draft-ietf-sip-outbound-03.txt   draft-ietf-sip-outbound-04.txt 
Network Working Group C. Jennings, Ed. Network Working Group C. Jennings, Ed.
Internet-Draft Cisco Systems Internet-Draft Cisco Systems
Updates: 3261,3327 (if approved) R. Mahy, Ed. Updates: 3261,3327 (if approved) R. Mahy, Ed.
Expires: September 21, 2006 Plantronics Expires: December 27, 2006 Plantronics
March 20, 2006 June 25, 2006
Managing Client Initiated Connections in the Session Initiation Protocol Managing Client Initiated Connections in the Session Initiation Protocol
(SIP) (SIP)
draft-ietf-sip-outbound-03 draft-ietf-sip-outbound-04
Status of this Memo Status of this Memo
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This Internet-Draft will expire on September 21, 2006. This Internet-Draft will expire on December 27, 2006.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
Session Initiation Protocol (SIP) allows proxy servers to initiate The Session Initiation Protocol (SIP) allows proxy servers to
TCP connections and send asynchronous UDP datagrams to User Agents in initiate TCP connections and send asynchronous UDP datagrams to User
order to deliver requests. However, many practical considerations, Agents in order to deliver requests. However, many practical
such as the existence of firewalls and Network Address Translators considerations, such as the existence of firewalls and Network
(NATs), prevent servers from connecting to User Agents in this way. Address Translators (NATs), prevent servers from connecting to User
Even when a proxy server can open a TCP connection to a User Agent, Agents in this way. This specification defines behaviors for User
most User Agents lack a certificate suitable to act as a TLS Agents, registrars and proxy servers that allow requests to be
(Transport Layer Security) server. This specification defines delivered on existing connections established by the User Agent. It
behaviors for User Agents, registrars and proxy servers that allow also defines keep alive behaviors needed to keep NAT bindings open
requests to be delivered on existing connections established by the and specifies the usage of multiple connections.
User Agent. It also defines keep alive behaviors needed to keep NAT
bindings open and specifies the usage of multiple connections.
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 . . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 4
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 . . . . . . . . . . 7
3.4 Edge Proxies . . . . . . . . . . . . . . . . . . . . . . . 9 3.4. Edge Proxies . . . . . . . . . . . . . . . . . . . . . . . 9
3.5 Keep Alive Technique . . . . . . . . . . . . . . . . . . . 10 3.5. Keepalive Technique . . . . . . . . . . . . . . . . . . . 10
4. User Agent Mechanisms . . . . . . . . . . . . . . . . . . . . 10 4. User Agent Mechanisms . . . . . . . . . . . . . . . . . . . . 11
4.1 Instance ID Creation . . . . . . . . . . . . . . . . . . . 10 4.1. Instance ID Creation . . . . . . . . . . . . . . . . . . . 11
4.2 Initial Registrations . . . . . . . . . . . . . . . . . . 12 4.2. Initial Registrations . . . . . . . . . . . . . . . . . . 13
4.2.1 Registration by Other Instances . . . . . . . . . . . 13 4.2.1. Registration by Other Instances . . . . . . . . . . . 14
4.3 Sending Requests . . . . . . . . . . . . . . . . . . . . . 13 4.3. Sending Requests . . . . . . . . . . . . . . . . . . . . . 14
4.3.1 Selecting the First Hop . . . . . . . . . . . . . . . 13 4.4. Detecting Flow Failure . . . . . . . . . . . . . . . . . . 14
4.3.2 Forming Flows . . . . . . . . . . . . . . . . . . . . 13 4.4.1. Keepalive with STUN . . . . . . . . . . . . . . . . . 15
4.4 Detecting Flow Failure . . . . . . . . . . . . . . . . . . 14 4.4.2. Flow Recovery . . . . . . . . . . . . . . . . . . . . 15
4.4.1 Keep Alive with STUN . . . . . . . . . . . . . . . . . 14 5. Edge Proxy Mechanisms . . . . . . . . . . . . . . . . . . . . 16
4.4.2 Flow Recovery . . . . . . . . . . . . . . . . . . . . 15 5.1. Processing Register Requests . . . . . . . . . . . . . . . 16
5. Edge Proxy Mechanisms . . . . . . . . . . . . . . . . . . . . 15 5.2. Generating Flow Tokens . . . . . . . . . . . . . . . . . . 16
5.1 Processing Register Requests . . . . . . . . . . . . . . . 15 5.3. Forwarding Requests . . . . . . . . . . . . . . . . . . . 17
5.2 Generating Flow Tokens . . . . . . . . . . . . . . . . . . 16 6. Registrar and Location Server Mechanisms . . . . . . . . . . . 18
5.3 Forwarding Requests . . . . . . . . . . . . . . . . . . . 16 6.1. Processing REGISTER Requests . . . . . . . . . . . . . . . 18
6. Registrar and Location Server Mechanisms . . . . . . . . . . . 17 6.2. Forwarding Requests . . . . . . . . . . . . . . . . . . . 19
6.1 Processing Register Requests . . . . . . . . . . . . . . . 17 7. Mechanisms for All Servers (Proxys, Registars, UASs) . . . . . 20
6.2 Forwarding Requests . . . . . . . . . . . . . . . . . . . 18 7.1. STUN Processing . . . . . . . . . . . . . . . . . . . . . 20
7. Mechanisms for All Servers (Proxys, Registars, UAS) . . . . . 19 8. Example Message Flow . . . . . . . . . . . . . . . . . . . . . 21
7.1 STUN Processing . . . . . . . . . . . . . . . . . . . . . 19 9. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
8. Example Message Flow . . . . . . . . . . . . . . . . . . . . . 20 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
9. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 10.1. Contact Header Field . . . . . . . . . . . . . . . . . . . 25
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . 24 10.2. SIP/SIPS URI Parameters . . . . . . . . . . . . . . . . . 25
10.1 Contact Header Field . . . . . . . . . . . . . . . . . . . 24 10.3. SIP Option Tag . . . . . . . . . . . . . . . . . . . . . . 26
10.2 SIP/SIPS URI Paramters . . . . . . . . . . . . . . . . . . 24 10.4. Media Feature Tag . . . . . . . . . . . . . . . . . . . . 26
10.3 SIP Option Tag . . . . . . . . . . . . . . . . . . . . . . 24 11. Security Considerations . . . . . . . . . . . . . . . . . . . 27
10.4 Media Feature Tag . . . . . . . . . . . . . . . . . . . . 25 12. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 28
11. Security Considerations . . . . . . . . . . . . . . . . . . 26 13. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
12. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 26 13.1. Changes from 03 Version . . . . . . . . . . . . . . . . . 28
13. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . 27 13.2. Changes from 02 Version . . . . . . . . . . . . . . . . . 29
13.1 Changes from 02 Version . . . . . . . . . . . . . . . . . 27 13.3. Changes from 01 Version . . . . . . . . . . . . . . . . . 29
13.2 Changes from 01 Version . . . . . . . . . . . . . . . . . 27 13.4. Changes from 00 Version . . . . . . . . . . . . . . . . . 29
13.3 Changes from 00 Version . . . . . . . . . . . . . . . . . 27 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 29
14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 27 Appendix A. Default Flow Registration Backoff Times . . . . . . . 30
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 30
15.1 Normative References . . . . . . . . . . . . . . . . . . . 28 15.1. Normative References . . . . . . . . . . . . . . . . . . . 30
15.2 Informative References . . . . . . . . . . . . . . . . . . 29 15.2. Informative References . . . . . . . . . . . . . . . . . . 31
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 30 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 33
Intellectual Property and Copyright Statements . . . . . . . . 31 Intellectual Property and Copyright Statements . . . . . . . . . . 34
1. Introduction 1. Introduction
There are many environments for SIP [5] deployments in which the User There are many environments for SIP [RFC3261] deployments in which
Agent (UA) can form a connection to a Registrar or Proxy but in which the User Agent (UA) can form a connection to a Registrar or Proxy but
the connections in the reverse direction to the UA are not possible. in which connections in the reverse direction to the UA are not
This can happen for several reasons. Connection to the UA can be possible. This can happen for several reasons. Connections to the
blocked by a firewall device between the UA and the proxy or UA can be blocked by a firewall device between the UA and the proxy
registrar, which will only allow new connections in the direction of or registrar, which will only allow new connections in the direction
the UA to the Proxy. Similarly there may be a NAT, which are only of the UA to the Proxy. Similarly there may be a NAT, which are 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 SIP registration when the
UA is behind such a firewall or NAT. UA is behind such a firewall or NAT.
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 definitely do useful name in the Domain Name System (DNS), and they definitely do
not have a long-term, stable DNS name that is appropriate for binding not have a long-term, stable DNS name that is appropriate for use in
to a certificate. It is impractical for them to have a certificate the subjectAltName of a certificate, as required by [RFC3261].
that can be used as a client-side TLS certificate for SIP. However, However, these systems can still act as a TLS client and form
these systems can still form TLS connections to a proxy or registrar connections to a proxy or registrar which authenticates with a server
which authenticates with a server certificate. The server can certificate. The server can authenticate the UA using a shared
authenticate the UA using a shared secret in a digest challenge over secret in a digest challenge over that TLS connection.
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 request, the proxy can later use this same network "flow", whether
this is a bidirectional stream of UDP datagrams, a TCP connection, or this is a bidirectional stream of UDP datagrams, a TCP connection, or
an analogous concept of another transport protocol--to forward any an analogous concept of another transport protocol to forward any
requests that need to go to this UA. For a UA to receive incoming requests that need to go to this UA. For a UA to receive incoming
requests, the UA has to connect to a server. Since the server can't requests, the UA has to connect to a server. Since the server can't
connect to the UA, the UA has to make sure that a flow is always 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, active. This requires the UA to detect when a flow fails. Since
such detection takes time and leaves a window of opportunity for such detection takes time and leaves a window of opportunity for
missed incoming requests, this mechanism allows the UA to use missed incoming requests, this mechanism allows the UA to use
multiple flows to the proxy or registrar. This mechanism also uses a multiple flows to the proxy or registrar. This mechanism also uses a
keep alive mechanism over each flow so that the UA can detect when a keep alive mechanism over each flow so that the UA can detect when a
flow has failed. 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 [4]. document are to be interpreted as described in RFC 2119 [RFC2119].
2.1 Definitions 2.1. Definitions
Edge Proxy: An Edge Proxy is any proxy that is located topologically Edge Proxy: An Edge Proxy is any proxy that is located topologically
between the registering User Agent and the registrar. between the registering User Agent and the registrar.
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 simultaneous registration gets a unique reg-id value.
instance-id: This specification uses the word instance-id to refer to instance-id: This specification uses the word instance-id to refer to
the value of the "sip.instance" media feature tag in the Contact the value of the "sip.instance" media feature tag in the Contact
header field. This is a Uniform Resource Name (URN) that uniquely header field. This is a Uniform Resource Name (URN) that uniquely
identifies this specific UA instance. identifies this specific UA instance.
outbound-proxy-set A configured set of SIP URIs (Uniform Resource outbound-proxy-set A set of SIP URIs (Uniform Resource Identifiers)
Identifiers) that represents each of the outbound proxies (often that represents each of the outbound proxies (often Edge Proxies)
Edge Proxies) with which the UA will attempt to maintain a direct with which the UA will attempt to maintain a direct flow. The
flow. first URI in the set is often refereed to as the primary outbound
proxy and the second as the secondary outbound proxy. There is no
difference between any of the URIs in this set, nor does the
primary/secondary terminology imply that one is preferred over the
other.
3. Overview 3. Overview
Several scenarios in which this technique is useful are discussed Several scenarios in which this technique is useful are discussed
below, including the simple co-located registrar and proxy, a User below, including the simple co-located registrar and proxy, a User
Agent desiring multiple connections to a resource (for redundancy for Agent desiring multiple connections to a resource (for redundancy,
example), and a system that uses Edge Proxies. 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. recognize that a UA is registering 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 on a particular flow can
be tried again on an alternate flow. Proxies can determine which be tried again on an alternate flow. Proxies can determine which
flows go to the same UA by comparing the instance-id. Proxies can flows go to the same UA by comparing the instance-id. Proxies can
tell that a flow replaces a previously abandoned flow by looking at tell that a flow replaces a previously abandoned flow by looking at
the reg-id. the reg-id.
UAs use the STUN (Simple Traversal of UDP through NATs) protocol as UAs use the STUN (Simple Traversal of UDP through NATs) protocol as
the keep alive mechanism to keep their flow to the proxy or registrar the keep alive mechanism to keep their flow to the proxy or registrar
alive. alive.
3.2 Single Registrar and UA 3.2. Single Registrar and UA
In this example, a single server is acting as both a registrar and In the topology shown below, a single server is acting as both a
proxy. registrar and proxy.
+-----------+ +-----------+
| Registrar | | Registrar |
| Proxy | | Proxy |
+-----+-----+ +-----+-----+
| |
| |
+----+--+ +----+--+
| User | | User |
| Agent | | Agent |
+-------+ +-------+
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 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 using invalid contacts when a UA registrar to detect and avoid using 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 SIP/2.0 REGISTER sip:example.com SIP/2.0
Via: SIP/2.0/TCP 192.0.2.1;branch=z9hG4bK-bad0ce-11-1036 Via: SIP/2.0/TCP 192.0.2.1;branch=z9hG4bK-bad0ce-11-1036
Max-Forwards: 70 Max-Forwards: 70
skipping to change at page 6, line 46 skipping to change at page 7, line 4
Via: SIP/2.0/TCP 192.0.2.1;branch=z9hG4bK-bad0ce-11-1036 Via: SIP/2.0/TCP 192.0.2.1;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
Contact: <sip:line1@192.168.0.2>; reg-id=1; Contact: <sip:line1@192.168.0.2>; reg-id=1;
;+sip.instance="<urn:uuid:00000000-0000-0000-0000-000A95A0E128>" ;+sip.instance="<urn:uuid:00000000-0000-0000-0000-000A95A0E128>"
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 and reg-id along with the rest of The registrar saves the instance-id
the Contact header field. If the instance-id and reg-id are the same ("urn:uuid:00000000-0000-0000-0000-000A95A0E128") and reg-id ("1")
as a previous registration for the same AOR, the proxy uses the most along with the rest of the Contact header field. If the instance-id
recently created registration first. This allows a UA that has and reg-id are the same as a previous registration for the same AOR,
rebooted to replace its previous registration for each flow with the proxy uses the most recently created registration first. This
minimal impact on overall system load. allows a UA that has rebooted to replace its previous registration
for each flow with minimal impact on overall system load.
When Alice sends a request to Bob, his proxy selects the target set. When Alice sends a request to Bob, his proxy selects the target set.
The proxy forwards the request to elements in the target set based on The proxy forwards the request to elements in the target set based on
the proxy's policy. The proxy looks at the target set and uses the the proxy's policy. The proxy looks at the target set and uses the
instance-id to understand that two targets both end up routing to the instance-id to understand that two targets both end up routing to the
same UA. When the proxy goes to forward a request to a given target, same UA. When the proxy goes to forward a request to a given target,
it looks and finds the flows that received the registration. The it looks and finds the flows over which it received the registration.
proxy then forwards the request on that flow instead of trying to The proxy then forwards the request on that flow instead of trying to
form a new flow to that contact. This allows the proxy to forward a form a new flow to that contact. This allows the proxy to forward a
request to a particular contact over the same flow that the UA used request to a particular contact over the same flow that the UA used
to register this AOR. If the proxy has multiple flows that all go to to register this AOR. If the proxy has multiple flows that all go to
this UA, it can choose any one of registration bindings for this AOR this UA, it can choose any one of registration bindings for this AOR
that has the same instance-id as the selected UA. In general, if two that has the same instance-id as the selected UA. In general, if two
registrations have the same reg-id and instance-id, the proxy will registrations have the same reg-id and instance-id, the proxy uses
favor the most recently registered flow. This is so that if a UA the most recently registered flow. This is so that if a UA reboots,
reboots, the proxy will prefer to use the most recent flow that goes the proxy uses the most recent flow that goes to this UA instead of
to this UA instead of trying one of the old flows which would trying one of the old flows which would presumably fail.
presumably fail.
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 this example system, the logical proxy/registrar for the domain is In the example system below, the logical outbound proxy/registrar for
running on two hosts that share the appropriate state and can both the domain is running on two hosts that share the appropriate state
provide registrar and proxy functionality for the domain. The UA and can both provide registrar and outbound proxy functionality for
will form connections to two of the physical hosts that can perform the domain. The UA will form connections to two of the physical
the proxy/registrar function for the domain. Reliability is achieved hosts that can perform the outbound proxy/registrar function for the
by having the UA form two TCP connections to the domain. Scalability domain. Reliability is achieved by having the UA form two TCP
is achieved by using DNS SRV to load balance the primary connection connections to the domain.
across a set of machines that can service the primary connection and
also using DNS SRV to load balance across a separate set of machines
that can service the backup connection. The deployment here requires
that DNS is configured with one entry that resolves to all the
primary hosts and another entry that resolves to all the backup
hosts. Designs having only one set were also considered, but in this
case there would have to be some way to ensure that the two
connection did not accidentally resolve to the same host. Various
approaches for this are possible but all probably require extensions
to the SIP protocol so they were not included in this specification.
This approach can work with the disadvantage that slightly more Scalability is achieved by using DNS SRV to load balance the primary
configuration of DNS is required. connection across a set of machines that can service the primary
connection and also using DNS SRV to load balance across a separate
set of machines that can service the secondary connection. The
deployment here requires that DNS is configured with one entry that
resolves to all the primary hosts and another entry that resolves to
all the secondary hosts. While this introduces additional DNS
configuration, the approach works and requires no addition SIP
extensions.
Note: Approaches which select multiple connections from a single
DNS SRV set were also considered, but cannot prevent two
connections from accidentally resolving to the same host. The
approach in this document does not prevent future extensions, such
as the SIP UA configuration framework [I-D.ietf-sipping-config-
framework], from adding other ways for a User Agent to discover
its outbound-proxy-set.
+-------------------+ +-------------------+
| Domain | | Domain |
| Logical Proxy/Reg | | Logical Proxy/Reg |
| | | |
|+-----+ +-----+| |+-----+ +-----+|
||Host1| |Host2|| ||Host1| |Host2||
|+-----+ +-----+| |+-----+ +-----+|
+---\------------/--+ +---\------------/--+
\ / \ /
\ / \ /
\ / \ /
\ / \ /
+------+ +------+
| User | | User |
| Agent| | Agent|
+------+ +------+
The UA is configured with a primary and backup registration URI. 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 or registrar address in the UA.
If the AOR is Alice@example.com, the outbound-proxy-set might look If the AOR is Alice@example.com, the outbound-proxy-set might look
something like "sip:primary.example.com;keepalive=stun" and "sip: something like "sip:primary.example.com;keepalive=stun" and "sip:
backup.example.com;keepalive=stun". The "keepalive=stun" tag secondary.example.com;keepalive=stun". The "keepalive=stun" tag
indicates that a SIP server supports STUN and SIP muxed over the same indicates that a SIP server supports STUN and SIP multiplexed over
flow, as described later in this specification. Note that each URI the same flow, as described later in this specification. Note that
in the outbound-proxy-set could resolve to several different physical each URI in the outbound-proxy-set could resolve to several different
hosts. The administrative domain that created these URIs should physical hosts. The administrative domain that created these URIs
ensure that the two URIs resolve to separate hosts. These URIs are should ensure that the two URIs resolve to separate hosts. These
handled according to normal SIP processing rules, so things like SRV URIs are handled according to normal SIP processing rules, so
can be used to do load balancing across a proxy farm. mechanisms like 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 (as described in the The domain might choose to use the Path header approach (as described
next section) approach 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
nearly simultaneously, this is referred to as the avalanche restart nearly simultaneously, this is referred to as the avalanche restart
problem, and is further discussed in Section 4.4.2. The multiple problem, and is further discussed in Section 4.4.2. The multiple
flows to many servers help reduce the load caused by the avalanche flows to many servers help reduce the load caused by the avalanche
restart. If a UA has multiple flows, and one of the servers fails, restart. If a UA has multiple flows, and one of the servers fails,
it can delay some significant time before trying to form a new the UA delays the specified time before trying to form a new
connection to replace the flow to the server that failed. By connection to replace the flow to the server that failed. By
spreading out the time used for all the UAs to reconnect to a server, spreading out the time used for all the UAs to reconnect to a server,
the load on the server farm is reduced. the load on the server farm is reduced.
3.4 Edge Proxies When used in this fashion to achieve high reliability, the operator
will need to configure DNS such that the various URIs in the outbound
proxy set do not resolve to the same host.
3.4. Edge Proxies
Some SIP deployments use edge proxies such that the UA sends the Some SIP deployments use edge proxies such that the UA sends the
REGISTER to an Edge Proxy that then forwards the REGISTER to the REGISTER to an Edge Proxy that then forwards the REGISTER to the
Registrar. The Edge Proxy includes a Path header [12] so that when Registrar. The Edge Proxy includes a Path header [RFC3327] so that
the registrar later forwards a request to this UA, the request is when the registrar later forwards a request to this UA, the request
routed through the Edge Proxy. There could be a NAT or firewall is routed through the Edge Proxy. There could be a NAT or firewall
between the UA and the Edge Proxy. between the UA and the Edge Proxy.
+---------+ +---------+
|Registrar| |Registrar|
|Proxy | |Proxy |
+---------+ +---------+
/ \ / \
/ \ / \
/ \ / \
+-----+ +-----+ +-----+ +-----+
|Edge1| |Edge2| |Edge1| |Edge2|
skipping to change at page 9, line 35 skipping to change at page 10, line 4
+-----+ +-----+ +-----+ +-----+
\ / \ /
\ / \ /
----------------------------NAT/FW ----------------------------NAT/FW
\ / \ /
\ / \ /
+------+ +------+
|User | |User |
|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 can addresses) and put this identifier in the Path header URI. This
be done by putting the value in the user portion of a loose route in identifier has two purposes. First, it allows the Edge Proxy to map
the path header. If the registration succeeds, the Edge Proxy needs future requests back to the correct flow. Second, because the
to map future requests that are routed to the identifier value from identifier will only be returned if the user authentication with the
the Path header, to the associated flow. registrar succeeds, it allows the Edge Proxy to indirectly check the
user's authentication information via the registrar. The identifier
SHOULD be placed in the user portion of a loose route in the Path
header. If the registration succeeds, the Edge Proxy needs to map
future requests that are routed to the identifier value from the Path
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
a service provider with no relationship to the enterprise. 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
Path header mechanism in RFC 3327 [12]. Path header mechanism in RFC 3327 [RFC3327].
3.5 Keep Alive Technique 3.5. Keepalive Technique
A keep alive mechanism needs to detect failure of a connection and A keep alive mechanism needs to detect failure of a connection and
changes to the NAT public mapping, as well as keeping any NAT changes to the NAT public mapping, as well as keeping any NAT
bindings refreshed. This specification describes using STUN [7] over bindings refreshed. This specification describes using STUN
the same flow as the SIP traffic to perform the keep alive. For [I-D.ietf-behave-rfc3489bis] over the same flow as the SIP traffic to
connection-oriented transports (e.g. TCP and TLS over TCP), the UAC perform the keepalive. For connection-oriented transports (e.g. TCP
MAY use TCP keep-alives to detect flow failure if the UAC can send and TLS over TCP), the UAC MAY use TCP keepalives to detect flow
these keep alives and detect a keep alive failure according to the failure if the UAC can send these keepalives and detect a keepalive
timeframes described in Section 4.4. failure according to the time frames described in Section 4.4.
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.
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, requests are sent over the same flow that is being used for the this, requests are sent over the same flow that is being used for the
SIP traffic. The proxy or registrar acts as a STUN server on the SIP SIP traffic. The proxy or registrar acts as a STUN server on the SIP
signaling port. signaling 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, since it the SIP Working Group selected the STUN-based approach, since it
works over any transport. Approaches using SIP requests were works over any transport. Approaches using SIP requests were
abandoned because to achieve the required performance, the server abandoned because to achieve the required performance, the server
needs to deviate from the SIP specification in significant ways. needs to deviate from the SIP specification in significant ways.
This would result in many undesirable and non-deterministic This would result in many undesirable and non-deterministic
behaviors in some environments. The TCP KEEP_ALIVE mechanism will behaviors in some environments.
not always work, since some operating systems and programming Another approach considered to detect a changed flow was using
environments do not allow the keep alive time to be set on a per OPTIONS messages and the rport parameter. Although the OPTIONS
connection basis. 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 that these
alternative designs.
When the UA detects that a flow has failed or that the flow When the UA detects that a flow has failed or that the flow
definition has changed, the UA needs to re-register and will use the definition has changed, the UA needs to re-register and will use the
back-off mechanism described in Section 4 to provide congestion back-off mechanism described in Section 4 to provide congestion
relief when a large number of agents simultaneously reboot. relief when a large number of agents simultaneously reboot.
4. User Agent Mechanisms 4. User Agent Mechanisms
4.1 Instance ID Creation 4.1. Instance ID Creation
Each UA MUST have an Instance Identifer 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 persitant across power uniqueness within the AOR. This URN MUST be persistent across power
cylces of the device. cycles of the device. The Instance ID MUST NOT change as the device
moves from one network to another.
A UA SHOULD use a UUID URN [9]. The UUID URN allows for non- A UA SHOULD use a UUID URN [RFC4122]. The UUID URN allows for non-
centralized computation of a URN based on time, unique names (such as centralized computation of a URN based on time, unique names (such as
a MAC address), or a random number generator. a MAC address), or a random number generator.
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 [9] and then save this in persistent storage for all future UUID [RFC4122] and then save this in persistent storage for all
use. For a device such as a hard phone, which will only ever have future use. For a device such as a hard phone, which will only
a single SIP UA present, the UUID can include the MAC address and ever have a single SIP UA present, the UUID can include the MAC
be generated at any time because it is guaranteed that no other address and be generated at any time because it is guaranteed that
UUID is being generated at the same time on that physical device. no other UUID is being generated at the same time on that physical
This means the value of the time component of the UUID can be device. This means the value of the time component of the UUID
arbitrarily selected to be any time less than the time when the can be arbitrarily selected to be any time less than the time when
device was manufactured. A time of 0 (as shown in the example in the device was manufactured. A time of 0 (as shown in the example
Section 3.2) is perfectly legal as long as the device knows no in 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.
If a URN scheme other than UUID is used, the URN MUST be selected If a URN scheme other than UUID is used, the URN MUST be selected
such that the instance can be certain that no other instance such that the instance can be certain that no other instance
registering against the same AOR would choose the same URN value. An registering against the same AOR would choose the same URN value. An
example of a URN that would not meet the requirements of this example of a URN that would not meet the requirements of this
specification is the national bibliographic number [15]. Since there specification is the national bibliographic number [RFC3188]. Since
is no clear relationship between a SIP UA instance and a URN in this there is no clear relationship between a SIP UA instance and a URN in
namespace, there is no way a selection of a value can be performed this namespace, there is no way a selection of a value can be
that guarantees that another UA instance doesn't choose the same performed that guarantees that another UA instance doesn't choose the
value. same value.
The UA SHOULD include a "sip.instance" media feature tag as a UA The UA SHOULD include a "sip.instance" media feature tag as a UA
characteristic [10] in requests and responses. As described in [10], characteristic [RFC3840] in requests and responses. As described in
this media feature tag will be encoded in the Contact header field as [RFC3840], this media feature tag will be encoded in the Contact
the "+sip.instance" Contact header field parameter. The value of header field as the "+sip.instance" Contact header field parameter.
this parameter MUST be a URN [3]. One case where a UA may not want The value of this parameter MUST be a URN [RFC2141]. One case where
to include the URN in the sip.instance media feature tag is when it a UA may not want to include the URN in the sip.instance media
is making an anoymous request or some other privacy concern requires feature tag is when it is making an anonymous request or some other
that the UA not reveal its identity. privacy concern requires that the UA not reveal its identity.
RFC 3840 [10] defines equality rules for callee capabilities RFC 3840 [RFC3840] 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 [10] and in the caller the generic usages defined in RFC 3840 [RFC3840] and in the caller
preferences specification [2]. When the instance ID is used in preferences specification [RFC3841]. When the instance ID is used
this specification, it is effectively "extracted" from the value in this specification, it is effectively "extracted" from the
in the "sip.instance" media feature tag. Thus, equality value 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 [3]. Lexical equality may result in two URNs being 2141 [RFC2141]. Lexical equality may 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 SHOULD 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 lexigraphically that it remains functionally equivalent yet lexigraphically
different to previous registrations. different from previous registrations.
4.2 Initial Registrations 4.2. Initial Registrations
UAs are configured with one or more SIP URIs representing the default UAs obtain at configuration time one or more SIP URIs representing
outbound-proxy-set. The specification assumes the set is determined the default outbound-proxy-set. This specification assumes the set
via configuration but future specifications may define other is determined via any of a number of configuration mechanisms and
mechanisms such as using DNS to discover this set. How the UA is future specifications may define additional mechanisms such as using
configured is outside the scope of this specification. However, a UA DNS to discover this set. How the UA is configured is outside the
MUST support sets with at least two outbound proxy URIs (primary and scope of this specification. However, a UA MUST support sets with at
backup) and SHOULD support sets with up to four URIs. For each least two outbound proxy URIs and SHOULD support sets with up to four
outbound proxy URI in the set, the UA MUST send a REGISTER in the URIs. For each outbound proxy URI in the set, the UA MUST send a
normal way using this URI as the default outbound proxy. Forming the REGISTER in the normal way using this URI as the default outbound
route set for the request is outside the scope of this document, but proxy. Forming the route set for the request is outside the scope of
typically results in sending the REGISTER such that the topmost Route this document, but typically results in sending the REGISTER such
header field contains a loose route to the outbound proxy URI. Other that the topmost Route header field contains a loose route to the
issues related to outbound route construction are discussed in [20]. outbound proxy URI. Other issues related to outbound route
construction are discussed in [I-D.rosenberg-sip-route-construct].
Registration requests, other than those described in Section 4.2.1, Registration requests, other than those described in Section 4.2.1,
MUST include the 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 MUST also add a distinct reg-id These ordinary registration requests MUST also add a distinct reg-id
parameter to the Contact header field. Each one of these parameter to 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
reg-id sequence does not have to be sequential but MUST be exactly reg-id sequence does not have to be sequential but MUST be exactly
the same reg-id sequence each time the device power cycles or reboots the same reg-id sequence each time the device power cycles or reboots
so that the reg-id values will collide with the previously used so that the reg-id values will collide with the previously used
reg-id values. This is so the proxy can realize that the older reg-id values. This is so the proxy can realize that the older
registrations are probably not useful. registrations are probably not useful.
The UAC MUST indicate that it supports the Path header [12] The UAC MUST indicate that it supports the Path header [RFC3327]
mechanism, by including the 'path' option-tag in a Supported header mechanism, by including the 'path' option-tag in a Supported header
field value in its REGISTER requests. Other than optionally field value in its REGISTER requests. Other than optionally
examining the Path vector in the response, this is all that is examining the Path vector in the response, this is all that is
required of the UAC to support Path. required of the UAC to support Path.
The UAC MAY examine successful registrations for the presence of an The UAC MAY examine successful registrations for the presence of an
'outbound' option-tag in a Supported header field value. Presence of 'outbound' option-tag in a Supported header field value. Presence of
this option-tag indicates that the registrar is compliant with this this option-tag indicates that the registrar is compliant with this
specification. specification.
Note that the UA needs to honor 503 responses to registrations as Note that the UA needs to honor 503 responses to registrations as
described in RFC 3261 and RFC 3263 [6]. In particular, implementors described in RFC 3261 and RFC 3263 [RFC3263]. In particular,
should note that when receiving a 503 response with a Retry-After implementors should note that when receiving a 503 response with a
header field, the UA should wait the indicated amount of time and Retry-After header field, the UA should wait the indicated amount of
retry the registration. A Retry-After header field value of 0 is time and retry the registration. A Retry-After header field value of
valid and indicates the UA should retry the REGISTER immediately. 0 is valid and indicates the UA should retry the REGISTER
Implementations need to ensure that when retrying the REGISTER they immediately. Implementations need to ensure that when retrying the
revisit the DNS resolution results such that the UA can select an REGISTER they revisit the DNS resolution results such that the UA can
alternate host from the one chosen the previous time the URI was select an alternate host from the one chosen the previous time the
resolved. URI was resolved.
4.2.1 Registration by Other Instances 4.2.1. Registration by Other Instances
A User Agent MUST NOT include an instance-id or reg-id in the Contact A User Agent MUST NOT include a reg-id header parameter in the
header field of a registration if the registering UA is not the same Contact header field of a registration if the registering UA is not
instance as the UA referred to by the target Contact header field. the same instance as the UA referred to by the target Contact header
(This practice is occasionally used to install forwarding policy into field. (This practice is occasionally used to install forwarding
registrars.) policy into registrars.)
Note that a UAC also MUST NOT include an instance-id or reg-id Note that a UAC also MUST NOT include an instance-id or reg-id
parameter in a request to deregister all Contacts (a single Contact parameter in a request to unregister all Contacts (a single Contact
header field value with the value of "*"). header field value with the value of "*").
4.3 Sending Requests 4.3. Sending Requests
As described in Section 4.1, all requests need to include the
instance-id media feature tag unless privacy concerns require
otherwise.
4.3.1 Selecting the First Hop
When an 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 [21] (Service but could include mechanisms specified in RFC 3608 [RFC3608] (Service
Route) and [20]. Route) and [I-D.rosenberg-sip-route-construct].
4.3.2 Forming Flows
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 [6]) to find a protocol, IP address, and port. described in RFC 3263 [RFC3263]) to find a protocol, IP address, and
For non TLS protocols, if the UA has an existing flow to this IP port. For non-TLS protocols, if the UA has an existing flow to this
address, and port with the correct protocol, then the UA MUST use the IP address, and port with the correct protocol, then the UA MUST use
existing connection. For TLS protocols, the existing flow is only the existing connection. For TLS protocols, there must also be a
used if, in addition to matching the IP address, port, and protocol, match between the host production in the next hop and one of the URIs
the host production in the next hop URI MUST match 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.
4.4 Detecting Flow Failure 4.4. Detecting Flow Failure
The UA needs to detect when a specific flow fails. If a flow has The UA needs to detect when a specific flow fails. The UA actively
tries to detect failure by periodically sending keepalive messages
using one of the techniques described in this section. If a flow has
failed, the UA follows the procedures in Section 4.2 to form a new failed, the UA follows the procedures in Section 4.2 to form a new
flow to replace the failed one. The UA proactively tries to detect flow to replace the failed one.
failure by periodically sending keep alive messages using one of the
techniques described in this section.
The time between keep alive requests when using UDP based transports The time between keepalive requests when using UDP-based transports
SHOULD be a random number between 24 and 29 seconds while for TCP SHOULD be a random number between 24 and 29 seconds while for TCP-
based transports it SHOULD be a random number between 95 and 120 based transports it SHOULD be a random number between 95 and 120
seconds. These times MAY be configurable. seconds. These times MAY be configurable.
o Note on selection of time values: For UDP, the upper bound of 29 o 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 based on information that many NATs have UDP
timeouts as low as 30 seconds. The 24 second lower bound was timeouts as low as 30 seconds. The 24 second lower bound was
selected so that after 10 minutes the jitter introduced by selected so that after 10 minutes the jitter introduced by
different timers will the keep alive requests unsynchronized to different timers will make the keepalive requests unsynchronized
evenly spread the load on the servers. For TCP, the 120 seconds to evenly spread the load on the servers. For TCP, the 120
was chosen based on the idea that for a good user experience, seconds upper bound was chosen based on the idea that for a good
failures should be detected in this amount of time and a new user experience, failures should be detected in this amount of
connection set up. Operators that wish to change the relationship time and a new connection set up. Operators that wish to change
between load on servers and the expected time that a user may not the relationship between load on servers and the expected time
receive inbound communications will probably adjust this time. that a user may not receive inbound communications will probably
The 95 seconds lower bound was chosen so that the jitter adjust this time. The 95 seconds lower bound was chosen so that
introduced will result in a relatively even load on the servers the jitter introduced will result in a relatively even load on the
after 30 minutes. servers after 30 minutes.
4.4.1 Keep Alive with STUN 4.4.1. Keepalive with STUN
User Agents that form flows MUST check if the configured URI they are User Agents that form flows MUST check if the configured URI they are
connecting to has a 'keepalive' URI parameter (defined in Section 10) connecting to has a 'keepalive' URI parameter (defined in Section 10)
with the value of 'stun'. If the parameter is present, the UA needs with the value of 'stun'. If the parameter is present, the UA needs
to periodically perform keep alive checks by sending a STUN [7] to periodically perform keepalive checks by sending a STUN [I-D.ietf-
Binding Requests over the flow. behave-rfc3489bis] Binding Requests over the flow.
If the XOR-MAPPED-ADDRESS in the STUN Binding Response changes, the If the XOR-MAPPED-ADDRESS in the STUN Binding Response changes, the
UA MUST treat this event as a failure on the flow. UA MUST treat this event as a failure on the flow.
4.4.2 Flow Recovery 4.4.2. 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 4.3.2; 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 time to wait is computed in the following way. If all of the The time to wait is computed in the following way. If all of the
flows to every URI in the proxy set have failed, the base time is set flows to every URI in the outbound proxy set have failed, the base
to 30 seconds; otherwise, in the case where at least one of the flows time is set to 30 seconds; otherwise, in the case where at least one
has not failed, the base time is set to 90 seconds. The wait time is of the flows has not failed, the base time is set to 90 seconds. The
computed by taking two raised to power of the number of consecutive wait time is computed by taking two raised to the power of the number
registration failures for that URI, and multiplying this by the base of consecutive registration failures for that URI, and multiplying
time, up to a maximum of 1800 seconds. this by the base time, up to a maximum of 1800 seconds.
wait-time = min( 1800, (base-time * (2 ^ consecutive-failures)))
These three times MAY be configurable in the UA. The three times are wait-time = min( max-time, (base-time * (2 ^ consecutive-failures)))
the max-time with a default of 1800 seconds, the base-time-all-fail
with a default of 30 seconds, and the base-time-not-failed with a These three times MAY be configurable in the UA. The three times
default of 60 seconds. For example if the base time was 30 seconds, are:
and there had been three failures, then the wait time would be o max-time with a default of 1800 seconds
min(1800,30*(2^3)) or 240 seconds. The delay time is computed by o base-time-all-fail with a default of 30 seconds
selecting a uniform random time between 50 and 100 percent of the o base-time-not-failed with a default of 90 seconds
wait time. The UA MUST wait for the value of the delay time before For example, if the base time was 30 seconds, and there had been
trying another registration to form a new flow for that URI. three failures, then the wait time would be min(1800,30*(2^3)) or 240
seconds. 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 of the delay time before trying another registration to
form a new 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
and 60 seconds after the failure of the first registration request. and 60 seconds after the failure of the first registration request.
If the number of consecutive-failures is large enough that the If the number of consecutive-failures is large enough that the
maximum of 1800 seconds is reached, the UA will keep trying forever maximum of 1800 seconds is reached, the UA will keep trying forever
with a random time between 900 and 1800 seconds between the attempts. with a random time between 900 and 1800 seconds between the attempts.
5. Edge Proxy Mechanisms 5. Edge Proxy Mechanisms
5.1 Processing Register Requests 5.1. Processing Register Requests
When an Edge Proxy receives a registration request with a When an Edge Proxy receives a registration request with a reg-id
sip.instance media feature tag in the Contact header field, it MUST header parameter in the Contact header field, it MUST form a flow
form a flow identifier token that is unique to this network flow. identifier token that is unique to this network flow. The Edge Proxy
The Edge Proxy MUST insert this token into a URI referring to this MUST insert this token into a URI referring to this proxy and place
proxy and place this URI into a Path header field as described in RFC this URI into a Path header field as described in RFC 3327 [RFC3327].
3327 [12]. The token MAY be placed in the userpart of the URI. The token MAY be placed in the userpart of the URI.
5.2 Generating Flow Tokens 5.2. Generating Flow Tokens
A trivial but impractical way to satisfy the flow token requirement A trivial but impractical way to satisfy the flow token requirement
Section 5.1 involves storing a mapping between an incrementing in Section 5.1 involves storing a mapping between an incrementing
counter and the connection information; however this would require counter and the connection information; however this would require
the Edge Proxy to keep an impractical amount of state. It is unclear the Edge Proxy to keep an impractical amount of state. It is unclear
when this state could be removed and the approach would have problems when this state could be removed and the approach would have problems
if the proxy crashed and lost the value of the counter. Two if the proxy crashed and lost the value of the counter. Two
stateless examples are provided below. A proxy can use any algorithm stateless examples are provided below. A proxy can use any algorithm
it wants as long as the flow token is unique to a flow, the flow can it wants as long as the flow token is unique to a flow, the flow can
be recovered from the token, and the token can not be modified by be recovered from the token, and the token can not be modified by
attackers. attackers.
Algorithm 1: The proxy generates a flow token for connection-oriented Algorithm 1: The proxy generates a flow token for connection-oriented
transports by concatenating the file descriptor (or equivalent) transports by concatenating the file descriptor (or equivalent)
with the NTP time the connection was created, and base64 encoding with the NTP time the connection was created, and base64 encoding
the result. This results in an approximately 16 octet identifier. the result. This results in an identifier approximately 16 octets
The proxy generates a flow token for UDP by concatenating the file long. The proxy generates a flow token for UDP by concatenating
descriptor and the remote IP address and port, then base64 the file descriptor and the remote IP address and port, then
encoding the result. This algorithm MUST NOT be used unless all base64 encoding the result. (No NTP time is needed for UDP.)
messages between the Edge proxy and Registrar use a SIPS protected This algorithm MUST NOT be used unless all messages between the
transport. If the SIPS level of integrity protection is not Edge proxy and Registrar use a SIPS protected transport. If the
available, an attacker can hijack another user's calls. SIPS level of integrity protection is not available, an attacker
Algorithm 2: When the proxy boots it selects a 20 byte crypto random can hijack another user's calls.
Algorithm 2: When the proxy boots it selects a 20-octet crypto random
key called K that only the Edge Proxy knows. A byte array, called key called K that only the Edge Proxy knows. A byte array, called
S, is formed that contains the following information about the 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 and 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- port. The HMAC of S is computed using the key K and the HMAC-
SHA1-80 algorithm, as defined in [16]. The concatenation of the SHA1-80 algorithm, as defined in [RFC2104]. The concatenation of
HMAC and S are base64 encoded, as defined in [18], and used as the the HMAC and S are base64 encoded, as defined in [RFC3548], and
flow identifier. When using IPv4 addresses, this will result in a used as the flow identifier. When using IPv4 addresses, this will
32 octet identifier. result in a 32-octet identifier.
5.3 Forwarding Requests 5.3. Forwarding Requests
When the Edge Proxy receives a request, it applies normal routing When the Edge Proxy receives a request, it applies normal routing
procedures with the following addition. If the top-most Route header procedures with the following addition. If the Edge Proxy receives a
refers to the Edge Proxy and contains a valid flow identifier token request over a flow already represented in a flow token in the top-
created by this proxy, the proxy MUST forward the request over the most Route header field value, the Edge Proxy pops the Route header
flow that received the REGISTER request that caused the flow and continues processing the request. Otherwise, if the top-most
identifier token to be created. For connection-oriented transports, Route header refers to the Edge Proxy and contains a valid flow
if the flow no longer exists the proxy SHOULD send a 410 response to identifier token created by this proxy, the proxy MUST forward the
the request. request over the flow that received the REGISTER request that caused
the flow identifier token to be created. For connection-oriented
transports, if the flow no longer exists the proxy SHOULD send a 410
response to the request.
The advantage to a stateless approach to managing the flow The advantage to a stateless approach to managing the flow
information is that there is no state on the edge proxy that information is that there is no state on the Edge Proxy that
requires clean up or that has to be synchronized with the requires clean up or that has to be synchronized with the
registrar. registrar.
Proxies which used one of the two algorithms described in this Proxies which used one of the two algorithms described in this
document to form a flow token follow the procedures below to document to form a flow token follow the procedures below to
determine the correct flow. determine the correct flow.
Algorithm 1: The proxy base64 decodes the user part of the Route Algorithm 1: The proxy base64 decodes the user part of the Route
header. For TCP, if a connection specified by the file descriptor header. For a TCP-based transport, if a connection specified by
is present and the creation time of the file descriptor matches the file descriptor is present and the creation time of the file
the creation time encoded in the Route header, the proxy forwards descriptor matches the creation time encoded in the Route header,
the request over that connection. For UDP, the proxy forwards the the proxy forwards the request over that connection. For a UDP-
request from the encoded file descriptor to the source IP address based transport, the proxy forwards the request from the encoded
and port. file descriptor to the source IP address and port.
Algorithm 2: To decode the flow token take the flow identifier in the Algorithm 2: To decode the flow token, take the flow identifier in
user portion of the URI, and base64 decode it, then verify the the user portion of the URI and base64 decode it, then verify the
HMAC is correct by recomputing the HMAC and checking it matches. HMAC is correct by recomputing the HMAC and checking it matches.
If the HMAC is not correct, the proxy SHOULD send a 403 response. If the HMAC is not correct, the proxy SHOULD send a 403 response.
If the HMAC was correct then the proxy should forward the request If the HMAC is correct then the proxy SHOULD forward the request
on the flow that was specified by the information in the flow on the flow that was specified by the information in the flow
identifier. If this flow no longer exists, the proxy SHOULD send identifier. If this flow no longer exists, the proxy SHOULD send
a 410 response to the request. a 410 response to the request.
Note that techniques to ensure that mid-dialog requests are routed Note that this specification needs mid-dialog requests to be routed
over an existing flow are out of scope and therefore not part of this over the same flow but techniques to ensure that mid-dialog requests
specification. However, an approach such as having the Edge Proxy are routed over an existing flow are not part of this specification.
Record-Route with a flow token is one way to ensure that mid-dialog However, an approach such as having the Edge Proxy Record-Route with
requests are routed over the correct flow. a flow token is one way to ensure that mid-dialog requests are routed
over the correct flow.
6. Registrar and Location Server Mechanisms 6. Registrar and Location Server Mechanisms
6.1 Processing Register Requests 6.1. 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
[5] Section 10 and RFC 3327 [12] Section 5.3. [RFC3261] Section 10 and RFC 3327 [RFC3327] Section 5.3.
When no instance-id is present in a Contact header field value in a When no reg-id header parameter is present in a Contact header field
REGISTER request, the corresponding binding is still between an AOR value in a REGISTER request, the corresponding binding is still
and the URI from that Contact header field value. When an between an AOR and the URI from that Contact header field value.
instance-id is present in a Contact header field value in a REGISTER When a reg-id header parameter is present in a Contact header field
request, the corresponding binding is between an AOR and the value in a REGISTER request, the corresponding binding is between an
combination of instance-id and reg-id. For a binding with an AOR and the combination of instance-id and reg-id. For a binding
instance-id, the registrar still stores the Contact header field with an instance-id, the registrar still stores the Contact header
value URI with the binding, but does not consider the Contact URI for field value URI with the binding, but does not consider the Contact
comparison purposes (the Contact URI is not part of the "key" for the URI for comparison purposes. The registrar MUST be prepared to
binding). The registrar MUST be prepared to receive, simultaneously receive, simultaneously for the same AOR, some registrations that use
for the same AOR, some registrations that use instance-id and reg-id instance-id and reg-id and some registrations that do not.
and some that do not.
Registrars which implement this specification, MUST support the Path Registrars which implement this specification MUST support the Path
header mechanism [12]. header mechanism [RFC3327].
In addition to the normal information stored in the binding record, In addition to the normal information stored in the binding record,
some additional information MUST be stored for any registration that some additional information MUST be stored for any registration that
contains a reg-id header parameter in the Contact header field value. contains a reg-id header parameter in the Contact header field value.
The registrar MUST store enough information to uniquely identify the The registrar MUST store enough information to uniquely identify the
network flow over which the request arrived. For common operating network flow over which the request arrived. For common operating
systems with TCP, this would typically just be the file descriptor. systems with TCP, this would typically just be the file descriptor.
For common operating systems with UDP this would typically be the For common operating systems with UDP this would typically be the
file descriptor for the local socket that received the request, the file descriptor for the local socket that received the request, the
local interface, and the IP address and port number of the remote local interface, and the IP address and port number of the remote
side that sent the request. side that sent the request.
The registrar MUST also store all the Contact header field The registrar MUST also store all the Contact header field
information including the reg-id and instance-id parameters and information including the reg-id and instance-id parameters and
SHOULD also store the time at which the binding was last updated. If SHOULD also store the time at which the binding was last updated. If
a Path header field is present, RFC 3327 [12] requires the registrar a Path header field is present, RFC 3327 [RFC3327] requires the
to store this information as well. If the registrar receives a re- registrar to store this information as well. If the registrar
registration, it MUST update the information that uniquely identifies receives a re-registration, it MUST update the information that
the network flow over which the request arrived and SHOULD update the uniquely identifies the network flow over which the request arrived
time the binding was last updated. and SHOULD update the time the binding was last updated.
The Registrar MUST include the 'outbound' option-tag in a Supported The Registrar MUST include the 'outbound' option-tag (defined in
header field value in its responses to REGISTER requests. The Section (Section 10.1)) in a Supported header field value in its
Registrar MAY be configured with local policy to reject any responses to REGISTER requests. The Registrar MAY be configured with
registrations that do not include the instance-id and reg-id to local policy to reject any registrations that do not include the
eliminate the amplification attack described in [19]. Note that the instance-id and reg-id. Note that the requirements in this section
requirements in this section applies to both REGISTER requests applies to both REGISTER requests received from an Edge Proxy as well
received from an Edge Proxy as well as requests received directly as requests received directly from the UAC.
from the UAC.
6.2 Forwarding Requests 6.2. 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. If a request contact with the same AOR and instance-id at a time. If a request
for a particular AOR and instance-id fails with a 410 response, for a particular AOR and instance-id fails with a 410 response,
the proxy SHOULD replace the failed branch with another target (if the proxy SHOULD replace the failed branch with another target (if
one is available) with the same AOR and instance-id, but a one is available) with the same AOR and instance-id, but a
different reg-id. different reg-id.
o If two bindings have the same instance-id and reg-id, the proxy o If two bindings have the same instance-id and reg-id, the proxy
SHOULD prefer the contact that was most recently updated. SHOULD prefer the contact that was most recently updated.
The proxy uses normal forwarding rules looking at the Route of the The proxy uses normal forwarding rules looking at the next-hop target
message and the value of any stored Path header field vector in the of the message and the value of any stored Path header field vector
registration binding to decide how to forward the request and in the registration binding to decide how to forward the request and
populate the Route header in the request. Additionally, when the populate the Route header in the request. Additionally, when the
proxy forwards a request to a binding that contains a reg-id, the proxy forwards a request to a binding that contains a reg-id, the
proxy MUST send the request over the same network flow that was saved proxy MUST send the request over the same network flow that was saved
with the binding. This means that for TCP, the request MUST be sent with the binding. This means that for TCP, the request MUST be sent
on the same TCP socket that received the REGISTER request. For UDP, on the same TCP socket that received the REGISTER request. For UDP,
the request MUST be sent from the same local IP address and port over the request MUST be sent from the same local IP address and port over
which the registration was received, to the same IP address and port which 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 that use that flow, then the proxy MUST invalidate all the bindings that use that
flow (regardless of AOR). Examples of this are a TCP socket closing flow (regardless of AOR). Examples of this are a TCP socket closing
or receiving a destination unreachable ICMP error on a UDP flow. or receiving a destination unreachable ICMP error on a UDP flow.
Similarly, if a proxy closes a file descriptor, it MUST invalidate Similarly, if a proxy closes a file descriptor, it MUST invalidate
all the bindings with flows that use that file descriptor. all the bindings with flows that use that file descriptor.
7. Mechanisms for All Servers (Proxys, Registars, UAS) 7. Mechanisms for All Servers (Proxys, Registars, UASs)
A SIP device that receives SIP messages directly from a UA needs to Any SIP device that receives SIP messages directly from a UA needs to
behave as specified in this section. Such devices would generally behave as specified in this section. Such devices would generally
include a Registrar and an Edge Proxy, as they both receive register include a Registrar and an Edge Proxy, as they both receive REGISTER
requests directly from a UA. requests directly from a UA.
7.1 STUN Processing 7.1. STUN Processing
This document defines a new STUN usage for inband connectivity This document defines a new STUN usage for connectivity checks. The
checks. The only STUN messages required by this usage are Binding only STUN messages required by this usage are Binding Requests,
Requests, Binding Responses, and Error Responses. The UAC sends Binding Responses, and Error Responses. The UAC sends Binding
Binding Requests over the same UDP flow, TCP connection, or TLS Requests over the same UDP flow, TCP connection, or TLS channel used
channel used for sending SIP messages, once a SIP registration has for sending SIP messages, once a SIP registration has been
been successfully processed on that flow. These Binding Requests do successfully processed on that flow. These Binding Requests do not
not require any STUN attributes. The UAS responds to a valid Binding require any STUN attributes. The UAS responds to a valid Binding
Request with a Binding Response which MUST include the XOR-MAPPED- Request with a Binding Response which MUST include the XOR-MAPPED-
ADDRESS attribute. After a successful STUN response is received over ADDRESS attribute. After a successful STUN response is received over
TCP or TLS over TCP, the underlying TCP connection is left in the TCP or TLS over TCP, the underlying TCP connection is left in the
active state. active state.
If the server receives SIP requests on a given interface and port, it If the server receives SIP requests on a given interface and port, it
MUST also provide a limited version of a STUN server on the same MUST also provide a limited version of a STUN server on the same
interface and port. Specifically it MUST be capable of receiving and interface and port. Specifically it MUST be capable of receiving and
responding to STUN Binding Requests. responding to STUN Binding Requests.
skipping to change at page 20, line 16 skipping to change at page 21, line 11
as described in this section, the 'keepalive' URI parameter, as as described in this section, the 'keepalive' URI parameter, as
defined in Section 10 MUST be added to the URI, with a value of defined in Section 10 MUST be added to the URI, with a value of
'stun'. This allows a UA to inspect the URI to decide if it should 'stun'. This allows a UA to inspect the URI to decide if it should
attempt to send STUN requests to this location. The 'keepalive' tag attempt to send STUN requests to this location. The 'keepalive' tag
typically would be present in the URI in the Route header field value typically would be present in the URI in the Route header field value
of a REGISTER request and not be in the Request URI. of a REGISTER request and not be in the Request URI.
8. Example Message Flow 8. Example Message Flow
The following call flow shows a basic registration and an incoming The following call flow shows a basic registration and an incoming
call. Part way through the call, the flow to the Primary proxy is call. At some point, the flow to the Primary proxy is lost. An
lost. The BYE message for the call is rerouted to the callee via the incoming INVITE tries to reach the Callee through the Primary flow,
Backup proxy. When connectivity to the primary proxy is established, but receives an ICMP Unreachable message. The Caller retries using
the Callee registers again to replace the lost flow as shown in the Secondary Edge Proxy, which uses a separate flow. Later, after
message 15. the Primary reboots, The Callee discovers the flow failure and
reestablishes a new flow to the Primary.
[-----example.com domain -------------------] [-----example.com domain -------------------]
Caller Backup 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 | |
| |------------------------------------>| | |------------------------------------>|
| | | |
| | CRASH X |
|(5) INVITE | | | |(5) INVITE | | |
|----------------------------------->| | |----------------------------------->| |
| | |(6) INVITE | |(6) ICMP Unreachable | |
| | |----------------->|
| | | (7) 200 OK |
| | |<-----------------|
| | (8) 200 OK | |
|<-----------------------------------| | |<-----------------------------------| |
|(9) ACK | | | |(7) INVITE | | |
|----------------------------------->| | |---------------->| | |
| | |(10) ACK | | |(8) INVITE | |
| | |----------------->|
| | CRASH X |
|(11) BYE | |
|---------------->| |
| | (12) BYE |
| |------------------------------------>| | |------------------------------------>|
| | (13) 200 OK | | |(9) 200 OK | |
| |<------------------------------------| | |<------------------------------------|
| (14) 200 OK | | |(10) 200 OK | | |
|<----------------| REBOOT | | |<----------------| | |
| | | (15) REGISTER | |(11) ACK | | |
|---------------->| | |
| |(12) ACK | |
| |------------------------------------>|
| | | |
| | REBOOT | |
| | |(13) REGISTER |
| | |<-----------------| | | |<-----------------|
| | |(16) 200 OK | | | |(14) 200 OK |
| | |----------------->| | | |----------------->|
| | | |
|(15) BYE | | |
|---------------->| | |
| | (16) BYE | |
| |------------------------------------>|
| | | (17) 200 OK |
| |<------------------------------------|
| (18) 200 OK | | |
|<----------------| | |
| | | |
This call flow assumes that the Callee has been configured with a This call flow assumes that the Callee has been configured with a
proxy set that consists of "sip: proxy set that consists of "sip:
primary.example.com;lr;keepalive=stun" and "sip: primary.example.com;lr;keepalive=stun" and "sip:
backup.example.com;lr;keepalive=stun". The Callee REGISTER in
secondary.example.com;lr;keepalive=stun". The Callee REGISTER in
message (1) looks like: message (1) looks like:
REGISTER sip:example.com SIP/2.0 REGISTER sip:example.com SIP/2.0
Via: SIP/2.0/UDP 10.0.1.1;branch=z9hG4bKnashds7 Via: SIP/2.0/UDP 192.0.2.1;branch=z9hG4bKnashds7
Max-Forwards: 70 Max-Forwards: 70
From: Callee <sip:callee@example.com>;tag=a73kszlfl From: Callee <sip:callee@example.com>;tag=7F94778B653B
To: Callee <sip:callee@example.com> To: Callee <sip:callee@example.com>
Call-ID: 1j9FpLxk3uxtm8tn@10.0.1.1 Call-ID: 16CB75F21C70
CSeq: 1 REGISTER CSeq: 1 REGISTER
Supported: path Supported: path
Route: <sip:primary.example.com;lr;keepalive=stun> Route: <sip:primary.example.com;lr;keepalive=stun>
Contact: <sip:callee@10.0.1.1> Contact: <sip:callee@192.0.2.1>
;+sip.instance="<urn:uuid:0C67446E-F1A1-11D9-94D3-000A95A0E128>" ;+sip.instance="<urn:uuid:0C67446E-F1A1-11D9-94D3-000A95A0E128>"
;reg-id=1 ;reg-id=1
Content-Length: 0 Content-Length: 0
In the message, note that the Route is set and the Contact header In the message, note that the Route is set and the Contact header
field value contains the instance-id and reg-id. The response to the field value contains the instance-id and reg-id. The response to the
REGISTER in message (2) would look like: REGISTER in message (2) would look like:
SIP/2.0 200 OK SIP/2.0 200 OK
Via: SIP/2.0/UDP 10.0.1.1;branch=z9hG4bKnashds7 Via: SIP/2.0/UDP 192.0.2.1;branch=z9hG4bKnashds7
From: Callee <sip:callee@example.com>;tag=a73kszlfl From: Callee <sip:callee@example.com>;tag=7F94778B653B
To: Callee <sip:callee@example.com> ;tag=b88sn To: Callee <sip:callee@example.com>;tag=6AF99445E44A
Call-ID: 1j9FpLxk3uxtm8tn@10.0.1.1 Call-ID: 16CB75F21C70
CSeq: 1 REGISTER CSeq: 1 REGISTER
Supported: outbound Supported: outbound
Contact: <sip:callee@10.0.1.1> Contact: <sip:callee@192.0.2.1>
;+sip.instance="<urn:uuid:0C67446E-F1A1-11D9-94D3-000A95A0E128>" ;+sip.instance="<urn:uuid:0C67446E-F1A1-11D9-94D3-000A95A0E128>"
;reg-id=1 ;reg-id=1
;expires=3600 ;expires=3600
Content-Length: 0 Content-Length: 0
The second registration in message 3 and 4 are similar other than the The second registration in message 3 and 4 are similar other than the
Call-ID has changed, the reg-id is 2, and the route is set to the Call-ID has changed, the reg-id is 2, and the route is set to the
backup instead of the primary. They look like: secondary instead of the primary. They look like:
REGISTER sip:example.com SIP/2.0 REGISTER sip:example.com SIP/2.0
Via: SIP/2.0/UDP 10.0.1.1;branch=z9hG4bKnashds7 Via: SIP/2.0/UDP 192.0.2.1;branch=z9hG4bKnqr9bym
Max-Forwards: 70 Max-Forwards: 70
From: Callee <sip:callee@example.com>;tag=a73kszlfl From: Callee <sip:callee@example.com>;tag=755285EABDE2
To: Callee <sip:callee@example.com> To: Callee <sip:callee@example.com>
Call-ID: 1j9FpLxk3uxtm8tn-2@10.0.1.1 Call-ID: E05133BD26DD
CSeq: 1 REGISTER CSeq: 1 REGISTER
Supported: path Supported: path
Route: <sip:backup.example.com;lr;keepalive=stun> Route: <sip:secondary.example.com;lr;keepalive=stun>
Contact: <sip:callee@10.0.1.1> Contact: <sip:callee@192.0.2.1>
;+sip.instance="<urn:uuid:0C67446E-F1A1-11D9-94D3-000A95A0E128>" ;+sip.instance="<urn:uuid:0C67446E-F1A1-11D9-94D3-000A95A0E128>"
;reg-id=2 ;reg-id=2
Content-Length: 0 Content-Length: 0
SIP/2.0 200 OK SIP/2.0 200 OK
Via: SIP/2.0/UDP 10.0.1.1;branch=z9hG4bKnashds7 Via: SIP/2.0/UDP 192.0.2.1;branch=z9hG4bKnqr9bym
From: Callee <sip:callee@example.com>;tag=a73kszlfl From: Callee <sip:callee@example.com>;tag=755285EABDE2
To: Callee <sip:callee@example.com> ;tag=b88sn To: Callee <sip:callee@example.com>;tag=49A9AD0B3F6A
Call-ID: 1j9FpLxk3uxtm8tn-2@10.0.1.1 Call-ID: E05133BD26DD
Supported: outbound Supported: outbound
CSeq: 1 REGISTER CSeq: 1 REGISTER
Contact: <sip:callee@10.0.1.1> Contact: <sip:callee@192.0.2.1>
;+sip.instance="<urn:uuid:0C67446E-F1A1-11D9-94D3-000A95A0E128>" ;+sip.instance="<urn:uuid:0C67446E-F1A1-11D9-94D3-000A95A0E128>"
;reg-id=1 ;reg-id=1
;expires=3600 ;expires=3600
Contact: <sip:callee@10.0.1.1> Contact: <sip:callee@192.0.2.1>
;+sip.instance="<urn:uuid:0C67446E-F1A1-11D9-94D3-000A95A0E128>" ;+sip.instance="<urn:uuid:0C67446E-F1A1-11D9-94D3-000A95A0E128>"
;reg-id=2 ;reg-id=2
;expires=3600 ;expires=3600
Content-Length: 0 Content-Length: 0
The messages in the call flow are very normal. The only interesting The messages in the call flow are very normal. The only interesting
thing to note is that the INVITE in message 6 contains the following thing to note is that the INVITE in message 8 contains a Record-Route
Record-Route header field: header for the Secondary proxy, with its flow token.
Record-Route: <sip:example.com;lr>
Message 11 seems seams strange in that it goes to the backup instead Record-Route:
of the primary. The Caller actually sends the message to the domain <sip:PQPbqQE+Ynf+tzRPD27lU6uxkjQ8LLUG@secondary.example.com;lr>
of the callee to a host (primary or backup) that is currently
available. How the domain does this is an implementation detail up
to the domain and not part of this specification.
The registrations in message 15 and 16 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 has changed. 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
and 2, this flow will partially supersede that for messages 1 and 2
and will be tried first by Primary.
9. Grammar 9. 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 [5] and includes the definition of uric from RFC 2396 [11]. RFC 3261 [RFC3261] and includes the definition of uric from RFC 2396
The ABNF[8] is: [RFC2396].
contact-params = c-p-q / c-p-expires / c-p-flow / c-p-instance Note: The "=/" syntax used in this ABNF indicates an extension of
/ contact-extension the production on the left hand side.
c-p-flow = "reg-id" EQUAL 1*DIGIT ; 1 to 2**31 The ABNF[RFC4234] is:
c-p-instance = "+sip.instance" EQUAL LDQUOT "<" contact-params =/ c-p-reg / c-p-instance
instance-val ">" RDQUOT
c-p-reg = "reg-id" EQUAL 1*DIGIT ; 1 to 2**31
c-p-instance = "+sip.instance" EQUAL
LDQUOT "<" instance-val ">" RDQUOT
instance-val = *uric ; defined in RFC 2396 instance-val = *uric ; defined in RFC 2396
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.
10. IANA Considerations 10. IANA Considerations
10.1 Contact Header Field 10.1. 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 [13] . The required sub-registry as per the registry created by [RFC3968]. The required
information is: information is:
Header Field Parameter Name Predefined Reference Header Field Parameter Name Predefined Reference
Values Values
____________________________________________________________________ ____________________________________________________________________
Contact reg-id Yes [RFC AAAA] Contact reg-id Yes [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.]
10.2 SIP/SIPS URI Paramters 10.2. SIP/SIPS URI Parameters
This specification arguments the "SIP/SIPS URI Parameters" sub- This specification arguments the "SIP/SIPS URI Parameters" sub-
registry as per the registry created by [14] . The required registry as per the registry created by [RFC3969]. The required
information is: information is:
Parameter Name Predefined Values Reference Parameter Name Predefined Values Reference
____________________________________________ ____________________________________________
keealive stun [RFC AAAA] keepalive stun [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.]
10.3 SIP Option Tag 10.3. 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 Registrars which
support extensions for Client Initiated Connections. A Registrar support extensions for Client Initiated Connections. A Registrar
places this option-tag in a Supported header to communicate to the places this option-tag in a Supported header to communicate the
registering User Agent the Registrars support for this extension. Registrar's support for this extension to the registering User
Agent.
10.4 Media Feature Tag 10.4. 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 [1]. The tag is placed into the sip tree, which defined in RFC 2506 [RFC2506]. The tag is placed into the sip tree,
is defined in RFC 3840 [10]. which is defined in RFC 3840 [RFC3840].
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.
Values appropriate for use with this feature tag: String. Values appropriate for use with this feature tag: String.
skipping to change at page 25, line 41 skipping to change at page 27, line 5
Examples of typical use: Routing a call to a specific device. Examples of typical use: Routing a call to a specific device.
Related standards or documents: RFC XXXX Related standards or documents: RFC XXXX
[[Note to IANA: Please replace XXXX with the RFC number of this [[Note to IANA: Please replace XXXX with the RFC number of this
specification.]] specification.]]
Security Considerations: This media feature tag can be used in ways Security Considerations: This media feature tag can be used in ways
which affect application behaviors. For example, the SIP caller which affect application behaviors. For example, the SIP caller
preferences extension [23] allows for call routing decisions to be preferences extension [RFC3841] allows for call routing decisions to
based on the values of these parameters. Therefore, if an attacker be based on the values of these parameters. Therefore, if an
can modify the values of this tag, they may be able to affect the attacker can modify the values of this tag, they may be able to
behavior of applications. As a result, applications which utilize affect the behavior of applications. As a result, applications which
this media feature tag SHOULD provide a means for ensuring its utilize this media feature tag SHOULD provide a means for ensuring
integrity. Similarly, this feature tag should only be trusted as its integrity. Similarly, this feature tag should only be trusted as
valid when it comes from the user or user agent described by the tag. valid when it comes from the user or user agent described by the tag.
As a result, protocols for conveying this feature tag SHOULD provide As a result, protocols for conveying this feature tag SHOULD provide
a mechanism for guaranteeing authenticity. a mechanism for guaranteeing authenticity.
11. Security Considerations 11. Security Considerations
One of the key security concerns in this work is making sure that an One of the key security concerns in this work is making sure that an
attacker cannot hijack the sessions of a valid user and cause all attacker cannot hijack the sessions of a valid user and cause all
calls destined to that user to be sent to the attacker. calls destined to that user to be sent to the attacker.
skipping to change at page 26, line 23 skipping to change at page 27, line 33
when the registration succeeds. SIP already protects against when the registration succeeds. SIP already protects against
attackers being able to successfully register, and this scheme relies attackers being able to successfully register, and this scheme relies
on that security. Some implementers have considered the idea of just on that security. Some implementers have considered the idea of just
saving the instance-id without relating it to the AOR with which it saving the instance-id without relating it to the AOR with which it
registered. This idea will not work because an attacker's UA can registered. This idea will not work because an attacker's UA can
impersonate a valid user's instance-id and hijack that user's calls. impersonate a valid user's instance-id and hijack that user's calls.
The more complex case involves one or more edge proxies. When a UA The more complex case involves one or more edge proxies. When a UA
sends a REGISTER request through an Edge Proxy on to the registrar, sends a REGISTER request through an Edge Proxy on to the registrar,
the Edge Proxy inserts a Path header field value. If the the Edge Proxy inserts a Path header field value. If the
registration is successfully authenticated, the proxy stores the registration is successfully authenticated, the registrar stores the
value of the Path header field. Later when the registrar forwards a value of the Path header field. Later when the registrar forwards a
request destined for the UA, it copies the stored value of the Path request destined for the UA, it copies the stored value of the Path
header field into the route header field of the request and forwards header field into the Route header field of the request and forwards
the request to the Edge Proxy. the request to the Edge Proxy.
The only time an Edge Proxy will route over a particular flow is when The only time an Edge Proxy will route over a particular flow is when
it has received a route header that has the flow identifier it has received a Route header that has the flow identifier
information that it has created. An incoming request would have information that it has created. An incoming request would have
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.
12. Requirements 12. Requirements
This specification was developed to meet the following requirements: This specification was developed to meet the following requirements:
1. Must be able to detect that a UA supports these mechanisms. 1. Must be able to detect that a UA supports these mechanisms.
2. Support UAs behind NATs. 2. Support UAs behind NATs.
3. Support TLS to a UA without a stable DNS name or IP address. 3. Support TLS to a UA without a stable DNS name or IP address.
4. Detect failure of connection and be able to correct for this. 4. Detect failure of a connection and be able to correct for this.
5. Support many UAs simultaneously rebooting. 5. Support many UAs simultaneously rebooting.
6. Support a NAT rebooting or resetting. 6. Support a NAT rebooting or resetting.
7. Minimize initial startup load on a proxy. 7. Minimize initial startup load on a proxy.
8. Support architectures with edge proxies. 8. Support architectures with edge proxies.
13. Changes 13. Changes
Note to RFC Editor: Please remove this whole section. Note to RFC Editor: Please remove this whole section.
13.1 Changes from 02 Version 13.1. Changes from 03 Version
Added non-normative text motivating STUN vs. SIP PING, OPTIONS, and
Double CRLF. Added discussion about why TCP Keepalives are not
always available.
Explained more clearly that outbound-proxy-set can be "configured"
using any current or future, manual or automatic configuration/
discovery mechanism.
Added a sentence which prevents an Edge Proxy from forwarding back
over the flow over which the request is received if the request
happens to contain a flow token for that flow. This was an
oversight.
Updated example message flow to show a failover example using a new
dialog-creating request instead of a mid-dialog request. The old
scenario was leftover from before the outbound/gruu reorganization.
Fixed tags, Call-IDs, and branch parameters in the example messages.
Made the ABNF use the "=/" production extension mechanism recommended
by Bill Fenner.
Added a table in an appendix expanding the default flow recovery
timers.
Incorporated numerous clarifications and rewordings for better
comprehension.
Fixed many typos and spelling misteaks.
13.2. 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.
13.2 Changes from 01 Version 13.3. Changes from 01 Version
Moved definition of instance-id from GRUU[17] draft to this draft. Moved definition of instance-id from GRUU[I-D.ietf-sip-gruu] draft to
this draft.
Added tentative text about Double CRLF Keep Alive 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
Added 'outbound' option-tag to detect if registrar supports outbound Added 'outbound' option-tag to detect if registrar supports outbound
13.3 Changes from 00 Version 13.4. Changes from 00 Version
Moved TCP keep alive to be STUN. Moved TCP keep alive 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.
14. Acknowledgments 14. Acknowledgments
skipping to change at page 28, line 11 skipping to change at page 30, line 7
came up with the idea of using the most recent registration first in came up with the idea of using the most recent registration first in
the proxy. Alan Hawrylyshen co-authored the draft that formed the the proxy. Alan Hawrylyshen co-authored the draft that formed the
initial text of this specification. Additionally, many of the initial text of this specification. Additionally, many of the
concepts here originated at a connection reuse meeting at IETF 60 concepts here originated at a connection reuse meeting at IETF 60
that included the authors, Jon Peterson, Jonathan Rosenberg, Alan that included the authors, Jon Peterson, Jonathan Rosenberg, Alan
Hawrylyshen, and Paul Kyzivat. The TCP design team consisting of Hawrylyshen, and Paul Kyzivat. The TCP design team consisting of
Chris Boulton, Scott Lawrence, Rajnish Jain, Vijay K. Gurbani, and Chris Boulton, Scott Lawrence, Rajnish Jain, Vijay K. Gurbani, and
Ganesh Jayadevan provided input and text. Nils Ohlmeier provided Ganesh Jayadevan provided input and text. Nils Ohlmeier provided
many fixes and initial implementation experience. In addition, many fixes and initial implementation experience. In addition,
thanks to the following folks for useful comments: Francois Audet, thanks to the following folks for useful comments: Francois Audet,
Flemming Andreasen, Mike Hammer, Dan Wing, Srivatsa Srinivasan, and Flemming Andreasen, Mike Hammer, Dan Wing, Srivatsa Srinivasan, Dale
Lyndsay Campbell. Worely, Juha Heinanen, Eric Rescorla, and Lyndsay Campbell.
15. References Appendix A. Default Flow Registration Backoff Times
15.1 Normative References The base-time used for the flow re-registration backoff times
described in Section 4.4.2 are configurable. If the base-time-all-
fail 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
shows the resulting delay values.
[1] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag +-------------------+--------------------+--------------------+
Registration Procedure", BCP 31, RFC 2506, March 1999. | # of reg failures | all flows unusable | >1 non-failed flow |
+-------------------+--------------------+--------------------+
| 0 | 0 secs | 0 secs |
| 1 | 30-60 secs | 90-180 secs |
| 2 | 1-2 mins | 3-6 mins |
| 3 | 2-4 mins | 6-12 mins |
| 4 | 4-8 mins | 12-24 mins |
| 5 | 8-16 mins | 15-30 mins |
| 6 or more | 15-30 mins | 15-30 mins |
+-------------------+--------------------+--------------------+
[2] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller 15. References
Preferences for the Session Initiation Protocol (SIP)",
RFC 3841, August 2004.
[3] Moats, R., "URN Syntax", RFC 2141, May 1997. 15.1. Normative References
[4] Bradner, S., "Key words for use in RFCs to Indicate Requirement [I-D.ietf-behave-rfc3489bis]
Levels", BCP 14, RFC 2119, March 1997. Rosenberg, J., "Simple Traversal of UDP Through Network
Address Translators (NAT) (STUN)",
draft-ietf-behave-rfc3489bis-02 (work in progress),
July 2005.
[5] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Requirement Levels", BCP 14, RFC 2119, March 1997.
Session Initiation Protocol", RFC 3261, June 2002.
[6] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol [RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997.
(SIP): Locating SIP Servers", RFC 3263, June 2002.
[7] Rosenberg, J., "Simple Traversal of UDP Through Network Address [RFC2396] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Translators (NAT) (STUN)", draft-ietf-behave-rfc3489bis-02 Resource Identifiers (URI): Generic Syntax", RFC 2396,
(work in progress), July 2005. August 1998.
[8] Crocker, D. and P. Overell, "Augmented BNF for Syntax [RFC2506] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag
Specifications: ABNF", RFC 2234, November 1997. Registration Procedure", BCP 31, RFC 2506, March 1999.
[9] Leach, P., Mealling, M., and R. Salz, "A Universally Unique [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
IDentifier (UUID) URN Namespace", RFC 4122, July 2005. A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[10] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Indicating [RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation
User Agent Capabilities in the Session Initiation Protocol Protocol (SIP): Locating SIP Servers", RFC 3263,
(SIP)", RFC 3840, August 2004. June 2002.
[11] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC3327] Willis, D. and B. Hoeneisen, "Session Initiation Protocol
Resource Identifiers (URI): Generic Syntax", RFC 2396, (SIP) Extension Header Field for Registering Non-Adjacent
August 1998. Contacts", RFC 3327, December 2002.
[12] Willis, D. and B. Hoeneisen, "Session Initiation Protocol (SIP) [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat,
Extension Header Field for Registering Non-Adjacent Contacts", "Indicating User Agent Capabilities in the Session
RFC 3327, December 2002. Initiation Protocol (SIP)", RFC 3840, August 2004.
[13] Camarillo, G., "The Internet Assigned Number Authority (IANA) [RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller
Header Field Parameter Registry for the Session Initiation Preferences for the Session Initiation Protocol (SIP)",
Protocol (SIP)", BCP 98, RFC 3968, December 2004. RFC 3841, August 2004.
[14] Camarillo, G., "The Internet Assigned Number Authority (IANA) [RFC3968] Camarillo, G., "The Internet Assigned Number Authority
Uniform Resource Identifier (URI) Parameter Registry for the (IANA) Header Field Parameter Registry for the Session
Session Initiation Protocol (SIP)", BCP 99, RFC 3969, Initiation Protocol (SIP)", BCP 98, RFC 3968,
December 2004. December 2004.
15.2 Informative References [RFC3969] Camarillo, G., "The Internet Assigned Number Authority
(IANA) Uniform Resource Identifier (URI) Parameter
Registry for the Session Initiation Protocol (SIP)",
BCP 99, RFC 3969, December 2004.
[15] Hakala, J., "Using National Bibliography Numbers as Uniform [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Resource Names", RFC 3188, October 2001. Unique IDentifier (UUID) URN Namespace", RFC 4122,
July 2005.
[16] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing [RFC4234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
for Message Authentication", RFC 2104, February 1997. Specifications: ABNF", RFC 4234, October 2005.
[17] Rosenberg, J., "Obtaining and Using Globally Routable User 15.2. Informative References
Agent (UA) URIs (GRUU) in the Session Initiation Protocol
(SIP)", draft-ietf-sip-gruu-04 (work in progress), July 2005.
[18] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", [I-D.ietf-sip-gruu]
RFC 3548, July 2003. Rosenberg, J., "Obtaining and Using Globally Routable User
Agent (UA) URIs (GRUU) in the Session Initiation Protocol
(SIP)", draft-ietf-sip-gruu-04 (work in progress),
July 2005.
[19] Lawrence, S., Hawrylyshen, A., and R. Sparks, "Problems with [I-D.ietf-sipping-config-framework]
Max-Forwards Processing (and Potential Solutions)", Petrie, D., "A Framework for Session Initiation Protocol
October 2005. User Agent Profile Delivery",
draft-ietf-sipping-config-framework-08 (work in progress),
Mar 2006.
[20] Rosenberg, J., "Clarifying Construction of the Route Header [I-D.rosenberg-sip-route-construct]
Field in the Session Initiation Protocol (SIP)", Rosenberg, J., "Clarifying Construction of the Route
Header Field in the Session Initiation Protocol (SIP)",
draft-rosenberg-sip-route-construct-00 (work in progress), draft-rosenberg-sip-route-construct-00 (work in progress),
July 2005. July 2005.
[21] Willis, D. and B. Hoeneisen, "Session Initiation Protocol (SIP) [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Extension Header Field for Service Route Discovery During Hashing for Message Authentication", RFC 2104,
Registration", RFC 3608, October 2003. February 1997.
[RFC3188] Hakala, J., "Using National Bibliography Numbers as
Uniform Resource Names", RFC 3188, October 2001.
[RFC3548] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 3548, July 2003.
[RFC3608] Willis, D. and B. Hoeneisen, "Session Initiation Protocol
(SIP) Extension Header Field for Service Route Discovery
During Registration", RFC 3608, October 2003.
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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