draft-ietf-sip-outbound-11.txt   draft-ietf-sip-outbound-12.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 November 18, 2007 Intended status: Standards Track February 24, 2008
Expires: May 21, 2008 Expires: August 27, 2008
Managing Client Initiated Connections in the Session Initiation Protocol Managing Client Initiated Connections in the Session Initiation Protocol
(SIP) (SIP)
draft-ietf-sip-outbound-11 draft-ietf-sip-outbound-12
Status of this Memo Status of this Memo
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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.
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This Internet-Draft will expire on May 21, 2008. This Internet-Draft will expire on August 27, 2008.
Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2008).
Abstract Abstract
The Session Initiation Protocol (SIP) allows proxy servers to The Session Initiation Protocol (SIP) allows proxy servers to
initiate TCP connections and send asynchronous UDP datagrams to User initiate TCP connections and send asynchronous UDP datagrams to User
Agents in order to deliver requests. However, many practical Agents in order to deliver requests. However, many practical
considerations, such as the existence of firewalls and Network considerations, such as the existence of firewalls and Network
Address Translators (NATs), prevent servers from connecting to User Address Translators (NATs), prevent servers from connecting to User
Agents in this way. This specification defines behaviors for User Agents in this way. This specification defines behaviors for User
Agents, registrars and proxy servers that allow requests to be Agents, registrars and proxy servers that allow requests to be
skipping to change at page 2, line 17 skipping to change at page 2, line 17
also defines keep alive behaviors needed to keep NAT bindings open also defines keep alive behaviors needed to keep NAT bindings open
and specifies the usage of multiple connections from the User Agent and specifies the usage of multiple connections from the User Agent
to its Registrar. to its Registrar.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 4 2. Conventions and Terminology . . . . . . . . . . . . . . . . . 4
2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 5 2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 5
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Summary of Mechanism . . . . . . . . . . . . . . . . . . 5 3.1. Summary of Mechanism . . . . . . . . . . . . . . . . . . 6
3.2. Single Registrar and UA . . . . . . . . . . . . . . . . . 6 3.2. Single Registrar and UA . . . . . . . . . . . . . . . . . 6
3.3. Multiple Connections from a User Agent . . . . . . . . . 8 3.3. Multiple Connections from a User Agent . . . . . . . . . 8
3.4. Edge Proxies . . . . . . . . . . . . . . . . . . . . . . 9 3.4. Edge Proxies . . . . . . . . . . . . . . . . . . . . . . 10
3.5. Keepalive Technique . . . . . . . . . . . . . . . . . . . 11 3.5. Keep alive Technique . . . . . . . . . . . . . . . . . . 11
3.5.1. CRLF Keepalive Technique . . . . . . . . . . . . . . . 11 3.5.1. CRLF Keep-alive Technique . . . . . . . . . . . . . . 12
3.5.2. STUN Keepalive Technique . . . . . . . . . . . . . . . 12 3.5.2. STUN Keep alive Technique . . . . . . . . . . . . . . 12
4. User Agent Mechanisms . . . . . . . . . . . . . . . . . . . . 12 4. User Agent Mechanisms . . . . . . . . . . . . . . . . . . . . 12
4.1. Instance ID Creation . . . . . . . . . . . . . . . . . . 12 4.1. Instance ID Creation . . . . . . . . . . . . . . . . . . 12
4.2. Registrations . . . . . . . . . . . . . . . . . . . . . . 13 4.2. Registrations . . . . . . . . . . . . . . . . . . . . . . 14
4.2.1. Non Outbound Registrations . . . . . . . . . . . . . . 15 4.2.1. Initial Registrations . . . . . . . . . . . . . . . . 14
4.3. Sending Non-REGISTER Requests . . . . . . . . . . . . . . 15 4.2.2. Subsequent REGISTER requests . . . . . . . . . . . . . 16
4.4. Detecting Flow Failure . . . . . . . . . . . . . . . . . 16 4.2.3. Non Outbound Registrations . . . . . . . . . . . . . . 16
4.4.1. Keepalive with CRLF . . . . . . . . . . . . . . . . . 17 4.3. Sending Non-REGISTER Requests . . . . . . . . . . . . . . 16
4.4.2. Keepalive with STUN . . . . . . . . . . . . . . . . . 18 4.4. Keep-alives and Detecting Flow Failure . . . . . . . . . 17
4.5. Flow Recovery . . . . . . . . . . . . . . . . . . . . . . 18 4.4.1. Keep alive with CRLF . . . . . . . . . . . . . . . . . 18
5. Edge Proxy Mechanisms . . . . . . . . . . . . . . . . . . . . 19 4.4.2. Keep alive with STUN . . . . . . . . . . . . . . . . . 19
5.1. Processing Register Requests . . . . . . . . . . . . . . 19 4.5. Flow Recovery . . . . . . . . . . . . . . . . . . . . . . 19
5. Edge Proxy Mechanisms . . . . . . . . . . . . . . . . . . . . 20
5.1. Processing Register Requests . . . . . . . . . . . . . . 20
5.2. Generating Flow Tokens . . . . . . . . . . . . . . . . . 20 5.2. Generating Flow Tokens . . . . . . . . . . . . . . . . . 20
5.3. Forwarding Non-REGISTER Requests . . . . . . . . . . . . 20 5.3. Forwarding Non-REGISTER Requests . . . . . . . . . . . . 21
5.4. Edge Proxy Keepalive Handling . . . . . . . . . . . . . . 21 5.4. Edge Proxy Keep alive Handling . . . . . . . . . . . . . 22
6. Registrar Mechanisms: Processing REGISTER Requests . . . . . . 21 6. Registrar Mechanisms: Processing REGISTER Requests . . . . . . 22
7. Authoritative Proxy Mechanisms: Forwarding Requests . . . . . 23 7. Authoritative Proxy Mechanisms: Forwarding Requests . . . . . 24
8. STUN Keepalive Processing . . . . . . . . . . . . . . . . . . 24 8. STUN Keep alive Processing . . . . . . . . . . . . . . . . . . 25
8.1. Use with Sigcomp . . . . . . . . . . . . . . . . . . . . 25 8.1. Use with Sigcomp . . . . . . . . . . . . . . . . . . . . 26
9. Example Message Flow . . . . . . . . . . . . . . . . . . . . . 26 9. Example Message Flow . . . . . . . . . . . . . . . . . . . . . 27
10. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 10. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
11. Definition of 430 Flow Failed response code . . . . . . . . . 30 11. New Response Codes . . . . . . . . . . . . . . . . . . . . . . 36
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 11.1. Definition of 430 Flow Failed response code . . . . . . . 36
12.1. Contact Header Field . . . . . . . . . . . . . . . . . . 30 11.2. Definition of 439 First Hop Lacks Outbound Support
12.2. SIP/SIPS URI Parameters . . . . . . . . . . . . . . . . . 31 response . . . . . . . . . . . . . . . . . . . . . . . . 36
12.3. SIP Option Tag . . . . . . . . . . . . . . . . . . . . . 31 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
12.4. Response Code . . . . . . . . . . . . . . . . . . . . . . 31 12.1. Flow-Timer Header Field . . . . . . . . . . . . . . . . . 37
12.5. Media Feature Tag . . . . . . . . . . . . . . . . . . . . 31 12.2. 'reg-id' Contact Header Field Parameter . . . . . . . . . 37
13. Security Considerations . . . . . . . . . . . . . . . . . . . 32 12.3. SIP/SIPS URI Parameters . . . . . . . . . . . . . . . . . 37
14. Operational Notes on Transports . . . . . . . . . . . . . . . 33 12.4. SIP Option Tag . . . . . . . . . . . . . . . . . . . . . 38
15. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 34 12.5. Response Codes . . . . . . . . . . . . . . . . . . . . . 38
16. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 12.5.1. 430 Response Code . . . . . . . . . . . . . . . . . . 38
16.1. Changes from 09 Version . . . . . . . . . . . . . . . . . 34 12.5.2. 439 Response Code . . . . . . . . . . . . . . . . . . 38
16.2. Changes from 08 Version . . . . . . . . . . . . . . . . . 34 12.6. Media Feature Tag . . . . . . . . . . . . . . . . . . . . 38
16.3. Changes from 07 Version . . . . . . . . . . . . . . . . . 35 13. Security Considerations . . . . . . . . . . . . . . . . . . . 39
16.4. Changes from 06 Version . . . . . . . . . . . . . . . . . 35 14. Operational Notes on Transports . . . . . . . . . . . . . . . 40
16.5. Changes from 05 Version . . . . . . . . . . . . . . . . . 35 15. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 41
16.6. Changes from 04 Version . . . . . . . . . . . . . . . . . 36 16. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
16.7. Changes from 03 Version . . . . . . . . . . . . . . . . . 37 16.1. Changes from 11 Version . . . . . . . . . . . . . . . . . 41
16.8. Changes from 02 Version . . . . . . . . . . . . . . . . . 38 16.2. Changes from 09 Version . . . . . . . . . . . . . . . . . 41
16.9. Changes from 01 Version . . . . . . . . . . . . . . . . . 38 16.3. Changes from 08 Version . . . . . . . . . . . . . . . . . 41
16.10. Changes from 00 Version . . . . . . . . . . . . . . . . . 38 16.4. Changes from 07 Version . . . . . . . . . . . . . . . . . 42
17. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 38 16.5. Changes from 06 Version . . . . . . . . . . . . . . . . . 42
Appendix A. Default Flow Registration Backoff Times . . . . . . . 39 16.6. Changes from 05 Version . . . . . . . . . . . . . . . . . 42
18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 39 16.7. Changes from 04 Version . . . . . . . . . . . . . . . . . 43
18.1. Normative References . . . . . . . . . . . . . . . . . . 39 16.8. Changes from 03 Version . . . . . . . . . . . . . . . . . 44
18.2. Informative References . . . . . . . . . . . . . . . . . 40 16.9. Changes from 02 Version . . . . . . . . . . . . . . . . . 45
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 41 16.10. Changes from 01 Version . . . . . . . . . . . . . . . . . 45
Intellectual Property and Copyright Statements . . . . . . . . . . 43 16.11. Changes from 00 Version . . . . . . . . . . . . . . . . . 45
17. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 45
18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 46
18.1. Normative References . . . . . . . . . . . . . . . . . . 46
18.2. Informational References . . . . . . . . . . . . . . . . 47
Appendix A. Default Flow Registration Backoff Times . . . . . . . 48
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 48
Intellectual Property and Copyright Statements . . . . . . . . . . 50
1. Introduction 1. Introduction
There are many environments for SIP [1] deployments in which the User There are many environments for SIP [RFC3261] deployments in which
Agent (UA) can form a connection to a Registrar or Proxy but in which the User Agent (UA) can form a connection to a Registrar or Proxy but
connections in the reverse direction to the UA are not possible. in which connections in the reverse direction to the UA are not
This can happen for several reasons. Connections to the UA can be possible. This can happen for several reasons. Connections to the
blocked by a firewall device between the UA and the proxy or UA can be blocked by a firewall device between the UA and the proxy
registrar, which will only allow new connections in the direction of or registrar, which will only allow new connections in the direction
the UA to the Proxy. Similarly a NAT could be present, which is only of the UA to the Proxy. Similarly a NAT could be present, which is
capable of allowing new connections from the private address side to only capable of allowing new connections from the private address
the public side. This specification allows a SIP User Agent behind side to the public side. This specification allows a SIP User Agent
such a firewall or NAT to receive inbound traffic associated with behind such a firewall or NAT to receive inbound traffic associated
registrations or dialogs that it initiates. with registrations or dialogs that it initiates.
Most IP phones and personal computers get their network Most IP phones and personal computers get their network
configurations dynamically via a protocol such as DHCP (Dynamic Host configurations dynamically via a protocol such as DHCP (Dynamic Host
Configuration Protocol). These systems typically do not have a Configuration Protocol). These systems typically do not have a
useful name in the Domain Name System (DNS), and they almost never useful name in the Domain Name System (DNS), and they almost never
have a long-term, stable DNS name that is appropriate for use in the have a long-term, stable DNS name that is appropriate for use in the
subjectAltName of a certificate, as required by [1]. However, these subjectAltName of a certificate, as required by [RFC3261]. However,
systems can still act as a Transport Layer Security (TLS) [18] client these systems can still act as a Transport Layer Security (TLS)
and form connections to a proxy or registrar which authenticates with [RFC4346] client and form connections to a proxy or registrar which
a server certificate. The server can authenticate the UA using a authenticates with a server certificate. The server can authenticate
shared secret in a digest challenge (as defined in Section 22 of RFC the UA using a shared secret in a digest challenge (as defined in
3261) over that TLS connection. Section 22 of RFC 3261) over that TLS connection.
The key idea of this specification is that when a UA sends a REGISTER The key idea of this specification is that when a UA sends a REGISTER
or a dialog-forming request, the proxy can later use this same or a dialog-forming request, the proxy can later use this same
network "flow"--whether this is a bidirectional stream of UDP network "flow"--whether this is a bidirectional stream of UDP
datagrams, a TCP connection, or an analogous concept of another datagrams, a TCP connection, or an analogous concept of another
transport protocol--to forward any incoming requests that need to go transport protocol--to forward any incoming requests that need to go
to this UA in the context of the registration or dialog. to this UA in the context of the registration or dialog.
For a UA to receive incoming requests, the UA has to connect to a For a UA to receive incoming requests, the UA has to connect to a
server. Since the server can't connect to the UA, the UA has to make server. Since the server can't connect to the UA, the UA has to make
sure that a flow is always active. This requires the UA to detect sure that a flow is always active. This requires the UA to detect
when a flow fails. Since such detection takes time and leaves a when a flow fails. Since such detection takes time and leaves a
window of opportunity for missed incoming requests, this mechanism window of opportunity for missed incoming requests, this mechanism
allows the UA to register over multiple flows at the same time. This allows the UA to register over multiple flows at the same time. This
specification also defines multiple keepalive schemes. The keepalive specification also defines multiple keep alive schemes. The keep
mechanism is used to keep NAT bindings fresh, and to allow the UA to alive mechanism is used to keep NAT bindings fresh, and to allow the
detect when a flow has failed. UA to detect when a flow has failed.
2. Conventions and Terminology 2. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [2]. document are to be interpreted as described in RFC 2119 [RFC2119].
2.1. Definitions 2.1. Definitions
Authoritative Proxy: A proxy that handles non-REGISTER requests for Authoritative Proxy: A proxy that handles non-REGISTER requests for
a specific Address-of-Record (AOR), performs the logical Location a specific Address-of-Record (AOR), performs the logical Location
Server lookup described in RFC 3261, and forwards those requests Server lookup described in RFC 3261, and forwards those requests
to specific Contact URIs. to specific Contact URIs.
Edge Proxy: An Edge Proxy is any proxy that is located topologically Edge Proxy: An Edge Proxy is any proxy that is located topologically
between the registering User Agent and the Authoritative Proxy. between the registering User Agent and the Authoritative Proxy.
Flow: A Flow is a network protocol layer (layer 4) association Flow: A Flow is a network protocol layer (layer 4) association
between two hosts that is represented by the network address and between two hosts that is represented by the network address and
port number of both ends and by the protocol. For TCP, a flow is port number of both ends and by the protocol. For TCP, a flow is
equivalent to a TCP connection. For UDP a flow is a bidirectional equivalent to a TCP connection. For UDP a flow is a bidirectional
stream of datagrams between a single pair of IP addresses and stream of datagrams between a single pair of IP addresses and
ports of both peers. With TCP, a flow often has a one to one ports of both peers. With TCP, a flow often has a one to one
correspondence with a single file descriptor in the operating correspondence with a single file descriptor in the operating
system. system.
Flow Token: An identifier which uniquely identifies a flow which can
be included in a SIP URI (Uniform Resource Identifier).
reg-id: This refers to the value of a new header field parameter reg-id: This refers to the value of a new header field parameter
value for the Contact header field. When a UA registers multiple value for the Contact header field. When a UA registers multiple
times, each concurrent registration gets a unique reg-id value. times, each concurrent registration gets a unique reg-id value.
instance-id: This specification uses the word instance-id to refer instance-id: This specification uses the word instance-id to refer
to the value of the "sip.instance" media feature tag in the to the value of the "sip.instance" media feature tag in the
Contact header field. This is a Uniform Resource Name (URN) that Contact header field. This is a Uniform Resource Name (URN) that
uniquely identifies this specific UA instance. uniquely identifies this specific UA instance.
'ob' Parameter: The 'ob' parameter is a SIP URI parameter which has
different meaning depending on context. In a Path header field
value it is used by the first edge proxy to indicate that a flow
token was added to the URI. In a Contact or Route header field
value it indicates that the UA would like other requests in the
same dialog routed over the same flow.
outbound-proxy-set: A set of SIP URIs (Uniform Resource Identifiers) outbound-proxy-set: A set of SIP URIs (Uniform Resource Identifiers)
that represents each of the outbound proxies (often Edge Proxies) that represents each of the outbound proxies (often Edge Proxies)
with which the UA will attempt to maintain a direct flow. The with which the UA will attempt to maintain a direct flow. The
first URI in the set is often referred to as the primary outbound first URI in the set is often referred to as the primary outbound
proxy and the second as the secondary outbound proxy. There is no proxy and the second as the secondary outbound proxy. There is no
difference between any of the URIs in this set, nor does the difference between any of the URIs in this set, nor does the
primary/secondary terminology imply that one is preferred over the primary/secondary terminology imply that one is preferred over the
other. other.
3. Overview 3. Overview
skipping to change at page 6, line 8 skipping to change at page 6, line 16
3.1. Summary of Mechanism 3.1. Summary of Mechanism
The overall approach is fairly simple. Each UA has a unique The overall approach is fairly simple. Each UA has a unique
instance-id that stays the same for this UA even if the UA reboots or instance-id that stays the same for this UA even if the UA reboots or
is power cycled. Each UA can register multiple times over different is power cycled. Each UA can register multiple times over different
connections for the same SIP Address of Record (AOR) to achieve high connections for the same SIP Address of Record (AOR) to achieve high
reliability. Each registration includes the instance-id for the UA reliability. Each registration includes the instance-id for the UA
and a reg-id label that is different for each flow. The registrar and a reg-id label that is different for each flow. The registrar
can use the instance-id to recognize that two different registrations can use the instance-id to recognize that two different registrations
both reach the same UA. The registrar can use the reg-id label to both reach the same UA. The registrar can use the reg-id label to
recognize whether a UA is creatin a new flow or refreshing or recognize whether a UA is creating a new flow or refreshing or
replacing an old one, possibly after a reboot or a network failure. replacing an old one, possibly after a reboot or a network failure.
When a proxy goes to route a message to a UA for which it has a When a proxy goes to route a message to a UA for which it has a
binding, it can use any one of the flows on which a successful binding, it can use any one of the flows on which a successful
registration has been completed. A failure to deliver a request on a registration has been completed. A failure to deliver a request on a
particular flow can be tried again on an alternate flow. Proxies can particular flow can be tried again on an alternate flow. Proxies can
determine which flows go to the same UA by comparing the instance-id. determine which flows go to the same UA by comparing the instance-id.
Proxies can tell that a flow replaces a previously abandoned flow by Proxies can tell that a flow replaces a previously abandoned flow by
looking at the reg-id. looking at the reg-id.
When sending a dialog-forming request, a UA can also ask its first
edge proxy to route subsequent requests in that dialog over the same
flow. This is necessary whether the UA has registered or not.
UAs can use a simple periodic message as a keepalive mechanism to UAs can use a simple periodic message as a keepalive mechanism to
keep their flow to the proxy or registrar alive. For connection keep their flow to the proxy or registrar alive. For connection
oriented transports such as TCP this is based on CRLF or a transport oriented transports such as TCP this is based on carriage-return and
specific keepalive while for transports that are not connection line-feed sequences (CRLF), while for transports that are not
oriented this is accomplished by using a SIP-specific usage profile connection oriented this is accomplished by using a SIP-specific
of STUN (Session Traversal Utilities for NAT) [3]. usage profile of STUN (Session Traversal Utilities for NAT)
[I-D.ietf-behave-rfc3489bis].
The UA can also ask its first hop proxy to use an specific flow for The UA can also ask its first hop proxy to use an specific flow for
subsequent messages when sending a dialog-forming request. This subsequent messages when sending a dialog-forming request. This
allows the UA to setup a subscription dialog for the SIP allows the UA to setup a subscription dialog for the SIP
configuration package [19] before the UA registers. configuration package [I-D.ietf-sipping-config-framework] before the
UA registers.
3.2. Single Registrar and UA 3.2. Single Registrar and UA
In the topology shown below, a single server is acting as both a In the topology shown below, a single server is acting as both a
registrar and proxy. registrar and proxy.
+-----------+ +-----------+
| Registrar | | Registrar |
| Proxy | | Proxy |
+-----+-----+ +-----+-----+
| |
| |
+----+--+ +----+--+
| User | | User |
| Agent | | Agent |
+-------+ +-------+
User Agents which form only a single flow continue to register User Agents which form only a single flow continue to register
normally but include the instance-id as described in Section 4.1. normally but include the instance-id as described in Section 4.1.
The UA can also include a reg-id parameter which is used to allow the The UA also includes a reg-id parameter which is used to allow the
registrar to detect and avoid keeping invalid contacts when a UA registrar to detect and avoid keeping invalid contacts when a UA
reboots or reconnects after its old connection has failed for some reboots or reconnects after its old connection has failed for some
reason. reason.
For clarity, here is an example. Bob's UA creates a new TCP flow to For clarity, here is an example. Bob's UA creates a new TCP flow to
the registrar and sends the following REGISTER request. the registrar and sends the following REGISTER request.
REGISTER sip:example.com;keep SIP/2.0 REGISTER sip:example.com SIP/2.0
Via: SIP/2.0/TCP 192.168.0.2;rport;branch=z9hG4bK-bad0ce-11-1036 Via: SIP/2.0/TCP 192.168.0.2;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, outbound Supported: path, outbound
Contact: <sip:line1@192.168.0.2;transport=tcp>; reg-id=1; Contact: <sip:line1@192.168.0.2;transport=tcp>; reg-id=1;
;+sip.instance="<urn:uuid:00000000-0000-1000-8000-000A95A0E128>" ;+sip.instance="<urn:uuid:00000000-0000-1000-8000-000A95A0E128>"
Content-Length: 0 Content-Length: 0
skipping to change at page 7, line 43 skipping to change at page 8, line 11
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 existing flow, instead of resolving the Contact URI using the that existing flow, instead of resolving the Contact URI using the
procedures in RFC 3263 [4] and trying to form a new flow to that procedures in RFC 3263 [RFC3263] and trying to form a new flow to
contact. that contact.
As described in the next section, if the proxy has multiple flows As described in the next section, if the proxy has multiple flows
that all go to this UA, the proxy can choose any one of the that all go to this UA, the proxy can choose any one of the
registration bindings for this AOR that has the same instance-id as registration bindings for this AOR that has the same instance-id as
the selected UA. the selected UA.
3.3. Multiple Connections from a User Agent 3.3. Multiple Connections from a User Agent
There are various ways to deploy SIP to build a reliable and scalable There are various ways to deploy SIP to build a reliable and scalable
system. This section discusses one such design that is possible with system. This section discusses one such design that is possible with
skipping to change at page 8, line 20 skipping to change at page 8, line 34
possible. possible.
In the example system below, the logical outbound proxy/registrar for In the example system below, the logical outbound proxy/registrar for
the domain is running on two hosts that share the appropriate state the domain is running on two hosts that share the appropriate state
and can both provide registrar and outbound proxy functionality for and can both provide registrar and outbound proxy functionality for
the domain. The UA will form connections to two of the physical the domain. The UA will form connections to two of the physical
hosts that can perform the authoritative proxy/registrar function for hosts that can perform the authoritative proxy/registrar function for
the domain. Reliability is achieved by having the UA form two TCP the domain. Reliability is achieved by having the UA form two TCP
connections to the domain. connections to the domain.
Scalability is achieved by using DNS SRV [20] to load balance the Scalability is achieved by using DNS SRV [RFC2782] to load balance
primary connection across a set of machines that can service the the primary connection across a set of machines that can service the
primary connection, and also using DNS SRV to load balance across a primary connection, and also using DNS SRV to load balance across a
separate set of machines that can service the secondary connection. separate set of machines that can service the secondary connection.
The deployment here requires that DNS is configured with one entry The deployment here requires that DNS is configured with one entry
that resolves to all the primary hosts and another entry that that resolves to all the primary hosts and another entry that
resolves to all the secondary hosts. While this introduces resolves to all the secondary hosts. While this introduces
additional DNS configuration, the approach works and requires no additional DNS configuration, the approach works and requires no
additional SIP extensions. additional SIP extensions.
Note: Approaches which select multiple connections from a single Note: Approaches which select multiple connections from a single
DNS SRV set were also considered, but cannot prevent two DNS SRV set were also considered, but cannot prevent two
connections from accidentally resolving to the same host. The connections from accidentally resolving to the same host. The
approach in this document does not prevent future extensions, such approach in this document does not prevent future extensions, such
as the SIP UA configuration framework [19], from adding other ways as the SIP UA configuration framework
for a User Agent to discover its outbound-proxy-set. [I-D.ietf-sipping-config-framework], from adding other ways for a
User Agent to discover its outbound-proxy-set.
+-------------------+ +-------------------+
| Domain | | Domain |
| Logical Proxy/Reg | | Logical Proxy/Reg |
| | | |
|+-----+ +-----+| |+-----+ +-----+|
||Host1| |Host2|| ||Host1| |Host2||
|+-----+ +-----+| |+-----+ +-----+|
+---\------------/--+ +---\------------/--+
\ / \ /
skipping to change at page 9, line 4 skipping to change at page 9, line 21
|+-----+ +-----+| |+-----+ +-----+|
+---\------------/--+ +---\------------/--+
\ / \ /
\ / \ /
\ / \ /
\ / \ /
+------+ +------+
| User | | User |
| Agent| | Agent|
+------+ +------+
The UA is configured with multiple outbound proxy registration URIs. The UA is configured with multiple outbound proxy registration URIs.
These URIs are configured into the UA through whatever the normal These URIs are configured into the UA through whatever the normal
mechanism is to configure the proxy address and AOR in the UA. If mechanism is to configure the proxy address and AOR in the UA. If
the AOR is alice@example.com, the outbound-proxy-set might look the AOR is alice@example.com, the outbound-proxy-set might look
something like "sip:primary.example.com;keep" and "sip: something like "sip:primary.example.com" and "sip:
secondary.example.com;keep". The "keep" tag indicates that a SIP secondary.example.com". Note that each URI in the outbound-proxy-set
server will respond correctly to the mandatory to implement keepalive could resolve to several different physical hosts. The
mechanisms described later in this specification. Note that each URI administrative domain that created these URIs should ensure that the
in the outbound-proxy-set could resolve to several different physical two URIs resolve to separate hosts. These URIs are handled according
hosts. The administrative domain that created these URIs should to normal SIP processing rules, so mechanisms like SRV can be used to
ensure that the two URIs resolve to separate hosts. These URIs are do load balancing across a proxy farm.
handled according to normal SIP processing rules, so mechanisms like
SRV can be used to do load balancing across a proxy farm.
The domain also needs to ensure that a request for the UA sent to The domain also needs to ensure that a request for the UA sent to
host1 or host2 is then sent across the appropriate flow to the UA. host1 or host2 is then sent across the appropriate flow to the UA.
The domain might choose to use the Path header approach (as described The domain might choose to use the Path header approach (as described
in the next section) to store this internal routing information on in the next section) to store this internal routing information on
host1 or host2. host1 or host2.
When a single server fails, all the UAs that have a flow through it When a single server fails, all the UAs that have a flow through it
will detect a flow failure and try to reconnect. This can cause will detect a flow failure and try to reconnect. This can cause
large loads on the server. When large numbers of hosts reconnect large loads on the server. When large numbers of hosts reconnect
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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 [5] so that when Registrar. The Edge Proxy includes a Path header [RFC3327] so that
the registrar later forwards a request to this UA, the request is when the registrar later forwards a request to this UA, the request
routed through the Edge Proxy. There could be a NAT or firewall is routed through the Edge Proxy. There could be a NAT or firewall
between the UA and the Edge Proxy. between the UA and the Edge Proxy.
+---------+ +---------+
|Registrar| |Registrar|
|Proxy | |Proxy |
+---------+ +---------+
/ \ / \
/ \ / \
/ \ / \
+-----+ +-----+ +-----+ +-----+
|Edge1| |Edge2| |Edge1| |Edge2|
skipping to change at page 10, line 48 skipping to change at page 11, line 15
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 [5]. Path header mechanism in RFC 3327 [RFC3327].
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 its place.
This document also suggests timer values for two of these client This document also suggests timer values for two of these client keep
keepalive mechanisms. These timer values were chosen to keep most alive mechanisms. These timer values were chosen to keep most NAT
NAT and firewall bindings open, to detect unresponsive servers within and firewall bindings open, to detect unresponsive servers within 2
2 minutes, and to prevent the avalanche restart problem. However, minutes, and to prevent the avalanche restart problem. However, the
the client may choose different timer values to suit its needs, for client may choose different timer values to suit its needs, for
example to optimize battery life. In some environments, the server 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 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 to guess the likelihood that the flow is still useful for delivering
SIP messages. In this case, the server provides an indicator (the SIP messages.
'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 keep
keepalive approach based on sending CRLFs, and for TCP, a usage of alive approach based on sending CRLFs. For connectionless transport,
TCP transport-layer keepalives. For connectionless transport, such such as UDP, this specification describes using STUN
as UDP, this specification describes using STUN [3] over the same [I-D.ietf-behave-rfc3489bis] over the same flow as the SIP traffic to
flow as the SIP traffic to perform the keepalive. perform the keepalive.
UAs are also free to use native transport keepalives, however the UA UAs are also free to use native transport keepalives, however the UA
application may not be able to set these timers on a per-connection application may not be able to set these timers on a per-connection
basis, and the server certainly cannot make any assumption about what basis, and the server certainly cannot make any assumption about what
values are used. Use of native transport keepalives is therefore values are used. Use of native transport keepalives is therefore
outside the scope of this document. outside the scope of this document.
3.5.1. CRLF Keepalive Technique 3.5.1. CRLF Keep-alive Technique
This approach can only be used with connection-oriented transports This approach can only be used with connection-oriented transports
such as TCP or SCTP. The client periodically sends a double-CRLF such as TCP or SCTP. The client periodically sends a double-CRLF
(the "ping") then waits to receive a single CRLF (the "pong"). If (the "ping") then waits to receive a single CRLF (the "pong"). If
the client does not receive a "pong" within an appropriate amount of the client does not receive a "pong" within an appropriate amount of
time, it considers the flow failed. time, it considers the flow failed.
Sending a CRLF over a connection-oriented transport is backwards
compatible (because of requirements in Section 7.5 of RFC 3261),
but only implementations which support this specification will
respond to a "ping" with a "pong".
3.5.2. STUN Keepalive Technique 3.5.2. STUN Keepalive Technique
This technique can only be used for connection-less transports, such This approach can only be used for connection-less transports, such
as UDP. as UDP.
For connection-less transports, a flow definition could change For connection-less transports, a flow definition could change
because a NAT device in the network path reboots and the resulting because a NAT device in the network path reboots and the resulting
public IP address or port mapping for the UA changes. To detect public IP address or port mapping for the UA changes. To detect
this, STUN requests are sent over the same flow that is being used this, STUN requests are sent over the same flow that is being used
for the SIP traffic. The proxy or registrar acts as a Session for the SIP traffic. The proxy or registrar acts as a Session
Traversal Utilities for NAT (STUN) [3] server on the SIP signaling Traversal Utilities for NAT (STUN) [I-D.ietf-behave-rfc3489bis]
port. server on the SIP signaling port.
Note: The STUN mechanism is very robust and allows the detection Note: The STUN mechanism is very robust and allows the detection
of a changed IP address. Many other options were considered, but of a changed IP address. Many other options were considered, but
the SIP Working Group selected the STUN-based approach. the SIP Working Group selected the STUN-based approach.
Approaches using SIP requests were abandoned because many believed Approaches using SIP requests were abandoned because many believed
that good performance and full backwards compatibility using this that good performance and full backwards compatibility using this
method were mutually exclusive. method were mutually exclusive.
4. User Agent Mechanisms 4. User Agent Mechanisms
4.1. Instance ID Creation 4.1. Instance ID Creation
Each UA MUST have an Instance Identifier URN that uniquely identifies Each UA MUST have an Instance Identifier Uniform Resource Name (URN)
the device. Usage of a URN provides a persistent and unique name for [RFC2141] that uniquely identifies the device. Usage of a URN
the UA instance. It also provides an easy way to guarantee provides a persistent and unique name for the UA instance. It also
uniqueness within the AOR. This URN MUST be persistent across power provides an easy way to guarantee uniqueness within the AOR. This
cycles of the device. The Instance ID MUST NOT change as the device URN MUST be persistent across power cycles of the device. The
moves from one network to another. Instance ID MUST NOT change as the device moves from one network to
another.
A UA SHOULD create a UUID URN [6] as its instance-id. The UUID URN A UA SHOULD create a UUID URN [RFC4122] as its instance-id. The UUID
allows for non-centralized computation of a URN based on time, unique URN allows for non-centralized computation of a URN based on time,
names (such as a MAC address), or a random number generator. 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 [6] and then save this in persistent storage for all future UUID [RFC4122] and then save this in persistent storage for all
use. For a device such as a hard phone, which will only ever have future use. For a device such as a hard phone, which will only
a single SIP UA present, the UUID can include the MAC address and ever have a single SIP UA present, the UUID can include the MAC
be generated at any time because it is guaranteed that no other address and be generated at any time because it is guaranteed that
UUID is being generated at the same time on that physical device. no other UUID is being generated at the same time on that physical
This means the value of the time component of the UUID can be device. This means the value of the time component of the UUID
arbitrarily selected to be any time less than the time when the can be arbitrarily selected to be any time less than the time when
device was manufactured. A time of 0 (as shown in the example in the device was manufactured. A time of 0 (as shown in the example
Section 3.2) is perfectly legal as long as the device knows no in Section 3.2) is perfectly legal as long as the device knows no
other UUIDs were generated at this time on this device. other UUIDs were generated at this time on this device.
If a URN scheme other than UUID is used, the UA MUST only use URNs If a URN scheme other than UUID is used, the UA MUST only use URNs
for which an IETF consensus RFC defines how the specific URN needs to for which an IETF consensus RFC defines how the specific URN needs to
be constructed and used in the sip.instance Contact parameter for be constructed and used in the sip.instance Contact parameter for
outbound behavior. outbound behavior.
To convey its instance-id in both requests and responses, the UA To convey its instance-id in both requests and responses, the UA
includes a "sip.instance" media feature tag as a UA characteristic includes a "sip.instance" media feature tag as a UA characteristic
[7] . As described in [7], this media feature tag will be encoded in [RFC3840] . As described in [RFC3840], this media feature tag will
the Contact header field as the "+sip.instance" Contact header field be encoded in the Contact header field as the "+sip.instance" Contact
parameter. The value of this parameter MUST be a URN [8]. One case header field parameter. One case where a UA may not want to include
where a UA may not want to include the sip.instance media feature tag the sip.instance media feature tag at all is when it is making an
at all is when it is making an anonymous request or some other anonymous request or some other privacy concern requires that the UA
privacy concern requires that the UA not reveal its identity. not reveal its identity.
RFC 3840 [7] defines equality rules for callee capabilities RFC 3840 [RFC3840] defines equality rules for callee capabilities
parameters, and according to that specification, the parameters, and according to that specification, the
"sip.instance" media feature tag will be compared by case- "sip.instance" media feature tag will be compared by case-
sensitive string comparison. This means that the URN will be sensitive string comparison. This means that the URN will be
encapsulated by angle brackets ("<" and ">") when it is placed encapsulated by angle brackets ("<" and ">") when it is placed
within the quoted string value of the +sip.instance Contact header within the quoted string value of the +sip.instance Contact header
field parameter. The case-sensitive matching rules apply only to field parameter. The case-sensitive matching rules apply only to
the generic usages defined in RFC 3840 [7] and in the caller the generic usages defined in RFC 3840 [RFC3840] and in the caller
preferences specification [9]. When the instance ID is used in preferences specification [RFC3841]. When the instance ID is used
this specification, it is effectively "extracted" from the value in this specification, it is effectively "extracted" from the
in the "sip.instance" media feature tag. Thus, equality value in the "sip.instance" media feature tag. Thus, equality
comparisons are performed using the rules for URN equality that comparisons are performed using the rules for URN equality that
are specific to the scheme in the URN. If the element performing are specific to the scheme in the URN. If the element performing
the comparisons does not understand the URN scheme, it performs the comparisons does not understand the URN scheme, it performs
the comparisons using the lexical equality rules defined in RFC the comparisons using the lexical equality rules defined in RFC
2141 [8]. Lexical equality could result in two URNs being 2141 [RFC2141]. 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
MUST provide lexically equivalent URNs in each registration it MUST provide lexically equivalent URNs in each registration it
generates. This is likely to be normal behavior in any case; generates. This is likely to be normal behavior in any case;
clients are not likely to modify the value of the instance ID so clients are not likely to modify the value of the instance ID so
that it remains functionally equivalent yet lexicographically that it remains functionally equivalent yet lexicographically
different from previous registrations. different from previous registrations.
4.2. Registrations 4.2. Registrations
4.2.1. Initial Registrations
At configuration time, UAs obtain one or more SIP URIs representing At configuration time, UAs obtain one or more SIP URIs representing
the default outbound-proxy-set. This specification assumes the set the default outbound-proxy-set. This specification assumes the set
is determined via any of a number of configuration mechanisms, and is determined via any of a number of configuration mechanisms, and
future specifications can define additional mechanisms such as using future specifications can define additional mechanisms such as using
DNS to discover this set. How the UA is configured is outside the DNS to discover this set. How the UA is configured is outside the
scope of this specification. However, a UA MUST support sets with at scope of this specification. However, a UA MUST support sets with at
least two outbound proxy URIs and SHOULD support sets with up to four least two outbound proxy URIs and SHOULD support sets with up to four
URIs. URIs.
For each outbound proxy URI in the set, the UA SHOULD send a REGISTER For each outbound proxy URI in the set, the UA SHOULD send a unique
in the normal way using this URI as the default outbound proxy. (The REGISTER in the normal way using this URI as the default outbound
UA could limit the number of flows formed to conserve battery power, proxy. (The UA could limit the number of flows formed to conserve
for example). All of these REGISTER requests will use the same battery power, for example). UAs that support this specification
Call-ID. [OPEN ISSUE: This is for consistency with GRUU, Section MUST include the outbound option tag in a Supported header field in a
5.1 paragraph 5. Is this a bad idea? Alternatively GRUU could check REGISTER request. Each of these REGISTER requests will use a unique
all reg-ids and preserve temporary GRUU if a registration used the Call-ID. Forming the route set for the request is outside the scope
same Call-ID as used by any of the current bindings for the same of this document, but typically results in sending the REGISTER such
instance.] Forming the route set for the request is outside the that the topmost Route header field contains a loose route to the
scope of this document, but typically results in sending the REGISTER outbound proxy URI.
such that the topmost Route header field contains a loose route to
the outbound proxy URI. Other issues related to outbound route
construction are discussed in [21].
Registration requests, other than those described in Section 4.2.1, Registration requests, other than those described in Section 4.2.3,
MUST include an instance-id media feature tag as specified in MUST include an instance-id media feature tag as specified in
Section 4.1. Section 4.1.
These ordinary registration requests include a distinct reg-id These ordinary registration requests include a distinct reg-id
parameter in the Contact header field. Each one of these parameter in the Contact header field. Each one of these
registrations will form a new flow from the UA to the proxy. The registrations will form a new flow from the UA to the proxy. The
sequence of reg-id values does not have to be sequential but MUST be sequence of reg-id values does not have to be sequential but MUST be
exactly the same sequence of reg-id values each time the UA instance exactly the same sequence of reg-id values each time the UA instance
power cycles or reboots so that the reg-id values will collide with power cycles or reboots so that the reg-id values will collide with
the previously used reg-id values. This is so the registrar can the previously used reg-id values. This is so the registrar can
skipping to change at page 14, line 47 skipping to change at page 15, line 15
The UAC can situationally decide whether to request outbound The UAC can situationally decide whether to request outbound
behavior by including or omitting the 'reg-id' parameter. For behavior by including or omitting the 'reg-id' parameter. For
example, imagine the outbound-proxy-set contains two proxies in example, imagine the outbound-proxy-set contains two proxies in
different domains, EP1 and EP2. If an outbound-style registration different domains, EP1 and EP2. If an outbound-style registration
succeeded for a flow through EP1, the UA might decide to include succeeded for a flow through EP1, the UA might decide to include
'outbound' in its Require header field when registering with EP2, 'outbound' in its Require header field when registering with EP2,
in order to insure consistency. Similarly, if the registration in order to insure consistency. Similarly, if the registration
through EP1 did not support outbound, the UA might not register through EP1 did not support outbound, the UA might not register
with EP2 at all. with EP2 at all.
The UAC MUST indicate that it supports the Path header [5] mechanism, The UAC MUST indicate that it supports the Path header [RFC3327]
by including the 'path' option-tag in a Supported header field value mechanism, by including the 'path' option-tag in a Supported header
in its REGISTER requests. Other than optionally examining the Path field value in its REGISTER requests. Other than optionally
vector in the response, this is all that is required of the UAC to examining the Path vector in the response, this is all that is
support Path. required of the UAC to support Path.
The UAC MAY examine successful registration responses for the The UAC examines successful registration responses for the presence
presence of an 'outbound' option-tag in a Require header field value. of an 'outbound' option-tag in a Require header field value.
Presence of this option-tag indicates that the registrar is compliant Presence of this option-tag indicates that the registrar is compliant
with this specification, and that any edge proxies which needed to with this specification, and that any edge proxies which needed to
participate are also compliant. If the registrar did not support participate are also compliant. If the registrar did not support
outbound, the UA may have unintentionally registered an unroutable outbound, the UA may have unintentionally registered an unroutable
contact. It is the responsiblity of the UA to remove any contact. It is the responsiblity of the UA to remove any
inappropriate Contacts. inappropriate Contacts.
If outbound registration succeeded, as indicated by the presence of
the outbound option-tag in the Require header field of a successful
registration response, the UA begins sending keepalives as described
in Section 4.4.
Note that the UA needs to honor 503 (Service Unavailable) responses Note that the UA needs to honor 503 (Service Unavailable) responses
to registrations as described in RFC 3261 and RFC 3263 [4]. In to registrations as described in RFC 3261 and RFC 3263 [RFC3263]. In
particular, implementors should note that when receiving a 503 particular, implementors should note that when receiving a 503
(Service Unavailable) response with a Retry-After header field, the (Service Unavailable) response with a Retry-After header field, the
UA is expected to wait the indicated amount of time and retry the UA is expected to wait the indicated amount of time and retry the
registration. A Retry-After header field value of 0 is valid and registration. A Retry-After header field value of 0 is valid and
indicates the UA is expected to retry the REGISTER immediately. indicates the UA is expected to retry the REGISTER immediately.
Implementations need to ensure that when retrying the REGISTER, they Implementations need to ensure that when retrying the REGISTER, they
revisit the DNS resolution results such that the UA can select an revisit the DNS resolution results such that the UA can select an
alternate host from the one chosen the previous time the URI was alternate host from the one chosen the previous time the URI was
resolved. resolved.
Finally, re-registrations which merely refresh an existing valid If the registering UA receives a 439 (First Hop Lacks Outbound
registration SHOULD be sent over the same flow as the original Support) response to a REGISTER request, it MAY re-attempt
registration without an outbound proxy (subject to local policy at
the client). If the client has one or more alternate outbound
proxies available, it MAY re-attempt registration through such
outbound proxies. See Section 11.2 for more information on the 439
response code.
4.2.2. Subsequent REGISTER requests
Re-registrations and single Contact de-registrations use the same
instance-id and reg-id values as the corresponding initial
registration. Re-registrations which merely refresh an existing
valid registration SHOULD be sent over the same flow as the original
registration. registration.
4.2.1. Non Outbound Registrations 4.2.3. Non Outbound Registrations
A User Agent MUST NOT include a reg-id header parameter in the A User Agent MUST NOT include a reg-id header parameter in the
Contact header field of a registration with a non-zero expiration, if Contact header field of a registration with a non-zero expiration, if
the registering UA is not the same instance as the UA referred to by the registering UA is not the same instance as the UA referred to by
the target Contact header field. (This practice is occasionally used the target Contact header field. (This practice is occasionally used
to install forwarding policy into registrars.) to install forwarding policy into registrars.)
A UAC also MUST NOT include an instance-id or reg-id parameter in a A UAC also MUST NOT include an instance-id or reg-id parameter in a
request to unregister all Contacts (a single Contact header field request to unregister all Contacts (a single Contact header field
value with the value of "*"). value with the value of "*").
4.3. Sending Non-REGISTER Requests 4.3. Sending Non-REGISTER Requests
When a UA is about to send a request, it first performs normal When a UA is about to send a request, it first performs normal
processing to select the next hop URI. The UA can use a variety of processing to select the next hop URI. The UA can use a variety of
techniques to compute the route set and accordingly the next hop URI. techniques to compute the route set and accordingly the next hop URI.
Discussion of these techniques is outside the scope of this document Discussion of these techniques is outside the scope of this document.
but could include mechanisms specified in RFC 3608 [22] (Service UAs that support this specification SHOULD include the outbound
Route) and [21]. option tag in a Supported header field in a non-Register REGISTER
request.
The UA performs normal DNS resolution on the next hop URI (as The UA performs normal DNS resolution on the next hop URI (as
described in RFC 3263 [4]) to find a protocol, IP address, and port. described in RFC 3263 [RFC3263]) to find a protocol, IP address, and
port. For protocols that don't use TLS, if the UA has an existing
For protocols that don't use TLS, if the UA has an existing flow to flow to this IP address, and port with the correct protocol, then the
this IP address, and port with the correct protocol, then the UA MUST UA MUST use the existing connection. For TLS protocols, there MUST
use the existing connection. For TLS protocols, there MUST also be a also be a match between the host production in the next hop and one
match between the host production in the next hop and one of the URIs of the URIs contained in the subjectAltName in the peer certificate.
contained in the subjectAltName in the peer certificate. If the UA If the UA cannot use one of the existing flows, then it SHOULD form a
cannot use one of the existing flows, then it SHOULD form a new flow new flow by sending a datagram or opening a new connection to the
by sending a datagram or opening a new connection to the next hop, as next hop, as appropriate for the transport protocol.
appropriate for the transport protocol.
If the UA is sending a dialog-forming request, and wants all If the UA is sending a dialog-forming request, and wants all
subsequent requests in the dialog to arrive over the same flow, the subsequent requests in the dialog to arrive over the same flow, the
UA adds an 'ob' parameter to its Contact header. Typically this is UA adds an 'ob' parameter to its Contact header. Typically this is
desirable, but it is not necessary for example if the Contact is a desirable, but it is not necessary for example if the Contact is a
GRUU [23]. The flow used for the request is typically the same flow GRUU [I-D.ietf-sip-gruu]. The flow used for the request is typically
the UA registered over, but it could be a new flow, for example the the same flow the UA registered over, but it could be a new flow, for
initial subcription dialog for the configuration framework [19] needs example the initial subcription dialog for the configuration
to exist before registration. framework [I-D.ietf-sipping-config-framework] needs to exist before
registration.
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
Via header field value, and send from the port it is prepared to
receive on. More general information about NAT traversal in SIP
is described in [24].
****** Note that if the UA wants a UDP flow to work through NATs or
firewalls it still needs to put the 'rport' parameter [RFC3581] in
its Via header field value, and send from the port it is prepared
to receive on. More general information about NAT traversal in
SIP is described in [I-D.ietf-sipping-nat-scenarios].
4.4. Detecting Flow Failure 4.4. Keep-alives and Detecting Flow Failure
The UA needs to detect when a specific flow fails. The UA actively The UA needs to detect when a specific flow fails. The UA actively
tries to detect failure by periodically sending keepalive messages tries to detect failure by periodically sending keepalive messages
using one of the techniques described in Section 4.4.1 or using one of the techniques described in Section 4.4.1 or
Section 4.4.2. If a flow has failed, the UA follows the procedures Section 4.4.2. If a flow has failed, the UA follows the procedures
in Section 4.2 to form a new flow to replace the failed one. in Section 4.2 to form a new flow to replace the failed one.
When the outbound-proxy-set contains the "timed-keepalives" When a successful registration response contains the Flow-Timer
parameter, the UA MUST send its keepalives according to the time header field, the value of this header field is the number of seconds
periods described in this section. The server can specify this so the server is prepared to wait without seeing keepalives before it
the server can detect liveness of the client within a predictable considers the corresponding flow dead. The UA MUST send keepalives
time scale. If the parameter is not present, the UA can send at least as often as this number of seconds. If the UA uses the
keepalives at its discretion. server recommended keepalive frequency it SHOULD send its keepalives
so that the interval between each keepalive is randomly distributed
between 80% and 100% of the server provided time. For example, it
the server suggests 120 seconds, the UA would send each keepalive
with a different frequency between 95 and 120 seconds.
The time between each keepalive request when using non connection If no Flow-Timer header field was present in a register response for
based transports such as UDP SHOULD be a random number between 24 and this flow, the UA can send keepalives at its discretion. The rest of
29 seconds while for connection based transports such as TCP it this paragraph provides RECOMMENDED default values for these
SHOULD be a random number between 95 and 120 seconds. These times keepalives. The time between each keep alive request when using non
MAY be configurable. To clarify, the random number will be different connection based transports such as UDP SHOULD be a random number
for each request. Issues such as battery consumption might motivate between 24 and 29 seconds. For connection based transports such as
longer keepalive intervals. If the 'timed-keepalives' parameter is TCP, correct selection of keepalive frequency is primarily a trade-
set on the outbound-proxy-set, the UA MUST use these recommended off between battery usage and availability. For devices where power
timer values. is not a significant concern, the UA SHOULD select a random number
between 95 and 120 seconds between keepalives. When battery power is
a concern, the UA SHOULD select a random number between 672 and 840
seconds (14 minutes). These times MAY be configurable. To clarify,
the random number will be different for each keepalive ping.
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, as many NATs have UDP timeouts as low as 30
before 30 seconds, as many NATs have UDP timeouts as low as 30
seconds. The 24 second lower bound was selected so that after 10 seconds. The 24 second lower bound was selected so that after 10
minutes the jitter introduced by different timers will make the minutes the jitter introduced by different timers will make the
keepalive requests unsynchronized to evenly spread the load on the keep alive requests unsynchronized to evenly spread the load on
servers. For TCP, the 120 seconds upper bound was chosen based on the servers. For TCP, the 120 seconds upper bound was chosen
the idea that for a good user experience, failures normally will based on the idea that for a good user experience, failures
be detected in this amount of time and a new connection set up. normally will be detected in this amount of time and a new
Operators that wish to change the relationship between load on connection set up. The 14 minute upper-bound for battery-powered
servers and the expected time that a user might not receive devices was selected based on NATs with TCP timeouts as low as 15
inbound communications will probably adjust this time. The 95 minutes. Operators that wish to change the relationship between
seconds lower bound was chosen so that the jitter introduced will load on servers and the expected time that a user might not
result in a relatively even load on the servers after 30 minutes. receive inbound communications will probably adjust this time.
The 95 seconds lower bound was chosen so that the jitter
introduced will result in a relatively even load on the servers
after 30 minutes.
The client needs to perform normal RFC 3263 [4] SIP DNS resolution on The client needs to perform normal RFC 3263 [RFC3263] SIP DNS
the URI from the outbound-proxy-set to pick a transport. Once a resolution on the URI from the outbound-proxy-set to pick a
transport is selected, if the 'keep' parameter is present in the URI, transport. Once a transport is selected, the UA selects the keep
the UA selects the keepalive approach that is recommended for that alive approach that is recommended for that transport.
transport.
4.4.1. Keepalive with CRLF 4.4.1. Keepalive with CRLF
This approach MUST only be used with connection oriented transports This approach MUST only be used with connection oriented transports
such as TCP or SCTP. such as TCP or SCTP.
A User Agent that forms flows, checks if the configured URI to which A User Agent that forms flows, checks if the configured URI to which
the UA is connecting resolves to a stream-based transport (ex: TCP the UA is connecting resolves to a stream-based transport (ex: TCP
and TLS over TCP) and has a 'keep' URI parameter (defined in and TLS over TCP).
Section 12). If the parameter is present, the UA can 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 sending over TLS, the CRLFs sent in the middle of a SIP message. If sending over TLS, the CRLFs
are sent inside the TLS protected channel. If sending over a SigComp are sent inside the TLS protected channel. If sending over a SigComp
[25] compressed data stream, the CRLF keepalives are sent inside the [RFC3320] compressed data stream, the CRLF keep alives are sent
compressed stream. The double CRLF is considered a single SigComp inside the compressed stream. The double CRLF is considered a single
message. The specific mechanism for representing these characters is SigComp message. The specific mechanism for representing these
an implementation specific matter to be handled by the SigComp characters is an implementation specific matter to be handled by the
compressor at the sending end. SigComp compressor at the sending end.
If a pong is not received within 10 seconds then the client MUST If a pong is not received within 10 seconds then the client MUST
treat the flow as failed. Clients MUST support this CRLF keepalive. treat the flow as failed. Clients MUST support this CRLF keepalive.
4.4.2. Keepalive with STUN 4.4.2. Keepalive with STUN
This approach MUST only be used with connection-less transports, such This approach MUST only be used with connection-less transports, such
as UDP. as UDP.
A User Agent that forms flows, checks if the configured URI to which A User Agent that forms flows, checks if the configured URI to which
the UA is connecting resolve to use the UDP transport, and has a the UA is connecting resolve to use the UDP transport. The UA can
'keep' URI parameter (defined in Section 12). If the parameter is periodically perform keep alive checks by sending STUN
present, the UA can periodically perform keepalive checks by sending [I-D.ietf-behave-rfc3489bis] Binding Requests over the flow as
STUN [3] Binding Requests over the flow as described in Section 8. described in Section 8. Clients MUST support STUN based keep alives.
Clients MUST support STUN based keepalives.
If a STUN Binding Error Response is received, or if no Binding If a STUN Binding Error Response is received, or if no Binding
Response is received after 7 retransmissions (16 times the STUN "RTO" Response is received after 7 retransmissions (16 times the STUN "RTO"
timer--RTO is an estimate of round-trip time), the UA considers the timer--RTO is an estimate of round-trip time), the UA considers the
flow failed. If the XOR-MAPPED-ADDRESS in the STUN Binding Response flow failed. If the XOR-MAPPED-ADDRESS in the STUN Binding Response
changes, the UA MUST treat this event as a failure on the flow. changes, the UA MUST treat this event as a failure on the flow.
4.5. Flow Recovery 4.5. Flow Recovery
When a flow to a particular URI in the outbound-proxy-set fails, the When a flow used for registration (through a particular URI in the
UA needs to form a new flow to replace the old flow and replace any outbound-proxy-set) fails, the UA needs to form a new flow to replace
registrations that were previously sent over this flow. Each new the old flow and replace any registrations that were previously sent
registration MUST have the same reg-id as the registration it over this flow. Each new registration MUST have the same reg-id as
replaces. This is done in much the same way as forming a brand new the registration it replaces. This is done in much the same way as
flow as described in Section 4.2; however, if there is a failure in forming a brand new flow as described in Section 4.2; however, if
forming this flow, the UA needs to wait a certain amount of time there is a failure in forming this flow, the UA needs to wait a
before retrying to form a flow to this particular next hop. certain amount of time before retrying to form a flow to this
particular next hop.
The amount of time to wait depends if the previous attempt at The amount of time to wait depends if the previous attempt at
establishing a flow was successful. For the purposes of this establishing a flow was successful. For the purposes of this
section, a flow is considered successful if outbound registration section, a flow is considered successful if outbound registration
succeeded, and if keepalives are in use on this flow, at least one succeeded, and if keepalives are in use on this flow, at least one
subsequent keepalive response was received. subsequent keepalive response was received.
The number of seconds to wait is computed in the following way. If The number of seconds to wait is computed in the following way. If
all of the flows to every URI in the outbound proxy set have failed, all of the flows to every URI in the outbound proxy set have failed,
the base-time is set to 30 seconds; otherwise, in the case where at the base-time is set to 30 seconds; otherwise, in the case where at
skipping to change at page 19, line 38 skipping to change at page 20, line 34
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 [5]. If the Edge Proxy is the first SIP node after the UAC, it 3327 [RFC3327]. If the Edge Proxy is the first SIP node after the
either MUST store a "flow token"--containing information about the UAC, it either MUST store a "flow token" (containing information
flow from the previous hop--in its Path URI, or reject the request. about the flow from the previous hop) in its Path URI or reject the
The flow token MUST be an identifier that is unique to this network request. The flow token MUST be an identifier that is unique to this
flow. The flow token MAY be placed in the userpart of the URI. In network flow. The flow token MAY be placed in the userpart of the
addition, the first node MUST include an 'ob' URI parameter in its URI. In addition, the first node MUST include an 'ob' URI parameter
Path header field value. If the Edge Proxy is not the first SIP node in its Path header field value. If the Edge Proxy is not the first
after the UAC it MUST NOT place an 'ob' URI parameter in a Path SIP node after the UAC it MUST NOT place an 'ob' URI parameter in a
header field value. The Edge Proxy can determine if it is the first Path header field value. The Edge Proxy can determine if it is the
hop by examining the Via header field. first 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 infeasible 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. A stateless if the proxy crashed and lost the value of the counter. A stateless
example is provided below. A proxy can use any algorithm it wants as example is provided below. A proxy can use any algorithm it wants as
long as the flow token is unique to a flow, the flow can be recovered long as the flow token is unique to a flow, the flow can be recovered
from the token, and the token cannot be modified by attackers. from the token, and the token cannot be modified by attackers.
Example Algorithm: When the proxy boots it selects a 20-octet crypto Example Algorithm: When the proxy boots it selects a 20-octet crypto
random key called K that only the Edge Proxy knows. A byte array, random key called K that only the Edge Proxy knows. A byte array,
called S, is formed that contains the following information about called S, is formed that contains the following information about
the flow the request was received on: an enumeration indicating the flow the request was received on: an enumeration indicating
the protocol, the local IP address and port, the remote IP address the protocol, the local IP address and port, the remote IP address
and port. The HMAC of S is computed using the key K and the HMAC- and port. The HMAC of S is computed using the key K and the HMAC-
SHA1-80 algorithm, as defined in [26]. The concatenation of the SHA1-80 algorithm, as defined in [RFC2104]. The concatenation of
HMAC and S are base64 encoded, as defined in [27], and used as the the HMAC and S are base64 encoded, as defined in [RFC4648], and
flow identifier. When using IPv4 addresses, this will result in a used as the flow identifier. When using IPv4 addresses, this will
32-octet identifier. result in a 32-octet identifier.
5.3. Forwarding Non-REGISTER Requests 5.3. Forwarding Non-REGISTER Requests
When an Edge Proxy receives a request, it applies normal routing When an Edge Proxy receives a request, it applies normal routing
procedures with the following addition. If the Edge Proxy receives a procedures with the following additions. If the Edge Proxy receives
request where the edge proxy is the host in the topmost Route header a request where the edge proxy is the host in the topmost Route
field value, and the Route header field value contains a flow token, header field value, and the Route header field value contains a flow
the proxy decodes the flow token and compares the flow in the flow token, the proxy may need to do additional processing.
token with the source of the request to determine if this is an
"incoming" or "outgoing" request. If the Route header value contains an 'ob' parameter, the Route
header was probably copied from the Path header in a registration.
If this is the case and the request is a new dialog-forming request,
the proxy needs to adjust the route set to insure that subsequent
requests in the dialog can be delivered over a valid flow to the UA
instance identified by the flow token.
A simple approach to satisfy this requirement is for the proxy to
add a Record-Route header field value that contains the flow-
token, by copying the URI in the Route header minus the 'ob'
parameter.
Whether the Route header contained an 'ob' parameter or not, next the
proxy decodes the flow token and compares the flow in the flow token
with the source of the request to determine if this is an "incoming"
or "outgoing" request.
If the flow in the flow token in the topmost Route header field value If the flow in the flow token in the topmost Route header field value
matches the source of the request, the request in an "outgoing" matches the source IP address and port of the request, the request is
request. For an "outgoing" request, the edge proxy just removes the an "outgoing" request. For an "outgoing" request, the edge proxy
Route header and continues processing the request. Otherwise, this just removes the Route header and continues processing the request.
is an "incoming" request. For an incoming request, the proxy removes Otherwise, this is an "incoming" request. For an incoming request,
the Route header field value and forwards the request over the the proxy removes the Route header field value and forwards the
'logical flow' identified by the flow token, that is known to deliver request over the 'logical flow' identified by the flow token, that is
data to the specific target UA instance. For connection-oriented known to deliver data to the specific target UA instance. For
transports, if the flow no longer exists the proxy SHOULD send a 430 connection-oriented transports, if the flow no longer exists the
(Flow Failed) response to the request. proxy SHOULD send a 430 (Flow Failed) response to the request.
Proxies which used the example algorithm described in this document Proxies which used the example algorithm described in this document
to form a flow token follow the procedures below to determine the to form a flow token follow the procedures below to determine the
correct flow. correct flow.
Example Algorithm: To decode the flow token, take the flow Example Algorithm: To decode the flow token, take the flow
identifier in the user portion of the URI and base64 decode it, identifier in the user portion of the URI and base64 decode it,
then verify the HMAC is correct by recomputing the HMAC and then verify the HMAC is correct by recomputing the HMAC and
checking that it matches. If the HMAC is not correct, the proxy checking that it matches. If the HMAC is not correct, the proxy
SHOULD send a 403 (Forbidden) response. If the HMAC is correct SHOULD send a 403 (Forbidden) response. (The proxy could ignore
then the proxy SHOULD forward the request on the flow that was such requests for prevention of denial of service attacks.) If
specified by the information in the flow identifier. If this flow the HMAC is correct then the proxy SHOULD forward the request on
no longer exists, the proxy SHOULD send a 430 (Flow Failed) the flow that was specified by the information in the flow
response to the request. 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 specific procedures at the edge proxy to initial registration, but specific procedures at the edge proxy to
ensure that mid-dialog requests are routed over an existing flow are ensure that mid-dialog requests are routed over an existing flow are
not part of this specification. However, an approach such as having not part of this specification. However, an approach such as having
the Edge Proxy add a Record-Route header with a flow token is one way the Edge Proxy add a Record-Route header with a flow token is one way
to ensure that mid-dialog requests are routed over the correct flow. to ensure that mid-dialog requests are routed over the correct flow.
The Edge Proxy can use the presence of the "ob" parameter in dialog- The Edge Proxy can use the presence of the "ob" parameter in dialog-
forming requests in the UAC's Contact URI to determine if it should forming requests in the UAC's Contact URI (or topmost Route header
add a flow token. field) to determine if it should add a flow token.
5.4. Edge Proxy Keepalive Handling 5.4. Edge Proxy Keepalive Handling
All edge proxies compliant with this specification MUST implement All edge proxies compliant with this specification MUST implement
support for STUN NAT Keepalives on its SIP UDP ports as described in support for STUN NAT Keepalives on its SIP UDP ports as described in
Section 8. Section 8.
When a server receives a double CRLF sequence on a connection When a server receives a double CRLF sequence on a connection
oriented transport such as TCP or SCTP, it MUST immediately respond oriented transport such as TCP or SCTP, it MUST immediately respond
with a single CRLF over the same connection. with a single CRLF over the same connection.
The last proxy to forward a successful registration response to a UA
MAY include a Flow-Timer header field if the response contains the
outbound option-tag in a Require header field value in the response.
6. Registrar Mechanisms: Processing REGISTER Requests 6. Registrar Mechanisms: Processing REGISTER Requests
This specification updates the definition of a binding in RFC 3261 This specification updates the definition of a binding in RFC 3261
[1] Section 10 and RFC 3327 [5] Section 5.3. [RFC3261] Section 10 and RFC 3327 [RFC3327] Section 5.3.
Registrars which implement this specification MUST support the Path Registrars which implement this specification MUST support the Path
header mechanism RFC 3327 [5]. header mechanism RFC 3327 [RFC3327].
When receiving a REGISTER request, the registrar first checks from When receiving a REGISTER request, the registrar first checks from
its Via header field if the registrar is the first hop or not. If its Via header field if the registrar is the first hop or not. If
the registrar is not the first hop, it examines the Path header of the registrar is not the first hop, it examines the Path header of
the request. If the Path header field is missing or it exists but the request. If the Path header field is missing or it exists but
the first URI does not have an 'ob' URI parameter, the registrar MUST the first URI does not have an 'ob' URI parameter, then outbound
ignore the reg-id parameter of the Contact header. processing cannot be applied to the registration. In this case, the
following processing applies: if the REGISTER request contains the
"outbound" option tag in a "Require" header field, then the registrar
MUST respond to the REGISTER request with a 439 (First Hop Lacks
Outbound Support) response; otherwise, the registrar MUST ignore the
reg-id parameter of the Contact header. See Section 11.2 for more
information on the 439 response code.
A Contact header field value with an instance-id but no reg-id is A Contact header field value with an instance-id but no reg-id is
valid (this combination can be used in the GRUU [23] specification), valid (this combination can be used in the GRUU [I-D.ietf-sip-gruu]
but one with a reg-id but no instance-id is not. If the registrar specification), but one with a reg-id but no instance-id is not. If
processes a Contact header field value with a reg-id but no the registrar processes a Contact header field value with a reg-id
instance-id, it simply ignores the reg-id parameter. If the Contact but no instance-id, it simply ignores the reg-id parameter. If the
header contains more than one header field value with a non-zero Contact header contains more than one header field value with a non-
expiration and a 'reg-id' parameter, the entire registration SHOULD zero expiration and a 'reg-id' parameter, the entire registration
be rejected with a 400 Bad Request response. If the Contact header SHOULD be rejected with a 400 Bad Request response. If the Contact
did not contain a 'reg-id' parameter or if that parameter became header did not contain a 'reg-id' parameter or if that parameter
ignored (as described above) the registrar MUST NOT include the became ignored (as described above) the registrar MUST NOT include
'outbound' option-tag in the Require header field of its response. the 'outbound' option-tag in the Require header field of its
response.
The registrar MUST be prepared to receive, simultaneously for the The registrar MUST be prepared to receive, simultaneously for the
same AOR, some registrations that use instance-id and reg-id and some same AOR, some registrations that use instance-id and reg-id and some
registrations that do not. The Registrar MAY be configured with registrations that do not. The Registrar MAY be configured with
local policy to reject any registrations that do not include the 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 instance-id and reg-id, or with Path header field values that do not
contain the 'ob' parameter. If the Contact header field does not contain the 'ob' parameter. If the Contact header field does not
contain a '+sip.instance' media feature parameter, the registrar contain a '+sip.instance' media feature parameter, the registrar
processes the request using the Contact binding rules in RFC 3261 processes the request using the Contact binding rules in RFC 3261
[1]. [RFC3261].
When a '+sip.instance' media feature parameter is present in a When a '+sip.instance' media feature parameter is present in a
Contact header field of a REGISTER request (after the Contact header Contact header field of a REGISTER request (after the Contact header
validation as described above), the corresponding binding is between validation as described above), the corresponding binding is between
an AOR and the combination of the instance-id (from the +sip.instance an AOR and the combination of the instance-id (from the +sip.instance
media feature parameter) and the value of reg-id parameter if it is media feature parameter) and the value of reg-id parameter if it is
present. The registrar MUST store in the binding the Contact URI, present. The registrar MUST store in the binding the Contact URI,
all the Contact head field parameters, and any Path header field all the Contact head field parameters, and any Path header field
values and SHOULD also store the time at which the binding was last values. (Even though the Contact URI is not used for binding
updated. (Even though the Contact URI is not used for binding
comparisons, it is still needed by the authoritative proxy to form comparisons, it is still needed by the authoritative proxy to form
the target set.) The Registrar MUST include the 'outbound' option- the target set.) The Registrar MUST include the 'outbound' option-
tag (defined in Section 12.1) in a Require header field value in its tag (defined in Section 12.2) in a Require header field value in its
response to the REGISTER request. response to the REGISTER request.
If the UAC has a direct flow with the registrar, the registrar MUST If the UAC has a direct flow with the registrar, the registrar MUST
store enough information to uniquely identify the network flow over store enough information to uniquely identify the network flow over
which the request arrived. For common operating systems with TCP, which the request arrived. For common operating systems with TCP,
this would typically just be the handle to the file descriptor where this would typically just be the handle to the file descriptor where
the handle would become invalid if the TCP session was closed. For the handle would become invalid if the TCP session was closed. For
common operating systems with UDP this would typically be the file common operating systems with UDP this would typically be the file
descriptor for the local socket that received the request, the local descriptor for the local socket that received the request, the local
interface, and the IP address and port number of the remote side that interface, and the IP address and port number of the remote side that
skipping to change at page 23, line 34 skipping to change at page 25, line 6
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 the next-hop target of the message and the value of The proxy uses the next-hop target of the message and the value of
any stored Path header field vector in the registration binding to any stored Path header field vector in the registration binding to
decide how to forward and populate the Route header in the request. decide how to forward and populate the Route header in the request.
If the proxy doubles as a registrar and stored information about the If the proxy is colocated with the registrar and stored information
flow that created the binding, then the proxy MUST send the request about the flow to the UA that created the binding, then the proxy
over the same 'logical flow' saved with the binding, since that flow MUST send the request over the same 'logical flow' saved with the
is known to deliver data to the specific target UA instance's network binding, since that flow is known to deliver data to the specific
flow that was saved with the binding. target UA instance's network flow that was saved with the binding.
Typically this means that for TCP, the request is sent on the same Typically this means that for TCP, the request is sent on the same
TCP socket that received the REGISTER request. For UDP, the TCP socket that received the REGISTER request. For UDP, the
request is sent from the same local IP address and port over which request is sent from the same local IP address and port over which
the registration was received, to the same IP address and port the registration was received, to the same IP address and port
from which the REGISTER was received. from which the REGISTER was received.
If a proxy or registrar receives information from the network that If a proxy or registrar receives information from the network that
indicates that no future messages will be delivered on a specific indicates that no future messages will be delivered on a specific
flow, then the proxy MUST invalidate all the bindings in the target flow, then the proxy MUST invalidate all the bindings in the target
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 [3] Binding Requests to be mixed over the same flow. SIP and STUN [I-D.ietf-behave-rfc3489bis] Binding Requests to be
This constitues a new STUN usage. The STUN messages are used to mixed over the same flow. This constitues a new STUN usage. The
verify that connectivity is still available over a UDP flow, and to STUN messages are used to verify that connectivity is still available
provide periodic keepalives. Note that these STUN keepalives are over a UDP flow, and to provide periodic keep alives. Note that
always sent to the next SIP hop. STUN messages are not delivered these STUN keep alives are always sent to the next SIP hop. STUN
end-to-end. messages are not delivered end-to-end.
The only STUN messages required by this usage are Binding Requests, The only STUN messages required by this usage are Binding Requests,
Binding Responses, and Binding Error Responses. The UAC sends Binding Responses, and Binding Error Responses. The UAC sends
Binding Requests over the same UDP flow that is used for sending SIP Binding Requests over the same UDP flow that is used for sending SIP
messages. These Binding Requests do not require any STUN attributes messages. These Binding Requests do not require any STUN attributes
except the XOR-MAPPED-ADDRESS and never use any form of except the XOR-MAPPED-ADDRESS and never use any form of
authentication. The UAS, proxy, or registrar responds to a valid authentication. The UAS, proxy, or registrar responds to a valid
Binding Request with a Binding Response which MUST include the XOR- Binding Request with a Binding Response which MUST include the XOR-
MAPPED-ADDRESS attribute. 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 UDP port, it MUST also provide a limited version given interface and UDP port, it MUST also provide a limited version
of a STUN server on the same interface and UDP port. of a STUN server on the same interface and UDP port.
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 Binding method has a value of 0 because the first octet of a STUN Binding method has a value of 0
or 1 while the first octet of a SIP message is never a 0 or 1. or 1 while the first octet of a SIP message is never a 0 or 1.
When a URI is created that refers to a SIP node that supports STUN as
described in this section, the 'keep' 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.
Because sending and receiving binary STUN data on the same ports used Because sending and receiving binary STUN data on the same ports used
for SIP is a significant and non-backwards compatible change to RFC for SIP is a significant and non-backwards compatible change to RFC
3261, this section requires a number of checks before sending STUN 3261, this section requires a number of checks before sending STUN
messages to a SIP node. If a SIP node sends STUN requests (for messages to a SIP node. If a SIP node sends STUN requests (for
example due to incorrect configuration) despite these warnings, the example due to incorrect configuration) despite these warnings, the
node could be blacklisted for UDP traffic. node could be blacklisted for UDP traffic.
A SIP node MUST NOT send STUN requests over a flow unless it has an A SIP node MUST NOT send STUN requests over a flow unless it has an
explicit indication that the target next hop SIP server claims to explicit indication that the target next hop SIP server claims to
support STUN. For example, automatic or manual configuration of an support this specification. Note that UACs MUST NOT use an ambiguous
outbound-proxy-set which contains the 'keep' parameter, or receiving configuration option such as "Work through NATs?" or "Do Keep
the parameter in the Path header of the edge proxy, is considered alives?" to imply next hop STUN support.
sufficient explicit indication. Note that UACs MUST NOT use an
ambiguous configuration option such as "Work through NATs?" or "Do
Keepalives?" to imply next hop STUN support.
Typically, a SIP node first sends a SIP request and waits to Typically, a SIP node first sends a SIP request and waits to
receive a 200-class response over a flow to a new target receive a 200-class response over a flow to a new target
destination, before sending any STUN messages. When scheduled for destination, before sending any STUN messages. When scheduled for
the next NAT refresh, the SIP node sends a STUN request to the the next NAT refresh, the SIP node sends a STUN request to the
target. target.
Once a flow is established, failure of a STUN request (including its Once a flow is established, failure of a STUN request (including its
retransmissions) is considered a failure of the underlying flow. For retransmissions) is considered a failure of the underlying flow. For
SIP over UDP flows, if the XOR-MAPPED-ADDRESS returned over the flow SIP over UDP flows, if the XOR-MAPPED-ADDRESS returned over the flow
changes, this indicates that the underlying connectivity has changed, changes, this indicates that the underlying connectivity has changed,
and is considered a flow failure. and is considered a flow failure.
The SIP keepalive STUN usage requires no backwards compatibility with The SIP keep alive STUN usage requires no backwards compatibility
RFC 3489 [11]. with RFC 3489 [RFC3489].
8.1. Use with Sigcomp 8.1. Use with Sigcomp
When STUN is used together with SigComp [25] compressed SIP messages When STUN is used together with SigComp [RFC3320] compressed SIP
over the same flow. For UDP flows, the STUN messages are simply sent messages over the same flow,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 [12] encoded text messages, so for applications which use UTF-8 [RFC3629] encoded text messages, so for applications which
this encoding (or ASCII encoding) it is possible to multiplex use this encoding (or ASCII encoding) it is possible to multiplex
uncompressed application messages and SigComp messages on the same uncompressed application messages and SigComp messages on the same
UDP port. UDP port.
The most significant two bits of every STUN Binding method are The most significant two bits of every STUN Binding method are
both zeroes. This, combined with the magic cookie, aids in both zeroes. This, combined with the magic cookie, aids in
differentiating STUN packets from other protocols when STUN is differentiating STUN packets from other protocols when STUN is
multiplexed with other protocols on the same port. multiplexed with other protocols on the same port.
9. Example Message Flow 9. Example Message Flow
[----example.com domain------] Below is an example message flow illustrating most of the concepts
Bob EP1 EP2 Proxy Alice discussed in this specification. In many cases, Via, Content-Length
and Max-Forwards headers are omitted for brevity and readability.
In the first part of this example message flow, Bob's UA sends a
SUBSCRIBE request for the UA profile configuration package. This
request is a poll (Expires is zero). After receiving the NOTIFY
request, Bob's UA fetches the external configuration using HTTPS (not
shown) and obtains a configuration file which contains the outbound-
proxy-set "sip:ep1.example.com;lr" and "sip:ep2.example.com;lr.
[----example.com domain-------------------------]
Bob EP1 EP2 Proxy Config
| | | | | | | | | |
1)|-REGISTER->| | | | 1)|SUBSCRIBE->| | | |
2)| |---REGISTER-->| | 2)| |---SUBSCRIBE Event: ua-profile ->|
3)| |<----200 OK---| | 3)| |<--200 OK -----------------------|
4)|<-200 OK---| | | | 4)|<--200 OK--| | | |
5)|----REGISTER---->| | | 5)| |<--NOTIFY------------------------|
6)| | |--REG-->| | 6)|<--NOTIFY--| | | |
7)| | |<-200---| | 7)|---200 OK->| | | |
8)|<----200 OK------| | | 8)| |---200 OK ---------------------->|
| | | | | | | | | |
| CRASH X | | |
| Reboot | | | Example Message #1:
9)| | | |<-INVITE-| SUBSCRIBE sip:00000000-0000-1000-8000-AABBCCDDEEFF@example.com SIP/2.0
10)| |<---INVITE----| | Via: SIP/2.0/TCP 192.168.1.2;branch=z9hG4bKnlsdkdj2
11)| |----430------>| | Max-Forwards: 70
12)| | |<-INVITE| | From: <anonymous@example.com>;tag=23324
13)|<---INVITE-------| | | To: <sip:00000000-0000-1000-8000-AABBCCDDEEFF@example.com>
14)|----200 OK------>| | | Call-ID: nSz1TWN54x7My0GvpEBj
15)| | |200 OK->| | CSeq: 1 SUBSCRIBE
16)| | | |-200 OK->| Event: ua-profile ;profile-type=device
17)| | | |<-ACK----| ;vendor="example.com";model="uPhone";version="1.1"
18)| | |<-ACK---| | Expires: 0
19)|<---ACK----------| | | Supported: path, outbound
Accept: message/external-body, application/x-uPhone-config
Contact: <sip:192.168.1.2;transport=tcp;ob>
;+sip.instance="<urn:uuid:00000000-0000-1000-8000-AABBCCDDEEFF>"
Content-Length: 0
In message #2, EP1 adds the following Record-Route header:
Record-Route:
<sip:GopIKSsn0oGLPXRdV9BAXpT3coNuiGKV@ep1.example.com;lr>
In message #5, the configuration server sends a NOTIFY with an
external URL for Bob to fetch his configuration. The NOTIFY has a
Subscription-State header that ends the subscription.
Message #5
NOTIFY sip:192.168.1.2;transport=tcp;ob SIP/2.0
Via: SIP/2.0/TCP 192.0.2.5;branch=z9hG4bKn81dd2
Max-Forwards: 70
To: <anonymous@example.com>;tag=23324
From: <sip:00000000-0000-1000-8000-AABBCCDDEEFF@example.com>;tag=0983
Call-ID: nSz1TWN54x7My0GvpEBj
CSeq: 1 NOTIFY
Route: <sip:GopIKSsn0oGLPXRdV9BAXpT3coNuiGKV@ep1.example.com;lr>
Subscription-State: terminated;reason=timeout
Event: ua-profile
Content-Type: message/external-body; access-type="URL"
;expiration="Thu, 01 Jan 2009 09:00:00 UTC"
;URL="http://example.com/uPhone.cfg"
;size=9999;hash=10AB568E91245681AC1B
Content-Length: 0
EP1 receives this NOTIFY request, strips off the Route header,
extracts the flow-token, calculates the correct flow and forwards the
request (Message #6) over that flow to Bob.
Bob's UA fetches the configuration file. Now that Bob's UA is
configured with the outbound-proxy-set, Bob's UA sends REGISTER
requests through each edge proxy in the set. Once the registrations
succeed, Bob's UA begins sending CRLF keepalives about every 2
minutes.
Bob EP1 EP2 Proxy Alice
| | | | | | | | | |
20)|--2CRLF->X | | | | 9)|-REGISTER->| | | |
10)| |---REGISTER-->| |
11)| |<----200 OK---| |
12)|<-200 OK---| | | |
13)|----REGISTER---->| | |
14)| | |--REG-->| |
15)| | |<-200---| |
16)|<----200 OK------| | |
| | | | | | | | | |
21)|-REGISTER->| | | | | about 120 seconds later... |
22)|<-200 OK---| | | | | | | | |
17)|--2CRLF--->| | | |
18)|<--CRLF----| | | |
19)|------2CRLF----->| | |
20)|<------CRLF------| | |
| | | | | | | | | |
[TODO FIX example] The following call flow shows a basic registration In message #9, Bob's UA sends its first registration through the
and an incoming call. At some point, the flow to the Primary proxy first edge proxy in the outbound-proxy-set by including a loose
is lost. An incoming INVITE tries to reach the Callee through the route. The UA includes an instance-id and reg-id in its Contact
Primary flow, but receives an ICMP Unreachable message. The Caller header field value. Note the option-tags in the Supported header.
retries using the Secondary Edge Proxy, which uses a separate flow.
Later, after the Primary reboots, The Callee discovers the flow
failure and reestablishes a new flow to the Primary.
[-----example.com domain -------------------]
Caller Secondary Primary Callee
| | | (1) REGISTER |
| | |<-----------------|
| | |(2) 200 OK |
| | |----------------->|
| | | (3) REGISTER |
| |<------------------------------------|
| |(4) 200 OK | |
| |------------------------------------>|
| | | |
| | CRASH X |
|(5) INVITE | | |
|----------------------------------->| |
|(6) ICMP Unreachable | |
|<-----------------------------------| |
|(7) INVITE | | |
|---------------->| | |
| |(8) INVITE | |
| |------------------------------------>|
| |(9) 200 OK | |
| |<------------------------------------|
|(10) 200 OK | | |
|<----------------| | |
|(11) ACK | | |
|---------------->| | |
| |(12) ACK | |
| |------------------------------------>|
| | | |
| | REBOOT | |
| | |(13) REGISTER |
| | |<-----------------|
| | |(14) 200 OK |
| | |----------------->|
| | | |
|(15) BYE | | |
|---------------->| | |
| | (16) BYE | |
| |------------------------------------>|
| | | (17) 200 OK |
| |<------------------------------------|
| (18) 200 OK | | |
|<----------------| | |
| | | |
This call flow assumes that the Callee has been configured with a
proxy set that consists of "sip:pri.example.com;lr;keep-stun" and
"sip:sec.example.com;lr;keep-stun". The Callee REGISTER in message
(1) looks like:
Message #9
REGISTER sip:example.com SIP/2.0 REGISTER sip:example.com SIP/2.0
Via: SIP/2.0/UDP 192.0.2.1;branch=z9hG4bKnashds7 Via: SIP/2.0/TCP 192.168.1.2;branch=z9hG4bKnashds7
Max-Forwards: 70 Max-Forwards: 70
From: Callee <sip:callee@example.com>;tag=7F94778B653B From: Bob <sip:bob@example.com>;tag=7F94778B653B
To: Callee <sip:callee@example.com> To: Bob <sip:bob@example.com>
Call-ID: 16CB75F21C70 Call-ID: 16CB75F21C70
CSeq: 1 REGISTER CSeq: 1 REGISTER
Supported: path Supported: path, outbound
Route: <sip:pri.example.com;lr;keep-stun> Route: <sip:ep1.example.com;lr>
Contact: <sip:callee@192.0.2.1> Contact: <sip:bob@192.168.1.2;transport=tcp>;reg-id=1
;+sip.instance="<urn:uuid:0C67446E-F1A1-11D9-94D3-000A95A0E128>" ;+sip.instance="<urn:uuid:00000000-0000-1000-8000-AABBCCDDEEFF>"
;reg-id=1
Content-Length: 0 Content-Length: 0
In the message, note that the Route is set and the Contact header Message #10 is similar. EP1 removes the Route header field value,
field value contains the instance-id and reg-id. The response to the decrements Max-Forwards, and adds its Via header field value. Since
REGISTER in message (2) would look like: EP1 is the first edge proxy, it adds a Path header with a flow token
and includes the 'ob' parameter.
Path: <sip:VskztcQ/S8p4WPbOnHbuyh5iJvJIW3ib@ep1.example.com;lr;ob>
Since the response to the REGISTER (message #11) contains the
outbound option-tag in the Require header field, Bob's UA will know
that the registrar used outbound binding rules. The response also
contains the currently active Contacts, the Path for the current
registration.
SIP/2.0 200 OK SIP/2.0 200 OK
Via: SIP/2.0/UDP 192.0.2.1;branch=z9hG4bKnashds7 Via: SIP/2.0/TCP 192.0.2.15;branch=z9hG4bKnuiqisi
From: Callee <sip:callee@example.com>;tag=7F94778B653B Via: SIP/2.0/TCP 192.168.1.2;branch=z9hG4bKnashds7
To: Callee <sip:callee@example.com>;tag=6AF99445E44A From: Bob <sip:bob@example.com>;tag=7F94778B653B
To: Bob <sip:bob@example.com>;tag=6AF99445E44A
Call-ID: 16CB75F21C70 Call-ID: 16CB75F21C70
CSeq: 1 REGISTER CSeq: 1 REGISTER
Supported: outbound Supported: path, outbound
Contact: <sip:callee@192.0.2.1> Require: outbound
;+sip.instance="<urn:uuid:0C67446E-F1A1-11D9-94D3-000A95A0E128>" Contact: <sip:bob@192.168.1.2;transport=tcp>;reg-id=1;expires=3600
;reg-id=1 ;+sip.instance="<urn:uuid:00000000-0000-1000-8000-AABBCCDDEEFF>"
;expires=3600 Path: <sip:VskztcQ-S8p4WPbOnHbuyh5iJvJIW3ib@ep1.example.com;lr;ob>
Content-Length: 0 Content-Length: 0
The second registration in message 3 and 4 are similar other than the The second registration through EP2 (message #13) is similar other
Call-ID has changed, the reg-id is 2, and the route is set to the than the Call-ID has changed, the reg-id is 2, and the Route header
secondary instead of the primary. They look like: goes through EP2.
REGISTER sip:example.com SIP/2.0 REGISTER sip:example.com SIP/2.0
Via: SIP/2.0/UDP 192.0.2.1;branch=z9hG4bKnqr9bym Via: SIP/2.0/TCP 192.168.1.2;branch=z9hG4bKnqr9bym
Max-Forwards: 70 Max-Forwards: 70
From: Callee <sip:callee@example.com>;tag=755285EABDE2 From: Bob <sip:bob@example.com>;tag=755285EABDE2
To: Callee <sip:callee@example.com> To: Bob <sip:bob@example.com>
Call-ID: E05133BD26DD Call-ID: E05133BD26DD
CSeq: 1 REGISTER CSeq: 1 REGISTER
Supported: path Supported: path, outbound
Route: <sip:sec.example.com;lr;keep-stun> Route: <sip:ep2.example.com;lr>
Contact: <sip:callee@192.0.2.1> Contact: <sip:bob@192.168.1.2;transport=tcp>;reg-id=2
;+sip.instance="<urn:uuid:0C67446E-F1A1-11D9-94D3-000A95A0E128>" ;+sip.instance="<urn:uuid:00000000-0000-1000-8000-AABBCCDDEEFF>"
;reg-id=2
Content-Length: 0 Content-Length: 0
Likewise in message #14, EP2 adds a Path header with flow token and
'ob' parameter.
Path: <sip:wazHDLdIMtUg6r0I/oRZ15zx3zHE1w1Z@ep2.example.com;lr;ob>
Message #16 tells Bob's UA that outbound registration was successful,
and shows both Contacts. Note that only the Path corresponding to
the current registration is returned.
SIP/2.0 200 OK SIP/2.0 200 OK
Via: SIP/2.0/UDP 192.0.2.1;branch=z9hG4bKnqr9bym Via: SIP/2.0/TCP 192.168.1.2;branch=z9hG4bKnqr9bym
From: Callee <sip:callee@example.com>;tag=755285EABDE2 From: Bob <sip:bob@example.com>;tag=755285EABDE2
To: Callee <sip:callee@example.com>;tag=49A9AD0B3F6A To: Bob <sip:bob@example.com>;tag=49A9AD0B3F6A
Call-ID: E05133BD26DD Call-ID: E05133BD26DD
Supported: outbound Supported: path, outbound
Require: outbound
CSeq: 1 REGISTER CSeq: 1 REGISTER
Contact: <sip:callee@192.0.2.1> Contact: <sip:bob@192.168.1.2;transport=tcp>;reg-id=1;expires=3600
;+sip.instance="<urn:uuid:0C67446E-F1A1-11D9-94D3-000A95A0E128>" ;+sip.instance="<urn:uuid:00000000-0000-1000-8000-AABBCCDDEEFF>"
;reg-id=1 Contact: <sip:bob@192.168.1.2;transport=tcp>;reg-id=2;expires=3600
;expires=3600 ;+sip.instance="<urn:uuid:00000000-0000-1000-8000-AABBCCDDEEFF>"
Contact: <sip:callee@192.0.2.1> Path: <sip:wazHDLdIMtUg6r0I/oRZ15zx3zHE1w1Z@ep2.example.com;lr;ob>
;+sip.instance="<urn:uuid:0C67446E-F1A1-11D9-94D3-000A95A0E128>"
;reg-id=2
;expires=3600
Content-Length: 0 Content-Length: 0
The messages in the call flow are very normal. The only interesting A bit later, EP1 crashes and reboots. Before Bob's UA notices that
thing to note is that the INVITE in message 8 contains a Record-Route its flow to EP1 is no longer responding, Alice calls Bob. Bob's
header for the Secondary proxy, with its flow token. authoritative proxy first tries the flow to EP1, but EP1 no longer
has a flow to Bob so it responds with a 430 Flow Failed response.
The proxy removes the stale registration and tries the next binding
for the same instance.
Record-Route: Bob EP1 EP2 Proxy Alice
<sip:PQPbqQE+Ynf+tzRPD27lU6uxkjQ8LLUG@sec.example.com;lr> | | | | |
| CRASH X | | |
| Reboot | | |
| | | | |
21)| | | |<-INVITE-|
22)| |<---INVITE----| |
23)| |----430------>| |
24)| | |<-INVITE| |
25)|<---INVITE-------| | |
26)|----200 OK------>| | |
27)| | |200 OK->| |
28)| | | |-200 OK->|
29)| | |<----------ACK----|
30)|<---ACK----------| | |
| | | | |
31)| | |<----------BYE----|
32)|<---BYE----------| | |
33)|----200 OK------>| | |
34)| | |--------200 OK--->|
| | | | |
Message #21
INVITE sip:bob@example.com SIP/2.0
To: Bob <sip:bob@example.com>
From: Alice <sip:alice@a.example>;tag=02935
Call-ID: klmvCxVWGp6MxJp2T2mb
CSeq: 1 INVITE
The registrations in message 13 and 14 are the same as message 1 and Bob's proxy rewrites the Request-URI to the Contact URI used in Bob's
2 other than the Call-ID and tags have changed. Because these registration, and places the path for one of the registrations
messages will contain the same instance-id and reg-id as those in 1 towards Bob's UA instance into a Route header field. This Route goes
and 2, this flow will partially supersede that for messages 1 and 2 through EP1.
and will be tried first by Primary.
Message #22
INVITE sip:bob@192.168.1.2;transport=tcp SIP/2.0
To: Bob <sip:bob@example.com>
From: Alice <sip:alice@a.example>;tag=02935
Call-ID: klmvCxVWGp6MxJp2T2mb
CSeq: 1 INVITE
Route: <sip:VskztcQ/S8p4WPbOnHbuyh5iJvJIW3ib@ep1.example.com;lr;ob>
Since EP1 just rebooted, it does not have the flow described in the
flow token. It returns a 430 Flow Failed response.
Message #23
SIP/2.0 430 Flow Failed
To: Bob <sip:bob@example.com>
From: Alice <sip:alice@a.example>;tag=02935
Call-ID: klmvCxVWGp6MxJp2T2mb
CSeq: 1 INVITE
The proxy deletes the binding for this path and tries to forward the
INVITE again, this time with the path through EP2.
Message #24
INVITE sip:bob@192.168.1.2;transport=tcp SIP/2.0
To: Bob <sip:bob@example.com>
From: Alice <sip:alice@a.example>;tag=02935
Call-ID: klmvCxVWGp6MxJp2T2mb
CSeq: 1 INVITE
Route: <sip:wazHDLdIMtUg6r0I/oRZ15zx3zHE1w1Z@ep2.example.com;lr;ob>
In message #25, EP2 needs to add a Record-Route header field value,
so that any subsequent in-dialog messages from Alice's UA arrive at
Bob's UA. EP2 can determine it needs to Record-Route since the
request is a dialog-forming request and the Route header contained a
flow token and an 'ob' parameter. This Record-Route information is
passed back to Alice's UA in the responses (messages #26, 27, and 28)
Message #25
INVITE sip:bob@192.168.1.2;transport=tcp SIP/2.0
To: Bob <sip:bob@example.com>
From: Alice <sip:alice@a.example>;tag=02935
Call-ID: klmvCxVWGp6MxJp2T2mb
CSeq: 1 INVITE
Record-Route: <sip:wazHDLdIMtUg6r0I/oRZ15zx3zHE1w1Z@ep2.example.com;lr>
Message #26
SIP/2.0 200 OK
To: Bob <sip:bob@example.com>;tag=skduk2
From: Alice <sip:alice@a.example>;tag=02935
Call-ID: klmvCxVWGp6MxJp2T2mb
CSeq: 1 INVITE
Record-Route: <sip:wazHDLdIMtUg6r0I/oRZ15zx3zHE1w1Z@ep2.example.com;lr>
At this point, both UAs have the correct route-set for the dialog.
Any subsequent requests in this dialog will route correctly. For
example, the ACK request in message #29 is sent form Alice's UA
directly to EP2. The BYE request in message #31 uses the same route-
set.
Message #29
ACK sip:bob@192.168.1.2;transport=tcp SIP/2.0
To: Bob <sip:bob@example.com>;tag=skduk2
From: Alice <sip:alice@a.example>;tag=02935
Call-ID: klmvCxVWGp6MxJp2T2mb
CSeq: 1 ACK
Route: <sip:wazHDLdIMtUg6r0I/oRZ15zx3zHE1w1Z@ep2.example.com;lr>
Message #31
BYE sip:bob@192.168.1.2;transport=tcp SIP/2.0
To: Bob <sip:bob@example.com>;tag=skduk2
From: Alice <sip:alice@a.example>;tag=02935
Call-ID: klmvCxVWGp6MxJp2T2mb
CSeq: 2 BYE
Route: <sip:wazHDLdIMtUg6r0I/oRZ15zx3zHE1w1Z@ep2.example.com;lr>
Somewhat later, Bob's UA sends keepalives to both its edge proxies,
but it discovers that the flow with EP1 failed. Bob's UA re-
registers through EP1 using the same reg-id and Call-ID it previously
used.
Bob EP1 EP2 Proxy Alice
| | | | |
35)|------2CRLF----->| | |
36)|<------CRLF------| | |
37)|--2CRLF->X | | | |
| | | | |
38)|-REGISTER->| | | |
39)| |---REGISTER-->| |
40)| |<----200 OK---| |
41)|<-200 OK---| | | |
| | | | |
Message #38
REGISTER sip:example.com SIP/2.0
From: Bob <sip:bob@example.com>;tag=7F94778B653B
To: Bob <sip:bob@example.com>
Call-ID: 16CB75F21C70
CSeq: 2 REGISTER
Supported: path, outbound
Route: <sip:ep1.example.com;lr>
Contact: <sip:bob@192.168.1.2;transport=tcp>;reg-id=1
;+sip.instance="<urn:uuid:00000000-0000-1000-8000-AABBCCDDEEFF>"
In message #39, EP1 inserts a Path header with a new flow token:
Path: <sip:3yJEbr1GYZK9cPYk5Snocez6DzO7w+AX@ep1.example.com;lr;ob>
Finally, Bob makes an outgoing call to Alice. Bob's UA includes an
'ob' parameter in its Contact URI in message #42. EP1 adds a Record-
Route with a flow-token in message #43. The route-set is returned to
Bob in the response (messages #45, 46, and 47) and either Bob or
Alice can send in-dialog requests.
Bob EP1 EP2 Proxy Alice
| | | | |
42)|--INVITE-->| | | |
43)| |---INVITE---->| |
44)| | | |-INVITE->|
45)| | | |<--200---|
46)| |<----200 OK---| |
47)|<-200 OK---| | | |
48)|--ACK----->| | | |
49)| |-----ACK--------------->|
| | | | |
50)|-- BYE---->| | | |
51)| |-----------BYE--------->|
52)| |<----------200 OK-------|
53)|<--200 OK--| | | |
| | | | |
Message #42
INVITE sip:alice@a.example SIP/2.0
From: Bob <sip:bob@example.com>;tag=ldw22z
To: Alice <sip:alice@a.example>
Call-ID: 95KGsk2V/Eis9LcpBYy3
CSeq: 1 INVITE
Route: <sip:ep1.example.com;lr>
Contact: <sip:bob@192.168.1.2;transport=tcp;ob>
In message #43, EP1 adds the following Record-Route header.
Record-Route: <sip:3yJEbr1GYZK9cPYk5Snocez6DzO7w+AX@ep1.example.com;lr>
When EP1 receives the BYE (message #50) from Bob's UA, it can tell
that the request is an "outgoing" request (since the source of the
request matches the flow in the flow token) and simply deletes its
Route header field value and forwards the request on to Alice's UA.
Message #50
BYE sip:alice@a.example SIP/2.0
From: Bob <sip:bob@example.com>;tag=ldw22z
To: Alice <sip:alice@a.example>;tag=plqus8
Call-ID: 95KGsk2V/Eis9LcpBYy3
CSeq: 2 BYE
Route: <sip:3yJEbr1GYZK9cPYk5Snocez6DzO7w+AX@ep1.example.com;lr>
Contact: <sip:bob@192.168.1.2;transport=tcp;ob>
10. Grammar 10. Grammar
This specification defines new Contact header field parameters, This specification defines a new header field, new Contact header
reg-id and +sip.instance. The grammar includes the definitions from field parameters, reg-id and +sip.instance. The grammar includes the
RFC 3261 [1] and includes the definition of uric from RFC 3986 [13]. definitions from RFC 3261 [RFC3261] and includes the definition of
uric from RFC 3986 [RFC3986].
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[RFC5234] is:
message-header =/ Flow-Timer
Flow-Timer = "Flow-Timer" HCOLON 1*DIGIT
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 - 1) c-p-reg = "reg-id" EQUAL 1*DIGIT ; 1 to (2**31 - 1)
c-p-instance = "+sip.instance" EQUAL c-p-instance = "+sip.instance" EQUAL
LDQUOT "<" instance-val ">" RDQUOT LDQUOT "<" instance-val ">" RDQUOT
instance-val = *uric ; defined in RFC 3986 instance-val = *uric ; defined in RFC 3986
The value of the reg-id MUST NOT be 0 and MUST be less than 2**31. The value of the reg-id MUST NOT be 0 and MUST be less than 2**31.
11. Definition of 430 Flow Failed response code 11. New Response Codes
11.1. 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.
11.2. Definition of 439 First Hop Lacks Outbound Support response
This specification defines a new SIP response code '439 First Hop
Lacks Outbound Support'. This response code is used by a registrar
to indicate that it supports the 'outbound' feature described in this
specifcation, but that the first outbound proxy that the user is
attempting to register through does not. Note that this response
code is only appropriate in the case that the registering user agent
is mandating outbound processing by including the 'outbound' option
tag in a 'Require' header field. Proxies MUST NOT send a 439
response to any requests that don't contain an 'outbound' option tag
in a 'Require' header field.
12. IANA Considerations 12. IANA Considerations
12.1. Contact Header Field 12.1. Flow-Timer Header Field
This specification defines a new SIP header field "Flow-Timer".
RFC Number: RFC XXXX
Header Field Name: Flow-Timer
Compact Form: none
[NOTE TO RFC Editor: Please replace AAAA with
the RFC number of this specification.]
12.2. 'reg-id' Contact Header Field Parameter
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 [RFC3968]. The required
information is: information is:
Header Field Parameter Name Predefined Reference Header Field Parameter Name Predefined Reference
Values Values
____________________________________________________________________ ____________________________________________________________________
Contact reg-id No [RFC AAAA] Contact reg-id No [RFC AAAA]
[NOTE TO RFC Editor: Please replace AAAA with [NOTE TO RFC Editor: Please replace AAAA with
the RFC number of this specification.] the RFC number of this specification.]
12.2. SIP/SIPS URI Parameters 12.3. SIP/SIPS URI Parameters
This specification augments the "SIP/SIPS URI Parameters" sub- This specification augments the "SIP/SIPS URI Parameters" sub-
registry as per the registry created by [16]. The required registry as per the registry created by [RFC3969]. The required
information is: information is:
Parameter Name Predefined Values Reference Parameter Name Predefined Values Reference
____________________________________________ ____________________________________________
keep No [RFC AAAA]
timed-keepalives No [RFC AAAA]
ob No [RFC AAAA] ob No [RFC AAAA]
[NOTE TO RFC Editor: Please replace AAAA with [NOTE TO RFC Editor: Please replace AAAA with
the RFC number of this specification.] the RFC number of this specification.]
12.3. SIP Option Tag 12.4. SIP Option Tag
This specification registers a new SIP option tag, as per the This specification registers a new SIP option tag, as per the
guidelines in Section 27.1 of RFC 3261. guidelines in Section 27.1 of RFC 3261.
Name: outbound Name: outbound
Description: This option-tag is used to identify UAs and Registrars Description: This option-tag is used to identify UAs and Registrars
which support extensions for Client Initiated Connections. A which support extensions for Client Initiated Connections. A UA
Registrar places this option-tag in a Supported header to places this option in a Supported header to communicate its
communicate the Registrar's support for this extension to the support for this extension. A Registrar places this option-tag in
registering User Agent, and vice versa. a Require header to indicate to the registering User Agent that
the Registrar used registrations using the binding rules defined
in this extension.
12.4. Response Code 12.5. Response Codes
This section registers a new SIP Response Code, as per the guidelines This section registers two new SIP Response Codes, as per the
in Section 27.4 of RFC 3261. guidelines in Section 27.4 of RFC 3261.
12.5.1. 430 Response Code
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 12.5.2. 439 Response Code
Code: 439
Default Reason Phrase: First Hop Lacks Outbound Support
Reference: This document
12.6. 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 [RFC2506]. The tag is placed into the sip tree,
is defined in RFC 3840 [7]. which is defined in RFC 3840 [RFC3840].
Media feature tag name: sip.instance Media feature tag name: sip.instance
ASN.1 Identifier: New assignment by IANA. ASN.1 Identifier: New assignment by IANA.
Summary of the media feature indicated by this tag: This feature tag Summary of the media feature indicated by this tag: This feature tag
contains a string containing a URN that indicates a unique identifier contains a string containing a URN that indicates a unique identifier
associated with the UA instance registering the Contact. associated with the UA instance registering the Contact.
Values appropriate for use with this feature tag: String. Values appropriate for use with this feature tag: String.
skipping to change at page 32, line 25 skipping to change at page 39, line 17
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 [9] allows for call routing decisions to be preferences extension [RFC3841] allows for call routing decisions to
based on the values of these parameters. Therefore, if an attacker be based on the values of these parameters. Therefore, if an
can modify the values of this tag, they might be able to affect the attacker can modify the values of this tag, they might be able to
behavior of applications. As a result, applications which utilize affect the behavior of applications. As a result, applications which
this media feature tag SHOULD provide a means for ensuring its utilize this media feature tag SHOULD provide a means for ensuring
integrity. Similarly, this feature tag should only be trusted as its integrity. Similarly, this feature tag should only be trusted as
valid when it comes from the user or user agent described by the tag. valid when it comes from the user or user agent described by the tag.
As a result, protocols for conveying this feature tag SHOULD provide As a result, protocols for conveying this feature tag SHOULD provide
a mechanism for guaranteeing authenticity. a mechanism for guaranteeing authenticity.
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. Note that 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 the intent is not to prevent existing active attacks on SIP UDP and
skipping to change at page 33, line 27 skipping to change at page 40, line 20
gotten this information from the registrar. The registrar will only gotten this information from the registrar. The registrar will only
save this information for a given AOR if the registration for the AOR save this information for a given AOR if the registration for the AOR
has been successful; and the registration will only be successful if has been successful; and the registration will only be successful if
the UA can correctly authenticate. Even if an attacker has spoofed the UA can correctly authenticate. Even if an attacker has spoofed
some bad information in the Path header sent to the registrar, the some bad information in the Path header sent to the registrar, the
attacker will not be able to get the registrar to accept this attacker will not be able to get the registrar to accept this
information for an AOR that does not belong to the attacker. The information for an AOR that does not belong to the attacker. The
registrar will not hand out this bad information to others, and registrar will not hand out this bad information to others, and
others will not be misled into contacting the attacker. others will not be misled into contacting the attacker.
The Security Considerations discussed in [1] and [5] are also The Security Considerations discussed in [RFC3261] and [RFC3327] are
relevant to this document. For the security considerations of also relevant to this document. For the security considerations of
generating flow tokens, please also see Section 5.2. A discussion of generating flow tokens, please also see Section 5.2. A discussion of
preventing the avalanche restart problem is in Section 4.5. preventing the avalanche restart problem is in Section 4.5.
This document does not change the mandatory to implement security This document does not change the mandatory to implement security
mechanisms in SIP. User Agents are already required to implement mechanisms in SIP. User Agents are already required to implement
Digest authentication while support of TLS is recommended; proxy Digest authentication while support of TLS is recommended; proxy
servers are already required to implement Digest and TLS. servers are already required to implement Digest and TLS.
14. Operational Notes on Transports 14. Operational Notes on Transports
skipping to change at page 34, line 31 skipping to change at page 41, line 25
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. Changes 16. Changes
Note to RFC Editor: Please remove this whole section. Note to RFC Editor: Please remove this whole section.
16.1. Changes from 09 Version 16.1. Changes from 11 Version
Added 439 response code to handle "Require: outbound" with first
outbound proxy that doesn't insert ";ob".
16.2. Changes from 09 Version
Make outbound consistent with the latest version of STUN 3489bis Make outbound consistent with the latest version of STUN 3489bis
draft. The STUN keepalive section of outbound is now a STUN usage draft. The STUN keepalive section of outbound is now a STUN usage
(much less formal). (much less formal).
Fixed references. Fixed references.
16.2. Changes from 08 Version 16.3. Changes from 08 Version
UAs now include the 'ob' parameter in their Contact header for non- 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- REGISTER requests, as a hint to the Edge Proxy (so the EP can Record-
Route with a flow-token for example). Route with a flow-token for example).
Switched to CRLF for keepalives of connection-oriented transports Switched to CRLF for keepalives of connection-oriented transports
after brutal consensus at IETF 68. after brutal consensus at IETF 68.
Added timed-keepalive parameter and removed the unnecessary keep-tcp Added timed-keepalive parameter and removed the unnecessary keep-tcp
param, per consensus at IETF68. param, per consensus at IETF68.
skipping to change at page 35, line 16 skipping to change at page 42, line 16
consensus at IETF68. consensus at IETF68.
Deleted text about probing and validating with options, per consensus Deleted text about probing and validating with options, per consensus
at IETF68. at IETF68.
Deleted provision for waiting 120 secs before declaring flow stable, Deleted provision for waiting 120 secs before declaring flow stable,
per consensus at IETF68. per consensus at IETF68.
fixed example UUIDs fixed example UUIDs
16.3. Changes from 07 Version 16.4. 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.
16.4. Changes from 06 Version 16.5. 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.
16.5. Changes from 05 Version 16.6. 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 13 skipping to change at page 43, line 13
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.
16.6. Changes from 04 Version 16.7. 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 19 skipping to change at page 44, line 19
Added text about the 'ob' parameter which is used in Path header Added text about the 'ob' parameter which is used in Path header
field URIs to make sure that the previous proxy that added a Path field URIs to make sure that the previous proxy that added a Path
understood outbound processing. The registrar doesn't include understood outbound processing. The registrar doesn't include
Supported: outbound unless it could actually do outbound processing Supported: outbound unless it could actually do outbound processing
(ex: any Path headers have to have the 'ob' parameter). (ex: any Path headers have to have the 'ob' parameter).
Added some text describing what a registration means when there is an Added some text describing what a registration means when there is an
instance-id, but no reg-id. instance-id, but no reg-id.
16.7. Changes from 03 Version 16.8. 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 5 skipping to change at page 45, line 5
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.
16.8. Changes from 02 Version 16.9. Changes from 02 Version
Removed Double CRLF Keepalive Removed Double CRLF Keepalive
Changed ;sip-stun syntax to ;keepalive=stun Changed ;sip-stun syntax to ;keepalive=stun
Fixed incorrect text about TCP keepalives. Fixed incorrect text about TCP keepalives.
16.9. Changes from 01 Version 16.10. Changes from 01 Version
Moved definition of instance-id from GRUU[23] draft to this draft. Moved definition of instance-id from GRUU[I-D.ietf-sip-gruu] draft to
this draft.
Added tentative text about Double CRLF 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
16.10. Changes from 00 Version 16.11. 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.
17. Acknowledgments 17. Acknowledgments
Jonathan Rosenberg, Erkki Koivusalo, and Byron Campben provided many Francois Audet acted as document shepherd for this draft, tracking
comments and useful text. Dave Oran came up with the idea of using hundreds of comments and incorporating many grammatical fixes as well
the most recent registration first in the proxy. Alan Hawrylyshen as prodding the editors to "get on with it". Jonathan Rosenberg,
co-authored the draft that formed the initial text of this Erkki Koivusalo, and Byron Campben provided many comments and useful
specification. Additionally, many of the concepts here originated at text. Dave Oran came up with the idea of using the most recent
a connection reuse meeting at IETF 60 that included the authors, Jon registration first in the proxy. Alan Hawrylyshen co-authored the
Peterson, Jonathan Rosenberg, Alan Hawrylyshen, and Paul Kyzivat. draft that formed the initial text of this specification.
The TCP design team consisting of Chris Boulton, Scott Lawrence, Additionally, many of the concepts here originated at a connection
Rajnish Jain, Vijay K. Gurbani, and Ganesh Jayadevan provided input reuse meeting at IETF 60 that included the authors, Jon Peterson,
and text. Nils Ohlmeier provided many fixes and initial Jonathan Rosenberg, Alan Hawrylyshen, and Paul Kyzivat. The TCP
implementation experience. In addition, thanks to the following design team consisting of Chris Boulton, Scott Lawrence, Rajnish
folks for useful comments: Francois Audet, Flemming Andreasen, Mike Jain, Vijay K. Gurbani, and Ganesh Jayadevan provided input and text.
Hammer, Dan Wing, Srivatsa Srinivasan, Dale Worely, Juha Heinanen, Nils Ohlmeier provided many fixes and initial implementation
Eric Rescorla, Lyndsay Campbell, Christer Holmberg, Kevin Johns, experience. In addition, thanks to the following folks for useful
Jeroen van Bemmel, and Derek MacDonald. comments: Francois Audet, Flemming Andreasen, Mike Hammer, Dan Wing,
Srivatsa Srinivasan, Dale Worely, Juha Heinanen, Eric Rescorla,
Lyndsay Campbell, Christer Holmberg, Kevin Johns, Jeroen van Bemmel,
and Derek MacDonald.
Appendix A. Default Flow Registration Backoff Times 18. References
The base-time used for the flow re-registration backoff times 18.1. Normative References
described in Section 4.5 are configurable. If the base-time-all-fail
value is set to the default of 30 seconds and the base-time-not-
failed value is set to the default of 90 seconds, the following table
shows the resulting delay values.
+-------------------+--------------------+--------------------+ [I-D.ietf-behave-rfc3489bis]
| # of reg failures | all flows unusable | >1 non-failed flow | Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
+-------------------+--------------------+--------------------+ "Session Traversal Utilities for (NAT) (STUN)",
| 0 | 0 secs | 0 secs | draft-ietf-behave-rfc3489bis-15 (work in progress),
| 1 | 30-60 secs | 90-180 secs | February 2008.
| 2 | 1-2 mins | 3-6 mins |
| 3 | 2-4 mins | 6-12 mins |
| 4 | 4-8 mins | 12-24 mins |
| 5 | 8-16 mins | 15-30 mins |
| 6 or more | 15-30 mins | 15-30 mins |
+-------------------+--------------------+--------------------+
18. References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
18.1. Normative References [RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997.
[1] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., [RFC2506] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Registration Procedure", BCP 31, RFC 2506, March 1999.
Session Initiation Protocol", RFC 3261, June 2002.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
Levels", BCP 14, RFC 2119, March 1997. A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[3] Rosenberg, J., "Simple Traversal Underneath Network Address [RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation
Translators (NAT) (STUN)", draft-ietf-behave-rfc3489bis-12 Protocol (SIP): Locating SIP Servers", RFC 3263,
(work in progress), November 2007. June 2002.
[4] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol [RFC3327] Willis, D. and B. Hoeneisen, "Session Initiation Protocol
(SIP): Locating SIP Servers", RFC 3263, June 2002. (SIP) Extension Header Field for Registering Non-Adjacent
Contacts", RFC 3327, December 2002.
[5] Willis, D. and B. Hoeneisen, "Session Initiation Protocol (SIP) [RFC3489] Rosenberg, J., Weinberger, J., Huitema, C., and R. Mahy,
Extension Header Field for Registering Non-Adjacent Contacts", "STUN - Simple Traversal of User Datagram Protocol (UDP)
RFC 3327, December 2002. Through Network Address Translators (NATs)", RFC 3489,
March 2003.
[6] Leach, P., Mealling, M., and R. Salz, "A Universally Unique [RFC3581] Rosenberg, J. and H. Schulzrinne, "An Extension to the
IDentifier (UUID) URN Namespace", RFC 4122, July 2005. Session Initiation Protocol (SIP) for Symmetric Response
Routing", RFC 3581, August 2003.
[7] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Indicating [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
User Agent Capabilities in the Session Initiation Protocol 10646", STD 63, RFC 3629, November 2003.
(SIP)", RFC 3840, August 2004.
[8] Moats, R., "URN Syntax", RFC 2141, May 1997. [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat,
"Indicating User Agent Capabilities in the Session
Initiation Protocol (SIP)", RFC 3840, August 2004.
[9] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller [RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller
Preferences for the Session Initiation Protocol (SIP)", Preferences for the Session Initiation Protocol (SIP)",
RFC 3841, August 2004. RFC 3841, August 2004.
[10] Rosenberg, J. and H. Schulzrinne, "An Extension to the Session [RFC3968] Camarillo, G., "The Internet Assigned Number Authority
Initiation Protocol (SIP) for Symmetric Response Routing", (IANA) Header Field Parameter Registry for the Session
RFC 3581, August 2003. Initiation Protocol (SIP)", BCP 98, RFC 3968,
December 2004.
[11] Rosenberg, J., Weinberger, J., Huitema, C., and R. Mahy, "STUN
- Simple Traversal of User Datagram Protocol (UDP) Through
Network Address Translators (NATs)", RFC 3489, March 2003.
[12] Yergeau, F., "UTF-8, a transformation format of ISO 10646", [RFC3969] Camarillo, G., "The Internet Assigned Number Authority
STD 63, RFC 3629, November 2003. (IANA) Uniform Resource Identifier (URI) Parameter
Registry for the Session Initiation Protocol (SIP)",
BCP 99, RFC 3969, December 2004.
[13] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Sy ntax", STD 66, RFC 3986, Resource Identifier (URI): Generic Syntax", STD 66,
January 2005. RFC 3986, January 2005.
[14] Crocker, D. and P. Overell, "Augmented BNF for Syntax [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Specifications: ABNF", RFC 4234, October 2005. Unique IDentifier (UUID) URN Namespace", RFC 4122,
July 2005.
[15] Camarillo, G., "The Internet Assigned Number Authority (IANA) [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Header Field Parameter Registry for the Session Initiation Specifications: ABNF", STD 68, RFC 5234, January 2008.
Protocol (SIP)", BCP 98, RFC 3968, December 2004.
[16] Camarillo, G., "The Internet Assigned Number Authority (IANA) 18.2. Informational References
Uniform Resource Identifier (URI) Parameter Registry for the
Session Initiation Protocol (SIP)", BCP 99, RFC 3969,
December 2004.
[17] Holtman, K., Mutz, A., and T. Hardie, "Media Feature Tag [I-D.ietf-sip-gruu]
Registration Procedure", BCP 31, RFC 2506, March 1999. Rosenberg, J., "Obtaining and Using Globally Routable User
Agent (UA) URIs (GRUU) in the Session Initiation Protocol
(SIP)", draft-ietf-sip-gruu-15 (work in progress),
October 2007.
18.2. Informative References [I-D.ietf-sipping-config-framework]
Channabasappa, S., "A Framework for Session Initiation
Protocol User Agent Profile Delivery",
draft-ietf-sipping-config-framework-15 (work in progress),
February 2008.
[18] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) [I-D.ietf-sipping-nat-scenarios]
Protocol Version 1.1", RFC 4346, April 2006. Boulton, C., "Best Current Practices for NAT Traversal for
SIP", draft-ietf-sipping-nat-scenarios-07 (work in
progress), July 2007.
[19] Petrie, D., "A Framework for Session Initiation Protocol User [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Agent Profile Delivery", draft-ietf-sipping-config-framework-13 Hashing for Message Authentication", RFC 2104,
(work in progress), October 2007. February 1997.
[20] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for [RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782, specifying the location of services (DNS SRV)", RFC 2782,
February 2000. February 2000.
[21] Rosenberg, J., "Construction of the Route Header Field in the [RFC3320] Price, R., Bormann, C., Christoffersson, J., Hannu, H.,
Session Initiation Protocol (SIP)", Liu, Z., and J. Rosenberg, "Signaling Compression
draft-rosenberg-sip-route-construct-02 (work in progress). (SigComp)", RFC 3320, January 2003.
[22] Willis, D. and B. Hoeneisen, "Session Initiation Protocol (SIP)
Extension Header Field for Service Route Discovery During
Registration", RFC 3608, October 2003.
[23] Rosenberg, J., "Obtaining and Using Globally Routable User [RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security
Agent (UA) URIs (GRUU) in the Session Initiation Protocol (TLS) Protocol Version 1.1", RFC 4346, April 2006.
(SIP)", draft-ietf-sip-gruu-15 (work in progress),
October 2007.
[24] Boulton, C., "Best Current Practices for NAT Traversal for [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
SIP", draft-ietf-sipping-nat-scenarios-07 (work in progress), Encodings", RFC 4648, October 2006.
July 2007.
[25] Price, R., Bormann, C., Christoffersson, J., Hannu, H., Liu, Appendix A. Default Flow Registration Backoff Times
Z., and J. Rosenberg, "Signaling Compression (SigComp)",
RFC 3320, January 2003.
[26] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-Hashing The base-time used for the flow re-registration backoff times
for Message Authentication", RFC 2104, February 1997. described in Section 4.5 are configurable. If the base-time-all-fail
value is set to the default of 30 seconds and the base-time-not-
failed value is set to the default of 90 seconds, the following table
shows the resulting delay values.
[27] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", +-------------------+--------------------+--------------------+
RFC 4648, October 2006. | # of reg failures | all flows unusable | >1 non-failed flow |
+-------------------+--------------------+--------------------+
| 0 | 0 secs | 0 secs |
| 1 | 30-60 secs | 90-180 secs |
| 2 | 1-2 mins | 3-6 mins |
| 3 | 2-4 mins | 6-12 mins |
| 4 | 4-8 mins | 12-24 mins |
| 5 | 8-16 mins | 15-30 mins |
| 6 or more | 15-30 mins | 15-30 mins |
+-------------------+--------------------+--------------------+
Authors' Addresses Authors' Addresses
Cullen Jennings (editor) Cullen Jennings (editor)
Cisco Systems Cisco Systems
170 West Tasman Drive 170 West Tasman Drive
Mailstop SJC-21/2 Mailstop SJC-21/2
San Jose, CA 95134 San Jose, CA 95134
USA USA
skipping to change at page 43, line 7 skipping to change at page 50, line 7
Rohan Mahy (editor) Rohan Mahy (editor)
Plantronics Plantronics
345 Encincal St 345 Encincal St
Santa Cruz, CA 95060 Santa Cruz, CA 95060
USA USA
Email: rohan@ekabal.com Email: rohan@ekabal.com
Full Copyright Statement Full Copyright Statement
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors contained in BCP 78, and except as set forth therein, the authors
retain all their rights. retain all their rights.
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
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