draft-ietf-sip-outbound-06.txt   draft-ietf-sip-outbound-07.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: May 26, 2007 Plantronics Intended status: Standards Track Plantronics
November 22, 2006 Expires: July 11, 2007 January 7, 2007
Managing Client Initiated Connections in the Session Initiation Protocol Managing Client Initiated Connections in the Session Initiation Protocol
(SIP) (SIP)
draft-ietf-sip-outbound-06 draft-ietf-sip-outbound-07
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on May 26, 2007. This Internet-Draft will expire on July 11, 2007.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2007).
Abstract Abstract
The Session Initiation Protocol (SIP) allows proxy servers to The Session Initiation Protocol (SIP) allows proxy servers to
initiate TCP connections and send asynchronous UDP datagrams to User initiate TCP connections and send asynchronous UDP datagrams to User
Agents in order to deliver requests. However, many practical Agents in order to deliver requests. However, many practical
considerations, such as the existence of firewalls and Network considerations, such as the existence of firewalls and Network
Address Translators (NATs), prevent servers from connecting to User Address Translators (NATs), prevent servers from connecting to User
Agents in this way. This specification defines behaviors for User Agents in this way. This specification defines behaviors for User
Agents, registrars and proxy servers that allow requests to be Agents, registrars and proxy servers that allow requests to be
delivered on existing connections established by the User Agent. It delivered on existing connections established by the User Agent. It
also defines keep alive behaviors needed to keep NAT bindings open also defines keep alive behaviors needed to keep NAT bindings open
and specifies the usage of multiple connections. and specifies the usage of multiple connections.
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 . . . . . . . . . . . . . . . . . . . . . . . 5
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1 Summary of Mechanism . . . . . . . . . . . . . . . . . . . 5 3.1. Summary of Mechanism . . . . . . . . . . . . . . . . . . . 5
3.2 Single Registrar and UA . . . . . . . . . . . . . . . . . 6 3.2. Single Registrar and UA . . . . . . . . . . . . . . . . . 6
3.3 Multiple Connections from a User Agent . . . . . . . . . . 7 3.3. Multiple Connections from a User Agent . . . . . . . . . . 7
3.4 Edge Proxies . . . . . . . . . . . . . . . . . . . . . . . 9 3.4. Edge Proxies . . . . . . . . . . . . . . . . . . . . . . . 9
3.5 Keepalive Technique . . . . . . . . . . . . . . . . . . . 10 3.5. Keepalive Technique . . . . . . . . . . . . . . . . . . . 11
4. User Agent Mechanisms . . . . . . . . . . . . . . . . . . . . 12 4. User Agent Mechanisms . . . . . . . . . . . . . . . . . . . . 12
4.1 Instance ID Creation . . . . . . . . . . . . . . . . . . . 12 4.1. Instance ID Creation . . . . . . . . . . . . . . . . . . . 12
4.2 Initial Registrations . . . . . . . . . . . . . . . . . . 13 4.2. Initial Registrations . . . . . . . . . . . . . . . . . . 13
4.2.1 Registration by Other Instances . . . . . . . . . . . 15 4.2.1. Registration by Other Instances . . . . . . . . . . . 15
4.3 Sending Requests . . . . . . . . . . . . . . . . . . . . . 15 4.3. Sending Requests . . . . . . . . . . . . . . . . . . . . . 15
4.4 Detecting Flow Failure . . . . . . . . . . . . . . . . . . 15 4.4. Detecting Flow Failure . . . . . . . . . . . . . . . . . . 15
4.4.1 Keepalive with TCP KEEPALIVE . . . . . . . . . . . . . 16 4.4.1. Keepalive with TCP KEEPALIVE . . . . . . . . . . . . . 16
4.4.2 Keepalive with STUN . . . . . . . . . . . . . . . . . 16 4.4.2. Keepalive with STUN . . . . . . . . . . . . . . . . . 16
4.4.3 Flow Recovery . . . . . . . . . . . . . . . . . . . . 16 4.4.3. Flow Recovery . . . . . . . . . . . . . . . . . . . . 16
5. Edge Proxy Mechanisms . . . . . . . . . . . . . . . . . . . . 18 5. Edge Proxy Mechanisms . . . . . . . . . . . . . . . . . . . . 18
5.1 Processing Register Requests . . . . . . . . . . . . . . . 18 5.1. Processing Register Requests . . . . . . . . . . . . . . . 18
5.2 Generating Flow Tokens . . . . . . . . . . . . . . . . . . 18 5.2. Generating Flow Tokens . . . . . . . . . . . . . . . . . . 18
5.3 Forwarding Requests . . . . . . . . . . . . . . . . . . . 19 5.3. Forwarding Requests . . . . . . . . . . . . . . . . . . . 19
5.4 Edge Proxy Keepalive Handling . . . . . . . . . . . . . . 20 5.4. Edge Proxy Keepalive Handling . . . . . . . . . . . . . . 20
6. Registrar Mechanisms: Processing REGISTER Requests . . . . . . 20 6. Registrar Mechanisms: Processing REGISTER Requests . . . . . . 20
7. Authoritative Proxy Mechansims: Forwarding Requests . . . . . 22 7. Authoritative Proxy Mechanisms: Forwarding Requests . . . . . 22
8. STUN Keepalive Processing . . . . . . . . . . . . . . . . . . 23 8. STUN Keepalive Processing . . . . . . . . . . . . . . . . . . 23
8.1 Explicit Probes . . . . . . . . . . . . . . . . . . . . . 25 8.1. Explicit Probes . . . . . . . . . . . . . . . . . . . . . 25
8.2 Use with Sigcomp . . . . . . . . . . . . . . . . . . . . . 25 8.2. Use with Sigcomp . . . . . . . . . . . . . . . . . . . . . 25
9. Example Message Flow . . . . . . . . . . . . . . . . . . . . . 26 9. Example Message Flow . . . . . . . . . . . . . . . . . . . . . 26
10. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . 29 10. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
11. Definition of 430 Flow Failed response code . . . . . . . . 30 11. Definition of 430 Flow Failed response code . . . . . . . . . 30
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . 30 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
12.1 Contact Header Field . . . . . . . . . . . . . . . . . . . 30 12.1. Contact Header Field . . . . . . . . . . . . . . . . . . . 30
12.2 SIP/SIPS URI Parameters . . . . . . . . . . . . . . . . . 31 12.2. SIP/SIPS URI Parameters . . . . . . . . . . . . . . . . . 31
12.3 SIP Option Tag . . . . . . . . . . . . . . . . . . . . . . 31 12.3. SIP Option Tag . . . . . . . . . . . . . . . . . . . . . . 31
12.4 Response Code . . . . . . . . . . . . . . . . . . . . . . 31 12.4. Response Code . . . . . . . . . . . . . . . . . . . . . . 31
12.5 Media Feature Tag . . . . . . . . . . . . . . . . . . . . 31 12.5. Media Feature Tag . . . . . . . . . . . . . . . . . . . . 31
13. Security Considerations . . . . . . . . . . . . . . . . . . 32 13. Security Considerations . . . . . . . . . . . . . . . . . . . 32
14. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 33 14. Operational Notes on Transports . . . . . . . . . . . . . . . 33
15. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . 33 15. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 34
15.1 Changes from 05 Version . . . . . . . . . . . . . . . . . 33 16. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
15.2 Changes from 04 Version . . . . . . . . . . . . . . . . . 34 16.1. Changes from 06 Version . . . . . . . . . . . . . . . . . 34
15.3 Changes from 03 Version . . . . . . . . . . . . . . . . . 35 16.2. Changes from 05 Version . . . . . . . . . . . . . . . . . 34
15.4 Changes from 02 Version . . . . . . . . . . . . . . . . . 36 16.3. Changes from 04 Version . . . . . . . . . . . . . . . . . 35
15.5 Changes from 01 Version . . . . . . . . . . . . . . . . . 36 16.4. Changes from 03 Version . . . . . . . . . . . . . . . . . 36
15.6 Changes from 00 Version . . . . . . . . . . . . . . . . . 36 16.5. Changes from 02 Version . . . . . . . . . . . . . . . . . 37
16. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 36 16.6. Changes from 01 Version . . . . . . . . . . . . . . . . . 37
A. Default Flow Registration Backoff Times . . . . . . . . . . . 37 16.7. Changes from 00 Version . . . . . . . . . . . . . . . . . 37
17. References . . . . . . . . . . . . . . . . . . . . . . . . . 37 17. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 37
17.1 Normative References . . . . . . . . . . . . . . . . . . . 37 Appendix A. Default Flow Registration Backoff Times . . . . . . . 38
17.2 Informative References . . . . . . . . . . . . . . . . . . 39 18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 40 18.1. Normative References . . . . . . . . . . . . . . . . . . . 38
Intellectual Property and Copyright Statements . . . . . . . . 41 18.2. Informative References . . . . . . . . . . . . . . . . . . 39
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 40
Intellectual Property and Copyright Statements . . . . . . . . . . 42
1. Introduction 1. Introduction
There are many environments for SIP [RFC3261] deployments in which There are many environments for SIP [1] deployments in which the User
the User Agent (UA) can form a connection to a Registrar or Proxy but Agent (UA) can form a connection to a Registrar or Proxy but in which
in which connections in the reverse direction to the UA are not connections in the reverse direction to the UA are not possible.
possible. This can happen for several reasons. Connections to the This can happen for several reasons. Connections to the UA can be
UA can be blocked by a firewall device between the UA and the proxy blocked by a firewall device between the UA and the proxy or
or registrar, which will only allow new connections in the direction registrar, which will only allow new connections in the direction of
of the UA to the Proxy. Similarly there a NAT could be present, the UA to the Proxy. Similarly there a NAT could be present, which
which is only capable of allowing new connections from the private is only capable of allowing new connections from the private address
address side to the public side. This specification allows SIP side to the public side. This specification allows SIP registration
registration when the UA is behind such a firewall or NAT. when the 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 almost never useful name in the Domain Name System (DNS), and they almost never
have a long-term, stable DNS name that is appropriate for use in the have a long-term, stable DNS name that is appropriate for use in the
subjectAltName of a certificate, as required by [RFC3261]. However, subjectAltName of a certificate, as required by [1]. However, these
these systems can still act as a TLS client and form connections to a systems can still act as a TLS client and form connections to a proxy
proxy or registrar which authenticates with a server certificate. or registrar which authenticates with a server certificate. The
The server can authenticate the UA using a shared secret in a digest server can authenticate the UA using a shared secret in a digest
challenge over that TLS connection. challenge over that TLS connection.
The key idea of this specification is that when a UA sends a REGISTER The key idea of this specification is that when a UA sends a REGISTER
request, the proxy can later use this same network "flow"--whether 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
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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 specification also multiple flows to the proxy or registrar. This specification also
defines how SIP implements the STUN keepalive usage. The keepalive defines how SIP implements the STUN keepalive usage. The keepalive
mechanism is used to keep NAT bindings fresh, and to allow the UA to mechanism is used to keep NAT bindings fresh, and to allow the UA to
detect when a flow has failed. detect when a flow has failed.
2. Conventions and Terminology 2. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [2].
2.1 Definitions 2.1. Definitions
Authoritative Proxy: A proxy that handles non-REGISTER requests for a
specific Address-of-Record (AOR), performs the logical Location Authoritative Proxy: A proxy that handles non-REGISTER requests for
a specific Address-of-Record (AOR), performs the logical Location
Server lookup described in RFC 3261, and forwards those requests Server lookup described in RFC 3261, and forwards those requests
to specific Contact URIs. to specific Contact URIs.
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 Authoritative Proxy. between the registering User Agent and the Authoritative Proxy.
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
the value of the "sip.instance" media feature tag in the Contact to the value of the "sip.instance" media feature tag in the
header field. This is a Uniform Resource Name (URN) that uniquely Contact header field. This is a Uniform Resource Name (URN) that
identifies this specific UA instance. uniquely identifies this specific UA instance.
outbound-proxy-set A set of SIP URIs (Uniform Resource Identifiers) outbound-proxy-set A set of SIP URIs (Uniform Resource Identifiers)
that represents each of the outbound proxies (often Edge Proxies) that represents each of the outbound proxies (often Edge Proxies)
with which the UA will attempt to maintain a direct flow. The with which the UA will attempt to maintain a direct flow. The
first URI in the set is often referred to as the primary outbound first URI in the set is often referred to as the primary outbound
proxy and the second as the secondary outbound proxy. There is no proxy and the second as the secondary outbound proxy. There is no
difference between any of the URIs in this set, nor does the difference between any of the URIs in this set, nor does the
primary/secondary terminology imply that one is preferred over the primary/secondary terminology imply that one is preferred over the
other. other.
3. Overview 3. Overview
Several scenarios in which this technique is useful are discussed 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, Agent desiring multiple connections to a resource (for redundancy,
for 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 or a network recognize that a UA is registering after a reboot or a network
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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 keepalive mechanism to keep their flow to the proxy or registrar the keepalive 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 the topology shown below, a single server is acting as both a In the topology shown below, a single server is acting as both a
registrar and proxy. registrar and proxy.
+-----------+ +-----------+
| Registrar | | Registrar |
| Proxy | | Proxy |
+-----+-----+ +-----+-----+
| |
| |
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end up routing to the same UA. When the proxy goes to forward a end up routing to the same UA. When the proxy goes to forward a
request to a given target, it looks and finds the flows over which it request to a given target, it looks and finds the flows over which it
received the registration. The proxy then forwards the request on received the registration. The proxy then forwards the request on
that flow instead of trying to form a new flow to that contact. This that flow instead of trying to form a new flow to that contact. This
allows the proxy to forward a request to a particular contact over allows the proxy to forward a request to a particular contact over
the same flow that the UA used to register this AOR. If the proxy the same flow that the UA used to register this AOR. If the proxy
has multiple flows that all go to this UA, it can choose any one of has multiple flows that all go to this UA, it can choose any one of
registration bindings for this AOR that has the same instance-id as registration bindings for this AOR that has the same instance-id as
the selected UA. the selected UA.
3.3 Multiple Connections from a User Agent 3.3. Multiple Connections from a User Agent
There are various ways to deploy SIP to build a reliable and scalable There are various ways to deploy SIP to build a reliable and scalable
system. This section discusses one such design that is possible with system. This section discusses one such design that is possible with
the mechanisms in this specification. Other designs are also the mechanisms in this specification. Other designs are also
possible. possible.
In the example system below, the logical outbound proxy/registrar for In the example system below, the logical outbound proxy/registrar for
the domain is running on two hosts that share the appropriate state the domain is running on two hosts that share the appropriate state
and can both provide registrar and outbound proxy functionality for and can both provide registrar and outbound proxy functionality for
the domain. The UA will form connections to two of the physical the domain. The UA will form connections to two of the physical
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deployment here requires that DNS is configured with one entry that deployment here requires that DNS is configured with one entry that
resolves to all the primary hosts and another entry that resolves to resolves to all the primary hosts and another entry that resolves to
all the secondary hosts. While this introduces additional DNS all the secondary hosts. While this introduces additional DNS
configuration, the approach works and requires no addition SIP configuration, the approach works and requires no addition SIP
extensions. extensions.
Note: Approaches which select multiple connections from a single Note: Approaches which select multiple connections from a single
DNS SRV set were also considered, but cannot prevent two DNS SRV set were also considered, but cannot prevent two
connections from accidentally resolving to the same host. The connections from accidentally resolving to the same host. The
approach in this document does not prevent future extensions, such approach in this document does not prevent future extensions, such
as the SIP UA configuration framework [I-D.ietf-sipping-config- as the SIP UA configuration framework [18], from adding other ways
framework], from adding other ways for a User Agent to discover for a User Agent to discover its outbound-proxy-set.
its outbound-proxy-set.
+-------------------+ +-------------------+
| Domain | | Domain |
| Logical Proxy/Reg | | Logical Proxy/Reg |
| | | |
|+-----+ +-----+| |+-----+ +-----+|
||Host1| |Host2|| ||Host1| |Host2||
|+-----+ +-----+| |+-----+ +-----+|
+---\------------/--+ +---\------------/--+
\ / \ /
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When used in this fashion to achieve high reliability, the operator When used in this fashion to achieve high reliability, the operator
will need to configure DNS such that the various URIs in the outbound will need to configure DNS such that the various URIs in the outbound
proxy set do not resolve to the same host. proxy set do not resolve to the same host.
Another motivation for maintaining multiple flows between the UA and Another motivation for maintaining multiple flows between the UA and
its registrar is related to multihomed UAs. Such UAs can benefit its registrar is related to multihomed UAs. Such UAs can benefit
from multiple connections from different interfaces to protect from multiple connections from different interfaces to protect
against the failure of an individual access link. against the failure of an individual access link.
3.4 Edge Proxies 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 [RFC3327] so that Registrar. The Edge Proxy includes a Path header [3] so that when
when the registrar later forwards a request to this UA, the request the registrar later forwards a request to this UA, the request is
is routed through the Edge Proxy. There could be a NAT or firewall 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 |
+---------+ +---------+
/ \ / \
/ \ / \
/ \ / \
+-----+ +-----+ +-----+ +-----+
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These systems can use effectively the same mechanism as described in These systems can use effectively the same mechanism as described in
the previous sections but need to use the Path header. When the Edge the previous sections but need to use the Path header. When the Edge
Proxy receives a registration, it needs to create an identifier value Proxy receives a registration, it needs to create an identifier value
that is unique to this flow (and not a subsequent flow with the same that is unique to this flow (and not a subsequent flow with the same
addresses) and put this identifier in the Path header URI. This addresses) and put this identifier in the Path header URI. This
identifier has two purposes. First, it allows the Edge Proxy to map identifier has two purposes. First, it allows the Edge Proxy to map
future requests back to the correct flow. Second, because the future requests back to the correct flow. Second, because the
identifier will only be returned if the user authentication with the identifier will only be returned if the user authentication with the
registrar succeeds, it allows the Edge Proxy to indirectly check the registrar succeeds, it allows the Edge Proxy to indirectly check the
user's authentication information via the registrar. The identifier user's authentication information via the registrar. The identifier
SHOULD be placed in the user portion of a loose route in the Path is placed in the user portion of a loose route in the Path header.
header. If the registration succeeds, the Edge Proxy needs to map If the registration succeeds, the Edge Proxy needs to map future
future requests that are routed to the identifier value from the Path requests that are routed to the identifier value from the Path
header, to the associated flow. header, to the associated flow.
The term Edge Proxy is often used to refer to deployments where the The term Edge Proxy is often used to refer to deployments where the
Edge Proxy is in the same administrative domain as the Registrar. Edge Proxy is in the same administrative domain as the Registrar.
However, in this specification we use the term to refer to any proxy However, in this specification we use the term to refer to any proxy
between the UA and the Registrar. For example the Edge Proxy may be between the UA and the Registrar. For example the Edge Proxy may be
inside an enterprise that requires its use and the registrar could be inside an enterprise that requires its use and the registrar could be
from a service provider with no relationship to the enterprise. from a service provider with no relationship to the enterprise.
Regardless if they are in the same administrative domain, this Regardless if they are in the same administrative domain, this
specification requires that Registrars and Edge proxies support the specification requires that Registrars and Edge proxies support the
Path header mechanism in RFC 3327 [RFC3327]. Path header mechanism in RFC 3327 [3].
3.5 Keepalive Technique 3.5. Keepalive Technique
A keepalive mechanism needs to detect failure of a connection and A keepalive 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 bindings refreshed. This specification describes using STUN [4] over
[I-D.ietf-behave-rfc3489bis] over the same flow as the SIP traffic to the same flow as the SIP traffic to perform the keepalive. For
perform the keepalive. For connection-oriented transports (e.g. TCP connection-oriented transports (e.g. TCP and TLS over TCP), the UAC
and TLS over TCP), the UAC MAY use TCP keepalives to detect flow MAY use TCP keepalives to detect flow failure if the UAC can send
failure if the UAC can send these keepalives and detect a keepalive these keepalives and detect a keepalive failure according to the time
failure according to the time frames described in Section 4.4. frames described in Section 4.4.
Note: when TCP is being used, it's natural to think of using TCP Note: when TCP is being used, it's natural to think of using TCP
KEEPALIVE. Unfortunately, many operating systems and programming KEEPALIVE. Unfortunately, many operating systems and programming
environments do not allow the keepalive time to be set on a per- environments do not allow the keepalive time to be set on a per-
connection basis. Thus, applications may not be able to set an connection basis. Thus, applications may not be able to set an
appropriate time. 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
skipping to change at page 12, line 7 skipping to change at page 12, line 9
consensus that the STUN approach was a better solution that these consensus that the STUN approach was a better solution that these
alternative designs. 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 Identifier URN that uniquely identifies Each UA MUST have an Instance Identifier URN that uniquely identifies
the device. Usage of a URN provides a persistent and unique name for the device. Usage of a URN provides a persistent and unique name for
the UA instance. It also provides an easy way to guarantee the UA instance. It also provides an easy way to guarantee
uniqueness within the AOR. This URN MUST be persistent across power uniqueness within the AOR. This URN MUST be persistent across power
cycles of the device. The Instance ID MUST NOT change as the device cycles of the device. The Instance ID MUST NOT change as the device
moves from one network to another. moves from one network to another.
A UA SHOULD use a UUID URN [RFC4122] as its instance-id. The UUID A UA SHOULD use a UUID URN [5] as its instance-id. The UUID URN
URN allows for non-centralized computation of a URN based on time, allows for non-centralized computation of a URN based on time, unique
unique names (such as a MAC address), or a random number generator. names (such as 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 [RFC4122] and then save this in persistent storage for all UUID [5] and then save this in persistent storage for all future
future use. For a device such as a hard phone, which will only use. For a device such as a hard phone, which will only ever have
ever have a single SIP UA present, the UUID can include the MAC a single SIP UA present, the UUID can include the MAC address and
address and be generated at any time because it is guaranteed that be generated at any time because it is guaranteed that no other
no other UUID is being generated at the same time on that physical UUID is being generated at the same time on that physical device.
device. This means the value of the time component of the UUID This means the value of the time component of the UUID can be
can be arbitrarily selected to be any time less than the time when arbitrarily selected to be any time less than the time when the
the device was manufactured. A time of 0 (as shown in the example device was manufactured. A time of 0 (as shown in the example in
in Section 3.2) is perfectly legal as long as the device knows no Section 3.2) is perfectly legal as long as the device knows no
other UUIDs were generated at this time. other UUIDs were generated at this time.
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 [RFC3188]. Since specification is the national bibliographic number [19]. Since there
there is no clear relationship between a SIP UA instance and a URN in is no clear relationship between a SIP UA instance and a URN in this
this namespace, there is no way a selection of a value can be namespace, there is no way a selection of a value can be performed
performed that guarantees that another UA instance doesn't choose the that guarantees that another UA instance doesn't choose the same
same value. 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 [RFC3840] in requests and responses. As described in characteristic [6] in requests and responses. As described in [6],
[RFC3840], this media feature tag will be encoded in the Contact this media feature tag will be encoded in the Contact header field as
header field as the "+sip.instance" Contact header field parameter. the "+sip.instance" Contact header field parameter. The value of
The value of this parameter MUST be a URN [RFC2141]. One case where this parameter MUST be a URN [7]. One case where a UA may not want
a UA may not want to include the URN in the sip.instance media to include the URN in the sip.instance media feature tag is when it
feature tag is when it is making an anonymous request or some other is making an anonymous request or some other privacy concern requires
privacy concern requires that the UA not reveal its identity. that the UA not reveal its identity.
RFC 3840 [RFC3840] defines equality rules for callee capabilities RFC 3840 [6] 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 [RFC3840] and in the caller the generic usages defined in RFC 3840 [6] and in the caller
preferences specification [RFC3841]. When the instance ID is used preferences specification [8]. When the instance ID is used in
in this specification, it is effectively "extracted" from the this specification, it is effectively "extracted" from the value
value in the "sip.instance" media feature tag. Thus, equality in the "sip.instance" media feature tag. Thus, equality
comparisons are performed using the rules for URN equality that comparisons are performed using the rules for URN equality that
are specific to the scheme in the URN. If the element performing are specific to the scheme in the URN. If the element performing
the comparisons does not understand the URN scheme, it performs the comparisons does not understand the URN scheme, it performs
the comparisons using the lexical equality rules defined in RFC the comparisons using the lexical equality rules defined in RFC
2141 [RFC2141]. Lexical equality could result in two URNs being 2141 [7]. Lexical equality could result in two URNs being
considered unequal when they are actually equal. In this specific considered unequal when they are actually equal. In this specific
usage of URNs, the only element which provides the URN is the SIP usage of URNs, the only element which provides the URN is the SIP
UA instance identified by that URN. As a result, the UA instance UA instance identified by that URN. As a result, the UA instance
SHOULD provide lexically equivalent URNs in each registration it 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 from previous registrations. different from previous registrations.
4.2 Initial Registrations 4.2. Initial Registrations
At configuration time UAs obtain one or more SIP URIs representing At configuration time UAs obtain one or more SIP URIs representing
the default outbound-proxy-set. This specification assumes the set the default outbound-proxy-set. This specification assumes the set
is determined via any of a number of configuration mechanisms, and is determined via any of a number of configuration mechanisms, and
future specifications can define additional mechanisms such as using future specifications can define additional mechanisms such as using
DNS to discover this set. How the UA is configured is outside the DNS to discover this set. How the UA is configured is outside the
scope of this specification. However, a UA MUST support sets with at scope of this specification. However, a UA MUST support sets with at
least two outbound proxy URIs and SHOULD support sets with up to four least two outbound proxy URIs and SHOULD support sets with up to four
URIs. For each outbound proxy URI in the set, the UA SHOULD send a URIs. For each outbound proxy URI in the set, the UA SHOULD send a
REGISTER in the normal way using this URI as the default outbound REGISTER in the normal way using this URI as the default outbound
proxy. Forming the route set for the request is outside the scope of proxy. Forming the route set for the request is outside the scope of
this document, but typically results in sending the REGISTER such this document, but typically results in sending the REGISTER such
that the topmost Route header field contains a loose route to the that the topmost Route header field contains a loose route to the
outbound proxy URI. Other issues related to outbound route outbound proxy URI. Other issues related to outbound route
construction are discussed in [I-D.rosenberg-sip-route-construct]. construction are discussed in [20].
Registration requests, other than those described in Section 4.2.1, Registration requests, other than those described in Section 4.2.1,
MUST include an instance-id media feature tag as specified in MUST include an instance-id media feature tag as specified in
Section 4.1. Section 4.1.
These ordinary registration requests include a distinct reg-id These ordinary registration requests include a distinct reg-id
parameter 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
sequence of reg-id values does not have to be sequential but MUST be sequence of reg-id values does not have to be sequential but MUST be
exactly the same sequence of reg-id values each time the UA instance exactly the same sequence of reg-id values each time the UA instance
skipping to change at page 14, line 21 skipping to change at page 14, line 24
The UAC can situationally decide whether to request outbound The UAC can situationally decide whether to request outbound
behavior by including or omitting the 'reg-id' parameter. For behavior by including or omitting the 'reg-id' parameter. For
example, imagine the outbound-proxy-set contains two proxies in example, imagine the outbound-proxy-set contains two proxies in
different domains, EP1 and EP2. If an outbound-style registration different domains, EP1 and EP2. If an outbound-style registration
succeeded for a flow through EP1, the UA might decide to include succeeded for a flow through EP1, the UA might decide to include
'outbound' in its option-tag when registering with EP2, in order 'outbound' in its option-tag when registering with EP2, in order
to insure consistency. Similarly, if the registration through EP1 to insure consistency. Similarly, if the registration through EP1
did not support outbound, the UA might decide to omit the 'reg-id' did not support outbound, the UA might decide to omit the 'reg-id'
parameter when registering with EP2. parameter when registering with EP2.
The UAC MUST indicate that it supports the Path header [RFC3327] The UAC MUST indicate that it supports the Path header [3] mechanism,
mechanism, by including the 'path' option-tag in a Supported header by including the 'path' option-tag in a Supported header field value
field value in its REGISTER requests. Other than optionally in its REGISTER requests. Other than optionally examining the Path
examining the Path vector in the response, this is all that is vector in the response, this is all that is required of the UAC to
required of the UAC to support Path. support Path.
The UAC MAY examine successful registrations for the presence of an The UAC MAY examine successful 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, and that any edge proxies which need to partcipate are specification, and that any edge proxies which need to participate
also compliant. are also compliant.
Note that the UA needs to honor 503 (Service Unavailable) responses Note that the UA needs to honor 503 (Service Unavailable) responses
to registrations as described in RFC 3261 and RFC 3263 [RFC3263]. In to registrations as described in RFC 3261 and RFC 3263 [9]. In
particular, implementors should note that when receiving a 503 particular, implementors should note that when receiving a 503
(Service Unavailable) response with a Retry-After header field, the (Service Unavailable) response with a Retry-After header field, the
UA is expected to wait the indicated amount of time and retry the UA is expected to wait the indicated amount of time and retry the
registration. A Retry-After header field value of 0 is valid and registration. A Retry-After header field value of 0 is valid and
indicates the UA is expected to retry the REGISTER immediately. indicates the UA is expected to retry the REGISTER immediately.
Implementations need to ensure that when retrying the REGISTER, they Implementations need to ensure that when retrying the REGISTER, they
revisit the DNS resolution results such that the UA can select an revisit the DNS resolution results such that the UA can select an
alternate host from the one chosen the previous time the URI was alternate host from the one chosen the previous time the URI was
resolved. resolved.
Use of outbound with UDP flows typically prevents messages larger
than 1300 bytes from being delivered using TCP as described in
Section 18.1.1 RFC 3261. Use of outbound in conjunction with UDP
flows in environments where requests are expected to be larger than
this size is therefore NOT RECOMMENDED.
Finally, re-registrations which merely refresh an existing valid Finally, re-registrations which merely refresh an existing valid
registration SHOULD be sent over the same flow as the original registration SHOULD be sent over the same flow as the original
registration. registration.
4.2.1 Registration by Other Instances 4.2.1. Registration by Other Instances
A User Agent MUST NOT include a reg-id header parameter in the A User Agent MUST NOT include a reg-id header parameter in the
Contact header field of a registration if the registering UA is not Contact header field of a registration if the registering UA is not
the same instance as the UA referred to by the target Contact header the same instance as the UA referred to by the target Contact header
field. (This practice is occasionally used to install forwarding field. (This practice is occasionally used to install forwarding
policy into 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 unregister 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
When a UA is about to send a request, it first performs normal When a UA is about to send a request, it first performs normal
processing to select the next hop URI. The UA can use a variety of processing to select the next hop URI. The UA can use a variety of
techniques to compute the route set and accordingly the next hop URI. techniques to compute the route set and accordingly the next hop URI.
Discussion of these techniques is outside the scope of this document Discussion of these techniques is outside the scope of this document
but could include mechanisms specified in RFC 3608 [RFC3608] (Service but could include mechanisms specified in RFC 3608 [21] (Service
Route) and [I-D.rosenberg-sip-route-construct]. Route) and [20].
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 [RFC3263]) to find a protocol, IP address, and described in RFC 3263 [9]) to find a protocol, IP address, and port.
port. For non-TLS protocols, if the UA has an existing flow to this For non-TLS protocols, if the UA has an existing flow to this IP
IP address, and port with the correct protocol, then the UA MUST use address, and port with the correct protocol, then the UA MUST use the
the existing connection. For TLS protocols, there MUST also be a existing connection. For TLS protocols, there MUST also be a match
match between the host production in the next hop and one of the URIs between the host production in the next hop and one of the URIs
contained in the subjectAltName in the peer certificate. If the UA contained in the subjectAltName in the peer certificate. If the UA
cannot use one of the existing flows, then it SHOULD form a new flow cannot use one of the existing flows, then it SHOULD form a new flow
by sending a datagram or opening a new connection to the next hop, as by sending a datagram or opening a new connection to the next hop, as
appropriate for the transport protocol. appropriate for the transport protocol.
Note that if the UA wants its flow to work through NATs or Note that if the UA wants its flow to work through NATs or
firewalls it still needs to put the 'rport' parameter [RFC3581] in firewalls it still needs to put the 'rport' parameter [10] in its
its Via header field value, and send from the port it is prepared Via header field value, and send from the port it is prepared to
to receive on. More general information about NAT traversal in receive on. More general information about NAT traversal in SIP
SIP is described in [I-D.ietf-sipping-nat-scenarios]. is described in [22].
4.4 Detecting Flow Failure 4.4. Detecting Flow Failure
The UA needs to detect when a specific flow fails. The UA actively The UA needs to detect when a specific flow fails. The UA actively
tries to detect failure by periodically sending keepalive messages tries to detect failure by periodically sending keepalive messages
using one of the techniques described in Section 4.4.1 or using one of the techniques described in Section 4.4.1 or
Section 4.4.2. If a flow has failed, the UA follows the procedures Section 4.4.2. If a flow has failed, the UA follows the procedures
in Section 4.2 to form a new flow to replace the failed one. in Section 4.2 to form a new flow to replace the failed one.
The time between keepalive 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
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to evenly spread the load on the servers. For TCP, the 120 to evenly spread the load on the servers. For TCP, the 120
seconds upper bound was chosen based on the idea that for a good seconds upper bound was chosen based on the idea that for a good
user experience, failures normally will be detected in this amount user experience, failures normally will be detected in this amount
of time and a new connection set up. Operators that wish to of time and a new connection set up. Operators that wish to
change the relationship between load on servers and the expected change the relationship between load on servers and the expected
time that a user might not receive inbound communications will time that a user might not receive inbound communications will
probably adjust this time. The 95 seconds lower bound was chosen probably adjust this time. The 95 seconds lower bound was chosen
so that the jitter introduced will result in a relatively even so that the jitter introduced will result in a relatively even
load on the servers after 30 minutes. load on the servers after 30 minutes.
4.4.1 Keepalive with TCP KEEPALIVE 4.4.1. Keepalive with TCP KEEPALIVE
User Agents that are capable of generating per-connection TCP User Agents that are capable of generating per-connection TCP
keepalives with timer values consistent with those in this section keepalives with timer values consistent with those in this section
MAY use TCP keepalives instead of using STUN keepalives for TCP-based MAY use TCP keepalives instead of using STUN keepalives for TCP-based
flows. flows.
4.4.2 Keepalive with STUN 4.4.2. Keepalive with STUN
User Agents that form flows, check if the configured URI they are User Agents that form flows, check if the configured URI they are
connecting to has a 'keepalive' URI parameter (defined in Section 12) connecting to has a 'keepalive' URI parameter (defined in Section 12)
with the value of 'stun'. If the parameter is present and the UA is with the value of 'stun'. If the parameter is present and the UA is
not already performing keepalives using another supported mechanism, not already performing keepalives using another supported mechanism,
the UA needs to periodically perform keepalive checks by sending STUN the UA needs to periodically perform keepalive checks by sending STUN
[I-D.ietf-behave-rfc3489bis] Binding Requests over the flow as [4] Binding Requests over the flow as described in Section 8.
described in Section 8.
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.
4.4.3 Flow Recovery 4.4.3. Flow Recovery
When a flow to a particular URI in the outbound-proxy-set fails, the When a flow to a particular URI in the outbound-proxy-set fails, the
UA needs to form a new flow to replace the old flow and replace any UA needs to form a new flow to replace the old flow and replace any
registrations that were previously sent over this flow. Each new registrations that were previously sent over this flow. Each new
registration MUST have the same reg-id as the registration it registration MUST have the same reg-id as the registration it
replaces. This is done in much the same way as forming a brand new replaces. This is done in much the same way as forming a brand new
flow as described in Section 4.2; however, if there is a failure in flow as described in Section 4.2; however, if there is a failure in
forming this flow, the UA needs to wait a certain amount of time forming this flow, the UA needs to wait a certain amount of time
before retrying to form a flow to this particular next hop. before retrying to form a flow to this particular next hop.
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50 and 100 percent of the wait time. The UA MUST wait for the value 50 and 100 percent of the wait time. The UA MUST wait for the value
of the delay time before trying another registration to form a new of the delay time before trying another registration to form a new
flow for that URI. flow for that URI.
To be explicitly clear on the boundary conditions: when the UA boots To be explicitly clear on the boundary conditions: when the UA boots
it immediately tries to register. If this fails and no registration it immediately tries to register. If this fails and no registration
on other flows succeed, the first retry happens somewhere between 30 on other flows succeed, the first retry happens somewhere between 30
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 maximum of 1800 seconds is reached, the UA will keep trying
indefinitely with a random time of 15 to 30 minutes (900 to 1800 indefinitely with a random time of 15 to 30 minutes between each
seconds) between each attempt. attempt.
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 reg-id When an Edge Proxy receives a registration request with a reg-id
header parameter in the Contact header field, it needs to determine header parameter in the Contact header field, it needs to determine
if it (the edge proxy) will have to be visited for any subsequent if it (the edge proxy) will have to be visited for any subsequent
requests sent to the user agent identified in the Contact header requests sent to the user agent identified in the Contact header
field, or not. If the Edge Proxy determines that this is the case, field, or not. If the Edge Proxy determines that this is the case,
it inserts its URI in a Path header field value as described in RFC it inserts its URI in a Path header field value as described in RFC
3327 [RFC3327]. If the Edge Proxy is the first SIP node after the 3327 [3]. If the Edge Proxy is the first SIP node after the UAC, it
UAC, it either MUST store a "flow token"--containing information either MUST store a "flow token"--containing information about the
about the flow from the previous hop--in its Path URI, or reject the flow from the previous hop--in its Path URI, or reject the request.
request. The flow token MAY be placed in the userpart of the URI. The flow token MUST be an identifier that is unique to this network
In addition, the first node MUST include an 'ob' URI parameter in its flow. The flow token MAY be placed in the userpart of the URI. In
addition, the first node MUST include an 'ob' URI parameter in its
Path header field value. If the Edge Proxy is not the first SIP node Path header field value. If the Edge Proxy is not the first SIP node
after the UAC it MUST NOT place an 'ob' URI parameter in a Path after the UAC it MUST NOT place an 'ob' URI parameter in a Path
header field value. The Edge Proxy can determine if it is the first header field value. The Edge Proxy can determine if it is the first
hop by examining the Via header field hop by examining the Via header field.
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
in 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-
transports by concatenating the file descriptor (or equivalent) oriented transports by concatenating the file descriptor (or
with the NTP time the connection was created, and base64 encoding equivalent) with the NTP time the connection was created, and
the result. This results in an identifier approximately 16 octets base64 encoding the result. This results in an identifier
long. The proxy generates a flow token for UDP by concatenating approximately 16 octets long. The proxy generates a flow token
the file descriptor and the remote IP address and port, then for UDP by concatenating the file descriptor and the remote IP
base64 encoding the result. (No NTP time is needed for UDP.) address and port, then base64 encoding the result. (No NTP time
This algorithm MUST NOT be used unless all messages between the is needed for UDP.) This algorithm MUST NOT be used unless all
Edge proxy and Registrar use a SIPS protected transport. If the messages between the Edge proxy and Registrar use a SIPS protected
SIPS level of integrity protection is not available, an attacker transport. If the SIPS level of integrity protection is not
can hijack another user's calls. available, an attacker can hijack another user's calls.
Algorithm 2: When the proxy boots it selects a 20-octet crypto random Algorithm 2: When the proxy boots it selects a 20-octet crypto
key called K that only the Edge Proxy knows. A byte array, called random key called K that only the Edge Proxy knows. A byte array,
S, is formed that contains the following information about the called S, is formed that contains the following information about
flow the request was received on: an enumeration indicating the the flow the request was received on: an enumeration indicating
protocol, the local IP address and port, the remote IP address and the protocol, the local IP address and port, the remote IP address
port. The HMAC of S is computed using the key K and the HMAC- and port. The HMAC of S is computed using the key K and the HMAC-
SHA1-80 algorithm, as defined in [RFC2104]. The concatenation of SHA1-80 algorithm, as defined in [11]. The concatenation of the
the HMAC and S are base64 encoded, as defined in [RFC3548], and HMAC and S are base64 encoded, as defined in [12], and used as the
used as the flow identifier. When using IPv4 addresses, this will flow identifier. When using IPv4 addresses, this will result in a
result in a 32-octet identifier. 32-octet identifier.
5.3 Forwarding Requests 5.3. Forwarding Requests
When an Edge Proxy receives a request, it applies normal routing When an Edge Proxy receives a request, it applies normal routing
procedures with the following addition. If the Edge Proxy receives a procedures with the following addition. If the Edge Proxy receives a
request where the edge proxy is the host in the topmost Route header request where the edge proxy is the host in the topmost Route header
field value, and the Route header contains a flow token, the proxy field value, and the Route header contains a flow token, the proxy
compares the flow in the flow token with the source of the request. compares the flow in the flow token with the source of the request.
If these refer to the same flow, the Edge Proxy removes the Route If these refer to the same flow, the Edge Proxy removes the Route
header and continues processing the request. Otherwise, if the top- header and continues processing the request. Otherwise, if the top-
most Route header refers to the Edge Proxy and contains a valid flow most Route header refers to the Edge Proxy and contains a valid flow
identifier token created by this proxy, the proxy MUST remove the identifier token created by this proxy, the proxy MUST remove the
skipping to change at page 20, line 23 skipping to change at page 20, line 23
request. request.
Note that this specification needs mid-dialog requests to be routed Note that this specification needs mid-dialog requests to be routed
over the same flows as those stored in the Path vector from the over the same flows as those stored in the Path vector from the
initial registration, but techniques to ensure that mid-dialog initial registration, but techniques to ensure that mid-dialog
requests are routed over an existing flow are not part of this requests are routed over an existing flow are not part of this
specification. However, an approach such as having the Edge Proxy specification. However, an approach such as having the Edge Proxy
Record-Route with a flow token is one way to ensure that mid-dialog Record-Route with a flow token is one way to ensure that mid-dialog
requests are routed over the correct flow. requests are routed over the correct flow.
5.4 Edge Proxy Keepalive Handling 5.4. Edge Proxy Keepalive Handling
All edge proxies compliant with this specification MUST implement All edge proxies compliant with this specification MUST implement
support for the STUN NAT Keepalive usage on its SIP ports as support for the STUN NAT Keepalive usage on its SIP ports as
described in Section 8. described in Section 8.
6. Registrar Mechanisms: Processing REGISTER Requests 6. Registrar Mechanisms: Processing REGISTER Requests
This specification updates the definition of a binding in RFC 3261 This specification updates the definition of a binding in RFC 3261
[RFC3261] Section 10 and RFC 3327 [RFC3327] Section 5.3. [1] Section 10 and RFC 3327 [3] Section 5.3.
When no +sip.instance media feature parameter is present in a Contact When no +sip.instance media feature parameter is present in a Contact
header field value in a REGISTER request, the corresponding binding header field value in a REGISTER request, the corresponding binding
is still between an AOR and the URI from that Contact header field is still between an AOR and the URI from that Contact header field
value. When a +sip.instance media feature parameter is present in a value. When a +sip.instance media feature parameter is present in a
Contact header field value in a REGISTER request, the corresponding Contact header field value in a REGISTER request, the corresponding
binding is between an AOR and the combination of the instance-id binding is between an AOR and the combination of the instance-id
(from the +sip.instance media feature parameter) and the value of (from the +sip.instance media feature parameter) and the value of
reg-id parameter if it is present. For a binding with an reg-id parameter if it is present. For a binding with an
instance-id, the registrar still stores the Contact header field instance-id, the registrar still stores the Contact header field
value URI with the binding, but does not consider the Contact URI for value URI with the binding, but does not consider the Contact URI for
comparison purposes. A Contact header field value with an comparison purposes. A Contact header field value with an
instance-id but no reg-id is valid, but one with a reg-id but no instance-id but no reg-id is valid, but one with a reg-id but no
instance-id is not. If the registrar processes a Contact header instance-id is not. If the registrar processes a Contact header
field value with a reg-id but no instance-id, it simply ignores the field value with a reg-id but no instance-id, it simply ignores the
reg-id parameter. The registrar MUST be prepared to receive, reg-id parameter. The registrar MUST be prepared to receive,
simultaneously for the same AOR, some registrations that use simultaneously for the same AOR, some registrations that use
instance-id and reg-id and some registrations that do not. instance-id and reg-id and some registrations that do not.
Registrars which implement this specification MUST support the Path Registrars which implement this specification MUST support the Path
header mechanism [RFC3327]. header mechanism [3].
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 needs to be stored for any registration some additional information needs to be stored for any registration
that contains an instance-id and a reg-id header parameter in the that contains an instance-id and a reg-id header parameter in the
Contact header field value. First the registrar examines the first Contact header field value. First the registrar examines the first
Path header field value, if any. If the Path header field exists and Path header field value, if any. If the Path header field exists and
the first URI does not have an 'ob' URI parameter, the registrar MUST the first URI does not have an 'ob' URI parameter, the registrar MUST
ignore the reg-id parameter and continue processing the request as if ignore the reg-id parameter and continue processing the request as if
it did not support this specification. Likewise if the REGISTER it did not support this specification. Likewise if the REGISTER
request visited an edge proxy, but no Path header field values are request visited an edge proxy, but no Path header field values are
present, the registrar MUST ignore the reg-id parameter. present, the registrar MUST ignore the reg-id parameter.
Specifically, the registrar MUST use RFC 3261 Contact binding rules, Specifically, the registrar MUST use RFC 3261 Contact binding rules,
and MUST NOT include the 'outbound' option-tag in its Supported and MUST NOT include the 'outbound' option-tag in its Supported
header field. The registrar can determine if it is the first hop by header field. The registrar can determine if it is the first hop by
examining the Via header field. examining the Via header field.
If the UAC has a direct flow with the registrar, the registrar MUST If the UAC has a direct flow with the registrar, the registrar MUST
store enough information to uniquely identify the network flow over store enough information to uniquely identify the network flow over
which the request arrived. For common operating systems with TCP, which the request arrived. For common operating systems with TCP,
this would typically just be the file descriptor and the time the this would typically just be the handle to file descriptor where the
file descriptor was opened. For common operating systems with UDP handle would become invalid if the TCP session was closed. For
this would typically be the file descriptor for the local socket that common operating systems with UDP this would typically be the file
received the request, the local interface, and the IP address and descriptor for the local socket that received the request, the local
port number of the remote side that sent the request. The registrar interface, and the IP address and port number of the remote side that
MAY store this information by adding itself to the Path header field sent the request. The registrar MAY store this information by adding
with an appropriate flow token. itself to the Path header field with an appropriate flow token.
The registrar MUST also store all the Contact header field 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 [RFC3327] requires the a Path header field is present, RFC 3327 [3] requires the registrar
registrar to store this information as well. If the registrar to store this information as well. If the registrar receives a re-
receives a re-registration, it MUST update any information that registration, it MUST update any information that uniquely identifies
uniquely identifies the network flow over which the request arrived the network flow over which the request arrived if that information
if that information has changed, and SHOULD update the time the has changed, and SHOULD update the time the binding was last updated.
binding was last updated.
The Registrar MUST include the 'outbound' option-tag (defined in The Registrar MUST include the 'outbound' option-tag (defined in
Section (Section 12.1)) in a Supported header field value in its Section (Section 12.1)) in a Supported header field value in its
responses to REGISTER requests for which it has performed outbound responses to REGISTER requests for which it has performed outbound
processing. The Registrar MAY be configured with local policy to processing. The Registrar MAY be configured with local policy to
reject any registrations that do not include the instance-id and reject any registrations that do not include the instance-id and
reg-id. Note that the requirements in this section applies to both reg-id. Note that the requirements in this section applies to both
REGISTER requests received from an Edge Proxy as well as requests REGISTER requests received from an Edge Proxy as well as requests
received directly from the UAC. received directly from the UAC.
To be compliant with this specification, registrars which can receive To be compliant with this specification, registrars which can receive
SIP requests directly from a UAC without intervening edge proxies SIP requests directly from a UAC without intervening edge proxies
MUST implement the STUN NAT Keepalive usage on its SIP ports as MUST implement the STUN NAT Keepalive usage on its SIP ports as
described in Section 8. described in Section 8.
7. Authoritative Proxy Mechansims: Forwarding Requests 7. Authoritative Proxy Mechanisms: Forwarding Requests
When a proxy uses the location service to look up a registration When a proxy uses the location service to look up a registration
binding and then proxies a request to a particular contact, it binding and then proxies a request to a particular contact, it
selects a contact to use normally, with a few additional rules: selects a contact to use normally, with a few additional rules:
o The proxy MUST NOT populate the target set with more than one o The proxy MUST NOT populate the target set with more than one
contact with the same AOR and instance-id at a time. 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 430 (Flow for a particular AOR and instance-id fails with a 430 (Flow
Failed) response, the proxy SHOULD replace the failed branch with Failed) response, the proxy SHOULD replace the failed branch with
another target (if one is available) with the same AOR and another target (if one is available) with the same AOR and
instance-id, but a different reg-id. instance-id, but a different reg-id.
o If the proxy receives a final response from a branch other than a o If the proxy receives a final response from a branch other than a
408 (Request Timeout) or a 430 (Flow Failed) response, the proxy 408 (Request Timeout) or a 430 (Flow Failed) response, the proxy
MUST NOT forward the same request to another target representing MUST NOT forward the same request to another target representing
the same AOR and instance-id. The targetted instance has already the same AOR and instance-id. The targeted instance has already
provided its response. provided its response.
The proxy uses normal forwarding rules looking at the next-hop target The proxy uses normal forwarding rules looking at the next-hop target
of the message and the value of any stored Path header field vector of the message and the value of any stored Path header field vector
in the 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. If the proxy stored populate the Route header in the request. If the proxy stored
information about the flow over which it received the REGISTER for information about the flow over which it received the REGISTER for
the binding, then the proxy MUST send the request over the same the binding, then the proxy MUST send the request over the same
'logical flow' saved with the binding that is known to deliver data 'logical flow' saved with the binding that is known to deliver data
to the specific target UA instance. to the specific target UA instance.
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flow, then the proxy MUST invalidate all the bindings in the target flow, then the proxy MUST invalidate all the bindings in the target
set that use that flow (regardless of AOR). Examples of this are a set that use that flow (regardless of AOR). Examples of this are a
TCP socket closing or receiving a destination unreachable ICMP error TCP socket closing or receiving a destination unreachable ICMP error
on a UDP flow. Similarly, if a proxy closes a file descriptor, it on a UDP flow. Similarly, if a proxy closes a file descriptor, it
MUST invalidate all the bindings in the target set with flows that MUST invalidate all the bindings in the target set with flows that
use that file descriptor. use that file descriptor.
8. STUN Keepalive Processing 8. STUN Keepalive Processing
This section describes changes to the SIP transport layer that allow This section describes changes to the SIP transport layer that allow
SIP and the STUN [I-D.ietf-behave-rfc3489bis] NAT Keepalive usage to SIP and the STUN [4] NAT Keepalive usage to be mixed over the same
be mixed over the same flow. The STUN messages are used to verify flow. The STUN messages are used to verify connectivity is still
connectivity is still available over a flow and to provide periodic available over a flow and to provide periodic keepalives. Note that
keepalives. Note that these STUN keepalives are always sent to the these STUN keepalives are always sent to the next SIP hop. STUN
next SIP hop. STUN messages are not delivered end-to-end. messages are not delivered end-to-end.
The only STUN messages required by this usage are Binding Requests, The only STUN messages required by this usage are Binding Requests,
Binding Responses, and Error Responses. The UAC sends Binding Binding Responses, and Error Responses. The UAC sends Binding
Requests over the same UDP flow, TCP connection, or TLS channel used Requests over the same UDP flow, TCP connection, or TLS channel used
for sending SIP messages. These Binding Requests do not require any for sending SIP messages. These Binding Requests do not require any
STUN attributes. The UAS responds to a valid Binding Request with a STUN attributes. The UAS responds to a valid Binding Request with a
Binding Response which MUST include the XOR-MAPPED-ADDRESS attribute. Binding Response which MUST include the XOR-MAPPED-ADDRESS attribute.
After a successful STUN response is received over TCP or TLS over After a successful STUN response is received over TCP or TLS over
TCP, the underlying TCP connection is left in the active state. TCP, the underlying TCP connection is left in the active state.
If a server compliant to this section receives SIP requests on a If a server compliant to this section receives SIP requests on a
given interface and port, it MUST also provide a limited version of a given interface and port, it MUST also provide a limited version of a
STUN server on the same interface and port as described in Section STUN server on the same interface and port as described in Section
12.3 of [I-D.ietf-behave-rfc3489bis]. When STUN messages are sent 12.3 of [4]. When STUN messages are sent with a SIP over TLS over
with a SIP over TLS over TCP flow, the STUN messages are sent inside TCP flow, the STUN messages are sent inside the TLS-protected
the TLS-protected channel. channel.
It is easy to distinguish STUN and SIP packets sent over UDP, It is easy to distinguish STUN and SIP packets sent over UDP,
because the first octet of a STUN packet has a value of 0 or 1 because the first octet of a STUN packet has a value of 0 or 1
while the first octet of a SIP message is never a 0 or 1. For TCP while the first octet of a SIP message is never a 0 or 1. For TCP
or TLS over TCP flows, determining if the first octet of the next or TLS over TCP flows, determining if the first octet of the next
message in a stream is SIP or STUN is still straightforward. As message in a stream is SIP or STUN is still straightforward. As
with any stream-based protocol, implementations need to be preared with any stream-based protocol, implementations need to be
to receive STUN messages which cross a stream buffer boundary, and prepared to receive STUN messages which cross a stream buffer
SIP and STUN messages which share the same stream buffer. boundary, and SIP and STUN messages which share the same stream
buffer.
Because sending and receiving binary STUN data on the same ports used Because sending and receiving binary STUN data on the same ports used
for SIP is a significant and non-backwards compatible change to RFC for SIP is a significant and non-backwards compatible change to RFC
3261, this section requires a number of checks before sending STUN 3261, this section requires a number of checks before sending STUN
messages to a SIP node. If a SIP node sends STUN requests (for messages to a SIP node. If a SIP node sends STUN requests (for
example due to misconfiguration) despite these warnings, the node example due to misconfiguration) despite these warnings, the node
could be blacklisted for UDP traffic, or cause its TCP server to could be blacklisted for UDP traffic, or cause its TCP server to
loose framing over its connection. For each target node (as loose framing over its connection. For each target node (as
determined by IP address, address family, and port number), the determined by IP address, address family, and port number), the
sender needs to determine if that destination is validated to support sender needs to determine if that destination is validated to support
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A SIP node MUST NOT send STUN requests over a flow unless it has an A SIP node MUST NOT send STUN requests over a flow unless it has an
explicit indication that the target next hop SIP server claims to explicit indication that the target next hop SIP server claims to
support STUN. For example, automatic or manual configuration of an support STUN. For example, automatic or manual configuration of an
outbound-proxy-set which contains the keepalive=stun parameter is outbound-proxy-set which contains the keepalive=stun parameter is
considered sufficient explicit indication. Note that UACs MUST NOT considered sufficient explicit indication. Note that UACs MUST NOT
use an ambiguous configuration option such as "Work through NATs?" or use an ambiguous configuration option such as "Work through NATs?" or
"Do Keepalives?" to imply next hop STUN support. A SIP node MAY also "Do Keepalives?" to imply next hop STUN support. A SIP node MAY also
probe the next hop using a SIP OPTIONS request to check for support probe the next hop using a SIP OPTIONS request to check for support
of the 'sip-stun' option tag in a Supported header field. of the 'sip-stun' option tag in a Supported header field.
Futhermore, even with explicit indication of next hop STUN support, a Furthermore, even with explicit indication of next hop STUN support,
SIP node needs to validate support for STUN the first time it sends a SIP node needs to validate support for STUN the first time it sends
traffic to a specific unvalidated target destination. If an explicit traffic to a specific invalidated target destination. A SIP node MAY
probe indicates support for the 'sip-stun' option-tag, that send one STUN request and its retransmissions to an invalidated
destination is validated for STUN support. If an explicit probe does destination. If a STUN request ever succeeds to a destination, that
not indicate support for the 'sip-stun' option-tag, the target destination is thereafter validated for STUN support. If this
destination does not support STUN request, and the UAC MUST NOT send initial STUN request does not result in a STUN response, the SIP node
further STUN requests to this destination. A SIP node MAY send one MUST NOT send additional STUN requests over this flow, unless a next-
STUN request and its retransmissions to an unvalidated destination. hop probe later validates the destination. In addition, the SIP node
If a STUN request ever succeeds to a destination, that destination is SHOULD remember invalidated destination nodes that have been used
thereafter validated for STUN support. If this initial STUN request
does not result in a STUN response, the SIP node MUST NOT send
additional STUN requests over this flow, unless and until a next-hop
probe later validates the destination. In addition, the SIP node
SHOULD remember unvalidated destination nodes that have been used
within one hour and SHOULD NOT send additional STUN messages to any within one hour and SHOULD NOT send additional STUN messages to any
of these destinations. Note that until STUN support has been of these destinations.
verified, an initial STUN failure over UDP is not considered a flow
failure. For UDP flows, an unvalidated flow can still be reused for If this initial STUN request does not result in a STUN response, the
SIP traffic, however for unvalidated TCP or TLS over TCP flows, the UA MAY send and explicit next-hop probe as described in Section 8.1.
connection over which STUN requests were sent MUST be closed. If an explicit probe indicates support for the 'sip-stun' option-tag,
that destination is validated for STUN support. If an explicit probe
does not indicate support for the 'sip-stun' option-tag, the target
destination does not support STUN request, and the UAC MUST NOT send
further STUN requests to this destination.
Note that until STUN support has been verified, an initial STUN
failure over UDP is not considered a flow failure. For UDP flows, an
invalidated flow can still be reused for SIP traffic, however for
invalidated TCP or TLS over TCP flows, the connection over which STUN
requests were sent MUST be closed.
Typically, a SIP node first sends a SIP request and waits to Typically, a SIP node first sends a SIP request and waits to
receive a final response (other than a 408 response) over a flow receive a final response (other than a 408 response) over a flow
to a new target destination, before sending any STUN messages. to a new target destination, before sending any STUN messages.
When scheduled for the next NAT refresh, the SIP node sends a STUN When scheduled for the next NAT refresh, the SIP node sends a STUN
request to the target. If none of the STUN requests succeed request to the target. If none of the STUN requests succeed
(result in a STUN success response), and the UAC has not already (result in a STUN success response), and the UAC has not already
done so, the UAC sends an OPTIONS request to the next hop to done so, the UAC sends an OPTIONS request to the next hop to
verify support for the 'sip-stun' option-tag. verify support for the 'sip-stun' option-tag.
Once a destination is validated to support STUN messages, failure of Once a destination is validated to support STUN messages, failure of
a STUN request (including its retransmissions) is considered a a STUN request (including its retransmissions) is considered a
failure of the underlying flow. For SIP over UDP flows, if the XOR- failure of the underlying flow. For SIP over UDP flows, if the XOR-
MAPPED-ADDRESS returned over the flow changes, this indicates that MAPPED-ADDRESS returned over the flow changes, this indicates that
the underlying connectivity has changed, and is considered a flow the underlying connectivity has changed, and is considered a flow
failure. A 408 response to a next-hop OPTIONS probe is also failure. A 408 response to a next-hop OPTIONS probe is also
considered a flow failure. considered a flow failure.
8.1 Explicit Probes Note that failure of a flow causes a new flow to be formed and that
the STUN validation needs to be done for this new flow even if it is
to a destination that had previously been validated for STUN.
8.1. Explicit Probes
This section defines a new SIP option-tag called 'sip-stun'. This section defines a new SIP option-tag called 'sip-stun'.
Advertising this option-tag indicates that the server can receive SIP Advertising this option-tag indicates that the server can receive SIP
messages and STUN messages as part of the NAT Keepalive usage on the messages and STUN messages as part of the NAT Keepalive usage on the
same port. Clients that want to probe a SIP server to determine same port. Clients that want to probe a SIP server to determine
support for STUN, can send an OPTIONS request to the next hop by support for STUN, can send an OPTIONS request to the next hop by
setting the Max-Forwards header field to 0. The OPTIONS response setting the Max-Forwards header field to zero or addressing the
will contain a Supported header field with a list of the server's request to that server. The OPTIONS response will contain a
supported option-tags. Supported header field with a list of the server's supported option-
tags.
A UAC SHOULD NOT include the 'sip-stun' option-tag in a Proxy- A UAC SHOULD NOT include the 'sip-stun' option-tag in a Proxy-
Require header. This is because a request with this header will Require header. This is because a request with this header will
fail in some topologies where the first proxy support sip-stun, fail in some topologies where the first proxy support sip-stun,
but a subsequent proxy does not. Note that RFC 3261 does not but a subsequent proxy does not. Note that RFC 3261 does not
allow proxies to remove option-tags from a Proxy-Require header allow proxies to remove option-tags from a Proxy-Require header
field. field.
8.2 Use with Sigcomp 8.2. Use with Sigcomp
When STUN is used together with SigComp [RFC3320] compressed SIP When STUN is used together with SigComp [23] compressed SIP messages
messages over the same flow, how the STUN messages are sent depends over the same flow, how the STUN messages are sent depends on the
on the transport protocol. For UDP flows, the STUN messages are transport protocol. For UDP flows, the STUN messages are simply sent
simply sent uncompressed, "outside" of SigComp. This is supported by uncompressed, "outside" of SigComp. This is supported by
multiplexing STUN messages with SigComp messages by checking the two multiplexing STUN messages with SigComp messages by checking the two
topmost bits of the message. These bits are always one for SigComp, topmost bits of the message. These bits are always one for SigComp,
or zero for STUN. or zero for STUN.
All SigComp messages contain a prefix (the five most-significant All SigComp messages contain a prefix (the five most-significant
bits of the first byte are set to one) that does not occur in bits of the first byte are set to one) that does not occur in
UTF-8 encoded text messages [RFC-2279], so for applications which UTF-8 encoded text messages [RFC-2279], so for applications which
use this encoding (or ASCII encoding) it is possible to multiplex use this encoding (or ASCII encoding) it is possible to multiplex
uncompressed application messages and SigComp messages on the same uncompressed application messages and SigComp messages on the same
UDP port. UDP port.
The most significant two bits of every STUN message are both The most significant two bits of every STUN message are both
zeroes. This, combined with the magic cookie, aids in zeroes. This, combined with the magic cookie, aids in
differentiating STUN packets from other protocols when STUN is differentiating STUN packets from other protocols when STUN is
multiplexed with other protocols on the same port. multiplexed with other protocols on the same port.
For TCP-based flows, SigComp requires that all messages are processed For TCP-based flows, SigComp requires that all messages are processed
by the SigComp compressor to facilitate framing. For these by the SigComp compressor to facilitate framing. For these
transports, STUN messages are sent encapsulated in the SigComp "well- transports, STUN messages are sent encapsulated in the SigComp "well-
known shim header" as described in Section 11 of [I-D.ietf-rohc- known shim header" as described in Section 11 of [24].
sigcomp-impl-guide].
Because the bytecodes expressed in the well-known shim header do Because the bytecodes expressed in the well-known shim header do
not store any state, correlation of such SigComp requests to a not store any state, correlation of such SigComp requests to a
compartment is not necessary. To avoid ambiguity, we add the compartment is not necessary. To avoid ambiguity, we add the
following requirement: any SigComp state that might result from a following requirement: any SigComp state that might result from a
message that, once decompressed, turns out to be a STUN message, message that, once decompressed, turns out to be a STUN message,
MUST be discarded. MUST be discarded.
9. Example Message Flow 9. Example Message Flow
skipping to change at page 29, line 41 skipping to change at page 29, line 41
;+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 8 contains a Record-Route thing to note is that the INVITE in message 8 contains a Record-Route
header for the Secondary proxy, with its flow token. header for the Secondary proxy, with its flow token.
Record-Route: Record-Route:
<sip:PQPbqQE+Ynf+tzRPD27lU6uxkjQ8LLUG@sec.example.com;lr;user=flow> <sip:PQPbqQE+Ynf+tzRPD27lU6uxkjQ8LLUG@sec.example.com;lr>
The registrations in message 13 and 14 are the same as message 1 and The registrations in message 13 and 14 are the same as message 1 and
2 other than the Call-ID and tags have changed. Because these 2 other than the Call-ID and tags have changed. Because these
messages will contain the same instance-id and reg-id as those in 1 messages will contain the same instance-id and reg-id as those in 1
and 2, this flow will partially supersede that for messages 1 and 2 and 2, this flow will partially supersede that for messages 1 and 2
and will be tried first by Primary. and will be tried first by Primary.
10. Grammar 10. Grammar
This specification defines new Contact header field parameters, This specification defines new Contact header field parameters,
reg-id and +sip.instance. The grammar includes the definitions from reg-id and +sip.instance. The grammar includes the definitions from
RFC 3261 [RFC3261] and includes the definition of uric from RFC 2396 RFC 3261 [1] and includes the definition of uric from RFC 2396 [13].
[RFC2396].
Note: The "=/" syntax used in this ABNF indicates an extension of Note: The "=/" syntax used in this ABNF indicates an extension of
the production on the left hand side. the production on the left hand side.
The ABNF[RFC4234] is: The ABNF[14] is:
contact-params =/ c-p-reg / c-p-instance contact-params =/ c-p-reg / c-p-instance
c-p-reg = "reg-id" EQUAL 1*DIGIT ; 1 to 2**31 c-p-reg = "reg-id" EQUAL 1*DIGIT ; 1 to 2**31
c-p-instance = "+sip.instance" EQUAL c-p-instance = "+sip.instance" EQUAL
LDQUOT "<" instance-val ">" RDQUOT LDQUOT "<" instance-val ">" RDQUOT
instance-val = *uric ; defined in RFC 2396 instance-val = *uric ; defined in RFC 2396
skipping to change at page 30, line 35 skipping to change at page 30, line 38
This specification defines a new SIP response code '430 Flow Failed'. This specification defines a new SIP response code '430 Flow Failed'.
This response code is used by an Edge Proxy to indicate to the This response code is used by an Edge Proxy to indicate to the
Authoritative Proxy that a specific flow to a UA instance has failed. Authoritative Proxy that a specific flow to a UA instance has failed.
Other flows to the same instance could still succeed. The Other flows to the same instance could still succeed. The
Authoritative Proxy SHOULD attempt to forward to another target Authoritative Proxy SHOULD attempt to forward to another target
(flow) with the same instance-id and AOR. (flow) with the same instance-id and AOR.
12. IANA Considerations 12. IANA Considerations
12.1 Contact Header Field 12.1. Contact Header Field
This specification defines a new Contact header field parameter This specification defines a new Contact header field parameter
called reg-id in the "Header Field Parameters and Parameter Values" called reg-id in the "Header Field Parameters and Parameter Values"
sub-registry as per the registry created by [RFC3968]. The required sub-registry as per the registry created by [15]. The required
information is: information is:
Header Field Parameter Name Predefined Reference Header Field Parameter Name Predefined Reference
Values Values
____________________________________________________________________ ____________________________________________________________________
Contact reg-id 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.]
12.2 SIP/SIPS URI Parameters 12.2. 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 [RFC3969]. The required registry as per the registry created by [16]. The required
information is: information is:
Parameter Name Predefined Values Reference Parameter Name Predefined Values Reference
____________________________________________ ____________________________________________
keepalive stun [RFC AAAA] keepalive stun [RFC AAAA]
ob [RFC AAAA] ob [RFC AAAA]
[NOTE TO RFC Editor: Please replace AAAA with [NOTE TO RFC Editor: Please replace AAAA with
the RFC number of this specification.] the RFC number of this specification.]
12.3 SIP Option Tag 12.3. SIP Option Tag
This specification registers two new SIP option tags, as per the This specification registers two new SIP option tags, 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 the places this option-tag in a Supported header to communicate the
Registrar's support for this extension to the registering User Registrar's support for this extension to the registering User
Agent. Agent.
Name: sip-stun Name: sip-stun
Description: This option-tag is used to identify SIP servers which Description: This option-tag is used to identify SIP servers which
can receive STUN requests described in the STUN NAT Keepalive can receive STUN requests described in the STUN NAT Keepalive
usage on the same ports they use to receive SIP messages. usage on the same ports they use to receive SIP messages.
12.4 Response Code 12.4. Response Code
This section registers a new SIP Response Code, as per the guidelines This section registers a new SIP Response Code, as per the guidelines
in Section 27.1 of RFC 3261. in Section 27.1 of RFC 3261.
Code: 430 Code: 430
Default Reason Phrase: Flow Failed Default Reason Phrase: Flow Failed
Reference: This document Reference: This document
12.5 Media Feature Tag 12.5. Media Feature Tag
This section registers a new media feature tag, per the procedures This section registers a new media feature tag, per the procedures
defined in RFC 2506 [RFC2506]. The tag is placed into the sip tree, defined in RFC 2506 [17]. The tag is placed into the sip tree, which
which is defined in RFC 3840 [RFC3840]. is defined in RFC 3840 [6].
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 32, line 26 skipping to change at page 32, line 26
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 [RFC3841] allows for call routing decisions to preferences extension [8] allows for call routing decisions to be
be based on the values of these parameters. Therefore, if an based on the values of these parameters. Therefore, if an attacker
attacker can modify the values of this tag, they might be able to can modify the values of this tag, they might be able to affect the
affect the behavior of applications. As a result, applications which behavior of applications. As a result, applications which utilize
utilize this media feature tag SHOULD provide a means for ensuring this media feature tag SHOULD provide a means for ensuring its
its integrity. Similarly, this feature tag should only be trusted as 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.
13. Security Considerations 13. 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 33, line 25 skipping to change at page 33, line 27
gotten this information from the registrar. The registrar will only gotten this information from the registrar. The registrar will only
save this information for a given AOR if the registration for the AOR save this information for a given AOR if the registration for the AOR
has been successful; and the registration will only be successful if has been successful; and the registration will only be successful if
the UA can correctly authenticate. Even if an attacker has spoofed the UA can correctly authenticate. Even if an attacker has spoofed
some bad information in the Path header sent to the registrar, the some bad information in the Path header sent to the registrar, the
attacker will not be able to get the registrar to accept this attacker will not be able to get the registrar to accept this
information for an AOR that does not belong to the attacker. The information for an AOR that does not belong to the attacker. The
registrar will not hand out this bad information to others, and registrar will not hand out this bad information to others, and
others will not be misled into contacting the attacker. others will not be misled into contacting the attacker.
14. Requirements 14. Operational Notes on Transports
RFC 3261 requires proxies, registrars, and UA to implement both TCP
and UDP but deployments can chose which protocols they want to use.
Deployments need to be careful in choosing what transports to use.
Many SIP features and extensions, such as large presence
subscriptions packages, result in SIP requests that can be too large
to be reasonably transported over UDP. RFC 3261 has an option of
when a request is too large for UDP, the device sending the request
can attempt to switch over to TCP. No known deployments currently
use this but it is important to note that when using outbound, this
will only work if the UA has formed both a UDP and TCP outbound
connection. The specification allows the UA to do this but in most
cases it will probably make more sense to only form TCP outbound
connection than forming both UDP and TCP. One of the key reasons
that many deployments choose not to use TCP has to do with the
difficulty of building proxies that can maintain a very large number
of active TCP connections. Many deployments today use SIP in such a
way that the message are small enough that they work over UDP but
they can not take advantage of all the functionality SIP offers.
Deployments that use only UDP outbound connections are going to fail
with sufficiently large SIP messages.
15. 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 a 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.
15. Changes 16. Changes
Note to RFC Editor: Please remove this whole section. Note to RFC Editor: Please remove this whole section.
15.1 Changes from 05 Version 16.1. Changes from 06 Version
Added the section on operational selection of transports.
Fixed various editorial typos.
Put back in requirement flow token needs to be unique to flow as it
had accidentally been dropped in earlier version. This did not
change any of the flow token algorithms.
Reordered some of the text on STUN keepalive validation to make it
clearer to implementors. Did not change the actual algorithm or
requirements. Added note to explain how if the proxy changes, the
revalidation will happen.
16.2. Changes from 05 Version
Mention the relevance of the 'rport' parameter. Mention the relevance of the 'rport' parameter.
Change registrar verification so that only first-hop proxy and the Change registrar verification so that only first-hop proxy and the
registrar need to support outbound. Other intermediaries in between registrar need to support outbound. Other intermediaries in between
do not any more. do not any more.
Relaxed flow-token language slightly. Instead of flow-token saving Relaxed flow-token language slightly. Instead of flow-token saving
specific UDP address/port tuples over which the request arrived, make specific UDP address/port tuples over which the request arrived, make
language fuzzy to save token which points to a 'logical flow' that is language fuzzy to save token which points to a 'logical flow' that is
skipping to change at page 34, line 17 skipping to change at page 35, line 13
Added comment that keepalive=stun could be added to Path. Added comment that keepalive=stun could be added to Path.
Added comment that battery concerns could motivate longer TCP Added comment that battery concerns could motivate longer TCP
keepalive intervals than the defaults. keepalive intervals than the defaults.
Scrubbed document for avoidable lowercase mays, shoulds, and musts. Scrubbed document for avoidable lowercase mays, shoulds, and musts.
Added text about how Edge Proxies could determine they are the first Added text about how Edge Proxies could determine they are the first
hop. hop.
15.2 Changes from 04 Version 16.3. Changes from 04 Version
Moved STUN to a separate section. Reference this section from within Moved STUN to a separate section. Reference this section from within
the relevant sections in the rest of the document. the relevant sections in the rest of the document.
Add language clarifying that UA MUST NOT send STUN without an Add language clarifying that UA MUST NOT send STUN without an
explicit indication the server supports STUN. explicit indication the server supports STUN.
Add language describing that UA MUST stop sending STUN if it appears Add language describing that UA MUST stop sending STUN if it appears
the server does not support it. the server does not support it.
skipping to change at page 35, line 25 skipping to change at page 36, line 19
Added text about the 'ob' parameter which is used in Path header Added text about the 'ob' parameter which is used in Path header
field URIs to make sure that the previous proxy that added a Path field URIs to make sure that the previous proxy that added a Path
understood outbound processing. The registrar doesn't include understood outbound processing. The registrar doesn't include
Supported: outbound unless it could actually do outbound processing Supported: outbound unless it could actually do outbound processing
(ex: any Path headers have to have the 'ob' parameter). (ex: any Path headers have to have the 'ob' parameter).
Added some text describing what a registration means when there is an Added some text describing what a registration means when there is an
instance-id, but no reg-id. instance-id, but no reg-id.
15.3 Changes from 03 Version 16.4. Changes from 03 Version
Added non-normative text motivating STUN vs. SIP PING, OPTIONS, and Added non-normative text motivating STUN vs. SIP PING, OPTIONS, and
Double CRLF. Added discussion about why TCP Keepalives are not Double CRLF. Added discussion about why TCP Keepalives are not
always available. always available.
Explained more clearly that outbound-proxy-set can be "configured" Explained more clearly that outbound-proxy-set can be "configured"
using any current or future, manual or automatic configuration/ using any current or future, manual or automatic configuration/
discovery mechanism. discovery mechanism.
Added a sentence which prevents an Edge Proxy from forwarding back Added a sentence which prevents an Edge Proxy from forwarding back
skipping to change at page 36, line 6 skipping to change at page 36, line 49
Made the ABNF use the "=/" production extension mechanism recommended Made the ABNF use the "=/" production extension mechanism recommended
by Bill Fenner. by Bill Fenner.
Added a table in an appendix expanding the default flow recovery Added a table in an appendix expanding the default flow recovery
timers. timers.
Incorporated numerous clarifications and rewordings for better Incorporated numerous clarifications and rewordings for better
comprehension. comprehension.
Fixed many typos and spelling misteaks. Fixed many typos and spelling steaks.
15.4 Changes from 02 Version 16.5. 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.
15.5 Changes from 01 Version 16.6. Changes from 01 Version
Moved definition of instance-id from GRUU[I-D.ietf-sip-gruu] draft to Moved definition of instance-id from GRUU[25] draft to this draft.
this draft.
Added tentative text about Double CRLF Keepalive Added tentative text about Double CRLF Keepalive
Removed pin-route stuff Removed pin-route stuff
Changed the name of "flow-id" to "reg-id" Changed the name of "flow-id" to "reg-id"
Reorganized document flow Reorganized document flow
Described the use of STUN as a proper STUN usage Described the use of STUN as a proper STUN usage
Added 'outbound' option-tag to detect if registrar supports outbound Added 'outbound' option-tag to detect if registrar supports outbound
15.6 Changes from 00 Version 16.7. Changes from 00 Version
Moved TCP keepalive to be STUN. Moved TCP keepalive to be STUN.
Allowed SUBSCRIBE to create flow mappings. Added pin-route option Allowed SUBSCRIBE to create flow mappings. Added pin-route option
tags to support this. tags to support this.
Added text about updating dialog state on each usage after a Added text about updating dialog state on each usage after a
connection failure. connection failure.
16. Acknowledgments 17. Acknowledgments
Jonathan Rosenberg provided many comments and useful text. Dave Oran Jonathan Rosenberg provided many comments and useful text. Dave Oran
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
skipping to change at page 37, line 32 skipping to change at page 38, line 28
+-------------------+--------------------+--------------------+ +-------------------+--------------------+--------------------+
| 0 | 0 secs | 0 secs | | 0 | 0 secs | 0 secs |
| 1 | 30-60 secs | 90-180 secs | | 1 | 30-60 secs | 90-180 secs |
| 2 | 1-2 mins | 3-6 mins | | 2 | 1-2 mins | 3-6 mins |
| 3 | 2-4 mins | 6-12 mins | | 3 | 2-4 mins | 6-12 mins |
| 4 | 4-8 mins | 12-24 mins | | 4 | 4-8 mins | 12-24 mins |
| 5 | 8-16 mins | 15-30 mins | | 5 | 8-16 mins | 15-30 mins |
| 6 or more | 15-30 mins | 15-30 mins | | 6 or more | 15-30 mins | 15-30 mins |
+-------------------+--------------------+--------------------+ +-------------------+--------------------+--------------------+
17. References 18. References
17.1 Normative References
[I-D.ietf-behave-rfc3489bis] 18.1. Normative References
Rosenberg, J., "Simple Traversal Underneath Network
Address Translators (NAT) (STUN)",
draft-ietf-behave-rfc3489bis-05 (work in progress),
October 2006.
[I-D.ietf-rohc-sigcomp-impl-guide] [1] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Surtees, A., "Implementer's Guide for SigComp", Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
draft-ietf-rohc-sigcomp-impl-guide-08 (work in progress), Session Initiation Protocol", RFC 3261, June 2002.
October 2006.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Requirement Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997. [3] Willis, D. and B. Hoeneisen, "Session Initiation Protocol (SIP)
Extension Header Field for Registering Non-Adjacent Contacts",
RFC 3327, December 2002.
[RFC2396] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [4] Rosenberg, J., "Simple Traversal Underneath Network Address
Resource Identifiers (URI): Generic Syntax", RFC 2396, Translators (NAT) (STUN)", draft-ietf-behave-rfc3489bis-05
August 1998. (work in progress), October 2006.
[RFC2506] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag [5] Leach, P., Mealling, M., and R. Salz, "A Universally Unique
Registration Procedure", BCP 31, RFC 2506, March 1999. IDentifier (UUID) URN Namespace", RFC 4122, July 2005.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, [6] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Indicating
A., Peterson, J., Sparks, R., Handley, M., and E. User Agent Capabilities in the Session Initiation Protocol
Schooler, "SIP: Session Initiation Protocol", RFC 3261, (SIP)", RFC 3840, August 2004.
June 2002.
[RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation [7] Moats, R., "URN Syntax", RFC 2141, May 1997.
Protocol (SIP): Locating SIP Servers", RFC 3263,
June 2002.
[RFC3320] Price, R., Bormann, C., Christoffersson, J., Hannu, H., [8] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller
Liu, Z., and J. Rosenberg, "Signaling Compression Preferences for the Session Initiation Protocol (SIP)",
(SigComp)", RFC 3320, January 2003. RFC 3841, August 2004.
[RFC3327] Willis, D. and B. Hoeneisen, "Session Initiation Protocol [9] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol
(SIP) Extension Header Field for Registering Non-Adjacent (SIP): Locating SIP Servers", RFC 3263, June 2002.
Contacts", RFC 3327, December 2002.
[RFC3581] Rosenberg, J. and H. Schulzrinne, "An Extension to the [10] Rosenberg, J. and H. Schulzrinne, "An Extension to the Session
Session Initiation Protocol (SIP) for Symmetric Response Initiation Protocol (SIP) for Symmetric Response Routing",
Routing", RFC 3581, August 2003. RFC 3581, August 2003.
[RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, [11] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing
"Indicating User Agent Capabilities in the Session for Message Authentication", RFC 2104, February 1997.
Initiation Protocol (SIP)", RFC 3840, August 2004.
[RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller [12] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings",
Preferences for the Session Initiation Protocol (SIP)", RFC 3548, July 2003.
RFC 3841, August 2004.
[RFC3968] Camarillo, G., "The Internet Assigned Number Authority [13] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
(IANA) Header Field Parameter Registry for the Session Resource Identifiers (URI): Generic Syntax", RFC 2396,
Initiation Protocol (SIP)", BCP 98, RFC 3968, August 1998.
December 2004.
[RFC3969] Camarillo, G., "The Internet Assigned Number Authority [14] Crocker, D. and P. Overell, "Augmented BNF for Syntax
(IANA) Uniform Resource Identifier (URI) Parameter Specifications: ABNF", RFC 4234, October 2005.
Registry for the Session Initiation Protocol (SIP)",
BCP 99, RFC 3969, December 2004.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally [15] Camarillo, G., "The Internet Assigned Number Authority (IANA)
Unique IDentifier (UUID) URN Namespace", RFC 4122, Header Field Parameter Registry for the Session Initiation
July 2005. Protocol (SIP)", BCP 98, RFC 3968, December 2004.
[RFC4234] Crocker, D. and P. Overell, "Augmented BNF for Syntax [16] Camarillo, G., "The Internet Assigned Number Authority (IANA)
Specifications: ABNF", RFC 4234, October 2005. Uniform Resource Identifier (URI) Parameter Registry for the
Session Initiation Protocol (SIP)", BCP 99, RFC 3969,
December 2004.
17.2 Informative References [17] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag
Registration Procedure", BCP 31, RFC 2506, March 1999.
[I-D.ietf-sip-gruu] 18.2. Informative References
Rosenberg, J., "Obtaining and Using Globally Routable User
Agent (UA) URIs (GRUU) in the Session Initiation Protocol
(SIP)", draft-ietf-sip-gruu-11 (work in progress),
October 2006.
[I-D.ietf-sipping-config-framework] [18] Petrie, D., "A Framework for Session Initiation Protocol User
Petrie, D., "A Framework for Session Initiation Protocol Agent Profile Delivery", draft-ietf-sipping-config-framework-09
User Agent Profile Delivery", (work in progress), October 2006.
draft-ietf-sipping-config-framework-09 (work in progress),
October 2006.
[I-D.ietf-sipping-nat-scenarios] [19] Hakala, J., "Using National Bibliography Numbers as Uniform
Boulton, C., "Best Current Practices for NAT Traversal for Resource Names", RFC 3188, October 2001.
SIP", draft-ietf-sipping-nat-scenarios-05 (work in
progress), June 2006.
[I-D.rosenberg-sip-route-construct] [20] Rosenberg, J., "Construction of the Route Header Field in the
Rosenberg, J., "Construction of the Route Header Field in Session Initiation Protocol (SIP)",
the Session Initiation Protocol (SIP)",
draft-rosenberg-sip-route-construct-02 (work in progress), draft-rosenberg-sip-route-construct-02 (work in progress),
October 2006. October 2006.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- [21] Willis, D. and B. Hoeneisen, "Session Initiation Protocol (SIP)
Hashing for Message Authentication", RFC 2104, Extension Header Field for Service Route Discovery During
February 1997. Registration", RFC 3608, October 2003.
[RFC3188] Hakala, J., "Using National Bibliography Numbers as [22] Boulton, C., "Best Current Practices for NAT Traversal for
Uniform Resource Names", RFC 3188, October 2001. SIP", draft-ietf-sipping-nat-scenarios-05 (work in progress),
June 2006.
[RFC3548] Josefsson, S., "The Base16, Base32, and Base64 Data [23] Price, R., Bormann, C., Christoffersson, J., Hannu, H., Liu,
Encodings", RFC 3548, July 2003. Z., and J. Rosenberg, "Signaling Compression (SigComp)",
RFC 3320, January 2003.
[RFC3608] Willis, D. and B. Hoeneisen, "Session Initiation Protocol [24] Surtees, A., "Implementer's Guide for SigComp",
(SIP) Extension Header Field for Service Route Discovery draft-ietf-rohc-sigcomp-impl-guide-08 (work in progress),
During Registration", RFC 3608, October 2003. October 2006.
[25] Rosenberg, J., "Obtaining and Using Globally Routable User
Agent (UA) URIs (GRUU) in the Session Initiation Protocol
(SIP)", draft-ietf-sip-gruu-11 (work in progress),
October 2006.
Authors' Addresses Authors' Addresses
Cullen Jennings (editor) Cullen Jennings (editor)
Cisco Systems Cisco Systems
170 West Tasman Drive 170 West Tasman Drive
Mailstop SJC-21/2 Mailstop SJC-21/2
San Jose, CA 95134 San Jose, CA 95134
USA USA
skipping to change at page 40, line 16 skipping to change at page 41, line 4
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
Phone: +1 408 902-3341 Phone: +1 408 902-3341
Email: fluffy@cisco.com Email: fluffy@cisco.com
Rohan Mahy (editor) Rohan Mahy (editor)
Plantronics Plantronics
345 Encincal St 345 Encincal St
Santa Cruz, CA 95060 Santa Cruz, CA 95060
USA USA
Email: rohan@ekabal.com Email: rohan@ekabal.com
Intellectual Property Statement Full Copyright Statement
Copyright (C) The Internet Society (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
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on the procedures with respect to rights in RFC documents can be on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79. found in BCP 78 and BCP 79.
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such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
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Copyright (C) The Internet Society (2006). This document is subject
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Acknowledgment Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is provided by the IETF
Internet Society. Administrative Support Activity (IASA).
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