send SIP REGISTER message which encloses all
available IP addresses. For IPv4-only and IPv6-only UAs, only one
single IP address is carried in SIP REGISTER messages. For DS UAs,
two IP addresses are enclosed. Upon receipt, of this message, the
registrar stores these addresses. Two registration databases may be
maintained, one for IPv4 and another one for IPv6. A second
alternative is to send several REGISTER request using available
connectivity types. In this case, a DS UA sends two REGISTER
messages. The first one is sent using its IPv4 connectivity and the
second one using its IPv6 ones. Two databases are maintained by the
conversational service platform. Consequently, upon receipt of an
INVITE, the SIP Proxy Server may question its databases to retrieve
the types of the involved parties. SIP ALG is invoked accordingly.
The drawback of this procedure is that it depends on the behaviour of
the terminal. A standardised behaviour should be encouraged. To
that aim, a new Media Feature Tag is introduced in this document.
More details are provided hereafter.
3. Relationship of atypes to ANAT/ICE
ICE [I-D.ietf-mmusic-ice] specification deprecates
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[RFC4091][RFC4092]. Like ANAT, ICE can be used to enclose both IPv4
and IPv6 information in a given SDP offer. In the remaining part,
ANAT and ICE are used interchangeably since, from IPv4-IPv6
interworking perspective, both provide the same solution.
ANAT/ICE makes it possible for Dual Stack UAs to provide both IPv4
and IPv6 addresses for a single logical media stream. This
singularly helps interworking as, whatever the distant UA version is
(IPv4/IPv6-only or Dual-Stack), this latter should be able to
understand at least one of the offers. In this way the ANAT/ICE
semantic provides a first approach to interworking problem, when
heterogeneous UAs are involved in the SIP communication. It indeed
improves SIP exchanges, in so far as it allows all sessions arising/
coming from Dual Stack UA to lead to successful calls.
This interesting feature needs however to be nuanced, as it
unfortunately does not fit all cases. [RFC4091] already lists some
cases where, depending on the implementation, recipients of an offer
using ANAT might have different behaviours, thus requiring the
introduction of the sdp-anat option-tag. ANAT also requires the UA
to be Dual Stack, which means it does not cover the case where UAs
belong to different and restrictive IP version realms. In other
words, the ANAT proposition does not help solving scenarios where
mono-stack (i.e. IPv4 or IPv6) UAs are involved. In this latter
case, SIP exchanges can only succeed if intermediary nodes or
functions (Proxy Servers, ALG, Session Border Controllers (SBCs),
etc.) intervene in the signalling path. This intervention, denoted
as adaptation function in the rest of this document, is necessary to
ensure a successful SIP exchange between these mono-satck UAs.
Unfortunately, in these situations, ANAT/ICE does not help SIP
servers situated all along the signalling path to take the right
decision when IPv4-IPv6 interconnection needs (or should need) to be
tackled.
The atypes Media Feature Tag helps to provide a global answer to the
interconnection problem, when heterogeneous SIP UAs are involved.
Moreover, it aids SIP nodes situated all along the signalling path,
to determine when to invoke the adaptation function helping the
routing of the call.
The atypes Media Feature Tag makes it possible for SIP Proxy Servers
to determine the IP versions supported by the distant and the
originating UA, when they process the initial SIP request. This
means that, the earlier possible in the exchange, a SIP node becomes
aware of the potential interconnection problem due to IP version
incompatibility. This also means that this particular node can
trigger the invocation of the adaptation function, which will modify
the initial SDP offer in order to make this SIP exchange successful.
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The atypes Media Feature Tag can therefore aid treatment of all
exchange types intervening between mono-stack (IPv4 or IPv6) or Dual
Stack UAs (whether they use ANAT or not). Anytime a potential
interconnection problem is suspected using the atypes Media Feature
Tag, the SIP Proxy will be able to drive the adaptation function
invocation and route the SIP exchange accordingly.
The atypes Media Feature Tag can also provide interesting
optimisation characteristics. For instance, a service provider might
force adaptation function like SIP ALGs to be invoked each time the
SIP message leave an IPv4 realm for an IPv6 realm (and vice-versa),
in order to modify the SDP offer accordingly. This kind of
modifications could happen more than once during the SIP signalling
exchanges (and even more than once in a single direction!). In the
end, both UAs intervening in the SIP exchange might be of the same
type, thus not requiring any change of the SDP offer! Using the
atypes Media Feature Tag such situation could be avoided, as the SIP
Proxy Server would determine UAs are compatible, thus no modification
should be make to SDP offers, even if layer 3 information are
modified during the routing of the SIP message.
The atypes Media Feature Tag can also help in the case where
different SIP realms are crossed, where the information from the
atypes Media Feature Tag for the distant UA is not available at the
originating Proxy Server. In this case, the atypes Media Feature Tag
can be included in the SIP request thus enabling the distant SIP
Proxy Server, which has the atypes Media Feature Tag information for
the remote UA, to determine whether to route the SIP request via its
adaptation function.
The atypes Media Feature Tag is not limited to the single IPv4-IPv6
interconnection problem, though this first version of the
specification is dedicated to this usage.
Further values of atypes can be defined in future specifications.
The atypes Media Feature Tag is also compatible with the parallel
usage of ICE or CCAP [I-D.boucadair-mmusic-ccap]..
4. sip.atypes Media Feature Tag
The 'sip.app-subtype' media feature tag is of type token with a case-
sensitive equality relationship. It indicates whether a
(communications) device supports IPv4 for both signaling and media,
IPv6 for both signaling and media, IPv6 for signaling and IPv4 for
media simultaneously, IPv4 for signaling and IPv6 for media
simultaneously. A plurality of tokens is included for all the
supported combinations. Its values include:
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- ipv4: The device can support IPv4 addresses for both signaling
and media.
- ipv6: The device can support IPv6 addresses for both signaling
and media.
- ipv4s-ipv6m: The device can support both IPv4 and IPv6 addresses
and use the IPv4 address for signaling and the IPv6 address for
media.
- ipv6s-ipv4m: The device can support both IPv4 and IPv6 addresses
and use the IPv6 address for signaling and the IPv4 address for
media.
Other values of atypes can be defined such as:
- ipv4_via_nat46: When enclosed in a SIP message, a given SIP UA
indicates "here is my IPv4 address, it goes through a translator
so avoid using it if you can utilize my IPv6 address"
- ipv6_via_nat64: When enclosed in a SIP message, a given SIP UA
indicates "here is my IPv6 address, it goes through a translator
so avoid using it if you can utilize my IPv4 address"
- ipv4_via_cgn: When enclosed in a SIP message, a given SIP UA
indicates "here is my IPv4 address, it goes through a CGN device
so avoid using it if you can utilize a public IPv4 or IPv6
address"
When included in the Contact header field of a REGISTER request or an
INVITE request, a UAC SHOULD include all atypes values that represent
the address type combinations it can currently support. When
included in the Contact header field of a response a UAS SHOULD
include all atypes values that represent the address type
combinations it can currently support.
A UAS that receives an OPTIONS request SHOULD include in the Contact
header field an atypes Media Feature Tag containing all atypes values
that represent the address type combinations it can currently
support.
A given UA MAY restrict its SIP communications to its IPv4-only
interface or IPv6-only ones or MAY use all available ones. The
selected local restriction is conveyed in the atypes Media Feature
Tag. Within this context, an IPv6 interface is judged available only
if the scope of this interface is global and not local to the link.
When included in the Accept-Contact or Reject-Contact header field,
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it indicates a desire on the part of a UAC to be connected to a UAS
which can support, or cannot support respectively, the address types
and address type combinations specified.
5. Session Routing Considerations
Based on atypes tag value, the Registrar classifies the UA IP address
capabilities for signaling and media.
In order to route calls and to decide the need to invoke a SIP ALG or
to alter SIP messages, which leads to a successful call between
heterogeneous parties, a SIP Proxy Server MAY act as follows:
a. A first alternative is to interrogate the registration database
maintained by the Registrar Server: In this alternative, the SIP
Proxy Server asks the Registrar Server about the type of the
Called and the Caller parties. The SIP Proxy Server decides to
invoke an ALG in case the two involved parties are either IPv4-
only or IPv6-only.
b. The second alternative is to examine the atypes Media Feature Tag
conveyed in the Contact header field of the INVITE request and
the atypes Media Feature Tag values stored by the Registrar
Server for the address type of the Called party. In this
scenario, the SIP Proxy Server routes the call by comparing the
compatibility of the two retrieved atypes values (types of Called
and Caller parties).
6. Examples of atypes tag usages
These sections provide a set of examples of SIP messages when atypes
media feature tag is used.
6.1. IPv4-only UA
Let consider an IPv4-only UA denoted A. Its IP address is
192.165.25.2. This UA has been provisioned with required contact
information to contact its Registrar (RS). In this example, a FQDN
is provided: rs.test.com. Means that have been used to provision the
UA are out of scope of this document.
(1) A sends this REGISTER message to its Registrar Server RS:
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REGISTER sip:rs.test.com SIP/2.0
Via: SIP/2.0/UDP 192.165.25.2:5062;branch=z9hG4bK00e31d6ed
Max-Forwards: 70
Content-Length: 0
To: A <sip:A@test.com>
From: A <sip:A@test.com>;tag=ed3833bd7363e68
Call-ID: a8a83b610ae5d242289dfc1c78b7f1d8@test.com
CSeq: 1830746364 REGISTER
Contact: A <sip:A@192.165.25.2:5062>
;atypes="ipv4";expires=900
(2) RS answers to A with a 200 OK message as follows:
SIP/2.0 200 OK
Call-ID: a8a83b610ae5d242289dfc1c78b7f1d8@test.com
CSeq: 1830746365 REGISTER
From: A <sip:A@test.com>;tag=ed3833bd7363e68
To: A <sip:A@test.com>;tag=3ab7fe89d998709
Via:SIP/2.0/UDP 192.165.25.2:5062;branch=z9hG4bK00e31d6ed
Content-Length: 0
Contact: A <sip:A@192.165.25.2:5062>
;atypes="ipv4";expires=900
6.2. IPv6-only UA
Let consider an IPv6-only UA called B which IP address is 2001:688:
1ffb:ff80::2. Its attached Registrar Server is identified by this
FQDN: r6.test.com.
(1) B sends to its Registrar Server the following message:
REGISTER sip:r6.test.com SIP/2.0
Via: SIP/2.0/UDP
[2001:688:1ffb:ff80::2]:5060;branch=z9hG4bK00e31d6ed
Max-Forwards: 70
Content-Length: 0
To: B <sip:B@test.com>
From: B <sip:B@test.com>;tag=ed3833bd7363e68
Call-ID: a8a83b610ae5d242289dfc1c78b7f1d8@test.com
CSeq: 1830746364 REGISTER
Contact: B <sip:B@[2001:688:1ffb:ff80::2]:5060>
;atypes="ipv6";expires=900
(2) The Registrar Server answers with the following 200 OK message:
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SIP/2.0 200 OK
Call-ID: a8a83b610ae5d242289dfc1c78b7f1d8@test.com
CSeq: 1830746365 REGISTER
From: B <sip: B@test.com>;tag=ed3833bd7363e68
To: B <sip: B@test.com>;tag=3ab7fe89d998709
Via:SIP/2.0/UDP[2001:688:1ffb:ff80::2]:5060;branch=z9hG4bK00e31d6ed
Content-Length: 0
Contact: B <sip:B@[2001:688:1ffb:ff80::2]:5060>
;atypes="ipv6";expires=900
One IP address MAY be enclosed in the Contact header field of a dual
stack registration message. The type of the contact address MAY be
distinct from the value of atypes. For instance:
o an IPv4 address may be enclosed in the Contact header field even
if the assigned atypes value is equal to "ipv6",
o or only one IP address may be carried in the Contact header field
even if the atypes value is set to "ipv6,ipv4".
The IP address in the Contact header field MAY be used by
intermediary proxies when contacting the UA.
6.3. Dual Stack REGISTER with one IP address in Contact header field
Let consider a dual-stack UA (DS) which IP addresses are 2001:688:
1ffb:ff80::2 and 192.168.25.5 which does not support IPv4 and IPv6
simultaneously. The FQDN of the Register Server is rs.test.com.
(1) DS sends a REGISTER message to its Registrar Server as follows:
REGISTER sip:rs.test.com SIP/2.0
Via: SIP/2.0/UDP 192.168.25.5:5060;branch=z9hG4bK00e31d6ed
Max-Forwards: 70
Content-Length: 0
To: DS <sip:DS@test.com>
From: DS <sip:DS@test.com>;tag=ed3833bd7363e68
Call-ID: a8a83b610ae5d242289dfc1c78b7f1d8@test.com
CSeq: 1830746364 REGISTER
Contact: DS <sip:DS@192.168.25.5:5060>
;atypes="ipv4,ipv6";expires=900
(2) The Registrar Server answers with a 200 OK message as shown
below:
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SIP/2.0 200 OK
Call-ID: a8a83b610ae5d242289dfc1c78b7f1d8@test.com
CSeq: 1830746365 REGISTER
From: DS <sip: DS@test.com>;tag=ed3833bd7363e68
To: DS <sip:DS@test.com>;tag=3ab7fe89d998709
Via:SIP/2.0/UDP 192.168.25.5:5060;branch=z9hG4bK00e31d6ed
Content-Length: 0
Contact: DS <sip:DS@192.168.25.5:5060>
;atypes="ipv4,ipv6";expires=900
6.4. Dual Stack REGISTER with two IP addresses in Contact header field
Let consider a dual-stack UA (DS) which IP addresses are 2001:688:
1ffb:ff80::2 and 192.168.25.5 which does not support IPv4 and IPv6
simultaneously on each interface. The FQDN of the Register Server is
rs.test.com.
(1) DS sends a REGISTER message to its Registrar Server as follows:
REGISTER sip:rs.test.com SIP/2.0
Via: SIP/2.0/UDP 192.168.25.5:5060;branch=z9hG4bK00e31d6ed
Max-Forwards: 70
Content-Length: 0
To: DS <sip:DS@test.com>
From: DS <sip:DS@test.com>;tag=ed3833bd7363e68
Call-ID: a8a83b610ae5d242289dfc1c78b7f1d8@test.com
CSeq: 1830746364 REGISTER
Contact: DS1 <sip:DS1@192.168.25.5:5060>
;atypes="ipv4";expires=900
Contact: DS2 <sip:DS2@[2001:688:1ffb:ff80::2]:5063>
;atypes="ipv6";expires=900
(2) The Registrar Server answers with a 200 OK message as shown
below:
SIP/2.0 200 OK
Call-ID: a8a83b610ae5d242289dfc1c78b7f1d8@test.com
CSeq: 1830746365 REGISTER
From: DS <sip: DS@test.com>;tag=ed3833bd7363e68
To: DS <sip:DS@test.com>;tag=3ab7fe89d998709
Via:SIP/2.0/UDP 192.168.25.5:5060;branch=z9hG4bK00e31d6ed
Content-Length: 0
Contact: DS1 <sip:DS1@192.168.25.5:5060>
;atypes="ipv4,ipv6";expires=900
Contact: DS2 <sip:DS2@[2001:688:1ffb:ff80::2]:5063>
;atypes="ipv4,ipv6";expires=900
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6.5. Dual Stack REGISTER with one IPv4-mapped IPv6 address in the
Contact header field
Let consider a dual-stack UA (DS) which the IPv4 address 192.168.25.5
is mapped to the IPV6 address ::ffff:192.168.25.5 and which does
support simultaneous use of IPv4 and IPv6. The FQDN of the Register
Server is rs.test.com.
(1) DS sends a REGISTER message to its Registrar Server as follows:
REGISTER sip:rs.test.com SIP/2.0
Via: SIP/2.0/UDP 192.168.25.5:5062;branch=z9hG4bK00e31d6ed
Max-Forwards: 70
Content-Length: 0
To: DS <sip:DS@test.com>
From: DS <sip:DS@test.com>;tag=ed3833bd7363e68
Call-ID: a8a83b610ae5d242289dfc1c78b7f1d8@test.com
CSeq: 1830746364 REGISTER
Contact: DS <sip:DS@[::ffff:192.168.25.5]>
;atypes="ipv6,ipv6s-ipv4m";expires=900
(2) The Registrar Server answers with a 200 OK message as shown
below:
SIP/2.0 200 OK
Call-ID: a8a83b610ae5d242289dfc1c78b7f1d8@test.com
CSeq: 1830746365 REGISTER
From: DS <sip: DS@test.com>;tag=ed3833bd7363e68
To: DS <sip:DS@test.com>;tag=3ab7fe89d998709
Via:SIP/2.0/UDP 192.168.25.5:5062;branch=z9hG4bK00e31d6ed
Content-Length: 0
Contact: DS <sip:DS@[::ffff:192.168.25.5]>
;atypes="ipv6,ipv6s-ipv4m";expires=900
7. IANA Considerations
This specification adds a new media feature tag to the SIP Media
Feature Tag Registration Tree defined in RFC 3840 [RFC3840].
Media feature tag name: sip.atypes
ASN.1 Identifier: TBD
Summary of the media feature indicated by this tag: The sip.atypes
media feature tag indicates whether a communications device supports
IPv4 for both signaling and media, IPv6 for both signaling and media,
IPv6 for signaling and IPv4 for media simultaneously, IPv4 for
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signaling and IPv6 for media simultaneously. A plurality of tokens
is included for all the supported combinations.
Values appropriate for use with this feature tag: Token with an
equality relationship.
Typical values include:
ipv4: The device can support IPv4 addresses for both signaling and
media.
ipv6: The device can support IPv6 addresses for both signaling and
media.
ipv4s-ipv6m: The device can support both IPv4 and IPv6 addresses and
use the IPv4 address for signaling and the IPv6 address for media.
ipv6s-ipv4m: The device can support both IPv4 and IPv6 addresses and
use the IPv6 address for signaling and the IPv4 address for media.
The feature tag is intended primarily for use in the following
applications, protocols, services, or negotiation mechanisms: This
feature tag is most useful in a communications application, for
describing the capabilities of a device, such as a phone or PDA.
Examples of typical use: Optimally routing a session and ensuring
compatibility between IP versions to successfully establish sessions.
Related standards or documents: RFC XXXX [[Note to IANA: Please
replace XXXX with the RFC number of this specification.]].
Security Considerations: Security considerations for this media
feature tag are discussed in Section 7 of RFC XXXX . [[Note to IANA:
Please replace XXXX with the RFC number of this specification.]]
8. Security Considerations
When present in a SIP request or response, this media feature tag may
be used to determine whether a session is routed via a ALG/NAT-PT/
NAT64 in order to successfully establish a session. If the values of
the atypes Media Feature Tags are modified by an intermediary then it
is possible that a session would fail to be established if the
modified values caused the network proxies to not insert a ALG/
NAT-PT/NAT64 when they are needed. However if the contact address
itself is also modified this could also prevent a session being
established. Integrity protection for the Contact header field
should be provided.
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9. Acknowledgements
TBC.
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.
[RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat,
"Indicating User Agent Capabilities in the Session
Initiation Protocol (SIP)", RFC 3840, August 2004.
10.2. Informative References
[I-D.boucadair-mmusic-ccap]
Boucadair, M. and H. Kaplan, "Session Description Protocol
(SDP) Connectivity Capability (CCAP) Attribute",
draft-boucadair-mmusic-ccap-00 (work in progress),
July 2009.
[I-D.ietf-mmusic-ice]
Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols",
draft-ietf-mmusic-ice-19 (work in progress), October 2007.
[I-D.ietf-sipping-v6-transition]
Camarillo, G., "IPv6 Transition in the Session Initiation
Protocol (SIP)", draft-ietf-sipping-v6-transition-07 (work
in progress), August 2007.
[RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller
Preferences for the Session Initiation Protocol (SIP)",
RFC 3841, August 2004.
[RFC4091] Camarillo, G. and J. Rosenberg, "The Alternative Network
Address Types (ANAT) Semantics for the Session Description
Protocol (SDP) Grouping Framework", RFC 4091, June 2005.
[RFC4092] Camarillo, G. and J. Rosenberg, "Usage of the Session
Description Protocol (SDP) Alternative Network Address
Types (ANAT) Semantics in the Session Initiation Protocol
(SIP)", RFC 4092, June 2005.
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Authors' Addresses
Mohamed Boucadair
France Telecom
3, av Francois Chateau
Rennes 35000
France
Email: mohamed.boucadair@orange-ftgroup.com
Yoann Noisette
France Telecom
Email: yoann.noisette@orange-ftgroup.com
Andrew Allen
Research in Motion (RIM)
300 Knightsbridge Parkway, Suite 360
Lincolnshire, Illinois 60069
USA
Email: aallen@rim.com
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