draft-ietf-sip-outbound-08.txt   draft-ietf-sip-outbound-09.txt 
Network Working Group C. Jennings, Ed. Network Working Group C. Jennings, Ed.
Internet-Draft Cisco Systems Internet-Draft Cisco Systems
Updates: 3261,3327 R. Mahy, Ed. Updates: 3261,3327 R. Mahy, Ed.
(if approved) Plantronics (if approved) Plantronics
Intended status: Standards Track March 4, 2007 Intended status: Standards Track June 25, 2007
Expires: September 5, 2007 Expires: December 27, 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-08 draft-ietf-sip-outbound-09
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
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
skipping to change at page 1, line 37 skipping to change at page 1, line 37
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on September 5, 2007. This Internet-Draft will expire on December 27, 2007.
Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2007).
Abstract Abstract
The Session Initiation Protocol (SIP) allows proxy servers to The Session Initiation Protocol (SIP) allows proxy servers to
initiate TCP connections and send asynchronous UDP datagrams to User initiate TCP connections and send asynchronous UDP datagrams to User
Agents in order to deliver requests. However, many practical Agents in order to deliver requests. However, many practical
skipping to change at page 2, line 22 skipping to change at page 2, line 22
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 4 2. Conventions and Terminology . . . . . . . . . . . . . . . . . 4
2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 5 2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 5
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Summary of Mechanism . . . . . . . . . . . . . . . . . . . 5 3.1. Summary of Mechanism . . . . . . . . . . . . . . . . . . . 5
3.2. Single Registrar and UA . . . . . . . . . . . . . . . . . 6 3.2. Single Registrar and UA . . . . . . . . . . . . . . . . . 6
3.3. Multiple Connections from a User Agent . . . . . . . . . . 7 3.3. Multiple Connections from a User Agent . . . . . . . . . . 7
3.4. Edge Proxies . . . . . . . . . . . . . . . . . . . . . . . 9 3.4. Edge Proxies . . . . . . . . . . . . . . . . . . . . . . . 9
3.5. Keepalive Technique . . . . . . . . . . . . . . . . . . . 11 3.5. Keepalive Technique . . . . . . . . . . . . . . . . . . . 11
3.5.1. CRLF Keepalive Technique . . . . . . . . . . . . . . . 11 3.5.1. CRLF Keepalive Technique . . . . . . . . . . . . . . . 11
3.5.2. TCP Keepalive Technique . . . . . . . . . . . . . . . 11 3.5.2. TCP Keepalive Technique . . . . . . . . . . . . . . . 12
3.5.3. STUN Keepalive Technique . . . . . . . . . . . . . . . 12 3.5.3. STUN Keepalive Technique . . . . . . . . . . . . . . . 12
4. User Agent Mechanisms . . . . . . . . . . . . . . . . . . . . 12 4. User Agent Mechanisms . . . . . . . . . . . . . . . . . . . . 13
4.1. Instance ID Creation . . . . . . . . . . . . . . . . . . . 12 4.1. Instance ID Creation . . . . . . . . . . . . . . . . . . . 13
4.2. Registrations . . . . . . . . . . . . . . . . . . . . . . 14 4.2. Registrations . . . . . . . . . . . . . . . . . . . . . . 14
4.2.1. Registration by Other Instances . . . . . . . . . . . 15 4.2.1. Registration by Other Instances . . . . . . . . . . . 16
4.3. Sending Requests . . . . . . . . . . . . . . . . . . . . . 16 4.3. Sending Requests . . . . . . . . . . . . . . . . . . . . . 16
4.4. Detecting Flow Failure . . . . . . . . . . . . . . . . . . 16 4.4. Detecting Flow Failure . . . . . . . . . . . . . . . . . . 17
4.4.1. Keepalive with TCP KEEPALIVE . . . . . . . . . . . . . 17 4.4.1. Keepalive with TCP KEEPALIVE . . . . . . . . . . . . . 18
4.4.2. Keepalive with CRLF . . . . . . . . . . . . . . . . . 17 4.4.2. Keepalive with CRLF . . . . . . . . . . . . . . . . . 18
4.4.3. Keepalive with STUN . . . . . . . . . . . . . . . . . 18 4.4.3. Keepalive with STUN . . . . . . . . . . . . . . . . . 18
4.5. Flow Recovery . . . . . . . . . . . . . . . . . . . . . . 18 4.5. Flow Recovery . . . . . . . . . . . . . . . . . . . . . . 19
5. Edge Proxy Mechanisms . . . . . . . . . . . . . . . . . . . . 19 5. Edge Proxy Mechanisms . . . . . . . . . . . . . . . . . . . . 20
5.1. Processing Register Requests . . . . . . . . . . . . . . . 19 5.1. Processing Register Requests . . . . . . . . . . . . . . . 20
5.2. Generating Flow Tokens . . . . . . . . . . . . . . . . . . 20 5.2. Generating Flow Tokens . . . . . . . . . . . . . . . . . . 20
5.3. Forwarding Requests . . . . . . . . . . . . . . . . . . . 21 5.3. Forwarding Requests . . . . . . . . . . . . . . . . . . . 21
5.4. Edge Proxy Keepalive Handling . . . . . . . . . . . . . . 22 5.4. Edge Proxy Keepalive Handling . . . . . . . . . . . . . . 22
6. Registrar Mechanisms: Processing REGISTER Requests . . . . . . 22 6. Registrar Mechanisms: Processing REGISTER Requests . . . . . . 22
7. Authoritative Proxy Mechanisms: Forwarding Requests . . . . . 24 7. Authoritative Proxy Mechanisms: Forwarding Requests . . . . . 24
8. STUN Keepalive Processing . . . . . . . . . . . . . . . . . . 24 8. STUN Keepalive Processing . . . . . . . . . . . . . . . . . . 24
8.1. Explicit Option Probes . . . . . . . . . . . . . . . . . . 27 8.1. Use with Sigcomp . . . . . . . . . . . . . . . . . . . . . 26
8.2. Use with Sigcomp . . . . . . . . . . . . . . . . . . . . . 27 9. Example Message Flow . . . . . . . . . . . . . . . . . . . . . 26
9. Example Message Flow . . . . . . . . . . . . . . . . . . . . . 27 10. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
10. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 11. Definition of 430 Flow Failed response code . . . . . . . . . 30
11. Definition of 430 Flow Failed response code . . . . . . . . . 31 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31 12.1. Contact Header Field . . . . . . . . . . . . . . . . . . . 30
12.1. Contact Header Field . . . . . . . . . . . . . . . . . . . 31 12.2. SIP/SIPS URI Parameters . . . . . . . . . . . . . . . . . 31
12.2. SIP/SIPS URI Parameters . . . . . . . . . . . . . . . . . 32 12.3. SIP Option Tag . . . . . . . . . . . . . . . . . . . . . . 31
12.3. SIP Option Tag . . . . . . . . . . . . . . . . . . . . . . 32 12.4. Response Code . . . . . . . . . . . . . . . . . . . . . . 31
12.4. Response Code . . . . . . . . . . . . . . . . . . . . . . 32 12.5. Media Feature Tag . . . . . . . . . . . . . . . . . . . . 31
12.5. Media Feature Tag . . . . . . . . . . . . . . . . . . . . 32 13. Security Considerations . . . . . . . . . . . . . . . . . . . 32
13. Security Considerations . . . . . . . . . . . . . . . . . . . 33 14. Operational Notes on Transports . . . . . . . . . . . . . . . 33
14. Operational Notes on Transports . . . . . . . . . . . . . . . 34 15. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 34
15. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 35 16. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
16. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 35 16.1. Changes from 08 Version . . . . . . . . . . . . . . . . . 34
17. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 16.2. Changes from 07 Version . . . . . . . . . . . . . . . . . 34
17.1. Changes from 07 Version . . . . . . . . . . . . . . . . . 35 16.3. Changes from 06 Version . . . . . . . . . . . . . . . . . 35
17.2. Changes from 06 Version . . . . . . . . . . . . . . . . . 35 16.4. Changes from 05 Version . . . . . . . . . . . . . . . . . 35
17.3. Changes from 05 Version . . . . . . . . . . . . . . . . . 36 16.5. Changes from 04 Version . . . . . . . . . . . . . . . . . 35
17.4. Changes from 04 Version . . . . . . . . . . . . . . . . . 36 16.6. Changes from 03 Version . . . . . . . . . . . . . . . . . 36
17.5. Changes from 03 Version . . . . . . . . . . . . . . . . . 37 16.7. Changes from 02 Version . . . . . . . . . . . . . . . . . 37
17.6. Changes from 02 Version . . . . . . . . . . . . . . . . . 38 16.8. Changes from 01 Version . . . . . . . . . . . . . . . . . 37
17.7. Changes from 01 Version . . . . . . . . . . . . . . . . . 38 16.9. Changes from 00 Version . . . . . . . . . . . . . . . . . 38
17.8. Changes from 00 Version . . . . . . . . . . . . . . . . . 38 17. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 38
18. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 39 Appendix A. Default Flow Registration Backoff Times . . . . . . . 38
Appendix A. Default Flow Registration Backoff Times . . . . . . . 39 18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 39
19. References . . . . . . . . . . . . . . . . . . . . . . . . . . 40 18.1. Normative References . . . . . . . . . . . . . . . . . . . 39
19.1. Normative References . . . . . . . . . . . . . . . . . . . 40 18.2. Informative References . . . . . . . . . . . . . . . . . . 40
19.2. Informative References . . . . . . . . . . . . . . . . . . 41
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 41 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 41
Intellectual Property and Copyright Statements . . . . . . . . . . 43 Intellectual Property and Copyright Statements . . . . . . . . . . 42
1. Introduction 1. Introduction
There are many environments for SIP [1] deployments in which the User There are many environments for SIP [1] deployments in which the User
Agent (UA) can form a connection to a Registrar or Proxy but in which Agent (UA) can form a connection to a Registrar or Proxy but in which
connections in the reverse direction to the UA are not possible. connections in the reverse direction to the UA are not possible.
This can happen for several reasons. Connections to the UA can be This can happen for several reasons. Connections to the UA can be
blocked by a firewall device between the UA and the proxy or blocked by a firewall device between the UA and the proxy or
registrar, which will only allow new connections in the direction of registrar, which will only allow new connections in the direction of
the UA to the Proxy. Similarly a NAT could be present, which is only the UA to the Proxy. Similarly a NAT could be present, which is only
skipping to change at page 6, line 17 skipping to change at page 6, line 17
failure. failure.
When a proxy goes to route a message to a UA for which it has a When a proxy goes to route a message to a UA for which it has a
binding, it can use any one of the flows on which a successful binding, it can use any one of the flows on which a successful
registration has been completed. A failure on a particular flow can registration has been completed. A failure on a particular flow can
be tried again on an alternate flow. Proxies can determine which be tried again on an alternate flow. Proxies can determine which
flows go to the same UA by comparing the instance-id. Proxies can flows go to the same UA by comparing the instance-id. Proxies can
tell that a flow replaces a previously abandoned flow by looking at tell that a flow replaces a previously abandoned flow by looking at
the reg-id. the reg-id.
UAs use a simple periodic message as a keepalive mechanism to keep UAs can use a simple periodic message as a keepalive mechanism to
their flow to the proxy or registrar alive. For connection oriented keep their flow to the proxy or registrar alive. For connection
transports such as TCP this is based on CRLF or a transport specific oriented transports such as TCP this is based on CRLF or a transport
keepalive while for transports that are not connection oriented this specific keepalive while for transports that are not connection
is accomplished by using a SIP specific usage of STUN. oriented this is accomplished by using the keepalive usage profile of
STUN (Session Traversal Utilities for NAT) [3].
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 |
+-----+-----+ +-----+-----+
skipping to change at page 7, line 5 skipping to change at page 7, line 5
User Agents which form only a single flow continue to register User Agents which form only a single flow continue to register
normally but include the instance-id as described in Section 4.1. normally but include the instance-id as described in Section 4.1.
The UA can also include a reg-id parameter which is used to allow the The UA can also include a reg-id parameter which is used to allow the
registrar to detect and avoid keeping invalid contacts when a UA registrar to detect and avoid keeping invalid contacts when a UA
reboots or reconnects after its old connection has failed for some reboots or reconnects after its old connection has failed for some
reason. reason.
For clarity, here is an example. Bob's UA creates a new TCP flow to For clarity, here is an example. Bob's UA creates a new TCP flow to
the registrar and sends the following REGISTER request. the registrar and sends the following REGISTER request.
REGISTER sip:example.com SIP/2.0 REGISTER sip:example.com;keep-crlf SIP/2.0
Via: SIP/2.0/TCP 192.0.2.1;branch=z9hG4bK-bad0ce-11-1036 Via: SIP/2.0/TCP 192.0.2.1;branch=z9hG4bK-bad0ce-11-1036
Max-Forwards: 70 Max-Forwards: 70
From: Bob <sip:bob@example.com>;tag=d879h76 From: Bob <sip:bob@example.com>;tag=d879h76
To: Bob <sip:bob@example.com> To: Bob <sip:bob@example.com>
Call-ID: 8921348ju72je840.204 Call-ID: 8921348ju72je840.204
CSeq: 1 REGISTER CSeq: 1 REGISTER
Supported: path Supported: path
Contact: <sip:line1@192.168.0.2>; reg-id=1; Contact: <sip:line1@192.168.0.2>; reg-id=1;
;+sip.instance="<urn:uuid:00000000-0000-0000-0000-000A95A0E128>" ;+sip.instance="<urn:uuid:00000000-0000-1000-8000-000A95A0E128>"
Content-Length: 0 Content-Length: 0
The registrar challenges this registration to authenticate Bob. When The registrar challenges this registration to authenticate Bob. When
the registrar adds an entry for this contact under the AOR for Bob, the registrar adds an entry for this contact under the AOR for Bob,
the registrar also keeps track of the connection over which it the registrar also keeps track of the connection over which it
received this registration. received this registration.
The registrar saves the instance-id The registrar saves the instance-id
("urn:uuid:00000000-0000-0000-0000-000A95A0E128") and reg-id ("1") ("urn:uuid:00000000-0000-1000-8000-000A95A0E128") and reg-id ("1")
along with the rest of the Contact header field. If the instance-id along with the rest of the Contact header field. If the instance-id
and reg-id are the same as a previous registration for the same AOR, and reg-id are the same as a previous registration for the same AOR,
the registrar replaces the old Contact URI and flow information. the registrar replaces the old Contact URI and flow information.
This allows a UA that has rebooted to replace its previous This allows a UA that has rebooted to replace its previous
registration for each flow with minimal impact on overall system registration for each flow with minimal impact on overall system
load. load.
When Alice sends a request to Bob, his authoritative proxy selects When Alice sends a request to Bob, his authoritative proxy selects
the target set. The proxy forwards the request to elements in the the target set. The proxy forwards the request to elements in the
target set based on the proxy's policy. The proxy looks at the target set based on the proxy's policy. The proxy looks at the
target set and uses the instance-id to understand if two targets both target set and uses the instance-id to understand if two targets both
end up routing to the same UA. When the proxy goes to forward a end up routing to the same UA. When the proxy goes to forward a
request to a given target, it looks and finds the flows over which it request to a given target, it looks and finds the flows over which it
received the registration. The proxy then forwards the request on received the registration. The proxy then forwards the request on
that flow instead of trying to form a new flow to that contact. This that flow, instead of resolving the Contact URI using the procedures
in RFC 3263 [4] and 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 the registration bindings for this AOR that has the same instance-id
the selected UA. as the selected UA.
3.3. Multiple Connections from a User Agent 3.3. Multiple Connections from a User Agent
There are various ways to deploy SIP to build a reliable and scalable There are various ways to deploy SIP to build a reliable and scalable
system. This section discusses one such design that is possible with system. This section discusses one such design that is possible with
the mechanisms in this specification. Other designs are also the mechanisms in this specification. Other designs are also
possible. possible.
In the example system below, the logical outbound proxy/registrar for In the example system below, the logical outbound proxy/registrar for
the domain is running on two hosts that share the appropriate state the domain is running on two hosts that share the appropriate state
skipping to change at page 8, line 18 skipping to change at page 8, line 20
domain. Reliability is achieved by having the UA form two TCP domain. Reliability is achieved by having the UA form two TCP
connections to the domain. connections to the domain.
Scalability is achieved by using DNS SRV to load balance the primary Scalability is achieved by using DNS SRV to load balance the primary
connection across a set of machines that can service the primary connection across a set of machines that can service the primary
connection, and also using DNS SRV to load balance across a separate connection, and also using DNS SRV to load balance across a separate
set of machines that can service the secondary connection. The set of machines that can service the secondary connection. The
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 additional 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 [18], from adding other ways as the SIP UA configuration framework [19], from adding other ways
for a User Agent to discover its outbound-proxy-set. for a User Agent to discover its outbound-proxy-set.
+-------------------+ +-------------------+
| Domain | | Domain |
| Logical Proxy/Reg | | Logical Proxy/Reg |
| | | |
|+-----+ +-----+| |+-----+ +-----+|
||Host1| |Host2|| ||Host1| |Host2||
|+-----+ +-----+| |+-----+ +-----+|
+---\------------/--+ +---\------------/--+
skipping to change at page 9, line 42 skipping to change at page 9, line 43
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 [3] so that when Registrar. The Edge Proxy includes a Path header [5] so that when
the registrar later forwards a request to this UA, the request is the registrar later forwards a request to this UA, the request 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 |
+---------+ +---------+
/ \ / \
/ \ / \
skipping to change at page 10, line 48 skipping to change at page 10, line 48
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 [3]. Path header mechanism in RFC 3327 [5].
3.5. Keepalive Technique 3.5. Keepalive Technique
This document describes three keepalive mechanisms. Each of these This document describes three keepalive mechanisms. Each of these
mechanisms uses a client-to-server "ping" keepalive and a mechanisms uses a client-to-server "ping" keepalive and a
corresponding server-to-client "pong" message. This ping-pong corresponding server-to-client "pong" message. This ping-pong
sequence allows the client, and optionally the server, to tell if its sequence allows the client, and optionally the server, to tell if its
flow is still active and useful for SIP traffic. The server responds flow is still active and useful for SIP traffic. The server responds
to pings by sending pongs. If the client does not receive a pong in to pings by sending pongs. If the client does not receive a pong in
response to its ping, it declares the flow dead and opens a new flow response to its ping, it declares the flow dead and opens a new flow
in its place. In some environments, the server can also keep track in its place.
of the time since a ping was received over a flow to guess the
likelihood that the flow is still useful for delivering SIP messages. This document also suggests timer values for two of these client
keepalive mechanisms. These timer values were chosen to keep most
NAT and firewall bindings open, to detect unresponsive servers within
2 minutes, and to prevent the avalanche restart problem. However,
the client may choose different timer values to suit its needs, for
example to optimize battery life. In some environments, the server
can also keep track of the time since a ping was received over a flow
to guess the likelihood that the flow is still useful for delivering
SIP messages. In this case, the server provides an indicator (the
'timed-keepalives' parameter) that the server requires the client to
use the suggested timer values.
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.
A keepalive mechanism needs to keep NAT bindings refreshed; for A keepalive mechanism needs to keep NAT bindings refreshed; for
connections, it also needs to detect failure of a connection; and for connections, it also needs to detect failure of a connection; and for
connectionless transports, it needs to detect flow failures including connectionless transports, it needs to detect flow failures including
changes to the NAT public mapping. For connection oriented changes to the NAT public mapping. For connection oriented
transports such as TCP and SCTP, this specification describes a transports such as TCP and SCTP, this specification describes a
keepalive approach based on sending CRLFs, and for TCP, a usage of keepalive approach based on sending CRLFs, and for TCP, a usage of
TCP transport-layer keepalives. For connectionless, such as UDP or TCP transport-layer keepalives. For connectionless transport, such
DCCP, this specification describes using STUN [4] over the same flow as UDP, this specification describes using STUN [3] over the same
as the SIP traffic to perform the keepalive. flow as the SIP traffic to perform the keepalive.
3.5.1. CRLF Keepalive Technique 3.5.1. CRLF Keepalive Technique
This approach can only be used with connection-oriented transports This approach can only be used with connection-oriented transports
such as TCP or SCTP. The client periodically sends a double-CRLF such as TCP or SCTP. The client periodically sends a double-CRLF
(the "ping") then waits to receive a single CRLF (the "pong"). If (the "ping") then waits to receive a single CRLF (the "pong"). If
the server does not receive a "pong" within an appropriate amount of the client does not receive a "pong" within an appropriate amount of
time, it considers the flow failed. time, it considers the flow failed.
3.5.2. TCP Keepalive Technique 3.5.2. TCP Keepalive Technique
This approach can only be used when the transport protocol is TCP. This approach can only be used when the transport protocol is TCP.
User Agents that are capable of generating per-connection TCP User Agents that are capable of generating per-connection TCP
keepalives can use TCP keepalives. When using this approach the keepalives can use TCP keepalives. When using this approach the
values of the keepalive timer are left to the client. Servers cannot values of the keepalive timer are left to the client. Servers cannot
make any assumption about what values are used. If this is not make any assumption about what values are used.
acceptable in the deployment, then the outbound-proxy-set needs to be
configured without this option.
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.
3.5.3. STUN Keepalive Technique 3.5.3. STUN Keepalive Technique
This technique can only be used for transports that are not This technique can only be used for transports, such as UDP, that are
connection oriented such as UDP and DCCP. not connection oriented.
For connection-less transports, a flow definition could change For connection-less transports, a flow definition could change
because a NAT device in the network path reboots and the resulting because a NAT device in the network path reboots and the resulting
public IP address or port mapping for the UA changes. To detect public IP address or port mapping for the UA changes. To detect
this, STUN requests are sent over the same flow that is being used this, STUN requests are sent over the same flow that is being used
for the SIP traffic. The proxy or registrar acts as a Simple for the SIP traffic. The proxy or registrar acts as a Session
Traversal Underneath NATs (STUN) [4] server on the SIP signaling Traversal Utilities for NAT (STUN) [3] server on the SIP signaling
port. port.
Note: The STUN mechanism is very robust and allows the detection Note: The STUN mechanism is very robust and allows the detection
of a changed IP address. Many other options were considered, but of a changed IP address. Many other options were considered, but
the SIP Working Group selected the STUN-based approach. the SIP Working Group selected the STUN-based approach.
Approaches using SIP requests were abandoned because to achieve Approaches using SIP requests were abandoned because to achieve
the required performance, the server needs to deviate from the SIP the required performance, the server needs to deviate from the SIP
specification in significant ways. This would result in many specification in significant ways. This would result in many
undesirable and non-deterministic behaviors in some environments. undesirable and non-deterministic behaviors in some environments.
Another approach considered to detect a changed flow was using Another approach considered to detect a changed flow was using
skipping to change at page 13, line 8 skipping to change at page 13, line 16
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 [5] as its instance-id unless it is an A UA SHOULD create a UUID URN [6] as its instance-id. The UUID URN
anonymous call and there are privacy reason not to include the allows for non-centralized computation of a URN based on time, unique
instance-id in this particular message.. The UUID URN allows for names (such as a MAC address), or a random number generator.
non-centralized computation of a URN based on time, unique 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 [5] and then save this in persistent storage for all future UUID [6] and then save this in persistent storage for all future
use. For a device such as a hard phone, which will only ever have use. For a device such as a hard phone, which will only ever have
a single SIP UA present, the UUID can include the MAC address and a single SIP UA present, the UUID can include the MAC address and
be generated at any time because it is guaranteed that no other be generated at any time because it is guaranteed that no other
UUID is being generated at the same time on that physical device. UUID is being generated at the same time on that physical device.
This means the value of the time component of the UUID can be This means the value of the time component of the UUID can be
arbitrarily selected to be any time less than the time when the arbitrarily selected to be any time less than the time when the
device was manufactured. A time of 0 (as shown in the example in device was manufactured. A time of 0 (as shown in the example in
Section 3.2) is perfectly legal as long as the device knows no Section 3.2) is perfectly legal as long as the device knows no
other UUIDs were generated at this time. other UUIDs were generated at this time.
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 [19]. Since there specification is the national bibliographic number [20]. Since there
is no clear relationship between a SIP UA instance and a URN in this is no clear relationship between a SIP UA instance and a URN in this
namespace, there is no way a selection of a value can be performed namespace, there is no way a selection of a value can be performed
that guarantees that another UA instance doesn't choose the same that guarantees that another UA instance doesn't choose the same
value. value.
The UA SHOULD include a "sip.instance" media feature tag as a UA To convey its instance-id in both requests and responses, the UA
characteristic [6] in requests and responses. As described in [6], includes a "sip.instance" media feature tag as a UA characteristic
this media feature tag will be encoded in the Contact header field as [7] . As described in [7], this media feature tag will be encoded in
the "+sip.instance" Contact header field parameter. The value of the Contact header field as the "+sip.instance" Contact header field
this parameter MUST be a URN [7]. One case where a UA may not want parameter. The value of this parameter MUST be a URN [8]. One case
to include the URN in the sip.instance media feature tag is when it where a UA may not want to include the URN in the sip.instance media
is making an anonymous request or some other privacy concern requires feature tag is when it is making an anonymous request or some other
that the UA not reveal its identity. privacy concern requires that the UA not reveal its identity.
RFC 3840 [6] defines equality rules for callee capabilities RFC 3840 [7] defines equality rules for callee capabilities
parameters, and according to that specification, the parameters, and according to that specification, the
"sip.instance" media feature tag will be compared by case- "sip.instance" media feature tag will be compared by case-
sensitive string comparison. This means that the URN will be sensitive string comparison. This means that the URN will be
encapsulated by angle brackets ("<" and ">") when it is placed encapsulated by angle brackets ("<" and ">") when it is placed
within the quoted string value of the +sip.instance Contact header within the quoted string value of the +sip.instance Contact header
field parameter. The case-sensitive matching rules apply only to field parameter. The case-sensitive matching rules apply only to
the generic usages defined in RFC 3840 [6] and in the caller the generic usages defined in RFC 3840 [7] and in the caller
preferences specification [8]. When the instance ID is used in preferences specification [9]. When the instance ID is used in
this specification, it is effectively "extracted" from the value this specification, it is effectively "extracted" from the value
in the "sip.instance" media feature tag. Thus, equality in the "sip.instance" media feature tag. Thus, equality
comparisons are performed using the rules for URN equality that comparisons are performed using the rules for URN equality that
are specific to the scheme in the URN. If the element performing are specific to the scheme in the URN. If the element performing
the comparisons does not understand the URN scheme, it performs the comparisons does not understand the URN scheme, it performs
the comparisons using the lexical equality rules defined in RFC the comparisons using the lexical equality rules defined in RFC
2141 [7]. Lexical equality could result in two URNs being 2141 [8]. Lexical equality could result in two URNs being
considered unequal when they are actually equal. In this specific considered unequal when they are actually equal. In this specific
usage of URNs, the only element which provides the URN is the SIP usage of URNs, the only element which provides the URN is the SIP
UA instance identified by that URN. As a result, the UA instance UA instance identified by that URN. As a result, the UA instance
SHOULD provide lexically equivalent URNs in each registration it 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 lexicographically that it remains functionally equivalent yet lexicographically
different from previous registrations. different from previous registrations.
4.2. Registrations 4.2. Registrations
skipping to change at page 14, line 37 skipping to change at page 14, line 45
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 [20]. construction are discussed in [21].
Registration requests, other than those described in Section 4.2.1, Registration requests, other than those described in Section 4.2.1,
MUST include an instance-id media feature tag as specified in MUST include an instance-id media feature tag as specified in
Section 4.1. Section 4.1.
These ordinary registration requests include a distinct reg-id These ordinary registration requests include a distinct reg-id
parameter to the Contact header field. Each one of these parameter in the Contact header field. Each one of these
registrations will form a new flow from the UA to the proxy. The registrations will form a new flow from the UA to the proxy. The
sequence of reg-id values does not have to be sequential but MUST be sequence of reg-id values does not have to be sequential but MUST be
exactly the same sequence of reg-id values each time the UA instance exactly the same sequence of reg-id values each time the UA instance
power cycles or reboots so that the reg-id values will collide with power cycles or reboots so that the reg-id values will collide with
the previously used reg-id values. This is so the registrar can the previously used reg-id values. This is so the registrar can
replace the older registration. replace the older registration.
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 Require header field when registering with EP2,
to insure consistency. Similarly, if the registration through EP1 in order to insure consistency. Similarly, if the registration
did not support outbound, the UA might decide to omit the 'reg-id' through EP1 did not support outbound, the UA might decide to omit
parameter when registering with EP2. the 'reg-id' parameter when registering with EP2.
The UAC MUST indicate that it supports the Path header [3] mechanism, The UAC MUST indicate that it supports the Path header [5] mechanism,
by including the 'path' option-tag in a Supported header field value by including the 'path' option-tag in a Supported header field value
in its REGISTER requests. Other than optionally examining the Path in its REGISTER requests. Other than optionally examining the Path
vector in the response, this is all that is required of the UAC to vector in the response, this is all that is required of the UAC to
support Path. support Path.
The UAC MAY examine successful registrations for the presence of an The UAC MAY examine successful 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 participate specification, and that any edge proxies which need to participate
are 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 [9]. In to registrations as described in RFC 3261 and RFC 3263 [4]. In
particular, implementors should note that when receiving a 503 particular, implementors should note that when receiving a 503
(Service Unavailable) response with a Retry-After header field, the (Service Unavailable) response with a Retry-After header field, the
UA is expected to wait the indicated amount of time and retry the UA is expected to wait the indicated amount of time and retry the
registration. A Retry-After header field value of 0 is valid and registration. A Retry-After header field value of 0 is valid and
indicates the UA is expected to retry the REGISTER immediately. indicates the UA is expected to retry the REGISTER immediately.
Implementations need to ensure that when retrying the REGISTER, they Implementations need to ensure that when retrying the REGISTER, they
revisit the DNS resolution results such that the UA can select an revisit the DNS resolution results such that the UA can select an
alternate host from the one chosen the previous time the URI was alternate host from the one chosen the previous time the URI was
resolved. resolved.
skipping to change at page 16, line 12 skipping to change at page 16, line 23
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 [21] (Service but could include mechanisms specified in RFC 3608 [22] (Service
Route) and [20]. Route) and [21].
The UA performs normal DNS resolution on the next hop URI (as The UA performs normal DNS resolution on the next hop URI (as
described in RFC 3263 [9]) to find a protocol, IP address, and port. described in RFC 3263 [4]) to find a protocol, IP address, and port.
For protocols that don't use TLS, if the UA has an existing flow to For protocols that don't use TLS, if the UA has an existing flow to
this IP address, and port with the correct protocol, then the UA MUST this IP address, and port with the correct protocol, then the UA MUST
use the existing connection. For TLS protocols, there MUST also be a use the existing connection. For TLS protocols, there MUST also be a
match between the host production in the next hop and one of the URIs match between the host production in the next hop and one of the URIs
contained in the subjectAltName in the peer certificate. If the UA contained in the subjectAltName in the peer certificate. If the UA
cannot use one of the existing flows, then it SHOULD form a new flow cannot use one of the existing flows, then it SHOULD form a new flow
by sending a datagram or opening a new connection to the next hop, as by sending a datagram or opening a new connection to the next hop, as
appropriate for the transport protocol. appropriate for the transport protocol.
The contact is formed normally in that uses the IP address of the The contact is formed normally in that the UAC uses the IP address of
device (even if the device is behind a NAT) and unless there are the device (even if the device is behind a NAT). Unless there are
privacy reason not to include an instance-id, the contact SHOULD privacy reason not to include an instance-id, the contact SHOULD
include the instance-id media feature tag as specified in include the instance-id media feature tag as specified in
Section 4.1. Section 4.1. The UAC MUST also include an "ob" parameter in the
Contact URI if, and only if, the UAC is sending the request over a
flow for which the Registrar applied outbound processing.
Note that if the UA wants its flow to work through NATs or Note that if the UA wants its flow to work through NATs or
firewalls it still needs to put the 'rport' parameter [10] in its firewalls it still needs to put the 'rport' parameter [10] in its
Via header field value, and send from the port it is prepared to Via header field value, and send from the port it is prepared to
receive on. More general information about NAT traversal in SIP receive on. More general information about NAT traversal in SIP
is described in [22]. is described in [23].
4.4. Detecting Flow Failure 4.4. Detecting Flow Failure
The UA needs to detect when a specific flow fails. The UA actively The UA needs to detect when a specific flow fails. The UA actively
tries to detect failure by periodically sending keepalive messages tries to detect failure by periodically sending keepalive messages
using one of the techniques described in Section 4.4.1, using one of the techniques described in Section 4.4.1,
Section 4.4.2, or Section 4.4.3. If a flow has failed, the UA Section 4.4.2, or Section 4.4.3. If a flow has failed, the UA
follows the procedures in Section 4.2 to form a new flow to replace follows the procedures in Section 4.2 to form a new flow to replace
the failed one. the failed one.
The time between each keepalive requests when using non connection When the outbound-proxy-set contains the "timed-keepalives"
parameter, the UA MUST send its keepalives according to the time
periods described in this section. The server can specify this so
the server can detect liveness of the client within a predictable
time scale. If the parameter is not present, the UA can send
keepalives at its discretion.
The time between each keepalive request when using non connection
based transports such as UDP SHOULD be a random number between 24 and based transports such as UDP SHOULD be a random number between 24 and
29 seconds while for connection based transports such as TCP it 29 seconds while for connection based transports such as TCP it
SHOULD be a random number between 95 and 120 seconds. These times SHOULD be a random number between 95 and 120 seconds. These times
MAY be configurable. To clarify, the random number will be different MAY be configurable. To clarify, the random number will be different
for each request. Issues such as battery consumption might motivate for each request. Issues such as battery consumption might motivate
longer keepalive intervals. longer keepalive intervals. If the 'timed-keepalives' parameter is
set on the outbound-proxy-set, the UA MUST use these recommended
timer values.
Note on selection of time values: For UDP, the upper bound of 29 Note on selection of time values: For UDP, the upper bound of 29
seconds was selected so that multiple STUN packets could be sent seconds was selected so that multiple STUN packets could be sent
before 30 seconds based on information that many NATs have UDP before 30 seconds based on information that many NATs have UDP
timeouts as low as 30 seconds. The 24 second lower bound was timeouts as low as 30 seconds. The 24 second lower bound was
selected so that after 10 minutes the jitter introduced by selected so that after 10 minutes the jitter introduced by
different timers will make the keepalive requests unsynchronized different timers will make the keepalive requests unsynchronized
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.
The client needs to perform normal RFC 3263 [9] SIP DNS resolution on The client needs to perform normal RFC 3263 [4] SIP DNS resolution on
the URI from the outbound-proxy-set to pick a transport. Once a the URI from the outbound-proxy-set to pick a transport. Once a
transport is selected, the UA selects a keepalive approach that is transport is selected, the UA selects a keepalive approach that is
allowed for that transport and that is allowed by the server based on allowed for that transport and that is allowed by the server based on
the tags in the URI from the outbound-proxy-set. If the transport is the tags in the URI from the outbound-proxy-set.
TCP and the URI contains both the 'keep-tcp' tag and the 'keep-crlf'
tag, then the client MAY choose either of these approaches based on
the preference of the client.
4.4.1. Keepalive with TCP KEEPALIVE 4.4.1. Keepalive with TCP KEEPALIVE
This approach MUST only be used with TCP. This approach MUST only be used with TCP.
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 'keep-tcp' URI parameter (defined in Section 12). connecting to has a 'timed-keepalives' URI parameter (defined in
If the parameter is present and the UA is not already performing Section 12). If the parameter is not present and the UA is not
keepalives using another supported mechanism, the UA needs to already performing keepalives using another supported mechanism, the
periodically perform keepalive checks by using the TCP Keepalive UA needs to periodically perform keepalive checks by using the TCP
mechanism. Not all environments can use this approach and it is not Keepalive mechanism. Not all environments can use this approach and
mandatory to implement. Deployments that use it should also include it is not mandatory to implement. Deployments that use it should
keep-crlf so that clients that do not implement this option but are also include keep-crlf so that clients that do not implement this
using TCP have an alternative approach to use. option but are using TCP have an alternative approach to use.
4.4.2. Keepalive with CRLF 4.4.2. Keepalive with CRLF
This approach MUST only be used with connection oriented transports This approach MUST only be used with connection oriented transports
such as TCP or SCTP. such as TCP or SCTP.
User Agents that form flows check if the configured URI they are User Agents that form flows check if the configured URI they are
connecting to has a 'keep-crlf' URI parameter (defined in connecting to has a 'keep-crlf' URI parameter (defined in
Section 12). If the parameter is present and the UA is not already Section 12). If the parameter is present and the UA is not already
performing keepalives using another supported mechanism, the UA MUST performing keepalives using another supported mechanism, the UA can
send keep alives as described in this section. send keep alives as described in this section.
For this mechanism, the client "ping" is a double-CRLF sequence, and For this mechanism, the client "ping" is a double-CRLF sequence, and
the server "pong" is a single CRLF, as defined in the ABNF below: the server "pong" is a single CRLF, as defined in the ABNF below:
CRLF = CR LF CRLF = CR LF
double-CRLF = CR LF CR LF double-CRLF = CR LF CR LF
CR = 0x0d CR = 0x0d
LF = 0x0a LF = 0x0a
The ping and pong need to be sent between SIP messages and cannot be The ping and pong need to be sent between SIP messages and cannot be
sent in the middle of a SIP message. If a pong is not received sent in the middle of a SIP message. If sending over a TLS protected
within 10 seconds (TODO - is 10 seconds the right amount of time) channel, the CRLFs are sent inside the TLS record layer. If a pong
then the client MUST treat the flow as failed. Clients MUST support is not received within 10 seconds then the client MUST treat the flow
this CRLF keepalive. as failed. Clients MUST support this CRLF keepalive.
4.4.3. Keepalive with STUN 4.4.3. Keepalive with STUN
This approach MUST only be used with transports that are not This approach MUST only be used with transports, such as UDP, that
connection oriented such as UDP or DCCP. are not connection oriented.
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 'keep-stun' URI parameter (defined in connecting to has a 'keep-stun' URI parameter (defined in
Section 12). If the parameter is present and the UA is not already Section 12). If the parameter is present and the UA is not already
performing keepalives using another supported mechanism, the UA MUST performing keepalives using another supported mechanism, the UA can
periodically perform keepalive checks by sending STUN [4] Binding periodically perform keepalive checks by sending STUN [3] Binding
Requests over the flow as described in Section 8. Clients MUST Requests over the flow as described in Section 8. Clients MUST
support STUN based keepalive. support STUN based keepalives.
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.
4.5. Flow Recovery 4.5. Flow Recovery
When a flow to a particular URI in the outbound-proxy-set fails, the When a flow to a particular URI in the outbound-proxy-set fails, the
UA needs to form a new flow to replace the old flow and replace any UA needs to form a new flow to replace the old flow and replace any
registrations that were previously sent over this flow. Each new registrations that were previously sent over this flow. Each new
registration MUST have the same reg-id as the registration it registration MUST have the same reg-id as the registration it
replaces. This is done in much the same way as forming a brand new replaces. This is done in much the same way as forming a brand new
flow as described in Section 4.2; however, if there is a failure in flow as described in Section 4.2; however, if there is a failure in
forming this flow, the UA needs to wait a certain amount of time forming this flow, the UA needs to wait a certain amount of time
before retrying to form a flow to this particular next hop. before retrying to form a flow to this particular next hop.
The amount of time to wait depends if the previous attempt at The amount of time to wait depends if the previous attempt at
establishing a flow was successful. For the purposes of this establishing a flow was successful. For the purposes of this
section, a flow is considered successful if outbound registration section, a flow is considered successful if outbound registration
succeeded and keepalives have not timed out for 120 seconds after a succeeded, and if keepalives are in use on this flow, at least one
registration. For STUN-based keepalives, this typically means three consecutive keepalive response was received.
successful STUN transactions over UDP or one successful STUN
transaction over TCP. If a flow is established and is alive after
this amount of time, the number of consecutive registration failures
is set to zero. Each time a flow fails before two minutes, the
number of consecutive registration failures is incremented by one.
Note that a failure during the initial STUN validation does not count
against the number of consecutive registration failures.
The number of seconds to wait is computed in the following way. If The number of seconds to wait is computed in the following way. If
all of the flows to every URI in the outbound proxy set have failed, all of the flows to every URI in the outbound proxy set have failed,
the base time is set to 30 seconds; otherwise, in the case where at the base time is set to 30 seconds; otherwise, in the case where at
least one of the flows has not failed, the base time is set to 90 least one of the flows has not failed, the base time is set to 90
seconds. The wait time is computed by taking two raised to the power seconds. The wait time is computed by taking two raised to the power
of the number of consecutive registration failures for that URI, and of the number of consecutive registration failures for that URI, and
multiplying this by the base time, up to a maximum of 1800 seconds. multiplying this by the base time, up to a maximum of 1800 seconds.
wait-time = min( max-time, (base-time * (2 ^ consecutive-failures))) wait-time = min( max-time, (base-time * (2 ^ consecutive-failures)))
skipping to change at page 20, line 8 skipping to change at page 20, line 20
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 [3]. If the Edge Proxy is the first SIP node after the UAC, it 3327 [5]. If the Edge Proxy is the first SIP node after the UAC, it
either MUST store a "flow token"--containing information about the either MUST store a "flow token"--containing information about the
flow from the previous hop--in its Path URI, or reject the request. flow from the previous hop--in its Path URI, or reject the request.
The flow token MUST be an identifier that is unique to this network The flow token MUST be an identifier that is unique to this network
flow. The flow token MAY be placed in the userpart of the URI. In 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 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. A stateless
stateless examples are provided below. A proxy can use any algorithm example is provided below. A proxy can use any algorithm it wants as
it wants as long as the flow token is unique to a flow, the flow can long as the flow token is unique to a flow, the flow can be recovered
be recovered from the token, and the token can not be modified by from the token, and the token cannot be modified by attackers.
attackers.
Algorithm 1: The proxy generates a flow token for connection- Example Algorithm: When the proxy boots it selects a 20-octet crypto
oriented transports by concatenating the file descriptor (or
equivalent) with the NTP time the connection was created, and
base64 encoding the result. This results in an identifier
approximately 16 octets long. The proxy generates a flow token
for UDP by concatenating the file descriptor and the remote IP
address and port, then base64 encoding the result. (No NTP time
is needed for UDP.) This algorithm MUST NOT be used unless all
messages between the Edge proxy and Registrar use a SIPS protected
transport. If the SIPS level of integrity protection is not
available, an attacker can hijack another user's calls.
Algorithm 2: When the proxy boots it selects a 20-octet crypto
random key called K that only the Edge Proxy knows. A byte array, random key called K that only the Edge Proxy knows. A byte array,
called S, is formed that contains the following information about called S, is formed that contains the following information about
the flow the request was received on: an enumeration indicating the flow the request was received on: an enumeration indicating
the protocol, the local IP address and port, the remote IP address the protocol, the local IP address and port, the remote IP address
and port. The HMAC of S is computed using the key K and the HMAC- and port. The HMAC of S is computed using the key K and the HMAC-
SHA1-80 algorithm, as defined in [11]. The concatenation of the SHA1-80 algorithm, as defined in [11]. The concatenation of the
HMAC and S are base64 encoded, as defined in [12], and used as the HMAC and S are base64 encoded, as defined in [12], and used as the
flow identifier. When using IPv4 addresses, this will result in a flow identifier. When using IPv4 addresses, this will result in a
32-octet identifier. 32-octet identifier.
5.3. Forwarding Requests 5.3. Forwarding 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 field value contains a flow token,
compares the flow in the flow token with the source of the request. the proxy compares the flow in the flow token with the source of the
If these refer to the same flow, the Edge Proxy removes the Route request to determine if this is an "incoming" or "outgoing" request.
header and continues processing the request. Otherwise, if the top- If the flow in the flow token in the topmost Route header field value
most Route header refers to the Edge Proxy and contains a valid flow matches the source of the request, the request in an "outgoing"
identifier token created by this proxy, the proxy MUST remove the request. For an "outgoing" request, the edge proxy just removes the
Route header and forward the request over the 'logical flow' Route header and continues processing the request. Otherwise, this
identified by the flow token, that is known to deliver data to the is an "incoming" request. For an incoming request, the proxy removes
specific target UA instance. For connection-oriented transports, if the Route header field value and forwards the request over the
the flow no longer exists the proxy SHOULD send a 430 (Flow Failed) 'logical flow' identified by the flow token, that is known to deliver
response to the request. data to the specific target UA instance. For connection-oriented
transports, if the flow no longer exists the proxy SHOULD send a 430
The advantage to a stateless approach to managing the flow (Flow Failed) response to the request.
information is that there is no state on the Edge Proxy that
requires clean up or that has to be synchronized with the
registrar.
Proxies which used one of the two algorithms described in this Proxies which used the example algorithm described in this document
document to form a flow token follow the procedures below to to form a flow token follow the procedures below to determine the
determine the correct flow. correct flow.
Algorithm 1: The proxy base64 decodes the user part of the Route Example Algorithm: To decode the flow token, take the flow
header. For a TCP-based transport, if a connection specified by identifier in the user portion of the URI and base64 decode it,
the file descriptor is present and the creation time of the file then verify the HMAC is correct by recomputing the HMAC and
descriptor matches the creation time encoded in the Route header, checking that it matches. If the HMAC is not correct, the proxy
the proxy forwards the request over that connection. For a UDP- SHOULD send a 403 (Forbidden) response. If the HMAC is correct
based transport, the proxy forwards the request from the encoded then the proxy SHOULD forward the request on the flow that was
file descriptor to the source IP address and port. specified by the information in the flow identifier. If this flow
Algorithm 2: To decode the flow token, take the flow identifier in no longer exists, the proxy SHOULD send a 430 (Flow Failed)
the user portion of the URI and base64 decode it, then verify the response to the request.
HMAC is correct by recomputing the HMAC and checking it matches.
If the HMAC is not correct, the proxy SHOULD send a 403
(Forbidden) response. If the HMAC is correct then the proxy
SHOULD forward the request on the flow that was specified by the
information in the flow identifier. If this flow no longer
exists, the proxy SHOULD send a 430 (Flow Failed) response to the
request.
Note that this specification needs mid-dialog requests to be routed Note that this specification needs mid-dialog requests to be routed
over the same flows as those stored in the Path vector from the over the same flows as those stored in the Path vector from the
initial registration, but techniques to ensure that mid-dialog initial registration, but 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. The Edge Proxy can use
the presence of the "ob" parameter in the UAC's Contact URI to
determine if it should add a flow token.
5.4. Edge Proxy Keepalive Handling 5.4. Edge Proxy Keepalive Handling
All edge proxies compliant with this specification MUST implement All edge proxies compliant with this specification MUST implement
support for the STUN NAT Keepalive usage on its SIP ports as support for the STUN NAT Keepalive usage on its SIP UDP ports as
described in Section 8. described in Section 8.
When a server receives a double-CRLF sequence on a connection When a server receives a double CRLF sequence on a connection
oriented transport such as TCP or SCTP, it MUST immediately responds oriented transport such as TCP or SCTP, it MUST immediately respond
with a single CRLF over the same connection. with a single CRLF over the same connection.
6. Registrar Mechanisms: Processing REGISTER Requests 6. Registrar Mechanisms: Processing REGISTER Requests
This specification updates the definition of a binding in RFC 3261 This specification updates the definition of a binding in RFC 3261
[1] Section 10 and RFC 3327 [3] Section 5.3. [1] Section 10 and RFC 3327 [5] Section 5.3.
When no +sip.instance media feature parameter is present in a Contact 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 [3]. header mechanism [5].
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, if it ignores the 'reg-id' parameter the registrar MUST
and MUST NOT include the 'outbound' option-tag in its Supported use RFC 3261 Contact binding rules, and MUST NOT include the
header field. The registrar can determine if it is the first hop by 'outbound' option-tag in its Supported header field. The registrar
examining the Via header field. can determine if it is the first hop by 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 handle to file descriptor where the this would typically just be the handle to the file descriptor where
handle would become invalid if the TCP session was closed. For the handle would become invalid if the TCP session was closed. For
common operating systems with UDP this would typically be the file common operating systems with UDP this would typically be the file
descriptor for the local socket that received the request, the local descriptor for the local socket that received the request, the local
interface, and the IP address and port number of the remote side that interface, and the IP address and port number of the remote side that
sent the request. The registrar MAY store this information by adding sent the request. The registrar MAY store this information by adding
itself to the Path header field with an appropriate flow token. itself to the Path header field with an appropriate flow token.
The registrar MUST also store all the Contact header field 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 [3] requires the registrar a Path header field is present, RFC 3327 [5] requires the registrar
to store this information as well. If the registrar receives a re- to store this information as well. If the registrar receives a re-
registration, it MUST update any information that uniquely identifies registration, it MUST update any information that uniquely identifies
the network flow over which the request arrived if that information the network flow over which the request arrived if that information
has changed, and SHOULD update the time the binding was last updated. has changed, and SHOULD update the time the 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, and MUST NOT include this option-tag if it did not
reject any registrations that do not include the instance-id and perform outbound processing. Furthermore, the Registrar MUST NOR
reg-id. Note that the requirements in this section applies to both include this option-tag in its response if the Registrar skipped
REGISTER requests received from an Edge Proxy as well as requests outbound processing by ignoring the reg-id parameter as described in
received directly from the UAC. this specification. Note that the requirements in this section
applies to both REGISTER requests received from an Edge Proxy as well
as requests received directly from the UAC. The Registrar MAY be
configured with local policy to reject any registrations that do not
include the instance-id and reg-id, or with Path header field values
that do not contain the 'ob' parameter.
To be compliant with this specification, registrars which can receive To be compliant with this specification, registrars which can receive
SIP requests directly from a UAC without intervening edge proxies SIP requests directly from a UAC without intervening edge proxies
MUST implement the STUN NAT Keepalive usage on its SIP ports as MUST implement the STUN NAT Keepalive usage on its SIP UDP ports as
described in Section 8 and when it receives a double-CRLF sequence on described in Section 8 and when it receives a double-CRLF sequence on
a connection oriented transport such as TCP or SCTP, it MUST a connection oriented transport such as TCP or SCTP, it MUST
immediately respond with a single CRLF over the same connection. immediately respond with a single CRLF over the same connection.
7. Authoritative Proxy Mechanisms: Forwarding Requests 7. Authoritative Proxy Mechanisms: Forwarding Requests
When a proxy uses the location service to look up a registration When a proxy uses the location service to look up a registration
binding and then proxies a request to a particular contact, it binding and then proxies a request to a particular contact, it
selects a contact to use normally, with a few additional rules: selects a contact to use normally, with a few additional rules:
o The proxy MUST NOT populate the target set with more than one o The proxy MUST NOT populate the target set with more than one
contact with the same AOR and instance-id at a time. If a request contact with the same AOR and instance-id at a time.
for a particular AOR and instance-id fails with a 430 (Flow o If a request for a particular AOR and instance-id fails with a 430
Failed) response, the proxy SHOULD replace the failed branch with (Flow Failed) response, the proxy SHOULD replace the failed branch
another target (if one is available) with the same AOR and with another target (if one is available) with the same AOR and
instance-id, but a different reg-id. instance-id, but a different reg-id.
o If the proxy receives a final response from a branch other than a o If the proxy receives a final response from a branch other than a
408 (Request Timeout) or a 430 (Flow Failed) response, the proxy 408 (Request Timeout) or a 430 (Flow Failed) response, the proxy
MUST NOT forward the same request to another target representing MUST NOT forward the same request to another target representing
the same AOR and instance-id. The targeted instance has already the same AOR and instance-id. The targeted instance has already
provided its response. provided its response.
The proxy uses normal forwarding rules looking at the next-hop target The proxy uses 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
skipping to change at page 24, line 50 skipping to change at page 24, line 50
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 [4] NAT Keepalive usage to be mixed over the same SIP and the STUN [3] NAT Keepalive usage to be mixed over the same
flow. The STUN messages are used to verify that connectivity is flow. The STUN messages are used to verify that connectivity is
still available over a UDP flow, and to provide periodic keepalives. still available over a UDP flow, and to provide periodic keepalives.
Note that these STUN keepalives are always sent to the next SIP hop. Note that these STUN keepalives are always sent to the next SIP hop.
STUN messages are not delivered end-to-end. STUN 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 Binding Error Responses. The UAC sends
Requests over the same UDP flow that is used for sending SIP Binding Requests over the same UDP flow that is used for sending SIP
messages. These Binding Requests do not require any STUN attributes. messages. These Binding Requests do not require any STUN attributes.
The UAS responds to a valid Binding Request with a Binding Response The UAS responds to a valid Binding Request with a Binding Response
which MUST include the XOR-MAPPED-ADDRESS attribute. which MUST include the XOR-MAPPED-ADDRESS attribute.
If a server compliant to this section receives SIP requests on a If a server compliant to this section receives SIP requests on a
given interface and port, it MUST also provide a limited version of a given interface and 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 [4]. 12.3 of [3].
It is easy to distinguish STUN and SIP packets sent over UDP, It is easy to distinguish STUN and SIP packets sent over UDP,
because the first octet of a STUN packet has a value of 0 or 1 because the first octet of a STUN packet has a value of 0 or 1
while the first octet of a SIP message is never a 0 or 1. while the first octet of a SIP message is never a 0 or 1.
When a URI is created that refers to a SIP node that supports STUN as
described in this section, the 'keep-stun' URI parameter, as defined
in Section 12 MUST be added to the URI. This allows a UA to inspect
the URI to decide if it should attempt to send STUN requests to this
location. For example, an edge proxy could insert this parameter
into its Path URI so that the registering UA can discover the edge
proxy supports STUN keepalives.
Because sending and receiving binary STUN data on the same ports used Because sending and receiving binary STUN data on the same ports used
for SIP is a significant and non-backwards compatible change to RFC for SIP is a significant and non-backwards compatible change to RFC
3261, this section requires a number of checks before sending STUN 3261, this section requires a number of checks before sending STUN
messages to a SIP node. If a SIP node sends STUN requests (for messages to a SIP node. If a SIP node sends STUN requests (for
example due to incorrect configuration) despite these warnings, the example due to incorrect configuration) despite these warnings, the
node could be blacklisted for UDP traffic. For each target node (as node could be blacklisted for UDP traffic.
determined by IP address, address family, and port number), the
sender needs to determine if that destination is validated to support
STUN, that it does not support STUN, or that it needs to be
validated.
When a URI is created that refers to a SIP node that supports STUN as
described in this section, the 'keep-stun' URI parameter, as defined
in Section 12 SHOULD be added to the URI. This allows a UA to
inspect the URI to decide if it should attempt to send STUN requests
to this location. For example, an edge proxy could insert this
parameter into its Path URI so that the registering UA can discover
the edge proxy supports STUN keepalives.
A SIP node MUST NOT send STUN requests over a flow unless it has an A SIP node MUST NOT send STUN requests over a flow unless it has an
explicit indication that the target next hop SIP server claims to explicit indication that the target next hop SIP server claims to
support STUN. For example, automatic or manual configuration of an support STUN. For example, automatic or manual configuration of an
outbound-proxy-set which contains the 'keep-stun' parameter, or outbound-proxy-set which contains the 'keep-stun' parameter, or
received the parameter in the Path header of the edge proxy, is receiving the parameter in the Path header of the edge proxy, 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.
probe the next hop using a SIP OPTIONS request to check for support
of the 'sip-stun' option tag in a Supported header field.
Furthermore, even with explicit indication of next hop STUN support,
a SIP node needs to validate support for STUN the first time it sends
STUN traffic to a specific invalidated target destination. A SIP
node MAY send one STUN request and its retransmissions to an
invalidated destination. If a STUN request ever succeeds to a
destination, that destination is 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 a next-hop probe later validates the destination.
In addition, the SIP node SHOULD remember invalidated destination
nodes that have been used within one hour and SHOULD NOT send
additional STUN messages to any of these destinations.
If this initial STUN request does not result in a STUN response, the
UA MAY send and explicit next-hop probe as described in Section 8.1.
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.
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.
(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
verify support for the 'sip-stun' option-tag.
Once a destination is validated to support STUN messages, failure of
a STUN request (including its retransmissions) is considered a
failure of the underlying flow. For SIP over UDP flows, if the XOR-
MAPPED-ADDRESS returned over the flow changes, this indicates that
the underlying connectivity has changed, and is considered a flow
failure. A 408 response to a next-hop OPTIONS probe is also
considered a flow failure.
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 Option Probes
This section defines a new SIP option-tag called 'sip-stun'.
Advertising this option-tag indicates that the server can receive SIP
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
support for STUN, can send an OPTIONS request to the next hop by
setting the Max-Forwards header field to zero or addressing the
request to that server. The OPTIONS response will contain a
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- Once a flow is established, failure of a STUN request (including its
Require header. This is because a request with this header will retransmissions) is considered a failure of the underlying flow. For
fail in some topologies where the first proxy support sip-stun, SIP over UDP flows, if the XOR-MAPPED-ADDRESS returned over the flow
but a subsequent proxy does not. Note that RFC 3261 does not changes, this indicates that the underlying connectivity has changed,
allow proxies to remove option-tags from a Proxy-Require header and is considered a flow failure.
field.
8.2. Use with Sigcomp 8.1. Use with Sigcomp
When STUN is used together with SigComp [23] compressed SIP messages When STUN is used together with SigComp [24] compressed SIP messages
over the same flow, how the STUN messages are sent depends on the over the same flow, how the STUN messages are sent depends on the
transport protocol. For UDP flows, the STUN messages are simply sent transport protocol. For UDP flows, the STUN messages are simply sent
uncompressed, "outside" of SigComp. This is supported by uncompressed, "outside" of SigComp. This is supported by
multiplexing STUN messages with SigComp messages by checking the two multiplexing STUN messages with SigComp messages by checking the two
topmost bits of the message. These bits are always one for SigComp, topmost bits of the message. These bits are always one for SigComp,
or zero for STUN. or zero for STUN.
All SigComp messages contain a prefix (the five most-significant All SigComp messages contain a prefix (the five most-significant
bits of the first byte are set to one) that does not occur in bits of the first byte are set to one) that does not occur in
UTF-8 encoded text messages [RFC-2279], so for applications which UTF-8 [13] encoded text messages, so for applications which use
use this encoding (or ASCII encoding) it is possible to multiplex this encoding (or ASCII encoding) it is possible to multiplex
uncompressed application messages and SigComp messages on the same uncompressed application messages and SigComp messages on the same
UDP port. UDP port.
The most significant two bits of every STUN message are both The most significant two bits of every STUN 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.
9. Example Message Flow 9. Example Message Flow
The following call flow shows a basic registration and an incoming The following call flow shows a basic registration and an incoming
skipping to change at page 31, line 9 skipping to change at page 30, line 9
The registrations in message 13 and 14 are the same as message 1 and The registrations in message 13 and 14 are the same as message 1 and
2 other than the Call-ID and tags have changed. Because these 2 other than the Call-ID and tags have changed. Because these
messages will contain the same instance-id and reg-id as those in 1 messages will contain the same instance-id and reg-id as those in 1
and 2, this flow will partially supersede that for messages 1 and 2 and 2, this flow will partially supersede that for messages 1 and 2
and will be tried first by Primary. and will be tried first by Primary.
10. Grammar 10. Grammar
This specification defines new Contact header field parameters, This specification defines new Contact header field parameters,
reg-id and +sip.instance. The grammar includes the definitions from reg-id and +sip.instance. The grammar includes the definitions from
RFC 3261 [1] and includes the definition of uric from RFC 2396 [13]. RFC 3261 [1] and includes the definition of uric from RFC 3986 [14].
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[14] is: The ABNF[15] 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 3986
The value of the reg-id MUST NOT be 0 and MUST be less than 2**31. The value of the reg-id MUST NOT be 0 and MUST be less than 2**31.
11. Definition of 430 Flow Failed response code 11. Definition of 430 Flow Failed response code
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 [15]. The required sub-registry as per the registry created by [16]. 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 No [RFC AAAA]
[NOTE TO RFC Editor: Please replace AAAA with [NOTE TO RFC Editor: Please replace AAAA with
the RFC number of this specification.] the RFC number of this specification.]
12.2. SIP/SIPS URI Parameters 12.2. SIP/SIPS URI Parameters
This specification arguments the "SIP/SIPS URI Parameters" sub- This specification augments the "SIP/SIPS URI Parameters" sub-
registry as per the registry created by [16]. The required registry as per the registry created by [17]. The required
information is: information is:
Parameter Name Predefined Values Reference Parameter Name Predefined Values Reference
____________________________________________ ____________________________________________
keep-stun [RFC AAAA] keep-crlf No [RFC AAAA]
keep-tcp [RFC AAAA] keep-stun No [RFC AAAA]
keep-crlf [RFC AAAA] timed-keepalive No [RFC AAAA]
ob [RFC AAAA] ob No [RFC AAAA]
[NOTE TO RFC Editor: Please replace AAAA with [NOTE TO RFC Editor: Please replace AAAA with
the RFC number of this specification.] the RFC number of this specification.]
12.3. SIP Option Tag 12.3. SIP Option Tag
This specification registers two new SIP option tags, as per the This specification registers a new SIP option tag, as per the
guidelines in Section 27.1 of RFC 3261. guidelines in Section 27.1 of RFC 3261.
Name: outbound Name: outbound
Description: This option-tag is used to identify Registrars which Description: This option-tag is used to identify Registrars which
support extensions for Client Initiated Connections. A Registrar support extensions for Client Initiated Connections. A Registrar
places this option-tag in a Supported header to communicate 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
Description: This option-tag is used to identify SIP servers which
can receive STUN requests described in the STUN NAT Keepalive
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 27.4 of RFC 3261.
Code: 430 Code: 430
Default Reason Phrase: Flow Failed Default Reason Phrase: Flow Failed
Reference: This document Reference: This document
12.5. Media Feature Tag 12.5. Media Feature Tag
This section registers a new media feature tag, per the procedures This section registers a new media feature tag, per the procedures
defined in RFC 2506 [17]. The tag is placed into the sip tree, which defined in RFC 2506 [18]. The tag is placed into the sip tree, which
is defined in RFC 3840 [6]. is defined in RFC 3840 [7].
Media feature tag name: sip.instance Media feature tag name: sip.instance
ASN.1 Identifier: New assignment by IANA. ASN.1 Identifier: New assignment by IANA.
Summary of the media feature indicated by this tag: This feature tag Summary of the media feature indicated by this tag: This feature tag
contains a string containing a URN that indicates a unique identifier contains a string containing a URN that indicates a unique identifier
associated with the UA instance registering the Contact. associated with the UA instance registering the Contact.
Values appropriate for use with this feature tag: String. Values appropriate for use with this feature tag: String.
skipping to change at page 33, line 29 skipping to change at page 32, line 25
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 [8] allows for call routing decisions to be preferences extension [9] allows for call routing decisions to be
based on the values of these parameters. Therefore, if an attacker based on the values of these parameters. Therefore, if an attacker
can modify the values of this tag, they might be able to affect the can modify the values of this tag, they might be able to affect the
behavior of applications. As a result, applications which utilize behavior of applications. As a result, applications which utilize
this media feature tag SHOULD provide a means for ensuring its this media feature tag SHOULD provide a means for ensuring 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. Note that
the intent is not to prevent existing active attacks on SIP UDP and
TCP traffic, but to insure that no new attacks are added by
introducing the outbound mechanism.
The simple case is when there are no edge proxies. In this case, the The simple case is when there are no edge proxies. In this case, the
only time an entry can be added to the routing for a given AOR is only time an entry can be added to the routing for a given AOR is
when the registration succeeds. SIP already protects against when the registration succeeds. SIP already protects against
attackers being able to successfully register, and this scheme relies attackers being able to successfully register, and this scheme relies
on that security. Some implementers have considered the idea of just on that security. Some implementers have considered the idea of just
saving the instance-id without relating it to the AOR with which it saving the instance-id without relating it to the AOR with which it
registered. This idea will not work because an attacker's UA can registered. This idea will not work because an attacker's UA can
impersonate a valid user's instance-id and hijack that user's calls. impersonate a valid user's instance-id and hijack that user's calls.
skipping to change at page 34, line 30 skipping to change at page 33, line 29
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. Operational Notes on Transports 14. Operational Notes on Transports
RFC 3261 requires proxies, registrars, and UA to implement both TCP This entire section is non-normative.
and UDP but deployments can chose which transport protocols they want
to use. Deployments need to be careful in choosing what transports RFC 3261 requires proxies, registrars, and User Agents to implement
to use. Many SIP features and extensions, such as large presence both TCP and UDP but deployments can chose which transport protocols
subscriptions packages, result in SIP requests that can be too large they want to use. Deployments need to be careful in choosing what
to be reasonably transported over UDP. RFC 3261 has an option of transports to use. Many SIP features and extensions, such as large
presence notification bodies, result in SIP requests that can be too
large to be reasonably transported over UDP. RFC 3261 states that
when a request is too large for UDP, the device sending the request when a request is too large for UDP, the device sending the request
can attempt to switch over to TCP. No known deployments currently attempts to switch over to TCP. No known deployments currently use
use this but it is important to note that when using outbound, this this feature but it is important to note that when using outbound,
will only work if the UA has formed both a UDP and TCP outbound this will only work if the UA has formed both UDP and TCP outbound
connection. The specification allows the UA to do this but in most flows. This specification allows the UA to do so but in most cases
cases it will probably make more sense to only form TCP outbound it will probably make more sense for the UA to form a TCP outbound
connection than forming both UDP and TCP. One of the key reasons connection only, rather than forming both UDP and TCP flows. One of
that many deployments choose not to use TCP has to do with the the key reasons that many deployments choose not to use TCP has to do
difficulty of building proxies that can maintain a very large number with the difficulty of building proxies that can maintain a very
of active TCP connections. Many deployments today use SIP in such a large number of active TCP connections. Many deployments today use
way that the message are small enough that they work over UDP but SIP in such a way that the messages are small enough that they work
they can not take advantage of all the functionality SIP offers. over UDP but they can not take advantage of all the functionality SIP
Deployments that use only UDP outbound connections are going to fail offers. Deployments that use only UDP outbound connections are going
with sufficiently large SIP messages. to fail with sufficiently large SIP messages.
15. Requirements 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.
16. Open Issues 16. Changes
This draft documents what having CRLF keep alives would look like so Note to RFC Editor: Please remove this whole section.
that the working group can decide if they want to do this or not.
Having multiple keep alive options that are only valid with some 16.1. Changes from 08 Version
transports, combined with SRV providing multiple transport options,
opens the possibility for configurations that make no sense and cause
the system to fail. For example, if the outbound proxy set is sip:
example.com;keep-tcp and the SRV only resolves to a UDP transports,
the system will not work.
17. Changes UAs now include the 'ob' parameter in their Contact header for non-
REGISTER requests, as a hint to the Edge Proxy (so the EP can Record-
Route with a flow-token for example).
Note to RFC Editor: Please remove this whole section. Switched to CRLF for keepalives of connection-oriented transports
after brutal consensus at IETF 68.
17.1. Changes from 07 Version Added timed-keepalive parameter and removed the unnecessary keep-tcp
param, per consensus at IETF68.
Removed example "Algorithm 1" which only worked over SIPS, per
consensus at IETF68.
Deleted text about probing and validating with options, per consensus
at IETF68.
Deleted provision for waiting 120 secs before declaring flow stable,
per consensus at IETF68.
fixed example UUIDs
16.2. Changes from 07 Version
Add language to show the working group what adding CRLF keepalives Add language to show the working group what adding CRLF keepalives
would look like. would look like.
Changed syntax of keep-alive=stun to keep-stun so that it was easier Changed syntax of keep-alive=stun to keep-stun so that it was easier
to support multiple tags in the same URI. to support multiple tags in the same URI.
17.2. Changes from 06 Version 16.3. Changes from 06 Version
Added the section on operational selection of transports. Added the section on operational selection of transports.
Fixed various editorial typos. Fixed various editorial typos.
Put back in requirement flow token needs to be unique to flow as it Put back in requirement flow token needs to be unique to flow as it
had accidentally been dropped in earlier version. This did not had accidentally been dropped in earlier version. This did not
change any of the flow token algorithms. change any of the flow token algorithms.
Reordered some of the text on STUN keepalive validation to make it Reordered some of the text on STUN keepalive validation to make it
clearer to implementors. Did not change the actual algorithm or clearer to implementors. Did not change the actual algorithm or
requirements. Added note to explain how if the proxy changes, the requirements. Added note to explain how if the proxy changes, the
revalidation will happen. revalidation will happen.
17.3. Changes from 05 Version 16.4. 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 36, line 33 skipping to change at page 35, line 43
Added comment that keep-stun could be added to Path. Added comment that keep-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 may, should, and must. Scrubbed document for avoidable lowercase may, should, and must.
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.
17.4. Changes from 04 Version 16.5. 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 37, line 39 skipping to change at page 36, line 49
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.
17.5. Changes from 03 Version 16.6. 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 38, line 22 skipping to change at page 37, line 32
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 steaks. Fixed many typos and spelling steaks.
17.6. Changes from 02 Version 16.7. 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.
17.7. Changes from 01 Version 16.8. Changes from 01 Version
Moved definition of instance-id from GRUU[24] draft to this draft. Moved definition of instance-id from GRUU[25] draft to this draft.
Added tentative text about Double CRLF Keepalive Added tentative text about Double CRLF Keepalive
Removed pin-route stuff Removed pin-route stuff
Changed the name of "flow-id" to "reg-id" Changed the name of "flow-id" to "reg-id"
Reorganized document flow Reorganized document flow
Described the use of STUN as a proper STUN usage Described the use of STUN as a proper STUN usage
Added 'outbound' option-tag to detect if registrar supports outbound Added 'outbound' option-tag to detect if registrar supports outbound
17.8. Changes from 00 Version 16.9. 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.
18. 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 39, line 45 skipping to change at page 39, line 17
+-------------------+--------------------+--------------------+ +-------------------+--------------------+--------------------+
| 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 |
+-------------------+--------------------+--------------------+ +-------------------+--------------------+--------------------+
19. References 18. References
19.1. Normative References 18.1. Normative References
[1] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., [1] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002. Session Initiation Protocol", RFC 3261, June 2002.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[3] Willis, D. and B. Hoeneisen, "Session Initiation Protocol (SIP) [3] Rosenberg, J., "Simple Traversal Underneath Network Address
Extension Header Field for Registering Non-Adjacent Contacts",
RFC 3327, December 2002.
[4] Rosenberg, J., "Simple Traversal Underneath Network Address
Translators (NAT) (STUN)", draft-ietf-behave-rfc3489bis-05 Translators (NAT) (STUN)", draft-ietf-behave-rfc3489bis-05
(work in progress), October 2006. (work in progress), October 2006.
[5] Leach, P., Mealling, M., and R. Salz, "A Universally Unique [4] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol
(SIP): Locating SIP Servers", RFC 3263, June 2002.
[5] Willis, D. and B. Hoeneisen, "Session Initiation Protocol (SIP)
Extension Header Field for Registering Non-Adjacent Contacts",
RFC 3327, December 2002.
[6] Leach, P., Mealling, M., and R. Salz, "A Universally Unique
IDentifier (UUID) URN Namespace", RFC 4122, July 2005. IDentifier (UUID) URN Namespace", RFC 4122, July 2005.
[6] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Indicating [7] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Indicating
User Agent Capabilities in the Session Initiation Protocol User Agent Capabilities in the Session Initiation Protocol
(SIP)", RFC 3840, August 2004. (SIP)", RFC 3840, August 2004.
[7] Moats, R., "URN Syntax", RFC 2141, May 1997. [8] Moats, R., "URN Syntax", RFC 2141, May 1997.
[8] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller [9] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller
Preferences for the Session Initiation Protocol (SIP)", Preferences for the Session Initiation Protocol (SIP)",
RFC 3841, August 2004. RFC 3841, August 2004.
[9] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol
(SIP): Locating SIP Servers", RFC 3263, June 2002.
[10] Rosenberg, J. and H. Schulzrinne, "An Extension to the Session [10] Rosenberg, J. and H. Schulzrinne, "An Extension to the Session
Initiation Protocol (SIP) for Symmetric Response Routing", Initiation Protocol (SIP) for Symmetric Response Routing",
RFC 3581, August 2003. RFC 3581, August 2003.
[11] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing [11] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing
for Message Authentication", RFC 2104, February 1997. for Message Authentication", RFC 2104, February 1997.
[12] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", [12] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings",
RFC 3548, July 2003. RFC 3548, July 2003.
[13] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [13] Yergeau, F., "UTF-8, a transformation format of ISO 10646",
Resource Identifiers (URI): Generic Syntax", RFC 2396, STD 63, RFC 3629, November 2003.
August 1998.
[14] Crocker, D. and P. Overell, "Augmented BNF for Syntax [14] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Sy ntax", STD 66, RFC 3986,
January 2005.
[15] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005. Specifications: ABNF", RFC 4234, October 2005.
[15] Camarillo, G., "The Internet Assigned Number Authority (IANA) [16] Camarillo, G., "The Internet Assigned Number Authority (IANA)
Header Field Parameter Registry for the Session Initiation Header Field Parameter Registry for the Session Initiation
Protocol (SIP)", BCP 98, RFC 3968, December 2004. Protocol (SIP)", BCP 98, RFC 3968, December 2004.
[16] Camarillo, G., "The Internet Assigned Number Authority (IANA) [17] Camarillo, G., "The Internet Assigned Number Authority (IANA)
Uniform Resource Identifier (URI) Parameter Registry for the Uniform Resource Identifier (URI) Parameter Registry for the
Session Initiation Protocol (SIP)", BCP 99, RFC 3969, Session Initiation Protocol (SIP)", BCP 99, RFC 3969,
December 2004. December 2004.
[17] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag [18] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag
Registration Procedure", BCP 31, RFC 2506, March 1999. Registration Procedure", BCP 31, RFC 2506, March 1999.
19.2. Informative References 18.2. Informative References
[18] Petrie, D., "A Framework for Session Initiation Protocol User [19] Petrie, D., "A Framework for Session Initiation Protocol User
Agent Profile Delivery", draft-ietf-sipping-config-framework-09 Agent Profile Delivery", draft-ietf-sipping-config-framework-09
(work in progress), October 2006. (work in progress), October 2006.
[19] Hakala, J., "Using National Bibliography Numbers as Uniform [20] Hakala, J., "Using National Bibliography Numbers as Uniform
Resource Names", RFC 3188, October 2001. Resource Names", RFC 3188, October 2001.
[20] Rosenberg, J., "Construction of the Route Header Field in the [21] Rosenberg, J., "Construction of the Route Header Field in the
Session Initiation Protocol (SIP)", Session Initiation Protocol (SIP)",
draft-rosenberg-sip-route-construct-02 (work in progress), draft-rosenberg-sip-route-construct-02 (work in progress),
October 2006. October 2006.
[21] Willis, D. and B. Hoeneisen, "Session Initiation Protocol (SIP) [22] Willis, D. and B. Hoeneisen, "Session Initiation Protocol (SIP)
Extension Header Field for Service Route Discovery During Extension Header Field for Service Route Discovery During
Registration", RFC 3608, October 2003. Registration", RFC 3608, October 2003.
[22] Boulton, C., "Best Current Practices for NAT Traversal for [23] Boulton, C., "Best Current Practices for NAT Traversal for
SIP", draft-ietf-sipping-nat-scenarios-05 (work in progress), SIP", draft-ietf-sipping-nat-scenarios-05 (work in progress),
June 2006. June 2006.
[23] Price, R., Bormann, C., Christoffersson, J., Hannu, H., Liu, [24] Price, R., Bormann, C., Christoffersson, J., Hannu, H., Liu,
Z., and J. Rosenberg, "Signaling Compression (SigComp)", Z., and J. Rosenberg, "Signaling Compression (SigComp)",
RFC 3320, January 2003. RFC 3320, January 2003.
[24] Rosenberg, J., "Obtaining and Using Globally Routable User [25] Rosenberg, J., "Obtaining and Using Globally Routable User
Agent (UA) URIs (GRUU) in the Session Initiation Protocol Agent (UA) URIs (GRUU) in the Session Initiation Protocol
(SIP)", draft-ietf-sip-gruu-11 (work in progress), (SIP)", draft-ietf-sip-gruu-11 (work in progress),
October 2006. 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
 End of changes. 135 change blocks. 
393 lines changed or deleted 342 lines changed or added

This html diff was produced by rfcdiff 1.33. The latest version is available from http://tools.ietf.org/tools/rfcdiff/