draft-ietf-sip-outbound-10.txt   draft-ietf-sip-outbound-11.txt 
Network Working Group C. Jennings, Ed. Network Working Group C. Jennings, Ed.
Internet-Draft Cisco Systems Internet-Draft Cisco Systems
Updates: 3261,3327 R. Mahy, Ed. Updates: 3261,3327 R. Mahy, Ed.
(if approved) Plantronics (if approved) Plantronics
Intended status: Standards Track July 5, 2007 Intended status: Standards Track November 18, 2007
Expires: January 6, 2008 Expires: May 21, 2008
Managing Client Initiated Connections in the Session Initiation Protocol Managing Client Initiated Connections in the Session Initiation Protocol
(SIP) (SIP)
draft-ietf-sip-outbound-10 draft-ietf-sip-outbound-11
Status of this Memo Status of this Memo
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This Internet-Draft will expire on January 6, 2008. This Internet-Draft will expire on May 21, 2008.
Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2007).
Abstract Abstract
The Session Initiation Protocol (SIP) allows proxy servers to The Session Initiation Protocol (SIP) allows proxy servers to
initiate TCP connections and send asynchronous UDP datagrams to User initiate TCP connections and send asynchronous UDP datagrams to User
Agents in order to deliver requests. However, many practical Agents in order to deliver requests. However, many practical
considerations, such as the existence of firewalls and Network considerations, such as the existence of firewalls and Network
Address Translators (NATs), prevent servers from connecting to User Address Translators (NATs), prevent servers from connecting to User
Agents in this way. This specification defines behaviors for User Agents in this way. This specification defines behaviors for User
Agents, registrars and proxy servers that allow requests to be Agents, registrars and proxy servers that allow requests to be
delivered on existing connections established by the User Agent. It delivered on existing connections established by the User Agent. It
also defines keep alive behaviors needed to keep NAT bindings open also defines keep alive behaviors needed to keep NAT bindings open
and specifies the usage of multiple connections. and specifies the usage of multiple connections from the User Agent
to its Registrar.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 4 2. Conventions and Terminology . . . . . . . . . . . . . . . . . 4
2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 5 2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 5
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Summary of Mechanism . . . . . . . . . . . . . . . . . . 5 3.1. Summary of Mechanism . . . . . . . . . . . . . . . . . . 5
3.2. Single Registrar and UA . . . . . . . . . . . . . . . . . 6 3.2. Single Registrar and UA . . . . . . . . . . . . . . . . . 6
3.3. Multiple Connections from a User Agent . . . . . . . . . 7 3.3. Multiple Connections from a User Agent . . . . . . . . . 8
3.4. Edge Proxies . . . . . . . . . . . . . . . . . . . . . . 9 3.4. Edge Proxies . . . . . . . . . . . . . . . . . . . . . . 9
3.5. Keepalive Technique . . . . . . . . . . . . . . . . . . . 11 3.5. Keepalive Technique . . . . . . . . . . . . . . . . . . . 11
3.5.1. CRLF Keepalive Technique . . . . . . . . . . . . . . . 11 3.5.1. CRLF Keepalive Technique . . . . . . . . . . . . . . . 11
3.5.2. TCP Keepalive Technique . . . . . . . . . . . . . . . 12 3.5.2. STUN Keepalive Technique . . . . . . . . . . . . . . . 12
3.5.3. STUN Keepalive Technique . . . . . . . . . . . . . . . 12 4. User Agent Mechanisms . . . . . . . . . . . . . . . . . . . . 12
4. User Agent Mechanisms . . . . . . . . . . . . . . . . . . . . 13 4.1. Instance ID Creation . . . . . . . . . . . . . . . . . . 12
4.1. Instance ID Creation . . . . . . . . . . . . . . . . . . 13 4.2. Registrations . . . . . . . . . . . . . . . . . . . . . . 13
4.2. Registrations . . . . . . . . . . . . . . . . . . . . . . 14 4.2.1. Non Outbound Registrations . . . . . . . . . . . . . . 15
4.2.1. Registration by Other Instances . . . . . . . . . . . 16 4.3. Sending Non-REGISTER Requests . . . . . . . . . . . . . . 15
4.3. Sending Requests . . . . . . . . . . . . . . . . . . . . 16 4.4. Detecting Flow Failure . . . . . . . . . . . . . . . . . 16
4.4. Detecting Flow Failure . . . . . . . . . . . . . . . . . 17 4.4.1. Keepalive with CRLF . . . . . . . . . . . . . . . . . 17
4.4.1. Keepalive with TCP KEEPALIVE . . . . . . . . . . . . . 18 4.4.2. Keepalive with STUN . . . . . . . . . . . . . . . . . 18
4.4.2. Keepalive with CRLF . . . . . . . . . . . . . . . . . 18 4.5. Flow Recovery . . . . . . . . . . . . . . . . . . . . . . 18
4.4.3. Keepalive with STUN . . . . . . . . . . . . . . . . . 18 5. Edge Proxy Mechanisms . . . . . . . . . . . . . . . . . . . . 19
4.5. Flow Recovery . . . . . . . . . . . . . . . . . . . . . . 19 5.1. Processing Register Requests . . . . . . . . . . . . . . 19
5. Edge Proxy Mechanisms . . . . . . . . . . . . . . . . . . . . 20
5.1. Processing Register Requests . . . . . . . . . . . . . . 20
5.2. Generating Flow Tokens . . . . . . . . . . . . . . . . . 20 5.2. Generating Flow Tokens . . . . . . . . . . . . . . . . . 20
5.3. Forwarding Requests . . . . . . . . . . . . . . . . . . . 21 5.3. Forwarding Non-REGISTER Requests . . . . . . . . . . . . 20
5.4. Edge Proxy Keepalive Handling . . . . . . . . . . . . . . 22 5.4. Edge Proxy Keepalive Handling . . . . . . . . . . . . . . 21
6. Registrar Mechanisms: Processing REGISTER Requests . . . . . . 22 6. Registrar Mechanisms: Processing REGISTER Requests . . . . . . 21
7. Authoritative Proxy Mechanisms: Forwarding Requests . . . . . 24 7. Authoritative Proxy Mechanisms: Forwarding Requests . . . . . 23
8. STUN Keepalive Processing . . . . . . . . . . . . . . . . . . 24 8. STUN Keepalive Processing . . . . . . . . . . . . . . . . . . 24
8.1. Use with Sigcomp . . . . . . . . . . . . . . . . . . . . 26 8.1. Use with Sigcomp . . . . . . . . . . . . . . . . . . . . 25
9. Example Message Flow . . . . . . . . . . . . . . . . . . . . . 26 9. Example Message Flow . . . . . . . . . . . . . . . . . . . . . 26
10. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 10. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
11. Definition of 430 Flow Failed response code . . . . . . . . . 30 11. Definition of 430 Flow Failed response code . . . . . . . . . 30
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
12.1. Contact Header Field . . . . . . . . . . . . . . . . . . 30 12.1. Contact Header Field . . . . . . . . . . . . . . . . . . 30
12.2. SIP/SIPS URI Parameters . . . . . . . . . . . . . . . . . 31 12.2. SIP/SIPS URI Parameters . . . . . . . . . . . . . . . . . 31
12.3. SIP Option Tag . . . . . . . . . . . . . . . . . . . . . 31 12.3. SIP Option Tag . . . . . . . . . . . . . . . . . . . . . 31
12.4. Response Code . . . . . . . . . . . . . . . . . . . . . . 31 12.4. Response Code . . . . . . . . . . . . . . . . . . . . . . 31
12.5. Media Feature Tag . . . . . . . . . . . . . . . . . . . . 31 12.5. Media Feature Tag . . . . . . . . . . . . . . . . . . . . 31
13. Security Considerations . . . . . . . . . . . . . . . . . . . 32 13. Security Considerations . . . . . . . . . . . . . . . . . . . 32
14. Operational Notes on Transports . . . . . . . . . . . . . . . 33 14. Operational Notes on Transports . . . . . . . . . . . . . . . 33
15. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 34 15. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 34
16. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 16. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
16.1. Changes from 09 Version . . . . . . . . . . . . . . . . . 34 16.1. Changes from 09 Version . . . . . . . . . . . . . . . . . 34
16.2. Changes from 08 Version . . . . . . . . . . . . . . . . . 34 16.2. Changes from 08 Version . . . . . . . . . . . . . . . . . 34
16.3. Changes from 07 Version . . . . . . . . . . . . . . . . . 35 16.3. Changes from 07 Version . . . . . . . . . . . . . . . . . 35
16.4. Changes from 06 Version . . . . . . . . . . . . . . . . . 35 16.4. Changes from 06 Version . . . . . . . . . . . . . . . . . 35
16.5. Changes from 05 Version . . . . . . . . . . . . . . . . . 35 16.5. Changes from 05 Version . . . . . . . . . . . . . . . . . 35
16.6. Changes from 04 Version . . . . . . . . . . . . . . . . . 36 16.6. Changes from 04 Version . . . . . . . . . . . . . . . . . 36
16.7. Changes from 03 Version . . . . . . . . . . . . . . . . . 37 16.7. Changes from 03 Version . . . . . . . . . . . . . . . . . 37
16.8. Changes from 02 Version . . . . . . . . . . . . . . . . . 37 16.8. Changes from 02 Version . . . . . . . . . . . . . . . . . 38
16.9. Changes from 01 Version . . . . . . . . . . . . . . . . . 38 16.9. Changes from 01 Version . . . . . . . . . . . . . . . . . 38
16.10. Changes from 00 Version . . . . . . . . . . . . . . . . . 38 16.10. Changes from 00 Version . . . . . . . . . . . . . . . . . 38
17. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 38 17. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 38
Appendix A. Default Flow Registration Backoff Times . . . . . . . 38 Appendix A. Default Flow Registration Backoff Times . . . . . . . 39
18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 39 18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 39
18.1. Normative References . . . . . . . . . . . . . . . . . . 39 18.1. Normative References . . . . . . . . . . . . . . . . . . 39
18.2. Informative References . . . . . . . . . . . . . . . . . 40 18.2. Informative References . . . . . . . . . . . . . . . . . 40
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 41 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 41
Intellectual Property and Copyright Statements . . . . . . . . . . 42 Intellectual Property and Copyright Statements . . . . . . . . . . 43
1. Introduction 1. Introduction
There are many environments for SIP [1] deployments in which the User There are many environments for SIP [1] deployments in which the User
Agent (UA) can form a connection to a Registrar or Proxy but in which Agent (UA) can form a connection to a Registrar or Proxy but in which
connections in the reverse direction to the UA are not possible. connections in the reverse direction to the UA are not possible.
This can happen for several reasons. Connections to the UA can be This can happen for several reasons. Connections to the UA can be
blocked by a firewall device between the UA and the proxy or blocked by a firewall device between the UA and the proxy or
registrar, which will only allow new connections in the direction of registrar, which will only allow new connections in the direction of
the UA to the Proxy. Similarly a NAT could be present, which is only the UA to the Proxy. Similarly a NAT could be present, which is only
capable of allowing new connections from the private address side to capable of allowing new connections from the private address side to
the public side. This specification allows SIP registration when the the public side. This specification allows a SIP User Agent behind
UA is behind such a firewall or NAT. such a firewall or NAT to receive inbound traffic associated with
registrations or dialogs that it initiates.
Most IP phones and personal computers get their network Most IP phones and personal computers get their network
configurations dynamically via a protocol such as DHCP (Dynamic Host configurations dynamically via a protocol such as DHCP (Dynamic Host
Configuration Protocol). These systems typically do not have a Configuration Protocol). These systems typically do not have a
useful name in the Domain Name System (DNS), and they almost never useful name in the Domain Name System (DNS), and they almost never
have a long-term, stable DNS name that is appropriate for use in the have a long-term, stable DNS name that is appropriate for use in the
subjectAltName of a certificate, as required by [1]. However, these subjectAltName of a certificate, as required by [1]. However, these
systems can still act as a TLS client and form connections to a proxy systems can still act as a Transport Layer Security (TLS) [18] client
or registrar which authenticates with a server certificate. The and form connections to a proxy or registrar which authenticates with
server can authenticate the UA using a shared secret in a digest a server certificate. The server can authenticate the UA using a
challenge over that TLS connection. shared secret in a digest challenge (as defined in Section 22 of RFC
3261) over that TLS connection.
The key idea of this specification is that when a UA sends a REGISTER The key idea of this specification is that when a UA sends a REGISTER
request, the proxy can later use this same network "flow"--whether or a dialog-forming request, the proxy can later use this same
this is a bidirectional stream of UDP datagrams, a TCP connection, or network "flow"--whether this is a bidirectional stream of UDP
an analogous concept of another transport protocol--to forward any datagrams, a TCP connection, or an analogous concept of another
requests that need to go to this UA. For a UA to receive incoming transport protocol--to forward any incoming requests that need to go
requests, the UA has to connect to a server. Since the server can't to this UA in the context of the registration or dialog.
connect to the UA, the UA has to make sure that a flow is always
active. This requires the UA to detect when a flow fails. Since For a UA to receive incoming requests, the UA has to connect to a
such detection takes time and leaves a window of opportunity for server. Since the server can't connect to the UA, the UA has to make
missed incoming requests, this mechanism allows the UA to use sure that a flow is always active. This requires the UA to detect
multiple flows to the proxy or registrar. This specification also when a flow fails. Since such detection takes time and leaves a
defines multiple keepalive schemes. The keepalive mechanism is used window of opportunity for missed incoming requests, this mechanism
to keep NAT bindings fresh, and to allow the UA to detect when a flow allows the UA to register over multiple flows at the same time. This
has failed. specification also defines multiple keepalive schemes. The keepalive
mechanism is used to keep NAT bindings fresh, and to allow the UA to
detect when a flow has failed.
2. Conventions and Terminology 2. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [2]. document are to be interpreted as described in RFC 2119 [2].
2.1. Definitions 2.1. Definitions
Authoritative Proxy: A proxy that handles non-REGISTER requests for Authoritative Proxy: A proxy that handles non-REGISTER requests for
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Flow: A Flow is a network protocol layer (layer 4) association Flow: A Flow is a network protocol layer (layer 4) association
between two hosts that is represented by the network address and between two hosts that is represented by the network address and
port number of both ends and by the protocol. For TCP, a flow is port number of both ends and by the protocol. For TCP, a flow is
equivalent to a TCP connection. For UDP a flow is a bidirectional equivalent to a TCP connection. For UDP a flow is a bidirectional
stream of datagrams between a single pair of IP addresses and stream of datagrams between a single pair of IP addresses and
ports of both peers. With TCP, a flow often has a one to one ports of both peers. With TCP, a flow often has a one to one
correspondence with a single file descriptor in the operating correspondence with a single file descriptor in the operating
system. system.
reg-id: This refers to the value of a new header field parameter reg-id: This refers to the value of a new header field parameter
value for the Contact header field. When a UA registers multiple value for the Contact header field. When a UA registers multiple
times, each simultaneous registration gets a unique reg-id value. times, each concurrent registration gets a unique reg-id value.
instance-id: This specification uses the word instance-id to refer instance-id: This specification uses the word instance-id to refer
to the value of the "sip.instance" media feature tag in the to the value of the "sip.instance" media feature tag in the
Contact header field. This is a Uniform Resource Name (URN) that Contact header field. This is a Uniform Resource Name (URN) that
uniquely identifies this specific UA instance. uniquely identifies this specific UA instance.
outbound-proxy-set A set of SIP URIs (Uniform Resource Identifiers) outbound-proxy-set: A set of SIP URIs (Uniform Resource Identifiers)
that represents each of the outbound proxies (often Edge Proxies) that represents each of the outbound proxies (often Edge Proxies)
with which the UA will attempt to maintain a direct flow. The with which the UA will attempt to maintain a direct flow. The
first URI in the set is often referred to as the primary outbound first URI in the set is often referred to as the primary outbound
proxy and the second as the secondary outbound proxy. There is no proxy and the second as the secondary outbound proxy. There is no
difference between any of the URIs in this set, nor does the difference between any of the URIs in this set, nor does the
primary/secondary terminology imply that one is preferred over the primary/secondary terminology imply that one is preferred over the
other. other.
3. Overview 3. Overview
Several scenarios in which this technique is useful are discussed The mechanisms defined in this document are useful in several
below, including the simple co-located registrar and proxy, a User scenarios discussed below, including the simple co-located registrar
Agent desiring multiple connections to a resource (for redundancy, and proxy, a User Agent desiring multiple connections to a resource
for example), and a system that uses Edge Proxies. (for redundancy, for example), and a system that uses Edge Proxies.
3.1. Summary of Mechanism 3.1. Summary of Mechanism
The overall approach is fairly simple. Each UA has a unique The overall approach is fairly simple. Each UA has a unique
instance-id that stays the same for this UA even if the UA reboots or instance-id that stays the same for this UA even if the UA reboots or
is power cycled. Each UA can register multiple times over different is power cycled. Each UA can register multiple times over different
connections for the same SIP Address of Record (AOR) to achieve high connections for the same SIP Address of Record (AOR) to achieve high
reliability. Each registration includes the instance-id for the UA reliability. Each registration includes the instance-id for the UA
and a reg-id label that is different for each flow. The registrar and a reg-id label that is different for each flow. The registrar
can use the instance-id to recognize that two different registrations can use the instance-id to recognize that two different registrations
both reach the same UA. The registrar can use the reg-id label to both reach the same UA. The registrar can use the reg-id label to
recognize that a UA is registering after a reboot or a network recognize whether a UA is creatin a new flow or refreshing or
failure. replacing an old one, possibly after a reboot or a network failure.
When a proxy goes to route a message to a UA for which it has a When a proxy goes to route a message to a UA for which it has a
binding, it can use any one of the flows on which a successful binding, it can use any one of the flows on which a successful
registration has been completed. A failure on a particular flow can registration has been completed. A failure to deliver a request on a
be tried again on an alternate flow. Proxies can determine which particular flow can be tried again on an alternate flow. Proxies can
flows go to the same UA by comparing the instance-id. Proxies can determine which flows go to the same UA by comparing the instance-id.
tell that a flow replaces a previously abandoned flow by looking at Proxies can tell that a flow replaces a previously abandoned flow by
the reg-id. looking at the reg-id.
UAs can use a simple periodic message as a keepalive mechanism to UAs can use a simple periodic message as a keepalive mechanism to
keep their flow to the proxy or registrar alive. For connection keep their flow to the proxy or registrar alive. For connection
oriented transports such as TCP this is based on CRLF or a transport oriented transports such as TCP this is based on CRLF or a transport
specific keepalive while for transports that are not connection specific keepalive while for transports that are not connection
oriented this is accomplished by using a SIP-specific usage profile oriented this is accomplished by using a SIP-specific usage profile
of STUN (Session Traversal Utilities for NAT) [3]. of STUN (Session Traversal Utilities for NAT) [3].
The UA can also ask its first hop proxy to use an specific flow for
subsequent messages when sending a dialog-forming request. This
allows the UA to setup a subscription dialog for the SIP
configuration package [19] before the UA registers.
3.2. Single Registrar and UA 3.2. Single Registrar and UA
In the topology shown below, a single server is acting as both a In the topology shown below, a single server is acting as both a
registrar and proxy. registrar and proxy.
+-----------+ +-----------+
| Registrar | | Registrar |
| Proxy | | Proxy |
+-----+-----+ +-----+-----+
| |
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User Agents which form only a single flow continue to register User Agents which form only a single flow continue to register
normally but include the instance-id as described in Section 4.1. normally but include the instance-id as described in Section 4.1.
The UA can also include a reg-id parameter which is used to allow the The UA can also include a reg-id parameter which is used to allow the
registrar to detect and avoid keeping invalid contacts when a UA registrar to detect and avoid keeping invalid contacts when a UA
reboots or reconnects after its old connection has failed for some reboots or reconnects after its old connection has failed for some
reason. reason.
For clarity, here is an example. Bob's UA creates a new TCP flow to For clarity, here is an example. Bob's UA creates a new TCP flow to
the registrar and sends the following REGISTER request. the registrar and sends the following REGISTER request.
REGISTER sip:example.com;keep-crlf SIP/2.0 REGISTER sip:example.com;keep SIP/2.0
Via: SIP/2.0/TCP 192.0.2.1;branch=z9hG4bK-bad0ce-11-1036 Via: SIP/2.0/TCP 192.168.0.2;rport;branch=z9hG4bK-bad0ce-11-1036
Max-Forwards: 70 Max-Forwards: 70
From: Bob <sip:bob@example.com>;tag=d879h76 From: Bob <sip:bob@example.com>;tag=d879h76
To: Bob <sip:bob@example.com> To: Bob <sip:bob@example.com>
Call-ID: 8921348ju72je840.204 Call-ID: 8921348ju72je840.204
CSeq: 1 REGISTER CSeq: 1 REGISTER
Supported: path Supported: path, outbound
Contact: <sip:line1@192.168.0.2>; reg-id=1; Contact: <sip:line1@192.168.0.2;transport=tcp>; reg-id=1;
;+sip.instance="<urn:uuid:00000000-0000-1000-8000-000A95A0E128>" ;+sip.instance="<urn:uuid:00000000-0000-1000-8000-000A95A0E128>"
Content-Length: 0 Content-Length: 0
The registrar challenges this registration to authenticate Bob. When The registrar challenges this registration to authenticate Bob. When
the registrar adds an entry for this contact under the AOR for Bob, the registrar adds an entry for this contact under the AOR for Bob,
the registrar also keeps track of the connection over which it the registrar also keeps track of the connection over which it
received this registration. received this registration.
The registrar saves the instance-id The registrar saves the instance-id
("urn:uuid:00000000-0000-1000-8000-000A95A0E128") and reg-id ("1") ("urn:uuid:00000000-0000-1000-8000-000A95A0E128") and reg-id ("1")
skipping to change at page 7, line 38 skipping to change at page 7, line 42
registration for each flow with minimal impact on overall system registration for each flow with minimal impact on overall system
load. load.
When Alice sends a request to Bob, his authoritative proxy selects When Alice sends a request to Bob, his authoritative proxy selects
the target set. The proxy forwards the request to elements in the the target set. The proxy forwards the request to elements in the
target set based on the proxy's policy. The proxy looks at the target set based on the proxy's policy. The proxy looks at the
target set and uses the instance-id to understand if two targets both target set and uses the instance-id to understand if two targets both
end up routing to the same UA. When the proxy goes to forward a end up routing to the same UA. When the proxy goes to forward a
request to a given target, it looks and finds the flows over which it request to a given target, it looks and finds the flows over which it
received the registration. The proxy then forwards the request on received the registration. The proxy then forwards the request on
that flow, instead of resolving the Contact URI using the procedures that existing flow, instead of resolving the Contact URI using the
in RFC 3263 [4] and trying to form a new flow to that contact. This procedures in RFC 3263 [4] and trying to form a new flow to that
allows the proxy to forward a request to a particular contact over contact.
the same flow that the UA used to register this AOR. If the proxy
has multiple flows that all go to this UA, it can choose any one of As described in the next section, if the proxy has multiple flows
the registration bindings for this AOR that has the same instance-id that all go to this UA, the proxy can choose any one of the
as the selected UA. registration bindings for this AOR that has the same instance-id as
the selected UA.
3.3. Multiple Connections from a User Agent 3.3. Multiple Connections from a User Agent
There are various ways to deploy SIP to build a reliable and scalable There are various ways to deploy SIP to build a reliable and scalable
system. This section discusses one such design that is possible with system. This section discusses one such design that is possible with
the mechanisms in this specification. Other designs are also the mechanisms in this specification. Other designs are also
possible. possible.
In the example system below, the logical outbound proxy/registrar for In the example system below, the logical outbound proxy/registrar for
the domain is running on two hosts that share the appropriate state the domain is running on two hosts that share the appropriate state
and can both provide registrar and outbound proxy functionality for and can both provide registrar and outbound proxy functionality for
the domain. The UA will form connections to two of the physical the domain. The UA will form connections to two of the physical
hosts that can perform the outbound proxy/registrar function for the hosts that can perform the authoritative proxy/registrar function for
domain. Reliability is achieved by having the UA form two TCP the domain. Reliability is achieved by having the UA form two TCP
connections to the domain. connections to the domain.
Scalability is achieved by using DNS SRV to load balance the primary Scalability is achieved by using DNS SRV [20] to load balance the
connection across a set of machines that can service the primary primary connection across a set of machines that can service the
connection, and also using DNS SRV to load balance across a separate primary connection, and also using DNS SRV to load balance across a
set of machines that can service the secondary connection. The separate set of machines that can service the secondary connection.
deployment here requires that DNS is configured with one entry that The deployment here requires that DNS is configured with one entry
resolves to all the primary hosts and another entry that resolves to that resolves to all the primary hosts and another entry that
all the secondary hosts. While this introduces additional DNS resolves to all the secondary hosts. While this introduces
configuration, the approach works and requires no additional SIP additional DNS configuration, the approach works and requires no
extensions. additional SIP extensions.
Note: Approaches which select multiple connections from a single Note: Approaches which select multiple connections from a single
DNS SRV set were also considered, but cannot prevent two DNS SRV set were also considered, but cannot prevent two
connections from accidentally resolving to the same host. The connections from accidentally resolving to the same host. The
approach in this document does not prevent future extensions, such approach in this document does not prevent future extensions, such
as the SIP UA configuration framework [19], from adding other ways as the SIP UA configuration framework [19], from adding other ways
for a User Agent to discover its outbound-proxy-set. for a User Agent to discover its outbound-proxy-set.
+-------------------+ +-------------------+
| Domain | | Domain |
skipping to change at page 8, line 46 skipping to change at page 9, line 4
|+-----+ +-----+| |+-----+ +-----+|
+---\------------/--+ +---\------------/--+
\ / \ /
\ / \ /
\ / \ /
\ / \ /
+------+ +------+
| User | | User |
| Agent| | Agent|
+------+ +------+
The UA is configured with multiple outbound proxy registration URIs. The UA is configured with multiple outbound proxy registration URIs.
These URIs are configured into the UA through whatever the normal These URIs are configured into the UA through whatever the normal
mechanism is to configure the proxy or registrar address in the UA. mechanism is to configure the proxy address and AOR in the UA. If
If the AOR is Alice@example.com, the outbound-proxy-set might look the AOR is alice@example.com, the outbound-proxy-set might look
something like "sip:primary.example.com;keep-stun" and "sip: something like "sip:primary.example.com;keep" and "sip:
secondary.example.com;keep-stun". The "keep-stun" tag indicates that secondary.example.com;keep". The "keep" tag indicates that a SIP
a SIP server supports STUN and SIP multiplexed over the same flow, as server will respond correctly to the mandatory to implement keepalive
described later in this specification. Note that each URI in the mechanisms described later in this specification. Note that each URI
outbound-proxy-set could resolve to several different physical hosts. in the outbound-proxy-set could resolve to several different physical
The administrative domain that created these URIs should ensure that hosts. The administrative domain that created these URIs should
the two URIs resolve to separate hosts. These URIs are handled ensure that the two URIs resolve to separate hosts. These URIs are
according to normal SIP processing rules, so mechanisms like SRV can handled according to normal SIP processing rules, so mechanisms like
be used to do load balancing across a proxy farm. SRV can be used to do load balancing across a proxy farm.
The domain also needs to ensure that a request for the UA sent to The domain also needs to ensure that a request for the UA sent to
host1 or host2 is then sent across the appropriate flow to the UA. host1 or host2 is then sent across the appropriate flow to the UA.
The domain might choose to use the Path header approach (as described The domain might choose to use the Path header approach (as described
in the next section) to store this internal routing information on in the next section) to store this internal routing information on
host1 or host2. host1 or host2.
When a single server fails, all the UAs that have a flow through it When a single server fails, all the UAs that have a flow through it
will detect a flow failure and try to reconnect. This can cause will detect a flow failure and try to reconnect. This can cause
large loads on the server. When large numbers of hosts reconnect large loads on the server. When large numbers of hosts reconnect
skipping to change at page 10, line 32 skipping to change at page 10, line 32
|Agent | |Agent |
+------+ +------+
These systems can use effectively the same mechanism as described in These systems can use effectively the same mechanism as described in
the previous sections but need to use the Path header. When the Edge the previous sections but need to use the Path header. When the Edge
Proxy receives a registration, it needs to create an identifier value Proxy receives a registration, it needs to create an identifier value
that is unique to this flow (and not a subsequent flow with the same that is unique to this flow (and not a subsequent flow with the same
addresses) and put this identifier in the Path header URI. This addresses) and put this identifier in the Path header URI. This
identifier has two purposes. First, it allows the Edge Proxy to map identifier has two purposes. First, it allows the Edge Proxy to map
future requests back to the correct flow. Second, because the future requests back to the correct flow. Second, because the
identifier will only be returned if the user authentication with the identifier will only be returned if the user authenticates with the
registrar succeeds, it allows the Edge Proxy to indirectly check the registrar successfully, it allows the Edge Proxy to indirectly check
user's authentication information via the registrar. The identifier the user's authentication information via the registrar. The
is placed in the user portion of a loose route in the Path header. identifier is placed in the user portion of a loose route in the Path
If the registration succeeds, the Edge Proxy needs to map future header. If the registration succeeds, the Edge Proxy needs to map
requests that are routed to the identifier value from the Path future requests that are routed to the identifier value from the Path
header, to the associated flow. header, to the associated flow.
The term Edge Proxy is often used to refer to deployments where the The term Edge Proxy is often used to refer to deployments where the
Edge Proxy is in the same administrative domain as the Registrar. Edge Proxy is in the same administrative domain as the Registrar.
However, in this specification we use the term to refer to any proxy However, in this specification we use the term to refer to any proxy
between the UA and the Registrar. For example the Edge Proxy may be between the UA and the Registrar. For example the Edge Proxy may be
inside an enterprise that requires its use and the registrar could be inside an enterprise that requires its use and the registrar could be
from a service provider with no relationship to the enterprise. from a service provider with no relationship to the enterprise.
Regardless if they are in the same administrative domain, this Regardless if they are in the same administrative domain, this
specification requires that Registrars and Edge proxies support the specification requires that Registrars and Edge proxies support the
skipping to change at page 11, line 43 skipping to change at page 11, line 43
A keepalive mechanism needs to keep NAT bindings refreshed; for A keepalive mechanism needs to keep NAT bindings refreshed; for
connections, it also needs to detect failure of a connection; and for connections, it also needs to detect failure of a connection; and for
connectionless transports, it needs to detect flow failures including connectionless transports, it needs to detect flow failures including
changes to the NAT public mapping. For connection oriented changes to the NAT public mapping. For connection oriented
transports such as TCP and SCTP, this specification describes a transports such as TCP and SCTP, this specification describes a
keepalive approach based on sending CRLFs, and for TCP, a usage of keepalive approach based on sending CRLFs, and for TCP, a usage of
TCP transport-layer keepalives. For connectionless transport, such TCP transport-layer keepalives. For connectionless transport, such
as UDP, this specification describes using STUN [3] over the same as UDP, this specification describes using STUN [3] over the same
flow as the SIP traffic to perform the keepalive. flow as the SIP traffic to perform the keepalive.
UAs are also free to use native transport keepalives, however the UA
application may not be able to set these timers on a per-connection
basis, and the server certainly cannot make any assumption about what
values are used. Use of native transport keepalives is therefore
outside the scope of this document.
3.5.1. CRLF Keepalive Technique 3.5.1. CRLF Keepalive Technique
This approach can only be used with connection-oriented transports This approach can only be used with connection-oriented transports
such as TCP or SCTP. The client periodically sends a double-CRLF such as TCP or SCTP. The client periodically sends a double-CRLF
(the "ping") then waits to receive a single CRLF (the "pong"). If (the "ping") then waits to receive a single CRLF (the "pong"). If
the client does not receive a "pong" within an appropriate amount of the client does not receive a "pong" within an appropriate amount of
time, it considers the flow failed. time, it considers the flow failed.
3.5.2. TCP Keepalive Technique 3.5.2. STUN Keepalive Technique
This approach can only be used when the transport protocol is TCP.
User Agents that are capable of generating per-connection TCP
keepalives can use TCP keepalives. When using this approach the
values of the keepalive timer are left to the client. Servers cannot
make any assumption about what values are used.
Note: when TCP is being used, it's natural to think of using TCP
KEEPALIVE. Unfortunately, many operating systems and programming
environments do not allow the keepalive time to be set on a per-
connection basis. Thus, applications may not be able to set an
appropriate time.
3.5.3. STUN Keepalive Technique
This technique can only be used for transports, such as UDP, that are This technique can only be used for connection-less transports, such
not connection oriented. as UDP.
For connection-less transports, a flow definition could change For connection-less transports, a flow definition could change
because a NAT device in the network path reboots and the resulting because a NAT device in the network path reboots and the resulting
public IP address or port mapping for the UA changes. To detect public IP address or port mapping for the UA changes. To detect
this, STUN requests are sent over the same flow that is being used this, STUN requests are sent over the same flow that is being used
for the SIP traffic. The proxy or registrar acts as a Session for the SIP traffic. The proxy or registrar acts as a Session
Traversal Utilities for NAT (STUN) [3] server on the SIP signaling Traversal Utilities for NAT (STUN) [3] server on the SIP signaling
port. port.
Note: The STUN mechanism is very robust and allows the detection Note: The STUN mechanism is very robust and allows the detection
of a changed IP address. Many other options were considered, but of a changed IP address. Many other options were considered, but
the SIP Working Group selected the STUN-based approach. the SIP Working Group selected the STUN-based approach.
Approaches using SIP requests were abandoned because to achieve Approaches using SIP requests were abandoned because many believed
the required performance, the server needs to deviate from the SIP that good performance and full backwards compatibility using this
specification in significant ways. This would result in many method were mutually exclusive.
undesirable and non-deterministic behaviors in some environments.
Another approach considered to detect a changed flow was using
OPTIONS messages and the rport parameter. Although the OPTIONS
approach has the advantage of being backwards compatible, it also
significantly increases the load on the proxy or registrar server.
Related to this idea was an idea of creating a new SIP PING method
that was like OPTIONS but faster. It would be critical that this
PING method did not violate the processing requirements of a
proxies and UAS so it was never clear how it would be
significantly faster than OPTIONS given it would still have to
obey things like checking the Proxy-Require header. After
considerable consideration the working group came to some
consensus that the STUN approach was a better solution than these
alternative designs.
4. User Agent Mechanisms 4. User Agent Mechanisms
4.1. Instance ID Creation 4.1. Instance ID Creation
Each UA MUST have an Instance Identifier URN that uniquely identifies Each UA MUST have an Instance Identifier URN that uniquely identifies
the device. Usage of a URN provides a persistent and unique name for the device. Usage of a URN provides a persistent and unique name for
the UA instance. It also provides an easy way to guarantee the UA instance. It also provides an easy way to guarantee
uniqueness within the AOR. This URN MUST be persistent across power uniqueness within the AOR. This URN MUST be persistent across power
cycles of the device. The Instance ID MUST NOT change as the device cycles of the device. The Instance ID MUST NOT change as the device
skipping to change at page 13, line 30 skipping to change at page 13, line 6
A device like a soft-phone, when first installed, can generate a A device like a soft-phone, when first installed, can generate a
UUID [6] and then save this in persistent storage for all future UUID [6] and then save this in persistent storage for all future
use. For a device such as a hard phone, which will only ever have use. For a device such as a hard phone, which will only ever have
a single SIP UA present, the UUID can include the MAC address and a single SIP UA present, the UUID can include the MAC address and
be generated at any time because it is guaranteed that no other be generated at any time because it is guaranteed that no other
UUID is being generated at the same time on that physical device. UUID is being generated at the same time on that physical device.
This means the value of the time component of the UUID can be This means the value of the time component of the UUID can be
arbitrarily selected to be any time less than the time when the arbitrarily selected to be any time less than the time when the
device was manufactured. A time of 0 (as shown in the example in device was manufactured. A time of 0 (as shown in the example in
Section 3.2) is perfectly legal as long as the device knows no Section 3.2) is perfectly legal as long as the device knows no
other UUIDs were generated at this time. other UUIDs were generated at this time on this device.
If a URN scheme other than UUID is used, the URN MUST be selected If a URN scheme other than UUID is used, the UA MUST only use URNs
such that the instance can be certain that no other instance for which an IETF consensus RFC defines how the specific URN needs to
registering against the same AOR would choose the same URN value. An be constructed and used in the sip.instance Contact parameter for
example of a URN that would not meet the requirements of this outbound behavior.
specification is the national bibliographic number [20]. Since there
is no clear relationship between a SIP UA instance and a URN in this
namespace, there is no way a selection of a value can be performed
that guarantees that another UA instance doesn't choose the same
value.
To convey its instance-id in both requests and responses, the UA To convey its instance-id in both requests and responses, the UA
includes a "sip.instance" media feature tag as a UA characteristic includes a "sip.instance" media feature tag as a UA characteristic
[7] . As described in [7], this media feature tag will be encoded in [7] . As described in [7], this media feature tag will be encoded in
the Contact header field as the "+sip.instance" Contact header field the Contact header field as the "+sip.instance" Contact header field
parameter. The value of this parameter MUST be a URN [8]. One case parameter. The value of this parameter MUST be a URN [8]. One case
where a UA may not want to include the URN in the sip.instance media where a UA may not want to include the sip.instance media feature tag
feature tag is when it is making an anonymous request or some other at all is when it is making an anonymous request or some other
privacy concern requires that the UA not reveal its identity. privacy concern requires that the UA not reveal its identity.
RFC 3840 [7] defines equality rules for callee capabilities RFC 3840 [7] defines equality rules for callee capabilities
parameters, and according to that specification, the parameters, and according to that specification, the
"sip.instance" media feature tag will be compared by case- "sip.instance" media feature tag will be compared by case-
sensitive string comparison. This means that the URN will be sensitive string comparison. This means that the URN will be
encapsulated by angle brackets ("<" and ">") when it is placed encapsulated by angle brackets ("<" and ">") when it is placed
within the quoted string value of the +sip.instance Contact header within the quoted string value of the +sip.instance Contact header
field parameter. The case-sensitive matching rules apply only to field parameter. The case-sensitive matching rules apply only to
the generic usages defined in RFC 3840 [7] and in the caller the generic usages defined in RFC 3840 [7] and in the caller
skipping to change at page 14, line 24 skipping to change at page 13, line 41
this specification, it is effectively "extracted" from the value this specification, it is effectively "extracted" from the value
in the "sip.instance" media feature tag. Thus, equality in the "sip.instance" media feature tag. Thus, equality
comparisons are performed using the rules for URN equality that comparisons are performed using the rules for URN equality that
are specific to the scheme in the URN. If the element performing are specific to the scheme in the URN. If the element performing
the comparisons does not understand the URN scheme, it performs the comparisons does not understand the URN scheme, it performs
the comparisons using the lexical equality rules defined in RFC the comparisons using the lexical equality rules defined in RFC
2141 [8]. Lexical equality could result in two URNs being 2141 [8]. Lexical equality could result in two URNs being
considered unequal when they are actually equal. In this specific considered unequal when they are actually equal. In this specific
usage of URNs, the only element which provides the URN is the SIP usage of URNs, the only element which provides the URN is the SIP
UA instance identified by that URN. As a result, the UA instance UA instance identified by that URN. As a result, the UA instance
SHOULD provide lexically equivalent URNs in each registration it MUST provide lexically equivalent URNs in each registration it
generates. This is likely to be normal behavior in any case; generates. This is likely to be normal behavior in any case;
clients are not likely to modify the value of the instance ID so clients are not likely to modify the value of the instance ID so
that it remains functionally equivalent yet lexicographically that it remains functionally equivalent yet lexicographically
different from previous registrations. different from previous registrations.
4.2. Registrations 4.2. Registrations
At configuration time UAs obtain one or more SIP URIs representing At configuration time, UAs obtain one or more SIP URIs representing
the default outbound-proxy-set. This specification assumes the set the default outbound-proxy-set. This specification assumes the set
is determined via any of a number of configuration mechanisms, and is determined via any of a number of configuration mechanisms, and
future specifications can define additional mechanisms such as using future specifications can define additional mechanisms such as using
DNS to discover this set. How the UA is configured is outside the DNS to discover this set. How the UA is configured is outside the
scope of this specification. However, a UA MUST support sets with at scope of this specification. However, a UA MUST support sets with at
least two outbound proxy URIs and SHOULD support sets with up to four least two outbound proxy URIs and SHOULD support sets with up to four
URIs. For each outbound proxy URI in the set, the UA SHOULD send a URIs.
REGISTER in the normal way using this URI as the default outbound
proxy. Forming the route set for the request is outside the scope of For each outbound proxy URI in the set, the UA SHOULD send a REGISTER
this document, but typically results in sending the REGISTER such in the normal way using this URI as the default outbound proxy. (The
that the topmost Route header field contains a loose route to the UA could limit the number of flows formed to conserve battery power,
outbound proxy URI. Other issues related to outbound route for example). All of these REGISTER requests will use the same
Call-ID. [OPEN ISSUE: This is for consistency with GRUU, Section
5.1 paragraph 5. Is this a bad idea? Alternatively GRUU could check
all reg-ids and preserve temporary GRUU if a registration used the
same Call-ID as used by any of the current bindings for the same
instance.] Forming the route set for the request is outside the
scope of this document, but typically results in sending the REGISTER
such that the topmost Route header field contains a loose route to
the outbound proxy URI. Other issues related to outbound route
construction are discussed in [21]. construction are discussed in [21].
Registration requests, other than those described in Section 4.2.1, Registration requests, other than those described in Section 4.2.1,
MUST include an instance-id media feature tag as specified in MUST include an instance-id media feature tag as specified in
Section 4.1. Section 4.1.
These ordinary registration requests include a distinct reg-id These ordinary registration requests include a distinct reg-id
parameter in the Contact header field. Each one of these parameter in the Contact header field. Each one of these
registrations will form a new flow from the UA to the proxy. The registrations will form a new flow from the UA to the proxy. The
sequence of reg-id values does not have to be sequential but MUST be sequence of reg-id values does not have to be sequential but MUST be
exactly the same sequence of reg-id values each time the UA instance exactly the same sequence of reg-id values each time the UA instance
power cycles or reboots so that the reg-id values will collide with power cycles or reboots so that the reg-id values will collide with
the previously used reg-id values. This is so the registrar can the previously used reg-id values. This is so the registrar can
replace the older registration. replace the older registrations.
The UAC can situationally decide whether to request outbound The UAC can situationally decide whether to request outbound
behavior by including or omitting the 'reg-id' parameter. For behavior by including or omitting the 'reg-id' parameter. For
example, imagine the outbound-proxy-set contains two proxies in example, imagine the outbound-proxy-set contains two proxies in
different domains, EP1 and EP2. If an outbound-style registration different domains, EP1 and EP2. If an outbound-style registration
succeeded for a flow through EP1, the UA might decide to include succeeded for a flow through EP1, the UA might decide to include
'outbound' in its Require header field when registering with EP2, 'outbound' in its Require header field when registering with EP2,
in order to insure consistency. Similarly, if the registration in order to insure consistency. Similarly, if the registration
through EP1 did not support outbound, the UA might decide to omit through EP1 did not support outbound, the UA might not register
the 'reg-id' parameter when registering with EP2. with EP2 at all.
The UAC MUST indicate that it supports the Path header [5] mechanism, The UAC MUST indicate that it supports the Path header [5] mechanism,
by including the 'path' option-tag in a Supported header field value by including the 'path' option-tag in a Supported header field value
in its REGISTER requests. Other than optionally examining the Path in its REGISTER requests. Other than optionally examining the Path
vector in the response, this is all that is required of the UAC to vector in the response, this is all that is required of the UAC to
support Path. support Path.
The UAC MAY examine successful registrations for the presence of an The UAC MAY examine successful registration responses for the
'outbound' option-tag in a Supported header field value. Presence of presence of an 'outbound' option-tag in a Require header field value.
this option-tag indicates that the registrar is compliant with this Presence of this option-tag indicates that the registrar is compliant
specification, and that any edge proxies which need to participate with this specification, and that any edge proxies which needed to
are also compliant. participate are also compliant. If the registrar did not support
outbound, the UA may have unintentionally registered an unroutable
contact. It is the responsiblity of the UA to remove any
inappropriate Contacts.
Note that the UA needs to honor 503 (Service Unavailable) responses Note that the UA needs to honor 503 (Service Unavailable) responses
to registrations as described in RFC 3261 and RFC 3263 [4]. In to registrations as described in RFC 3261 and RFC 3263 [4]. In
particular, implementors should note that when receiving a 503 particular, implementors should note that when receiving a 503
(Service Unavailable) response with a Retry-After header field, the (Service Unavailable) response with a Retry-After header field, the
UA is expected to wait the indicated amount of time and retry the UA is expected to wait the indicated amount of time and retry the
registration. A Retry-After header field value of 0 is valid and registration. A Retry-After header field value of 0 is valid and
indicates the UA is expected to retry the REGISTER immediately. indicates the UA is expected to retry the REGISTER immediately.
Implementations need to ensure that when retrying the REGISTER, they Implementations need to ensure that when retrying the REGISTER, they
revisit the DNS resolution results such that the UA can select an revisit the DNS resolution results such that the UA can select an
alternate host from the one chosen the previous time the URI was alternate host from the one chosen the previous time the URI was
resolved. resolved.
Finally, re-registrations which merely refresh an existing valid Finally, re-registrations which merely refresh an existing valid
registration SHOULD be sent over the same flow as the original registration SHOULD be sent over the same flow as the original
registration. registration.
4.2.1. Registration by Other Instances 4.2.1. Non Outbound Registrations
A User Agent MUST NOT include a reg-id header parameter in the A User Agent MUST NOT include a reg-id header parameter in the
Contact header field of a registration if the registering UA is not Contact header field of a registration with a non-zero expiration, if
the same instance as the UA referred to by the target Contact header the registering UA is not the same instance as the UA referred to by
field. (This practice is occasionally used to install forwarding the target Contact header field. (This practice is occasionally used
policy into registrars.) to install forwarding policy into registrars.)
Note that a UAC also MUST NOT include an instance-id or reg-id A UAC also MUST NOT include an instance-id or reg-id parameter in a
parameter in a request to unregister all Contacts (a single Contact request to unregister all Contacts (a single Contact header field
header field value with the value of "*"). value with the value of "*").
4.3. Sending Requests 4.3. Sending Non-REGISTER Requests
When a UA is about to send a request, it first performs normal When a UA is about to send a request, it first performs normal
processing to select the next hop URI. The UA can use a variety of processing to select the next hop URI. The UA can use a variety of
techniques to compute the route set and accordingly the next hop URI. techniques to compute the route set and accordingly the next hop URI.
Discussion of these techniques is outside the scope of this document Discussion of these techniques is outside the scope of this document
but could include mechanisms specified in RFC 3608 [22] (Service but could include mechanisms specified in RFC 3608 [22] (Service
Route) and [21]. Route) and [21].
The UA performs normal DNS resolution on the next hop URI (as The UA performs normal DNS resolution on the next hop URI (as
described in RFC 3263 [4]) to find a protocol, IP address, and port. described in RFC 3263 [4]) to find a protocol, IP address, and port.
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When a UA is about to send a request, it first performs normal When a UA is about to send a request, it first performs normal
processing to select the next hop URI. The UA can use a variety of processing to select the next hop URI. The UA can use a variety of
techniques to compute the route set and accordingly the next hop URI. techniques to compute the route set and accordingly the next hop URI.
Discussion of these techniques is outside the scope of this document Discussion of these techniques is outside the scope of this document
but could include mechanisms specified in RFC 3608 [22] (Service but could include mechanisms specified in RFC 3608 [22] (Service
Route) and [21]. Route) and [21].
The UA performs normal DNS resolution on the next hop URI (as The UA performs normal DNS resolution on the next hop URI (as
described in RFC 3263 [4]) to find a protocol, IP address, and port. described in RFC 3263 [4]) to find a protocol, IP address, and port.
For protocols that don't use TLS, if the UA has an existing flow to For protocols that don't use TLS, if the UA has an existing flow to
this IP address, and port with the correct protocol, then the UA MUST this IP address, and port with the correct protocol, then the UA MUST
use the existing connection. For TLS protocols, there MUST also be a use the existing connection. For TLS protocols, there MUST also be a
match between the host production in the next hop and one of the URIs match between the host production in the next hop and one of the URIs
contained in the subjectAltName in the peer certificate. If the UA contained in the subjectAltName in the peer certificate. If the UA
cannot use one of the existing flows, then it SHOULD form a new flow cannot use one of the existing flows, then it SHOULD form a new flow
by sending a datagram or opening a new connection to the next hop, as by sending a datagram or opening a new connection to the next hop, as
appropriate for the transport protocol. appropriate for the transport protocol.
The contact is formed normally in that the UAC uses the IP address of If the UA is sending a dialog-forming request, and wants all
the device (even if the device is behind a NAT). Unless there are subsequent requests in the dialog to arrive over the same flow, the
privacy reason not to include an instance-id, the contact SHOULD UA adds an 'ob' parameter to its Contact header. Typically this is
include the instance-id media feature tag as specified in desirable, but it is not necessary for example if the Contact is a
Section 4.1. The UAC MUST also include an "ob" parameter in the GRUU [23]. The flow used for the request is typically the same flow
Contact URI if, and only if, the UAC is sending the request over a the UA registered over, but it could be a new flow, for example the
flow for which the Registrar applied outbound processing. initial subcription dialog for the configuration framework [19] needs
to exist before registration.
Note that if the UA wants its flow to work through NATs or Note that if the UA wants its flow to work through NATs or
firewalls it still needs to put the 'rport' parameter [10] in its firewalls it still needs to put the 'rport' parameter [10] in its
Via header field value, and send from the port it is prepared to Via header field value, and send from the port it is prepared to
receive on. More general information about NAT traversal in SIP receive on. More general information about NAT traversal in SIP
is described in [23]. is described in [24].
******
4.4. Detecting Flow Failure 4.4. Detecting Flow Failure
The UA needs to detect when a specific flow fails. The UA actively The UA needs to detect when a specific flow fails. The UA actively
tries to detect failure by periodically sending keepalive messages tries to detect failure by periodically sending keepalive messages
using one of the techniques described in Section 4.4.1, using one of the techniques described in Section 4.4.1 or
Section 4.4.2, or Section 4.4.3. If a flow has failed, the UA Section 4.4.2. If a flow has failed, the UA follows the procedures
follows the procedures in Section 4.2 to form a new flow to replace in Section 4.2 to form a new flow to replace the failed one.
the failed one.
When the outbound-proxy-set contains the "timed-keepalives" When the outbound-proxy-set contains the "timed-keepalives"
parameter, the UA MUST send its keepalives according to the time parameter, the UA MUST send its keepalives according to the time
periods described in this section. The server can specify this so periods described in this section. The server can specify this so
the server can detect liveness of the client within a predictable the server can detect liveness of the client within a predictable
time scale. If the parameter is not present, the UA can send time scale. If the parameter is not present, the UA can send
keepalives at its discretion. keepalives at its discretion.
The time between each keepalive request when using non connection The time between each keepalive request when using non connection
based transports such as UDP SHOULD be a random number between 24 and based transports such as UDP SHOULD be a random number between 24 and
29 seconds while for connection based transports such as TCP it 29 seconds while for connection based transports such as TCP it
SHOULD be a random number between 95 and 120 seconds. These times SHOULD be a random number between 95 and 120 seconds. These times
MAY be configurable. To clarify, the random number will be different MAY be configurable. To clarify, the random number will be different
for each request. Issues such as battery consumption might motivate for each request. Issues such as battery consumption might motivate
longer keepalive intervals. If the 'timed-keepalives' parameter is longer keepalive intervals. If the 'timed-keepalives' parameter is
set on the outbound-proxy-set, the UA MUST use these recommended set on the outbound-proxy-set, the UA MUST use these recommended
timer values. timer values.
Note on selection of time values: For UDP, the upper bound of 29 Note on selection of time values: For UDP, the upper bound of 29
seconds was selected so that multiple STUN packets could be sent seconds was selected so that multiple STUN packets could be sent
before 30 seconds based on information that many NATs have UDP before 30 seconds, as many NATs have UDP timeouts as low as 30
timeouts as low as 30 seconds. The 24 second lower bound was seconds. The 24 second lower bound was selected so that after 10
selected so that after 10 minutes the jitter introduced by minutes the jitter introduced by different timers will make the
different timers will make the keepalive requests unsynchronized keepalive requests unsynchronized to evenly spread the load on the
to evenly spread the load on the servers. For TCP, the 120 servers. For TCP, the 120 seconds upper bound was chosen based on
seconds upper bound was chosen based on the idea that for a good the idea that for a good user experience, failures normally will
user experience, failures normally will be detected in this amount be detected in this amount of time and a new connection set up.
of time and a new connection set up. Operators that wish to Operators that wish to change the relationship between load on
change the relationship between load on servers and the expected servers and the expected time that a user might not receive
time that a user might not receive inbound communications will inbound communications will probably adjust this time. The 95
probably adjust this time. The 95 seconds lower bound was chosen seconds lower bound was chosen so that the jitter introduced will
so that the jitter introduced will result in a relatively even result in a relatively even load on the servers after 30 minutes.
load on the servers after 30 minutes.
The client needs to perform normal RFC 3263 [4] SIP DNS resolution on The client needs to perform normal RFC 3263 [4] SIP DNS resolution on
the URI from the outbound-proxy-set to pick a transport. Once a the URI from the outbound-proxy-set to pick a transport. Once a
transport is selected, the UA selects a keepalive approach that is transport is selected, if the 'keep' parameter is present in the URI,
allowed for that transport and that is allowed by the server based on the UA selects the keepalive approach that is recommended for that
the tags in the URI from the outbound-proxy-set. transport.
4.4.1. Keepalive with TCP KEEPALIVE
This approach MUST only be used with TCP.
User Agents that form flows, check if the configured URI they are
connecting to has a 'timed-keepalives' URI parameter (defined in
Section 12). If the parameter is not present and the UA is not
already performing keepalives using another supported mechanism, the
UA needs to periodically perform keepalive checks by using the TCP
Keepalive mechanism. Not all environments can use this approach and
it is not mandatory to implement. Deployments that use it should
also include keep-crlf so that clients that do not implement this
option but are using TCP have an alternative approach to use.
4.4.2. Keepalive with CRLF 4.4.1. Keepalive with CRLF
This approach MUST only be used with connection oriented transports This approach MUST only be used with connection oriented transports
such as TCP or SCTP. such as TCP or SCTP.
User Agents that form flows check if the configured URI they are A User Agent that forms flows, checks if the configured URI to which
connecting to has a 'keep-crlf' URI parameter (defined in the UA is connecting resolves to a stream-based transport (ex: TCP
Section 12). If the parameter is present and the UA is not already and TLS over TCP) and has a 'keep' URI parameter (defined in
performing keepalives using another supported mechanism, the UA can Section 12). If the parameter is present, the UA can send keep
send keep alives as described in this section. alives as described in this section.
For this mechanism, the client "ping" is a double-CRLF sequence, and For this mechanism, the client "ping" is a double-CRLF sequence, and
the server "pong" is a single CRLF, as defined in the ABNF below: the server "pong" is a single CRLF, as defined in the ABNF below:
CRLF = CR LF CRLF = CR LF
double-CRLF = CR LF CR LF double-CRLF = CR LF CR LF
CR = 0x0d CR = 0x0d
LF = 0x0a LF = 0x0a
The ping and pong need to be sent between SIP messages and cannot be The ping and pong need to be sent between SIP messages and cannot be
sent in the middle of a SIP message. If sending over a TLS protected sent in the middle of a SIP message. If sending over TLS, the CRLFs
channel, the CRLFs are sent inside the TLS record layer. If a pong are sent inside the TLS protected channel. If sending over a SigComp
is not received within 10 seconds then the client MUST treat the flow [25] compressed data stream, the CRLF keepalives are sent inside the
as failed. Clients MUST support this CRLF keepalive. compressed stream. The double CRLF is considered a single SigComp
message. The specific mechanism for representing these characters is
an implementation specific matter to be handled by the SigComp
compressor at the sending end.
4.4.3. Keepalive with STUN If a pong is not received within 10 seconds then the client MUST
treat the flow as failed. Clients MUST support this CRLF keepalive.
This approach MUST only be used with transports, such as UDP, that 4.4.2. Keepalive with STUN
are not connection oriented.
User Agents that form flows, check if the configured URI they are This approach MUST only be used with connection-less transports, such
connecting to has a 'keep-stun' URI parameter (defined in as UDP.
Section 12). If the parameter is present and the UA is not already
performing keepalives using another supported mechanism, the UA can
periodically perform keepalive checks by sending STUN [3] Binding
Requests over the flow as described in Section 8. Clients MUST
support STUN based keepalives.
If the XOR-MAPPED-ADDRESS in the STUN Binding Response changes, the A User Agent that forms flows, checks if the configured URI to which
UA MUST treat this event as a failure on the flow. the UA is connecting resolve to use the UDP transport, and has a
'keep' URI parameter (defined in Section 12). If the parameter is
present, the UA can periodically perform keepalive checks by sending
STUN [3] Binding Requests over the flow as described in Section 8.
Clients MUST support STUN based keepalives.
If a STUN Binding Error Response is received, or if no Binding
Response is received after 7 retransmissions (16 times the STUN "RTO"
timer--RTO is an estimate of round-trip time), the UA considers the
flow failed. If the XOR-MAPPED-ADDRESS in the STUN Binding Response
changes, the UA MUST treat this event as a failure on the flow.
4.5. Flow Recovery 4.5. Flow Recovery
When a flow to a particular URI in the outbound-proxy-set fails, the When a flow to a particular URI in the outbound-proxy-set fails, the
UA needs to form a new flow to replace the old flow and replace any UA needs to form a new flow to replace the old flow and replace any
registrations that were previously sent over this flow. Each new registrations that were previously sent over this flow. Each new
registration MUST have the same reg-id as the registration it registration MUST have the same reg-id as the registration it
replaces. This is done in much the same way as forming a brand new replaces. This is done in much the same way as forming a brand new
flow as described in Section 4.2; however, if there is a failure in flow as described in Section 4.2; however, if there is a failure in
forming this flow, the UA needs to wait a certain amount of time forming this flow, the UA needs to wait a certain amount of time
before retrying to form a flow to this particular next hop. before retrying to form a flow to this particular next hop.
The amount of time to wait depends if the previous attempt at The amount of time to wait depends if the previous attempt at
establishing a flow was successful. For the purposes of this establishing a flow was successful. For the purposes of this
section, a flow is considered successful if outbound registration section, a flow is considered successful if outbound registration
succeeded, and if keepalives are in use on this flow, at least one succeeded, and if keepalives are in use on this flow, at least one
consecutive keepalive response was received. subsequent keepalive response was received.
The number of seconds to wait is computed in the following way. If The number of seconds to wait is computed in the following way. If
all of the flows to every URI in the outbound proxy set have failed, all of the flows to every URI in the outbound proxy set have failed,
the base time is set to 30 seconds; otherwise, in the case where at the base-time is set to 30 seconds; otherwise, in the case where at
least one of the flows has not failed, the base time is set to 90 least one of the flows has not failed, the base-time is set to 90
seconds. The wait time is computed by taking two raised to the power seconds. The wait time is computed by taking two raised to the power
of the number of consecutive registration failures for that URI, and of the number of consecutive registration failures for that URI, and
multiplying this by the base time, up to a maximum of 1800 seconds. multiplying this by the base time, up to a maximum of 1800 seconds.
wait-time = min( max-time, (base-time * (2 ^ consecutive-failures))) wait-time = min( max-time, (base-time * (2 ^ consecutive-failures)))
These times MAY be configurable in the UA. The three times are: These times MAY be configurable in the UA. The three times are:
o max-time with a default of 1800 seconds o max-time with a default of 1800 seconds
o base-time-all-fail with a default of 30 seconds o base-time (if all failed) with a default of 30 seconds
o base-time-not-failed with a default of 90 seconds o base-time (if all have not failed) with a default of 90 seconds
For example, if the base time is 30 seconds, and there were three For example, if the base time is 30 seconds, and there were three
failures, then the wait time is min(1800,30*(2^3)) or 240 seconds. failures, then the wait time is min(1800,30*(2^3)) or 240 seconds.
The delay time is computed by selecting a uniform random time between The delay time is computed by selecting a uniform random time between
50 and 100 percent of the wait time. The UA MUST wait for the value 50 and 100 percent of the wait time. The UA MUST wait for the value
of the delay time before trying another registration to form a new of the delay time before trying another registration to form a new
flow for that URI. flow for that URI.
To be explicitly clear on the boundary conditions: when the UA boots To be explicitly clear on the boundary conditions: when the UA boots
it immediately tries to register. If this fails and no registration it immediately tries to register. If this fails and no registration
on other flows succeed, the first retry happens somewhere between 30 on other flows succeed, the first retry happens somewhere between 30
skipping to change at page 20, line 49 skipping to change at page 20, line 23
example is provided below. A proxy can use any algorithm it wants as example is provided below. A proxy can use any algorithm it wants as
long as the flow token is unique to a flow, the flow can be recovered long as the flow token is unique to a flow, the flow can be recovered
from the token, and the token cannot be modified by attackers. from the token, and the token cannot be modified by attackers.
Example Algorithm: When the proxy boots it selects a 20-octet crypto Example Algorithm: When the proxy boots it selects a 20-octet crypto
random key called K that only the Edge Proxy knows. A byte array, random key called K that only the Edge Proxy knows. A byte array,
called S, is formed that contains the following information about called S, is formed that contains the following information about
the flow the request was received on: an enumeration indicating the flow the request was received on: an enumeration indicating
the protocol, the local IP address and port, the remote IP address the protocol, the local IP address and port, the remote IP address
and port. The HMAC of S is computed using the key K and the HMAC- and port. The HMAC of S is computed using the key K and the HMAC-
SHA1-80 algorithm, as defined in [11]. The concatenation of the SHA1-80 algorithm, as defined in [26]. The concatenation of the
HMAC and S are base64 encoded, as defined in [12], and used as the HMAC and S are base64 encoded, as defined in [27], and used as the
flow identifier. When using IPv4 addresses, this will result in a flow identifier. When using IPv4 addresses, this will result in a
32-octet identifier. 32-octet identifier.
5.3. Forwarding Requests 5.3. Forwarding Non-REGISTER Requests
When an Edge Proxy receives a request, it applies normal routing When an Edge Proxy receives a request, it applies normal routing
procedures with the following addition. If the Edge Proxy receives a procedures with the following addition. If the Edge Proxy receives a
request where the edge proxy is the host in the topmost Route header request where the edge proxy is the host in the topmost Route header
field value, and the Route header field value contains a flow token, field value, and the Route header field value contains a flow token,
the proxy compares the flow in the flow token with the source of the the proxy decodes the flow token and compares the flow in the flow
request to determine if this is an "incoming" or "outgoing" request. token with the source of the request to determine if this is an
"incoming" or "outgoing" request.
If the flow in the flow token in the topmost Route header field value If the flow in the flow token in the topmost Route header field value
matches the source of the request, the request in an "outgoing" matches the source of the request, the request in an "outgoing"
request. For an "outgoing" request, the edge proxy just removes the request. For an "outgoing" request, the edge proxy just removes the
Route header and continues processing the request. Otherwise, this Route header and continues processing the request. Otherwise, this
is an "incoming" request. For an incoming request, the proxy removes is an "incoming" request. For an incoming request, the proxy removes
the Route header field value and forwards the request over the the Route header field value and forwards the request over the
'logical flow' identified by the flow token, that is known to deliver 'logical flow' identified by the flow token, that is known to deliver
data to the specific target UA instance. For connection-oriented data to the specific target UA instance. For connection-oriented
transports, if the flow no longer exists the proxy SHOULD send a 430 transports, if the flow no longer exists the proxy SHOULD send a 430
(Flow Failed) response to the request. (Flow Failed) response to the request.
skipping to change at page 21, line 42 skipping to change at page 21, line 17
then verify the HMAC is correct by recomputing the HMAC and then verify the HMAC is correct by recomputing the HMAC and
checking that it matches. If the HMAC is not correct, the proxy checking that it matches. If the HMAC is not correct, the proxy
SHOULD send a 403 (Forbidden) response. If the HMAC is correct SHOULD send a 403 (Forbidden) response. If the HMAC is correct
then the proxy SHOULD forward the request on the flow that was then the proxy SHOULD forward the request on the flow that was
specified by the information in the flow identifier. If this flow specified by the information in the flow identifier. If this flow
no longer exists, the proxy SHOULD send a 430 (Flow Failed) no longer exists, the proxy SHOULD send a 430 (Flow Failed)
response to the request. response to the request.
Note that this specification needs mid-dialog requests to be routed Note that this specification needs mid-dialog requests to be routed
over the same flows as those stored in the Path vector from the over the same flows as those stored in the Path vector from the
initial registration, but techniques to ensure that mid-dialog initial registration, but specific procedures at the edge proxy to
requests are routed over an existing flow are not part of this ensure that mid-dialog requests are routed over an existing flow are
specification. However, an approach such as having the Edge Proxy not part of this specification. However, an approach such as having
Record-Route with a flow token is one way to ensure that mid-dialog the Edge Proxy add a Record-Route header with a flow token is one way
requests are routed over the correct flow. The Edge Proxy can use to ensure that mid-dialog requests are routed over the correct flow.
the presence of the "ob" parameter in the UAC's Contact URI to The Edge Proxy can use the presence of the "ob" parameter in dialog-
determine if it should add a flow token. forming requests in the UAC's Contact URI to determine if it should
add a flow token.
5.4. Edge Proxy Keepalive Handling 5.4. Edge Proxy Keepalive Handling
All edge proxies compliant with this specification MUST implement All edge proxies compliant with this specification MUST implement
support for STUN NAT Keepalives on its SIP UDP ports as described in support for STUN NAT Keepalives on its SIP UDP ports as described in
Section 8. Section 8.
When a server receives a double CRLF sequence on a connection When a server receives a double CRLF sequence on a connection
oriented transport such as TCP or SCTP, it MUST immediately respond oriented transport such as TCP or SCTP, it MUST immediately respond
with a single CRLF over the same connection. with a single CRLF over the same connection.
6. Registrar Mechanisms: Processing REGISTER Requests 6. Registrar Mechanisms: Processing REGISTER Requests
This specification updates the definition of a binding in RFC 3261 This specification updates the definition of a binding in RFC 3261
[1] Section 10 and RFC 3327 [5] Section 5.3. [1] Section 10 and RFC 3327 [5] Section 5.3.
When no +sip.instance media feature parameter is present in a Contact
header field value in a REGISTER request, the corresponding binding
is still between an AOR and the URI from that Contact header field
value. When a +sip.instance media feature parameter is present in a
Contact header field value in a REGISTER request, the corresponding
binding is between an AOR and the combination of the instance-id
(from the +sip.instance media feature parameter) and the value of
reg-id parameter if it is present. For a binding with an
instance-id, the registrar still stores the Contact header field
value URI with the binding, but does not consider the Contact URI for
comparison purposes. A Contact header field value with an
instance-id but no reg-id is valid, but one with a reg-id but no
instance-id is not. If the registrar processes a Contact header
field value with a reg-id but no instance-id, it simply ignores the
reg-id parameter. The registrar MUST be prepared to receive,
simultaneously for the same AOR, some registrations that use
instance-id and reg-id and some registrations that do not.
Registrars which implement this specification MUST support the Path Registrars which implement this specification MUST support the Path
header mechanism [5]. header mechanism RFC 3327 [5].
In addition to the normal information stored in the binding record, When receiving a REGISTER request, the registrar first checks from
some additional information needs to be stored for any registration its Via header field if the registrar is the first hop or not. If
that contains an instance-id and a reg-id header parameter in the the registrar is not the first hop, it examines the Path header of
Contact header field value. First the registrar examines the first the request. If the Path header field is missing or it exists but
Path header field value, if any. If the Path header field exists and
the first URI does not have an 'ob' URI parameter, the registrar MUST the first URI does not have an 'ob' URI parameter, the registrar MUST
ignore the reg-id parameter and continue processing the request as if ignore the reg-id parameter of the Contact header.
it did not support this specification. Likewise if the REGISTER
request visited an edge proxy, but no Path header field values are A Contact header field value with an instance-id but no reg-id is
present, the registrar MUST ignore the reg-id parameter. valid (this combination can be used in the GRUU [23] specification),
Specifically, if it ignores the 'reg-id' parameter the registrar MUST but one with a reg-id but no instance-id is not. If the registrar
use RFC 3261 Contact binding rules, and MUST NOT include the processes a Contact header field value with a reg-id but no
'outbound' option-tag in its Supported header field. The registrar instance-id, it simply ignores the reg-id parameter. If the Contact
can determine if it is the first hop by examining the Via header header contains more than one header field value with a non-zero
field. expiration and a 'reg-id' parameter, the entire registration SHOULD
be rejected with a 400 Bad Request response. If the Contact header
did not contain a 'reg-id' parameter or if that parameter became
ignored (as described above) the registrar MUST NOT include the
'outbound' option-tag in the Require header field of its response.
The registrar MUST be prepared to receive, simultaneously for the
same AOR, some registrations that use instance-id and reg-id and some
registrations that do not. The Registrar MAY be configured with
local policy to reject any registrations that do not include the
instance-id and reg-id, or with Path header field values that do not
contain the 'ob' parameter. If the Contact header field does not
contain a '+sip.instance' media feature parameter, the registrar
processes the request using the Contact binding rules in RFC 3261
[1].
When a '+sip.instance' media feature parameter is present in a
Contact header field of a REGISTER request (after the Contact header
validation as described above), the corresponding binding is between
an AOR and the combination of the instance-id (from the +sip.instance
media feature parameter) and the value of reg-id parameter if it is
present. The registrar MUST store in the binding the Contact URI,
all the Contact head field parameters, and any Path header field
values and SHOULD also store the time at which the binding was last
updated. (Even though the Contact URI is not used for binding
comparisons, it is still needed by the authoritative proxy to form
the target set.) The Registrar MUST include the 'outbound' option-
tag (defined in Section 12.1) in a Require header field value in its
response to the REGISTER request.
If the UAC has a direct flow with the registrar, the registrar MUST If the UAC has a direct flow with the registrar, the registrar MUST
store enough information to uniquely identify the network flow over store enough information to uniquely identify the network flow over
which the request arrived. For common operating systems with TCP, which the request arrived. For common operating systems with TCP,
this would typically just be the handle to the file descriptor where this would typically just be the handle to the file descriptor where
the handle would become invalid if the TCP session was closed. For the handle would become invalid if the TCP session was closed. For
common operating systems with UDP this would typically be the file common operating systems with UDP this would typically be the file
descriptor for the local socket that received the request, the local descriptor for the local socket that received the request, the local
interface, and the IP address and port number of the remote side that interface, and the IP address and port number of the remote side that
sent the request. The registrar MAY store this information by adding sent the request. The registrar MAY store this information by adding
itself to the Path header field with an appropriate flow token. itself to the Path header field with an appropriate flow token.
The registrar MUST also store all the Contact header field If the registrar receives a re-registration for a specific
information including the reg-id and instance-id parameters and combination of AOR, instance-id and reg-id values, the registrar MUST
SHOULD also store the time at which the binding was last updated. If update any information that uniquely identifies the network flow over
a Path header field is present, RFC 3327 [5] requires the registrar which the request arrived if that information has changed, and SHOULD
to store this information as well. If the registrar receives a re- update the time the binding was last updated.
registration, it MUST update any information that uniquely identifies
the network flow over which the request arrived if that information
has changed, and SHOULD update the time the binding was last updated.
The Registrar MUST include the 'outbound' option-tag (defined in
Section (Section 12.1)) in a Supported header field value in its
responses to REGISTER requests for which it has performed outbound
processing, and MUST NOT include this option-tag if it did not
perform outbound processing. Furthermore, the Registrar MUST NOR
include this option-tag in its response if the Registrar skipped
outbound processing by ignoring the reg-id parameter as described in
this specification. Note that the requirements in this section
applies to both REGISTER requests received from an Edge Proxy as well
as requests received directly from the UAC. The Registrar MAY be
configured with local policy to reject any registrations that do not
include the instance-id and reg-id, or with Path header field values
that do not contain the 'ob' parameter.
To be compliant with this specification, registrars which can receive To be compliant with this specification, registrars which can receive
SIP requests directly from a UAC without intervening edge proxies SIP requests directly from a UAC without intervening edge proxies
MUST implement STUN NAT Keepalives on its SIP UDP ports as described MUST implement the same keepalive mechanisms as Edge Proxies
in Section 8 and when it receives a double-CRLF sequence on a (Section 5.4).
connection oriented transport such as TCP or SCTP, it MUST
immediately respond with a single CRLF over the same connection.
7. Authoritative Proxy Mechanisms: Forwarding Requests 7. Authoritative Proxy Mechanisms: Forwarding Requests
When a proxy uses the location service to look up a registration When a proxy uses the location service to look up a registration
binding and then proxies a request to a particular contact, it binding and then proxies a request to a particular contact, it
selects a contact to use normally, with a few additional rules: selects a contact to use normally, with a few additional rules:
o The proxy MUST NOT populate the target set with more than one o The proxy MUST NOT populate the target set with more than one
contact with the same AOR and instance-id at a time. contact with the same AOR and instance-id at a time.
o If a request for a particular AOR and instance-id fails with a 430 o If a request for a particular AOR and instance-id fails with a 430
(Flow Failed) response, the proxy SHOULD replace the failed branch (Flow Failed) response, the proxy SHOULD replace the failed branch
with another target (if one is available) with the same AOR and with another target (if one is available) with the same AOR and
instance-id, but a different reg-id. instance-id, but a different reg-id.
o If the proxy receives a final response from a branch other than a o If the proxy receives a final response from a branch other than a
408 (Request Timeout) or a 430 (Flow Failed) response, the proxy 408 (Request Timeout) or a 430 (Flow Failed) response, the proxy
MUST NOT forward the same request to another target representing MUST NOT forward the same request to another target representing
the same AOR and instance-id. The targeted instance has already the same AOR and instance-id. The targeted instance has already
provided its response. provided its response.
The proxy uses normal forwarding rules looking at the next-hop target The proxy uses the next-hop target of the message and the value of
of the message and the value of any stored Path header field vector any stored Path header field vector in the registration binding to
in the registration binding to decide how to forward the request and decide how to forward and populate the Route header in the request.
populate the Route header in the request. If the proxy stored If the proxy doubles as a registrar and stored information about the
information about the flow over which it received the REGISTER for flow that created the binding, then the proxy MUST send the request
the binding, then the proxy MUST send the request over the same over the same 'logical flow' saved with the binding, since that flow
'logical flow' saved with the binding that is known to deliver data is known to deliver data to the specific target UA instance's network
to the specific target UA instance. flow that was saved with the binding.
Typically this means that for TCP, the request is sent on the same Typically this means that for TCP, the request is sent on the same
TCP socket that received the REGISTER request. For UDP, the TCP socket that received the REGISTER request. For UDP, the
request is sent from the same local IP address and port over which request is sent from the same local IP address and port over which
the registration was received, to the same IP address and port the registration was received, to the same IP address and port
from which the REGISTER was received. from which the REGISTER was received.
If a proxy or registrar receives information from the network that If a proxy or registrar receives information from the network that
indicates that no future messages will be delivered on a specific indicates that no future messages will be delivered on a specific
flow, then the proxy MUST invalidate all the bindings in the target flow, then the proxy MUST invalidate all the bindings in the target
skipping to change at page 25, line 13 skipping to change at page 24, line 22
This constitues a new STUN usage. The STUN messages are used to This constitues a new STUN usage. The STUN messages are used to
verify that connectivity is still available over a UDP flow, and to verify that connectivity is still available over a UDP flow, and to
provide periodic keepalives. Note that these STUN keepalives are provide periodic keepalives. Note that these STUN keepalives are
always sent to the next SIP hop. STUN messages are not delivered always sent to the next SIP hop. STUN messages are not delivered
end-to-end. end-to-end.
The only STUN messages required by this usage are Binding Requests, The only STUN messages required by this usage are Binding Requests,
Binding Responses, and Binding Error Responses. The UAC sends Binding Responses, and Binding Error Responses. The UAC sends
Binding Requests over the same UDP flow that is used for sending SIP Binding Requests over the same UDP flow that is used for sending SIP
messages. These Binding Requests do not require any STUN attributes messages. These Binding Requests do not require any STUN attributes
and never use any form of authentication. The UAS responds to a except the XOR-MAPPED-ADDRESS and never use any form of
valid Binding Request with a Binding Response which MUST include the authentication. The UAS, proxy, or registrar responds to a valid
XOR-MAPPED-ADDRESS attribute. Binding Request with a Binding Response which MUST include the XOR-
MAPPED-ADDRESS attribute.
If a server compliant to this section receives SIP requests on a If a server compliant to this section receives SIP requests on a
given interface and port, it MUST also provide a limited version of a given interface and UDP port, it MUST also provide a limited version
STUN server on the same interface and port as described in Section of a STUN server on the same interface and UDP port.
12.3 of [3].
It is easy to distinguish STUN and SIP packets sent over UDP, It is easy to distinguish STUN and SIP packets sent over UDP,
because the first octet of a STUN packet has a value of 0 or 1 because the first octet of a STUN Binding method has a value of 0
while the first octet of a SIP message is never a 0 or 1. or 1 while the first octet of a SIP message is never a 0 or 1.
When a URI is created that refers to a SIP node that supports STUN as When a URI is created that refers to a SIP node that supports STUN as
described in this section, the 'keep-stun' URI parameter, as defined described in this section, the 'keep' URI parameter, as defined in
in Section 12 MUST be added to the URI. This allows a UA to inspect Section 12 SHOULD be added to the URI. This allows a UA to inspect
the URI to decide if it should attempt to send STUN requests to this the URI to decide if it should attempt to send STUN requests to this
location. For example, an edge proxy could insert this parameter location. For example, an edge proxy could insert this parameter
into its Path URI so that the registering UA can discover the edge into its Path URI so that the registering UA can discover the edge
proxy supports STUN keepalives. proxy supports STUN keepalives.
Because sending and receiving binary STUN data on the same ports used Because sending and receiving binary STUN data on the same ports used
for SIP is a significant and non-backwards compatible change to RFC for SIP is a significant and non-backwards compatible change to RFC
3261, this section requires a number of checks before sending STUN 3261, this section requires a number of checks before sending STUN
messages to a SIP node. If a SIP node sends STUN requests (for messages to a SIP node. If a SIP node sends STUN requests (for
example due to incorrect configuration) despite these warnings, the example due to incorrect configuration) despite these warnings, the
node could be blacklisted for UDP traffic. node could be blacklisted for UDP traffic.
A SIP node MUST NOT send STUN requests over a flow unless it has an A SIP node MUST NOT send STUN requests over a flow unless it has an
explicit indication that the target next hop SIP server claims to explicit indication that the target next hop SIP server claims to
support STUN. For example, automatic or manual configuration of an support STUN. For example, automatic or manual configuration of an
outbound-proxy-set which contains the 'keep-stun' parameter, or outbound-proxy-set which contains the 'keep' parameter, or receiving
receiving the parameter in the Path header of the edge proxy, is the parameter in the Path header of the edge proxy, is considered
considered sufficient explicit indication. Note that UACs MUST NOT sufficient explicit indication. Note that UACs MUST NOT use an
use an ambiguous configuration option such as "Work through NATs?" or ambiguous configuration option such as "Work through NATs?" or "Do
"Do Keepalives?" to imply next hop STUN support. Keepalives?" to imply next hop STUN support.
Typically, a SIP node first sends a SIP request and waits to Typically, a SIP node first sends a SIP request and waits to
receive a final response (other than a 408 response) over a flow receive a 200-class response over a flow to a new target
to a new target destination, before sending any STUN messages. destination, before sending any STUN messages. When scheduled for
When scheduled for the next NAT refresh, the SIP node sends a STUN the next NAT refresh, the SIP node sends a STUN request to the
request to the target. target.
Once a flow is established, failure of a STUN request (including its Once a flow is established, failure of a STUN request (including its
retransmissions) is considered a failure of the underlying flow. For retransmissions) is considered a failure of the underlying flow. For
SIP over UDP flows, if the XOR-MAPPED-ADDRESS returned over the flow SIP over UDP flows, if the XOR-MAPPED-ADDRESS returned over the flow
changes, this indicates that the underlying connectivity has changed, changes, this indicates that the underlying connectivity has changed,
and is considered a flow failure. and is considered a flow failure.
The SIP keepalive STUN usage requires no backwards compatibility. The SIP keepalive STUN usage requires no backwards compatibility with
RFC 3489 [11].
8.1. Use with Sigcomp 8.1. Use with Sigcomp
When STUN is used together with SigComp [24] compressed SIP messages When STUN is used together with SigComp [25] compressed SIP messages
over the same flow, how the STUN messages are sent depends on the over the same flow. For UDP flows, the STUN messages are simply sent
transport protocol. For UDP flows, the STUN messages are simply sent
uncompressed, "outside" of SigComp. This is supported by uncompressed, "outside" of SigComp. This is supported by
multiplexing STUN messages with SigComp messages by checking the two multiplexing STUN messages with SigComp messages by checking the two
topmost bits of the message. These bits are always one for SigComp, topmost bits of the message. These bits are always one for SigComp,
or zero for STUN. or zero for STUN.
All SigComp messages contain a prefix (the five most-significant All SigComp messages contain a prefix (the five most-significant
bits of the first byte are set to one) that does not occur in bits of the first byte are set to one) that does not occur in
UTF-8 [13] encoded text messages, so for applications which use UTF-8 [12] encoded text messages, so for applications which use
this encoding (or ASCII encoding) it is possible to multiplex this encoding (or ASCII encoding) it is possible to multiplex
uncompressed application messages and SigComp messages on the same uncompressed application messages and SigComp messages on the same
UDP port. UDP port.
The most significant two bits of every STUN message are both The most significant two bits of every STUN Binding method are
zeroes. This, combined with the magic cookie, aids in both zeroes. This, combined with the magic cookie, aids in
differentiating STUN packets from other protocols when STUN is differentiating STUN packets from other protocols when STUN is
multiplexed with other protocols on the same port. multiplexed with other protocols on the same port.
9. Example Message Flow 9. Example Message Flow
The following call flow shows a basic registration and an incoming [----example.com domain------]
call. At some point, the flow to the Primary proxy is lost. An Bob EP1 EP2 Proxy Alice
incoming INVITE tries to reach the Callee through the Primary flow, | | | | |
but receives an ICMP Unreachable message. The Caller retries using 1)|-REGISTER->| | | |
the Secondary Edge Proxy, which uses a separate flow. Later, after 2)| |---REGISTER-->| |
the Primary reboots, The Callee discovers the flow failure and 3)| |<----200 OK---| |
reestablishes a new flow to the Primary. 4)|<-200 OK---| | | |
5)|----REGISTER---->| | |
6)| | |--REG-->| |
7)| | |<-200---| |
8)|<----200 OK------| | |
| | | | |
| CRASH X | | |
| Reboot | | |
9)| | | |<-INVITE-|
10)| |<---INVITE----| |
11)| |----430------>| |
12)| | |<-INVITE| |
13)|<---INVITE-------| | |
14)|----200 OK------>| | |
15)| | |200 OK->| |
16)| | | |-200 OK->|
17)| | | |<-ACK----|
18)| | |<-ACK---| |
19)|<---ACK----------| | |
| | | | |
20)|--2CRLF->X | | | |
| | | | |
21)|-REGISTER->| | | |
22)|<-200 OK---| | | |
| | | | |
[TODO FIX example] The following call flow shows a basic registration
and an incoming call. At some point, the flow to the Primary proxy
is lost. An incoming INVITE tries to reach the Callee through the
Primary flow, but receives an ICMP Unreachable message. The Caller
retries using the Secondary Edge Proxy, which uses a separate flow.
Later, after the Primary reboots, The Callee discovers the flow
failure and reestablishes a new flow to the Primary.
[-----example.com domain -------------------] [-----example.com domain -------------------]
Caller Secondary Primary Callee Caller Secondary Primary Callee
| | | (1) REGISTER | | | | (1) REGISTER |
| | |<-----------------| | | |<-----------------|
| | |(2) 200 OK | | | |(2) 200 OK |
| | |----------------->| | | |----------------->|
| | | (3) REGISTER | | | | (3) REGISTER |
| |<------------------------------------| | |<------------------------------------|
| |(4) 200 OK | | | |(4) 200 OK | |
skipping to change at page 30, line 9 skipping to change at page 30, line 9
The registrations in message 13 and 14 are the same as message 1 and The registrations in message 13 and 14 are the same as message 1 and
2 other than the Call-ID and tags have changed. Because these 2 other than the Call-ID and tags have changed. Because these
messages will contain the same instance-id and reg-id as those in 1 messages will contain the same instance-id and reg-id as those in 1
and 2, this flow will partially supersede that for messages 1 and 2 and 2, this flow will partially supersede that for messages 1 and 2
and will be tried first by Primary. and will be tried first by Primary.
10. Grammar 10. Grammar
This specification defines new Contact header field parameters, This specification defines new Contact header field parameters,
reg-id and +sip.instance. The grammar includes the definitions from reg-id and +sip.instance. The grammar includes the definitions from
RFC 3261 [1] and includes the definition of uric from RFC 3986 [14]. RFC 3261 [1] and includes the definition of uric from RFC 3986 [13].
Note: The "=/" syntax used in this ABNF indicates an extension of Note: The "=/" syntax used in this ABNF indicates an extension of
the production on the left hand side. the production on the left hand side.
The ABNF[15] is: The ABNF[14] is:
contact-params =/ c-p-reg / c-p-instance contact-params =/ c-p-reg / c-p-instance
c-p-reg = "reg-id" EQUAL 1*DIGIT ; 1 to 2**31 c-p-reg = "reg-id" EQUAL 1*DIGIT ; 1 to (2**31 - 1)
c-p-instance = "+sip.instance" EQUAL c-p-instance = "+sip.instance" EQUAL
LDQUOT "<" instance-val ">" RDQUOT LDQUOT "<" instance-val ">" RDQUOT
instance-val = *uric ; defined in RFC 3986 instance-val = *uric ; defined in RFC 3986
The value of the reg-id MUST NOT be 0 and MUST be less than 2**31. The value of the reg-id MUST NOT be 0 and MUST be less than 2**31.
11. Definition of 430 Flow Failed response code 11. Definition of 430 Flow Failed response code
skipping to change at page 30, line 42 skipping to change at page 30, line 42
Other flows to the same instance could still succeed. The Other flows to the same instance could still succeed. The
Authoritative Proxy SHOULD attempt to forward to another target Authoritative Proxy SHOULD attempt to forward to another target
(flow) with the same instance-id and AOR. (flow) with the same instance-id and AOR.
12. IANA Considerations 12. IANA Considerations
12.1. Contact Header Field 12.1. Contact Header Field
This specification defines a new Contact header field parameter This specification defines a new Contact header field parameter
called reg-id in the "Header Field Parameters and Parameter Values" called reg-id in the "Header Field Parameters and Parameter Values"
sub-registry as per the registry created by [16]. The required sub-registry as per the registry created by [15]. The required
information is: information is:
Header Field Parameter Name Predefined Reference Header Field Parameter Name Predefined Reference
Values Values
____________________________________________________________________ ____________________________________________________________________
Contact reg-id No [RFC AAAA] Contact reg-id No [RFC AAAA]
[NOTE TO RFC Editor: Please replace AAAA with [NOTE TO RFC Editor: Please replace AAAA with
the RFC number of this specification.] the RFC number of this specification.]
12.2. SIP/SIPS URI Parameters 12.2. SIP/SIPS URI Parameters
This specification augments the "SIP/SIPS URI Parameters" sub- This specification augments the "SIP/SIPS URI Parameters" sub-
registry as per the registry created by [17]. The required registry as per the registry created by [16]. The required
information is: information is:
Parameter Name Predefined Values Reference Parameter Name Predefined Values Reference
____________________________________________ ____________________________________________
keep-crlf No [RFC AAAA] keep No [RFC AAAA]
keep-stun No [RFC AAAA] timed-keepalives No [RFC AAAA]
timed-keepalive No [RFC AAAA]
ob No [RFC AAAA] ob No [RFC AAAA]
[NOTE TO RFC Editor: Please replace AAAA with [NOTE TO RFC Editor: Please replace AAAA with
the RFC number of this specification.] the RFC number of this specification.]
12.3. SIP Option Tag 12.3. SIP Option Tag
This specification registers a new SIP option tag, as per the This specification registers a new SIP option tag, as per the
guidelines in Section 27.1 of RFC 3261. guidelines in Section 27.1 of RFC 3261.
Name: outbound Name: outbound
Description: This option-tag is used to identify Registrars which Description: This option-tag is used to identify UAs and Registrars
support extensions for Client Initiated Connections. A Registrar which support extensions for Client Initiated Connections. A
places this option-tag in a Supported header to communicate the Registrar places this option-tag in a Supported header to
Registrar's support for this extension to the registering User communicate the Registrar's support for this extension to the
Agent. registering User Agent, and vice versa.
12.4. Response Code 12.4. Response Code
This section registers a new SIP Response Code, as per the guidelines This section registers a new SIP Response Code, as per the guidelines
in Section 27.4 of RFC 3261. in Section 27.4 of RFC 3261.
Code: 430 Code: 430
Default Reason Phrase: Flow Failed Default Reason Phrase: Flow Failed
Reference: This document Reference: This document
12.5. Media Feature Tag 12.5. Media Feature Tag
This section registers a new media feature tag, per the procedures This section registers a new media feature tag, per the procedures
defined in RFC 2506 [18]. The tag is placed into the sip tree, which defined in RFC 2506 [17]. The tag is placed into the sip tree, which
is defined in RFC 3840 [7]. is defined in RFC 3840 [7].
Media feature tag name: sip.instance Media feature tag name: sip.instance
ASN.1 Identifier: New assignment by IANA. ASN.1 Identifier: New assignment by IANA.
Summary of the media feature indicated by this tag: This feature tag Summary of the media feature indicated by this tag: This feature tag
contains a string containing a URN that indicates a unique identifier contains a string containing a URN that indicates a unique identifier
associated with the UA instance registering the Contact. associated with the UA instance registering the Contact.
skipping to change at page 33, line 27 skipping to change at page 33, line 27
gotten this information from the registrar. The registrar will only gotten this information from the registrar. The registrar will only
save this information for a given AOR if the registration for the AOR save this information for a given AOR if the registration for the AOR
has been successful; and the registration will only be successful if has been successful; and the registration will only be successful if
the UA can correctly authenticate. Even if an attacker has spoofed the UA can correctly authenticate. Even if an attacker has spoofed
some bad information in the Path header sent to the registrar, the some bad information in the Path header sent to the registrar, the
attacker will not be able to get the registrar to accept this attacker will not be able to get the registrar to accept this
information for an AOR that does not belong to the attacker. The information for an AOR that does not belong to the attacker. The
registrar will not hand out this bad information to others, and registrar will not hand out this bad information to others, and
others will not be misled into contacting the attacker. others will not be misled into contacting the attacker.
The Security Considerations discussed in [1] and [5] are also
relevant to this document. For the security considerations of
generating flow tokens, please also see Section 5.2. A discussion of
preventing the avalanche restart problem is in Section 4.5.
This document does not change the mandatory to implement security
mechanisms in SIP. User Agents are already required to implement
Digest authentication while support of TLS is recommended; proxy
servers are already required to implement Digest and TLS.
14. Operational Notes on Transports 14. Operational Notes on Transports
This entire section is non-normative. This entire section is non-normative.
RFC 3261 requires proxies, registrars, and User Agents to implement RFC 3261 requires proxies, registrars, and User Agents to implement
both TCP and UDP but deployments can chose which transport protocols both TCP and UDP but deployments can chose which transport protocols
they want to use. Deployments need to be careful in choosing what they want to use. Deployments need to be careful in choosing what
transports to use. Many SIP features and extensions, such as large transports to use. Many SIP features and extensions, such as large
presence notification bodies, result in SIP requests that can be too presence notification bodies, result in SIP requests that can be too
large to be reasonably transported over UDP. RFC 3261 states that large to be reasonably transported over UDP. RFC 3261 states that
skipping to change at page 38, line 7 skipping to change at page 38, line 15
16.8. Changes from 02 Version 16.8. Changes from 02 Version
Removed Double CRLF Keepalive Removed Double CRLF Keepalive
Changed ;sip-stun syntax to ;keepalive=stun Changed ;sip-stun syntax to ;keepalive=stun
Fixed incorrect text about TCP keepalives. Fixed incorrect text about TCP keepalives.
16.9. Changes from 01 Version 16.9. Changes from 01 Version
Moved definition of instance-id from GRUU[25] draft to this draft. Moved definition of instance-id from GRUU[23] draft to this draft.
Added tentative text about Double CRLF Keepalive Added tentative text about Double CRLF Keepalive
Removed pin-route stuff Removed pin-route stuff
Changed the name of "flow-id" to "reg-id" Changed the name of "flow-id" to "reg-id"
Reorganized document flow Reorganized document flow
Described the use of STUN as a proper STUN usage Described the use of STUN as a proper STUN usage
skipping to change at page 38, line 33 skipping to change at page 38, line 41
Moved TCP keepalive to be STUN. Moved TCP keepalive to be STUN.
Allowed SUBSCRIBE to create flow mappings. Added pin-route option Allowed SUBSCRIBE to create flow mappings. Added pin-route option
tags to support this. tags to support this.
Added text about updating dialog state on each usage after a Added text about updating dialog state on each usage after a
connection failure. connection failure.
17. Acknowledgments 17. Acknowledgments
Jonathan Rosenberg provided many comments and useful text. Dave Oran Jonathan Rosenberg, Erkki Koivusalo, and Byron Campben provided many
came up with the idea of using the most recent registration first in comments and useful text. Dave Oran came up with the idea of using
the proxy. Alan Hawrylyshen co-authored the draft that formed the the most recent registration first in the proxy. Alan Hawrylyshen
initial text of this specification. Additionally, many of the co-authored the draft that formed the initial text of this
concepts here originated at a connection reuse meeting at IETF 60 specification. Additionally, many of the concepts here originated at
that included the authors, Jon Peterson, Jonathan Rosenberg, Alan a connection reuse meeting at IETF 60 that included the authors, Jon
Hawrylyshen, and Paul Kyzivat. The TCP design team consisting of Peterson, Jonathan Rosenberg, Alan Hawrylyshen, and Paul Kyzivat.
Chris Boulton, Scott Lawrence, Rajnish Jain, Vijay K. Gurbani, and The TCP design team consisting of Chris Boulton, Scott Lawrence,
Ganesh Jayadevan provided input and text. Nils Ohlmeier provided Rajnish Jain, Vijay K. Gurbani, and Ganesh Jayadevan provided input
many fixes and initial implementation experience. In addition, and text. Nils Ohlmeier provided many fixes and initial
thanks to the following folks for useful comments: Francois Audet, implementation experience. In addition, thanks to the following
Flemming Andreasen, Mike Hammer, Dan Wing, Srivatsa Srinivasan, Dale folks for useful comments: Francois Audet, Flemming Andreasen, Mike
Worely, Juha Heinanen, Eric Rescorla, Lyndsay Campbell, Christer Hammer, Dan Wing, Srivatsa Srinivasan, Dale Worely, Juha Heinanen,
Holmberg, Kevin Johns, and Erkki Koivusalo. Eric Rescorla, Lyndsay Campbell, Christer Holmberg, Kevin Johns,
Jeroen van Bemmel, and Derek MacDonald.
Appendix A. Default Flow Registration Backoff Times Appendix A. Default Flow Registration Backoff Times
The base-time used for the flow re-registration backoff times The base-time used for the flow re-registration backoff times
described in Section 4.5 are configurable. If the base-time-all-fail described in Section 4.5 are configurable. If the base-time-all-fail
value is set to the default of 30 seconds and the base-time-not- value is set to the default of 30 seconds and the base-time-not-
failed value is set to the default of 90 seconds, the following table failed value is set to the default of 90 seconds, the following table
shows the resulting delay values. shows the resulting delay values.
+-------------------+--------------------+--------------------+ +-------------------+--------------------+--------------------+
skipping to change at page 39, line 33 skipping to change at page 39, line 41
18.1. Normative References 18.1. Normative References
[1] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., [1] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002. Session Initiation Protocol", RFC 3261, June 2002.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[3] Rosenberg, J., "Simple Traversal Underneath Network Address [3] Rosenberg, J., "Simple Traversal Underneath Network Address
Translators (NAT) (STUN)", draft-ietf-behave-rfc3489bis-07 Translators (NAT) (STUN)", draft-ietf-behave-rfc3489bis-12
(work in progress), July 2007. (work in progress), November 2007.
[4] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol [4] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol
(SIP): Locating SIP Servers", RFC 3263, June 2002. (SIP): Locating SIP Servers", RFC 3263, June 2002.
[5] Willis, D. and B. Hoeneisen, "Session Initiation Protocol (SIP) [5] Willis, D. and B. Hoeneisen, "Session Initiation Protocol (SIP)
Extension Header Field for Registering Non-Adjacent Contacts", Extension Header Field for Registering Non-Adjacent Contacts",
RFC 3327, December 2002. RFC 3327, December 2002.
[6] Leach, P., Mealling, M., and R. Salz, "A Universally Unique [6] Leach, P., Mealling, M., and R. Salz, "A Universally Unique
IDentifier (UUID) URN Namespace", RFC 4122, July 2005. IDentifier (UUID) URN Namespace", RFC 4122, July 2005.
skipping to change at page 40, line 13 skipping to change at page 40, line 22
[8] Moats, R., "URN Syntax", RFC 2141, May 1997. [8] Moats, R., "URN Syntax", RFC 2141, May 1997.
[9] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller [9] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller
Preferences for the Session Initiation Protocol (SIP)", Preferences for the Session Initiation Protocol (SIP)",
RFC 3841, August 2004. RFC 3841, August 2004.
[10] Rosenberg, J. and H. Schulzrinne, "An Extension to the Session [10] Rosenberg, J. and H. Schulzrinne, "An Extension to the Session
Initiation Protocol (SIP) for Symmetric Response Routing", Initiation Protocol (SIP) for Symmetric Response Routing",
RFC 3581, August 2003. RFC 3581, August 2003.
[11] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing [11] Rosenberg, J., Weinberger, J., Huitema, C., and R. Mahy, "STUN
for Message Authentication", RFC 2104, February 1997. - Simple Traversal of User Datagram Protocol (UDP) Through
Network Address Translators (NATs)", RFC 3489, March 2003.
[12] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings",
RFC 3548, July 2003.
[13] Yergeau, F., "UTF-8, a transformation format of ISO 10646", [12] Yergeau, F., "UTF-8, a transformation format of ISO 10646",
STD 63, RFC 3629, November 2003. STD 63, RFC 3629, November 2003.
[14] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [13] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Sy ntax", STD 66, RFC 3986, Resource Identifier (URI): Generic Sy ntax", STD 66, RFC 3986,
January 2005. January 2005.
[15] Crocker, D. and P. Overell, "Augmented BNF for Syntax [14] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005. Specifications: ABNF", RFC 4234, October 2005.
[16] Camarillo, G., "The Internet Assigned Number Authority (IANA) [15] Camarillo, G., "The Internet Assigned Number Authority (IANA)
Header Field Parameter Registry for the Session Initiation Header Field Parameter Registry for the Session Initiation
Protocol (SIP)", BCP 98, RFC 3968, December 2004. Protocol (SIP)", BCP 98, RFC 3968, December 2004.
[17] Camarillo, G., "The Internet Assigned Number Authority (IANA) [16] Camarillo, G., "The Internet Assigned Number Authority (IANA)
Uniform Resource Identifier (URI) Parameter Registry for the Uniform Resource Identifier (URI) Parameter Registry for the
Session Initiation Protocol (SIP)", BCP 99, RFC 3969, Session Initiation Protocol (SIP)", BCP 99, RFC 3969,
December 2004. December 2004.
[18] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag [17] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag
Registration Procedure", BCP 31, RFC 2506, March 1999. Registration Procedure", BCP 31, RFC 2506, March 1999.
18.2. Informative References 18.2. Informative References
[18] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS)
Protocol Version 1.1", RFC 4346, April 2006.
[19] Petrie, D., "A Framework for Session Initiation Protocol User [19] Petrie, D., "A Framework for Session Initiation Protocol User
Agent Profile Delivery", draft-ietf-sipping-config-framework-12 Agent Profile Delivery", draft-ietf-sipping-config-framework-13
(work in progress). (work in progress), October 2007.
[20] Hakala, J., "Using National Bibliography Numbers as Uniform [20] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
Resource Names", RFC 3188, October 2001. specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[21] Rosenberg, J., "Construction of the Route Header Field in the [21] Rosenberg, J., "Construction of the Route Header Field in the
Session Initiation Protocol (SIP)", Session Initiation Protocol (SIP)",
draft-rosenberg-sip-route-construct-02 (work in progress). draft-rosenberg-sip-route-construct-02 (work in progress).
[22] Willis, D. and B. Hoeneisen, "Session Initiation Protocol (SIP) [22] Willis, D. and B. Hoeneisen, "Session Initiation Protocol (SIP)
Extension Header Field for Service Route Discovery During Extension Header Field for Service Route Discovery During
Registration", RFC 3608, October 2003. Registration", RFC 3608, October 2003.
[23] Boulton, C., "Best Current Practices for NAT Traversal for [23] Rosenberg, J., "Obtaining and Using Globally Routable User
SIP", draft-ietf-sipping-nat-scenarios-06 (work in progress). Agent (UA) URIs (GRUU) in the Session Initiation Protocol
(SIP)", draft-ietf-sip-gruu-15 (work in progress),
October 2007.
[24] Price, R., Bormann, C., Christoffersson, J., Hannu, H., Liu, [24] Boulton, C., "Best Current Practices for NAT Traversal for
SIP", draft-ietf-sipping-nat-scenarios-07 (work in progress),
July 2007.
[25] Price, R., Bormann, C., Christoffersson, J., Hannu, H., Liu,
Z., and J. Rosenberg, "Signaling Compression (SigComp)", Z., and J. Rosenberg, "Signaling Compression (SigComp)",
RFC 3320, January 2003. RFC 3320, January 2003.
[25] Rosenberg, J., "Obtaining and Using Globally Routable User [26] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing
Agent (UA) URIs (GRUU) in the Session Initiation Protocol for Message Authentication", RFC 2104, February 1997.
(SIP)", draft-ietf-sip-gruu-14 (work in progress).
[27] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings",
RFC 4648, October 2006.
Authors' Addresses Authors' Addresses
Cullen Jennings (editor) Cullen Jennings (editor)
Cisco Systems Cisco Systems
170 West Tasman Drive 170 West Tasman Drive
Mailstop SJC-21/2 Mailstop SJC-21/2
San Jose, CA 95134 San Jose, CA 95134
USA USA
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