Internet DRAFT - draft-audet-sipping-add-realm
draft-audet-sipping-add-realm
SIPPING Working Group
Internet Draft Francois Audet
Document: draft-audet-sipping-add-realm-00.txt Nortel Networks
Expires on December 2003 June 2003
Identifying intra-realm calls with explicit addressing realm
identifier attribute
Status of this Memo
This document is an Internet-Draft and is in full conformance
with all provisions of Section 10 of RFC2026.
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This internet draft will expire on 20 December 2003.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This draft describes the use of an explicit addressing identifier
SDP attribute to assist in the process of choosing which addresses
shall be used by SIP User Agents (UAs) when multiple IP addresses
are known (STUN-derived, local, etc.). This draft complements the
Interactive Connectivity Establishment (ICE) draft.
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1 Introduction
This draft describes the use of an explicit addressing identifier
SDP attribute to assist in the process of choosing which addresses
shall be used by SIP UAs. It applies when multiple IP addresses are
known, e.g., STUN-derived IP addresses and local IP addresses. This
draft proposes to allow for an explicit realm identification SDP
attribute to be used as part of the Interactive Connectivity
Establishment (ICE) draft [1] to facilitate deployment in networks
where not all media termination support STUN server capabilities.
The objectives of the explicit realm identifier attribute are: (1)
to facilitate migration to universal deployment of ICE across all
media termination, provided that some media termination will get
there before others, (2) to support networks where some media
endpoint do not support STUN server capabilities, (3) to allow for
not using the peer-to-peer STUN mechanism defined in ICE when not
required, for efficiency purposes.
The core idea in this proposal is that if both media termination in
a session have a priori knowledge of having addresses in the same IP
addressing realm, it may not be necessary to perform the peer-to-
peer STUN requests between them.
This proposal should address the biggest difficulties facing ICE
which is that it requires all media termination devices to support
it to be effective, making it a chicken-and-egg problem. It also
gives the ability to optimize the performance of systems where it is
knows that the STUN requests between the media termination are not
required(for example, between large gateways).
2 Conventions used in this document
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.
3 Usage of explicit realm identifier attribute
This document proposes that SIP UAs could include an explicit realm
identifier attribute for advertised IP addresses included in SDP in
SIP. By adding an explicit addressing realm description, the UAs may
be able to make decisions on which IP addresses to use for sending
media. This explicit addressing realm indicator may be provided in
SDP in addition to the STUN indication support described in ICE, or
it can be provided alone when STUN is not supported by the media
termination device. The explicit realm identifier SHALL be globally
unique.
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Recognizing that many endpoints may not support the explicit realm
indication, the proposal is backward-compatible with systems that
don't indicate any addressing realm.
Care has been taken to make this proposal consistent with ICE. As
such, it inherits the same mechanisms to describe IP addresses, RTP
and RTCP ports in SDP.
Addresses can be gathered according the means discussed in ICE, in
particular, STUN derived addresses.
A SIP UAs can determine that the addresses of the media termination
and media source can be used directly, bypassing the ICE peer-to-
peer STUN requests between them, if and only if the media
termination addresses of the source and destination are located in
the same addressing realm. The SIP UAs MAY thus compare the realm
identifiers, and if the realm identifiers match, the addresses MAY
be used directly without further procedures (such as STUN requests).
If they do not match, or if one or both addressing realm identifiers
are not provided, the UAs SHALL NOT assume that the addresses are in
the same addressing realm, and normal treatment SHOULD apply: i.e.,
use STUN (as per ICE) if supported, or otherwise use the derived
address or local address as per normal policy.
The examples in this document describe the case where there is only
one level of NAT. However, it is possible that certain deployment
scenarios will include "nested NATs". The explicit realm identifier
method will function properly with nested NAT because the derived
addresses are included in the SDP, along with their respective realm
identifier. Each embedded realm will thus have its own realm
identifier. Correlating the realm identifier with a specific address
(and thus potentially with the STUN IP address discovery procedures)
will thus be necessary and may require some configuration.
4 Format of the addressing realm identifier attribute
The addressing realm identifier SHALL be globally unique. A unique
number or a unique random string of any sort, including a VPN
identifier such as defined in RFC 2685 [3], a unique global
identifier of any sort (e.g., [4]) would work. In the examples in
this proposal, we use a string of character that is similar to a
user and domain name, analogous to the way the phone-context is
defined in draft-antti-rfc2806bis-08 [2]. An addressing-realm-type
parameter is defined to indicate what type of format is used to
describe the unique addressing realm identifier.
The addressing realm indication format is defined as follows in
ABNF:
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addressing-realm-attribute = "addressing-realm" ":"
addressing-realm-type SP realm-descriptor
addressing-realm-type = "userdomain"
addressing-realm-descriptor = [ word "@" ] domainname
If allowing VPN identifiers or other mechanisms is required, more
addressing-realm-type and addressing-realm-descriptor elements would
need to be added to the ABNF.
The elements word and domainname are already defined in RFC3261 [5]
and draft-antti-rfc2806bis-08. They are transcribed below for the
reader's benefit:
domainname = *( domainlabel ... ) toplabel [ ... ]
domainlabel = alphanum / alphanum*(alphanum)/ .-. ) alphanum
toplabel = ALPHA / ALPHA *( alphanum / .-. ) alphanum
alphanum = ALPHA / DIGIT
DIGIT = %x30-39 ; 0-9
ALPHA = %x41-5A / %x61-7A ; A-Z / a-z
word = 1*(alphanum / "-" / "." / "!" / "%" / "*" / "_" / "+" /
"`" / "'"/ "~" / "(" / ")" / "<" / ">" / ":" / "\" /
DQUOTE / "/" / "[" / "]" / "?" / "{" / "}" )
The following are examples of addressing-realm attributes:
- Private Address in corporate network of Foo Inc.:
"a=addressing-realm:userdomain foo.com"
- Private Address in San Jose branch of Foo Inc.:
"a=addressing-realm:userdomain sanjose@foo.com"
- Private Address in NATed lab in San Jose branch of Foo Inc.:
"a=addressing-realm:userdomain lab3.sanjose@foo.com"
- Private Address behind NAT in home office:
"a=addressing-realm:userdomain audet@isp.net"
The means by which the UA gets the addressing realm identifier is
outside the scope of this document. It could be manually configured,
or some automated process could be used.
One advantage of this proposal is that for home users, there is no
need to configure an addressing realm identifier if there is no
possibility of 2 devices in the home network communicating together
through the home NAT.
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5 Example use cases
This section illustrates 3 different scenarios applicable to the
explicit realm identification method.
Configuration 1 is where A calls B, and A is behind a NAT and B is
in the public address space (i.e., in different IP addressing
realm). We assume the following:
A = RTP/47.0.2.1:54344, RTCP/ 47.0.2.2:44345 (derived), and
RTP/10.0.1.2:22334, RTCP/10.0.1.2:22335 (corporate.foo.com)
B = RTP/66.8.1.7:78122, RTCP/66.8.1.7:78123
Configuration 2 is where A calls B, and A and B are each behind
their own NAT (i.e., in different IP addressing realm). We assume
the following:
A = RTP/47.0.2.1:54344, RTCP/ 47.0.2.2:44345 (derived), and
RTP/10.0.1.2:22334, RTCP/10.0.1.2:22335 (corporate.foo.com)
B = RTP/66.8.1.7:78122, RTCP/66.8.1.10:66111 (derived), and
RTP/192.168.0.2:55000, RTCP/192.168.0.2:55001 (audet@isp.net)
Configuration 3 is where A calls B, and A and B are behind the same
NAT (i.e., in the same IP addressing realm). We assume the
following:
A = RTP/47.0.2.1:54344, RTCP/ 47.0.2.2:44345 (derived), and
RTP/10.0.1.2:22334, RTCP/10.0.1.2:22335 (corporate.foo.com)
B = RTP/66.8.1.7:78122, RTCP/66.8.1.10:66111 (derived), and
RTP/10.8.8.13:37880, RTCP/10.8.8.13:37881 (corporate.foo.com)
In the examples below, no stun-attribute are included. However, it
should be understood that stun-attribute could be present, as per
the ICE draft.
5.1 Configuration 1 - A behind a NAT
Offer:
v=0
o=alice 2890844730 2890844731 IN IP4 host.foo.com
s=
t=0 0
a=group:ALT 1 2
m=audio 22334 RTP/AVP 0
c=IN IP4 10.0.1.2
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a=mid:1
a=addressing-realm:userdomain corporate@foo.com
m=audio 54344 RTP/AVP 0
c=IN IP4 47.0.2.1
a=rtcp:44345 IN IP4 47.0.2.2
a=mid:1
a=derived:1
Answer:
v=0
o=bob 280744730 28977631 IN IP4 host2.isp.net
s=
t=0 0
a=group:ALT 1 2
m=audio 0 RTP/AVP 0 -- The "0" rejects the media stream
c=IN IP4 66.8.1.7 -- The value of the IP address is of no
importance
a=mid:1
m=audio 78122 RTP/AVP 0
c=IN IP4 66.8.1.7
a=mid:2
5.2 Configuration 2 - A and B each behind their own NAT
Offer:
v=0
o=alice 2890844730 2890844731 IN IP4 host.foo.com
s=
t=0 0
a=group:ALT 1 2
m=audio 22334 RTP/AVP 0
c=IN IP4 10.0.1.2
a=mid:1
a=addressing-realm:userdomain corporate@foo.com
m=audio 54344 RTP/AVP 0
c=IN IP4 47.0.2.1
a=rtcp:44345 IN IP4 47.0.2.2
a=mid:1
a=derived:1
Answer:
v=0
o=bob 280744730 28977631 IN IP4 host2.isp.net
s=
t=0 0
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a=group:ALT 1 2
m=audio 0 RTP/AVP 0 -- Port "0" rejects the media stream
c=IN IP4 192.168.0.2 -- Value of IP address is of no importance
a=mid:1
a=addressing-realm:userdomain audet@isp.net
m=audio 78122 RTP/AVP 0
c=IN IP4 66.8.1.7
a=rtcp:66111 IN IP4 66.8.1.10
a=mid:2
a=derived:2
5.3 Configuration 3 - A and B behind one common NAT
Offer:
v=0
o=alice 2890844730 2890844731 IN IP4 host.foo.com
s=
t=0 0
a=group:ALT 1 2
m=audio 22334 RTP/AVP 0
c=IN IP4 10.0.1.2
a=mid:1
a=addressing-realm:userdomain corporate@foo.com
m=audio 54344 RTP/AVP 0
c=IN IP4 47.0.2.1
a=rtcp:44345 IN IP4 47.0.2.2
a=mid:1
a=derived:1
Answer:
v=0
o=bob 280744730 28977631 IN IP4 host2.foo.com
s=
t=0 0
a=group:ALT 1 2
m=audio 37880 RTP/AVP 0
c=IN IP4 10.8.8.13
a=mid:1
a=addressing-realm:userdomain corporate@foo.com
m=audio 0 RTP/AVP 0 -- Port "0" rejects the media stream
c=IN IP4 66.8.1.7 -- Value of IP address is of no importance
a=mid:2
a=derived:2
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6 Security Considerations
No particular security issues are introduced by this proposal beyond
the ones mentioned in RFC 3261 [5] and the ICE draft [1].
7 IANA Considerations
This document registers a new SDP attribute: addressing-realm,
defined in section 4.
8 References
[1] Rosenberg, "Interactive Connectivity Establishment (ICE):
Methodology for Network Address Translator (NAT) Traversal for
the Session Initiation Protocol (SIP)", Internet draft
http://www.ietf.org/internet-drafts/draft-rosenberg-sipping-ice-
00.txt, February 2003
[2] Schulzrinne, Vaha-Sipila, "The tel URI for Telephone Calls",
Internet draft http://www.ietf.org/internet-drafts/draft-antti-
rfc2806bis-08.txt (work in progress), February 2003
[3] Fox, Gleeson, "Virtual Private Networks Identifier", RFC 2685,
http://www.ietf.org/rfc/rfc2685.txt, September 1999
[4] Ould-Brahim, Gleeson, Rekhter, "Global Unique Identifiers
(GID)", Internet draft http://www.ietf.org/internet-
drafts/draft-ouldbrahim-ppvpn-gid-02.txt (work in progress),
December 2002
[5] Rosenberg, Schulzrinne, et al., "SIP: Session Initiation
Protocol", http://www.ietf.org/rfc/rfc3261, June 2002
9 Contributors
The authors would like to thank the following people for their
useful comments and suggestions related to this draft: Cedric Aoun,
Mary Barnes, Julian Mitchell, Patrick Ma and Sean March.
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10 Author's Address
Comments can be sent to the author:
Francois Audet
Nortel Networks
4655 Great America Parkway
Santa Clara, CA 95054
USA
tel:+1-408-495-3756
mailto:audet@nortelnetworks.com
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