draft-ietf-sip-outbound-12.txt   draft-ietf-sip-outbound-13.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 February 24, 2008 Intended status: Standards Track March 21, 2008
Expires: August 27, 2008 Expires: September 22, 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-12 draft-ietf-sip-outbound-13
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
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This Internet-Draft will expire on August 27, 2008. This Internet-Draft will expire on September 22, 2008.
Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2008). 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
skipping to change at page 2, line 22 skipping to change at page 2, line 22
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 4 2. Conventions and Terminology . . . . . . . . . . . . . . . . . 4
2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 5 2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 5
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Summary of Mechanism . . . . . . . . . . . . . . . . . . 6 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 . . . . . . . . . . . . . . . . . . . . . . 10 3.4. Edge Proxies . . . . . . . . . . . . . . . . . . . . . . 10
3.5. Keep alive Technique . . . . . . . . . . . . . . . . . . 11 3.5. Keep alive Technique . . . . . . . . . . . . . . . . . . 11
3.5.1. CRLF Keep-alive Technique . . . . . . . . . . . . . . 12 3.5.1. CRLF Keep alive Technique . . . . . . . . . . . . . . 12
3.5.2. STUN Keep alive 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 . . . . . . . . . . . . . . . . . . . . . . 14 4.2. Registrations . . . . . . . . . . . . . . . . . . . . . . 14
4.2.1. Initial Registrations . . . . . . . . . . . . . . . . 14 4.2.1. Initial Registrations . . . . . . . . . . . . . . . . 14
4.2.2. Subsequent REGISTER requests . . . . . . . . . . . . . 16 4.2.2. Subsequent REGISTER requests . . . . . . . . . . . . . 15
4.2.3. Non Outbound Registrations . . . . . . . . . . . . . . 16 4.2.3. Non Outbound Registrations . . . . . . . . . . . . . . 16
4.3. Sending Non-REGISTER Requests . . . . . . . . . . . . . . 16 4.3. Sending Non-REGISTER Requests . . . . . . . . . . . . . . 16
4.4. Keep-alives and Detecting Flow Failure . . . . . . . . . 17 4.4. Keep-alives and Detecting Flow Failure . . . . . . . . . 17
4.4.1. Keep alive with CRLF . . . . . . . . . . . . . . . . . 18 4.4.1. Keep alive with CRLF . . . . . . . . . . . . . . . . . 18
4.4.2. Keep alive with STUN . . . . . . . . . . . . . . . . . 19 4.4.2. Keep alive with STUN . . . . . . . . . . . . . . . . . 19
4.5. Flow Recovery . . . . . . . . . . . . . . . . . . . . . . 19 4.5. Flow Recovery . . . . . . . . . . . . . . . . . . . . . . 20
5. Edge Proxy Mechanisms . . . . . . . . . . . . . . . . . . . . 20 5. Edge Proxy Mechanisms . . . . . . . . . . . . . . . . . . . . 21
5.1. Processing Register Requests . . . . . . . . . . . . . . 20 5.1. Processing Register Requests . . . . . . . . . . . . . . 21
5.2. Generating Flow Tokens . . . . . . . . . . . . . . . . . 20 5.2. Generating Flow Tokens . . . . . . . . . . . . . . . . . 21
5.3. Forwarding Non-REGISTER Requests . . . . . . . . . . . . 21 5.3. Forwarding Non-REGISTER Requests . . . . . . . . . . . . 22
5.4. Edge Proxy Keep alive Handling . . . . . . . . . . . . . 22 5.3.1. Processing Incoming Requests . . . . . . . . . . . . . 22
6. Registrar Mechanisms: Processing REGISTER Requests . . . . . . 22 5.3.2. Processing Outgoing Requests . . . . . . . . . . . . . 23
7. Authoritative Proxy Mechanisms: Forwarding Requests . . . . . 24 5.4. Edge Proxy Keep alive Handling . . . . . . . . . . . . . 23
8. STUN Keep alive Processing . . . . . . . . . . . . . . . . . . 25 6. Registrar Mechanisms . . . . . . . . . . . . . . . . . . . . . 23
8.1. Use with Sigcomp . . . . . . . . . . . . . . . . . . . . 26 7. Authoritative Proxy Mechanisms: Forwarding Requests . . . . . 25
9. Example Message Flow . . . . . . . . . . . . . . . . . . . . . 27 8. STUN Keep alive Processing . . . . . . . . . . . . . . . . . . 26
10. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 8.1. Use with Sigcomp . . . . . . . . . . . . . . . . . . . . 27
11. New Response Codes . . . . . . . . . . . . . . . . . . . . . . 36 9. Example Message Flow . . . . . . . . . . . . . . . . . . . . . 28
11.1. Definition of 430 Flow Failed response code . . . . . . . 36 9.1. Subscription to configuration package . . . . . . . . . . 28
11.2. Definition of 439 First Hop Lacks Outbound Support 9.2. Registration . . . . . . . . . . . . . . . . . . . . . . 30
response . . . . . . . . . . . . . . . . . . . . . . . . 36 9.3. Incoming call and proxy crash . . . . . . . . . . . . . . 33
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37 9.4. Re-registration . . . . . . . . . . . . . . . . . . . . . 35
12.1. Flow-Timer Header Field . . . . . . . . . . . . . . . . . 37 9.5. Outgoing call . . . . . . . . . . . . . . . . . . . . . . 36
12.2. 'reg-id' Contact Header Field Parameter . . . . . . . . . 37 10. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
12.3. SIP/SIPS URI Parameters . . . . . . . . . . . . . . . . . 37 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38
12.4. SIP Option Tag . . . . . . . . . . . . . . . . . . . . . 38 11.1. Flow-Timer Header Field . . . . . . . . . . . . . . . . . 38
12.5. Response Codes . . . . . . . . . . . . . . . . . . . . . 38 11.2. 'reg-id' Contact Header Field Parameter . . . . . . . . . 39
12.5.1. 430 Response Code . . . . . . . . . . . . . . . . . . 38 11.3. SIP/SIPS URI Parameters . . . . . . . . . . . . . . . . . 39
12.5.2. 439 Response Code . . . . . . . . . . . . . . . . . . 38 11.4. SIP Option Tag . . . . . . . . . . . . . . . . . . . . . 39
12.6. Media Feature Tag . . . . . . . . . . . . . . . . . . . . 38 11.5. 430 (Flow Failed) Response Code . . . . . . . . . . . . . 39
13. Security Considerations . . . . . . . . . . . . . . . . . . . 39 11.6. 439 (First Hop Lacks Outbound Support) Response Code . . 40
14. Operational Notes on Transports . . . . . . . . . . . . . . . 40 11.7. Media Feature Tag . . . . . . . . . . . . . . . . . . . . 40
15. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 41 12. Security Considerations . . . . . . . . . . . . . . . . . . . 41
16. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 13. Operational Notes on Transports . . . . . . . . . . . . . . . 42
16.1. Changes from 11 Version . . . . . . . . . . . . . . . . . 41 14. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 43
16.2. Changes from 09 Version . . . . . . . . . . . . . . . . . 41 15. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
16.3. Changes from 08 Version . . . . . . . . . . . . . . . . . 41 15.1. Changes from 12 Version . . . . . . . . . . . . . . . . . 43
16.4. Changes from 07 Version . . . . . . . . . . . . . . . . . 42 15.2. Changes from 11 Version . . . . . . . . . . . . . . . . . 43
16.5. Changes from 06 Version . . . . . . . . . . . . . . . . . 42 15.3. Changes from 09 Version . . . . . . . . . . . . . . . . . 43
16.6. Changes from 05 Version . . . . . . . . . . . . . . . . . 42 15.4. Changes from 08 Version . . . . . . . . . . . . . . . . . 43
16.7. Changes from 04 Version . . . . . . . . . . . . . . . . . 43 15.5. Changes from 07 Version . . . . . . . . . . . . . . . . . 44
16.8. Changes from 03 Version . . . . . . . . . . . . . . . . . 44 15.6. Changes from 06 Version . . . . . . . . . . . . . . . . . 44
16.9. Changes from 02 Version . . . . . . . . . . . . . . . . . 45 15.7. Changes from 05 Version . . . . . . . . . . . . . . . . . 44
16.10. Changes from 01 Version . . . . . . . . . . . . . . . . . 45 15.8. Changes from 04 Version . . . . . . . . . . . . . . . . . 45
16.11. Changes from 00 Version . . . . . . . . . . . . . . . . . 45 15.9. Changes from 03 Version . . . . . . . . . . . . . . . . . 46
17. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 45 15.10. Changes from 02 Version . . . . . . . . . . . . . . . . . 47
18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 46 15.11. Changes from 01 Version . . . . . . . . . . . . . . . . . 47
18.1. Normative References . . . . . . . . . . . . . . . . . . 46 15.12. Changes from 00 Version . . . . . . . . . . . . . . . . . 47
18.2. Informational References . . . . . . . . . . . . . . . . 47 16. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 47
Appendix A. Default Flow Registration Backoff Times . . . . . . . 48 17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 48 17.1. Normative References . . . . . . . . . . . . . . . . . . 48
Intellectual Property and Copyright Statements . . . . . . . . . . 50 17.2. Informational References . . . . . . . . . . . . . . . . 49
Appendix A. Default Flow Registration Backoff Times . . . . . . . 50
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 51
Intellectual Property and Copyright Statements . . . . . . . . . . 52
1. Introduction 1. Introduction
There are many environments for SIP [RFC3261] deployments in which There are many environments for SIP [RFC3261] deployments in which
the User Agent (UA) can form a connection to a Registrar or Proxy but the User Agent (UA) can form a connection to a Registrar or Proxy but
in which connections in the reverse direction to the UA are not in which connections in the reverse direction to the UA are not
possible. This can happen for several reasons. Connections to the possible. This can happen for several reasons, but the most likely
UA can be blocked by a firewall device between the UA and the proxy is a NAT or a firewall in between the SIP UA and the proxy. Many
or registrar, which will only allow new connections in the direction such devices will only allow outgoing connections. This
of the UA to the Proxy. Similarly a NAT could be present, which is specification allows a SIP User Agent behind such a firewall or NAT
only capable of allowing new connections from the private address to receive inbound traffic associated with registrations or dialogs
side to the public side. This specification allows a SIP User Agent that it initiates.
behind such a firewall or NAT to receive inbound traffic associated
with registrations or dialogs that it initiates.
Most IP phones and personal computers get their network Most IP phones and personal computers get their network
configurations dynamically via a protocol such as DHCP (Dynamic Host configurations dynamically via a protocol such as DHCP (Dynamic Host
Configuration Protocol). These systems typically do not have a Configuration Protocol). These systems typically do not have a
useful name in the Domain Name System (DNS), and they almost never useful name in the Domain Name System (DNS), and they almost never
have a long-term, stable DNS name that is appropriate for use in the have a long-term, stable DNS name that is appropriate for use in the
subjectAltName of a certificate, as required by [RFC3261]. However, subjectAltName of a certificate, as required by [RFC3261]. However,
these systems can still act as a Transport Layer Security (TLS) these systems can still act as a Transport Layer Security (TLS)
[RFC4346] client and form connections to a proxy or registrar which [RFC4346] client and form connections to a proxy or registrar which
authenticates with a server certificate. The server can authenticate authenticates with a server certificate. The server can authenticate
the UA using a shared secret in a digest challenge (as defined in the UA using a shared secret in a digest challenge (as defined in
Section 22 of RFC 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 in 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 keep alive schemes. The keep specification also defines multiple keep alive schemes. The keep
alive mechanism is used to keep NAT bindings fresh, and to allow the alive mechanism is used to keep NAT bindings fresh, and to allow the
UA to 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 [RFC2119]. document are to be interpreted as described in [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. (In RFC 3261, the role which is
authoritative for REGISTER requests for a specific AOR is a
Registration Server.)
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.
The "first" edge proxy refers to the first edge proxy encountered
when a UA sends a request.
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 Flow Token: An identifier which uniquely identifies a flow which can
be included in a SIP URI (Uniform Resource Identifier). be included in a SIP URI (Uniform Resource Identifier).
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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
The mechanisms defined in this document are useful in several The mechanisms defined in this document are useful in several
scenarios discussed below, including the simple co-located registrar scenarios discussed below, including the simple co-located registrar
and proxy, a User Agent desiring multiple connections to a resource and proxy, a User Agent desiring multiple connections to a resource
(for redundancy, for example), and a system that uses Edge Proxies. (for redundancy, for example), and a system that uses Edge Proxies.
This entire section is non-normative.
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 flows 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 correspond to the same UA. The registrar can use the reg-id
recognize whether a UA is creating a new flow or refreshing or label to recognize whether a UA is creating a new flow or refreshing
replacing an old one, possibly after a reboot or a network failure. or 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 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 edge proxy to route subsequent requests in that dialog over the same
flow. This is necessary whether the UA has registered or not. flow. This is necessary whether the UA has registered or not.
UAs can use a simple periodic message as a keep alive mechanism to UAs use a simple periodic message as a keep alive mechanism to keep
keep their flow to the proxy or registrar alive. For connection their flow to the proxy or registrar alive. For connection oriented
oriented transports such as TCP this is based on carriage-return and transports such as TCP this is based on carriage-return and line-feed
line-feed sequences (CRLF), while for transports that are not sequences (CRLF), while for transports that are not connection
connection oriented this is accomplished by using a SIP-specific oriented this is accomplished by using a SIP-specific usage profile
usage profile of STUN (Session Traversal Utilities for NAT) of STUN (Session Traversal Utilities for NAT)
[I-D.ietf-behave-rfc3489bis]. [I-D.ietf-behave-rfc3489bis].
The UA can also ask its first hop proxy to use an specific flow for
subsequent messages when sending a dialog-forming request. This
allows the UA to setup a subscription dialog for the SIP
configuration package [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 |
+-----+-----+ +-----+-----+
| |
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This allows a UA that has rebooted to replace its previous This allows a UA that has rebooted to replace its previous
registration for each flow with minimal impact on overall system registration for each flow with minimal impact on overall system
load. load.
When Alice sends a request to Bob, his authoritative proxy selects When Alice sends a request to Bob, his authoritative proxy selects
the target set. The proxy forwards the request to elements in the the target set. The proxy forwards the request to elements in the
target set based on the proxy's policy. The proxy looks at the target set based on the proxy's policy. The proxy looks at the
target set and uses the instance-id to understand if two targets both target set and uses the instance-id to understand if two targets both
end up routing to the same UA. When the proxy goes to forward a end up routing to the same UA. When the proxy goes to forward a
request to a given target, it looks and finds the flows over which it request to a given target, it looks and finds the flows over which it
received the registration. The proxy then forwards the request on received the registration. The proxy then forwards the request over
that existing flow, instead of resolving the Contact URI using the an existing flow, instead of resolving the Contact URI using the
procedures in RFC 3263 [RFC3263] and trying to form a new flow to procedures in [RFC3263] and trying to form a new flow to that
that contact. 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 34 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 [RFC2782] to load balance
the primary connection across a set of machines that can service the
primary connection, and also using DNS SRV to load balance across a
separate set of machines that can service the secondary connection.
The deployment here requires that DNS is configured with one entry
that resolves to all the primary hosts and another entry that
resolves to all the secondary hosts. While this introduces
additional DNS configuration, the approach works and requires no
additional SIP extensions.
Note: Approaches which select multiple connections from a single
DNS SRV set were also considered, but cannot prevent two
connections from accidentally resolving to the same host. The
approach in this document does not prevent future extensions, such
as the SIP UA configuration framework
[I-D.ietf-sipping-config-framework], from adding other ways for a
User Agent to discover its outbound-proxy-set.
+-------------------+ +-------------------+
| Domain | | Domain |
| Logical Proxy/Reg | | Logical Proxy/Reg |
| | | |
|+-----+ +-----+| |+-----+ +-----+|
||Host1| |Host2|| ||Host1| |Host2||
|+-----+ +-----+| |+-----+ +-----+|
+---\------------/--+ +---\------------/--+
\ / \ /
\ / \ /
skipping to change at page 9, line 23 skipping to change at page 9, line 4
\ / \ /
\ / \ /
\ / \ /
\ / \ /
+------+ +------+
| User | | User |
| Agent| | Agent|
+------+ +------+
The UA is configured with multiple outbound proxy registration URIs. The UA is configured with multiple outbound proxy registration URIs.
These URIs are configured into the UA through whatever the normal These URIs are configured into the UA through whatever the normal
mechanism is to configure the proxy 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" and "sip: something like "sip:primary.example.com" and "sip:
secondary.example.com". Note that each URI in the outbound-proxy-set secondary.example.com". Note that each URI in the outbound-proxy-set
could resolve to several different physical hosts. The could resolve to several different physical hosts. The
administrative domain that created these URIs should ensure that the administrative domain that created these URIs should ensure that the
two URIs resolve to separate hosts. These URIs are handled according two URIs resolve to separate hosts. These URIs are handled according
to normal SIP processing rules, so mechanisms like SRV can be used to to normal SIP processing rules, so mechanisms like DNS SRV [RFC2782]
do load balancing across a proxy farm. can be used to do load balancing across a proxy farm. The approach
in this document does not prevent future extensions, such as the SIP
UA configuration framework [I-D.ietf-sipping-config-framework], from
adding other ways for a User Agent to discover its outbound-proxy-
set.
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
nearly simultaneously, this is referred to as the avalanche restart nearly simultaneously, this is referred to as the avalanche restart
problem, and is further discussed in Section 4.5. The multiple flows problem, and is further discussed in Section 4.5. The multiple flows
to many servers help reduce the load caused by the avalanche restart. to many servers help reduce the load caused by the avalanche restart.
If a UA has multiple flows, and one of the servers fails, the UA If a UA has multiple flows, and one of the servers fails, the UA
delays the specified time before trying to form a new connection to delays a recommended amount of time before trying to form a new
replace the flow to the server that failed. By spreading out the connection to replace the flow to the server that failed. By
time used for all the UAs to reconnect to a server, the load on the spreading out the time used for all the UAs to reconnect to a server,
server farm is reduced. the load on the server farm is reduced.
When used in this fashion to achieve high reliability, the operator Scalability is achieved by using DNS SRV [RFC2782] to load balance
will need to configure DNS such that the various URIs in the outbound the primary connection across a set of machines that can service the
proxy set do not resolve to the same host. primary connection, and also using DNS SRV to load balance across a
separate set of machines that can service the secondary connection.
The deployment here requires that DNS is configured with one entry
that resolves to all the primary hosts and another entry that
resolves to all the secondary hosts. While this introduces
additional DNS configuration, the approach works and requires no
additional SIP extensions.
Another motivation for maintaining multiple flows between the UA and Another motivation for maintaining multiple flows between the UA and
its registrar is related to multihomed UAs. Such UAs can benefit its registrar is related to multihomed UAs. Such UAs can benefit
from multiple connections from different interfaces to protect from multiple connections from different interfaces to protect
against the failure of an individual access link. against the failure of an individual access link.
3.4. Edge Proxies 3.4. Edge Proxies
Some SIP deployments use edge proxies such that the UA sends the Some SIP deployments use edge proxies such that the UA sends the
REGISTER to an Edge Proxy that then forwards the REGISTER to the REGISTER to an Edge Proxy that then forwards the REGISTER to the
Registrar. The Edge Proxy includes a Path header [RFC3327] so that Registrar. There could be a NAT or firewall between the UA and the
when the registrar later forwards a request to this UA, the request Edge Proxy.
is routed through the Edge Proxy. There could be a NAT or firewall
between the UA and the Edge Proxy.
+---------+ +---------+
|Registrar| |Registrar|
|Proxy | |Proxy |
+---------+ +---------+
/ \ / \
/ \ / \
/ \ / \
+-----+ +-----+ +-----+ +-----+
|Edge1| |Edge2| |Edge1| |Edge2|
+-----+ +-----+ +-----+ +-----+
\ / \ /
\ / \ /
----------------------------NAT/FW ----------------------------NAT/FW
\ / \ /
\ / \ /
+------+ +------+
|User | |User |
|Agent | |Agent |
+------+ +------+
The Edge Proxy includes a Path header [RFC3327] so that when the
registrar later forwards a request to this UA, the request is routed
through the Edge Proxy.
These systems can use effectively the same mechanism as described in These systems can use effectively the same mechanism as described in
the previous sections but need to use the Path header. When the Edge the previous sections but need to use the Path header. When the Edge
Proxy receives a registration, it needs to create an identifier value Proxy receives a registration, it needs to create an identifier value
that is unique to this flow (and not a subsequent flow with the same that is unique to this flow (and not a subsequent flow with the same
addresses) and put this identifier in the Path header URI. This addresses) and put this identifier in the Path header URI. This
identifier has two purposes. First, it allows the Edge Proxy to map identifier has two purposes. First, it allows the Edge Proxy to map
future requests back to the correct flow. Second, because the future requests back to the correct flow. Second, because the
identifier will only be returned if the user authenticates with the identifier will only be returned if the user authenticates with the
registrar successfully, it allows the Edge Proxy to indirectly check registrar successfully, it allows the Edge Proxy to indirectly check
the user's authentication information via the registrar. The the user's authentication information via the registrar. The
skipping to change at page 11, line 15 skipping to change at page 11, line 9
header, to the associated flow. header, to the associated flow.
The term Edge Proxy is often used to refer to deployments where the The term Edge Proxy is often used to refer to deployments where the
Edge Proxy is in the same administrative domain as the Registrar. Edge Proxy is in the same administrative domain as the Registrar.
However, in this specification we use the term to refer to any proxy However, in this specification we use the term to refer to any proxy
between the UA and the Registrar. For example the Edge Proxy may be between the UA and the Registrar. For example the Edge Proxy may be
inside an enterprise that requires its use and the registrar could be inside an enterprise that requires its use and the registrar could be
from a service provider with no relationship to the enterprise. from a service provider with no relationship to the enterprise.
Regardless if they are in the same administrative domain, this Regardless if they are in the same administrative domain, this
specification requires that Registrars and Edge proxies support the specification requires that Registrars and Edge proxies support the
Path header mechanism in RFC 3327 [RFC3327]. Path header mechanism in [RFC3327].
3.5. Keep alive Technique 3.5. Keep alive Technique
This document describes three keep alive mechanisms. Each of these This document describes two keep alive mechanisms: a CRLF keep alive
mechanisms uses a client-to-server "ping" keep alive and a and a STUN keep alive. Each of these mechanisms uses a client-to-
corresponding server-to-client "pong" message. This ping-pong server "ping" keep alive and a corresponding server-to-client "pong"
sequence allows the client, and optionally the server, to tell if its message. This ping-pong sequence allows the client, and optionally
flow is still active and useful for SIP traffic. The server responds the server, to tell if its flow is still active and useful for SIP
to pings by sending pongs. If the client does not receive a pong in traffic. The server responds to pings by sending pongs. If the
response to its ping, it declares the flow dead and opens a new flow client does not receive a pong in response to its ping, it declares
in its place. the flow dead and opens a new flow in its place.
This document also suggests timer values for two of these client keep This document also suggests timer values for these client keep alive
alive mechanisms. These timer values were chosen to keep most NAT mechanisms. These timer values were chosen to keep most NAT and
and firewall bindings open, to detect unresponsive servers within 2 firewall bindings open, to detect unresponsive servers within 2
minutes, and to prevent the avalanche restart problem. However, the minutes, and to prevent the avalanche restart problem. However, 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. SIP messages.
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 4.5 to provide congestion
relief when a large number of agents simultaneously reboot. relief when a large number of agents simultaneously reboot.
A keep alive mechanism needs to keep NAT bindings refreshed; for A keep alive 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 keep transports such as TCP [RFC0793] and SCTP [RFC4966], this
alive approach based on sending CRLFs. For connectionless transport, specification describes a keep alive approach based on sending CRLFs.
such as UDP, this specification describes using STUN For connectionless transport, such as UDP [RFC0768], this
[I-D.ietf-behave-rfc3489bis] over the same flow as the SIP traffic to specification describes using STUN [I-D.ietf-behave-rfc3489bis] over
perform the keepalive. the same flow as the SIP traffic to perform the keepalive.
UAs are also free to use native transport keep alives, however the UA UAs and Proxies are also free to use native transport keep alives,
application may not be able to set these timers on a per-connection however the application may not be able to set these timers on a per-
basis, and the server certainly cannot make any assumption about what connection basis, and the server certainly cannot make any assumption
values are used. Use of native transport keep alives is therefore about what values are used. Use of native transport keep alives is
outside the scope of this document. outside the scope of this document.
3.5.1. CRLF Keep-alive 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 Sending a CRLF over a connection-oriented transport is backwards
compatible (because of requirements in Section 7.5 of RFC 3261), compatible (because of requirements in Section 7.5 of RFC 3261),
but only implementations which support this specification will but only implementations which support this specification will
skipping to change at page 13, line 38 skipping to change at page 13, line 32
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
[RFC3840] . As described in [RFC3840], this media feature tag will [RFC3840] . As described in [RFC3840], this media feature tag will
be encoded in the Contact header field as the "+sip.instance" Contact be encoded in the Contact header field as the "+sip.instance" Contact
header field parameter. One case where a UA may not want to include header field parameter. One case where a UA may not want to include
the sip.instance media feature tag at all is when it is making an the sip.instance media feature tag at all is when it is making an
anonymous request or some other privacy concern requires that the UA anonymous request or some other privacy concern requires that the UA
not reveal its identity. not reveal its identity.
RFC 3840 [RFC3840] defines equality rules for callee capabilities [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 [RFC3840] and in the caller the generic usages defined in the callee capabilities [RFC3841]
preferences specification [RFC3841]. When the instance ID is used and the caller preferences [RFC3841] specifications. When the
in this specification, it is effectively "extracted" from the instance ID is used in this specification, it is effectively
value in the "sip.instance" media feature tag. Thus, equality "extracted" from the value in the "sip.instance" media feature
comparisons are performed using the rules for URN equality that tag. Thus, equality comparisons are performed using the rules for
are specific to the scheme in the URN. If the element performing URN equality that are specific to the scheme in the URN. If the
the comparisons does not understand the URN scheme, it performs element performing the comparisons does not understand the URN
the comparisons using the lexical equality rules defined in RFC scheme, it performs the comparisons using the lexical equality
2141 [RFC2141]. Lexical equality could result in two URNs being rules defined in [RFC2141]. Lexical equality could result in two
considered unequal when they are actually equal. In this specific URNs being considered unequal when they are actually equal. In
usage of URNs, the only element which provides the URN is the SIP this specific usage of URNs, the only element which provides the
UA instance identified by that URN. As a result, the UA instance URN is the SIP UA instance identified by that URN. As a result,
MUST provide lexically equivalent URNs in each registration it the UA instance MUST provide lexically equivalent URNs in each
generates. This is likely to be normal behavior in any case; registration it generates. This is likely to be normal behavior
clients are not likely to modify the value of the instance ID so in any case; clients are not likely to modify the value of the
that it remains functionally equivalent yet lexicographically instance ID so that it remains functionally equivalent yet
different from previous registrations. lexicographically different from previous registrations.
4.2. Registrations 4.2. Registrations
4.2.1. Initial 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 unique For each outbound proxy URI in the set, the UAC SHOULD send a
REGISTER in the normal way using this URI as the default outbound REGISTER request using this URI as the default outbound proxy. (The
proxy. (The UA could limit the number of flows formed to conserve UA could limit the number of flows formed to conserve battery power,
battery power, for example). UAs that support this specification for example). UAs that support this specification MUST include the
MUST include the outbound option tag in a Supported header field in a outbound option tag in a Supported header field in a REGISTER
REGISTER request. Each of these REGISTER requests will use a unique request. Each of these REGISTER requests will use a unique Call-ID.
Call-ID. Forming the route set for the request is outside the scope Forming the route set for the request is outside the scope of this
of this document, but typically results in sending the REGISTER such document, but typically results in sending the REGISTER such that the
that the topmost Route header field contains a loose route to the topmost Route header field contains a loose route to the outbound
outbound proxy URI. proxy URI.
Registration requests, other than those described in Section 4.2.3, 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 registration requests include a distinct reg-id parameter in
parameter in the Contact header field. Each one of these the Contact header field. Each one of these registrations will form
registrations will form a new flow from the UA to the proxy. The a new flow from the UA to the proxy. The sequence of reg-id values
sequence of reg-id values does not have to be sequential but MUST be does not have to be sequential but MUST be exactly the same sequence
exactly the same sequence of reg-id values each time the UA instance of reg-id values each time the UA instance power cycles or reboots so
power cycles or reboots so that the reg-id values will collide with that the reg-id values will collide with the previously used reg-id
the previously used reg-id values. This is so the registrar can values. This is so the registrar can replace the older
replace the older registrations. registrations.
The UAC can situationally decide whether to request outbound The UAC can situationally decide whether to request outbound
behavior by including or omitting the 'reg-id' parameter. For behavior by including or omitting the 'reg-id' parameter. For
example, imagine the outbound-proxy-set contains two proxies in example, imagine the outbound-proxy-set contains two proxies in
different domains, EP1 and EP2. If an outbound-style registration different domains, EP1 and EP2. If an outbound-style registration
succeeded for a flow through EP1, the UA might decide to include succeeded for a flow through EP1, the UA might decide to include
'outbound' in its Require header field when registering with EP2, 'outbound' in its Require header field when registering with EP2,
in order to insure consistency. Similarly, if the registration in order to insure consistency. Similarly, if the registration
through EP1 did not support outbound, the UA might not register through EP1 did not support outbound, the UA might not register
with EP2 at all. with EP2 at all.
skipping to change at page 15, line 36 skipping to change at page 15, line 29
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 If outbound registration succeeded, as indicated by the presence of
the outbound option-tag in the Require header field of a successful the outbound option-tag in the Require header field of a successful
registration response, the UA begins sending keepalives as described registration response, the UA begins sending keepalives as described
in Section 4.4. 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 [RFC3263]. In to registrations as described in [RFC3261] and [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.
If the registering UA receives a 439 (First Hop Lacks Outbound If the registering UA receives a 439 (First Hop Lacks Outbound
Support) response to a REGISTER request, it MAY re-attempt Support) response to a REGISTER request, it MAY re-attempt
registration without an outbound proxy (subject to local policy at registration without an outbound proxy (subject to local policy at
the client). If the client has one or more alternate outbound the client). If the client has one or more alternate outbound
proxies available, it MAY re-attempt registration through such proxies available, it MAY re-attempt registration through such
outbound proxies. See Section 11.2 for more information on the 439 outbound proxies. See Section 11.6 for more information on the 439
response code. response code.
4.2.2. Subsequent REGISTER requests 4.2.2. Subsequent REGISTER requests
Re-registrations and single Contact de-registrations use the same Re-registrations and single Contact de-registrations use the same
instance-id and reg-id values as the corresponding initial instance-id and reg-id values as the corresponding initial
registration. Re-registrations which merely refresh an existing registration. Re-registrations which merely refresh an existing
valid registration SHOULD be sent over the same flow as the original valid registration are sent over the same flow as the original
registration. registration.
If a re-registration is rejected with a recoverable error response,
for example by a 503 (Service Unavailable) containing a Retry-After
header, the UAC SHOULD NOT tear down the corresponding flow if the
flow uses a connection-oriented transport such as TCP. As long as
"pongs" are received in response to "pings", the flow SHOULD be kept
active until a non-recoverable error response is received. This
prevents unnecessary closing and opening of connections.
4.2.3. Non Outbound Registrations 4.2.3. Non Outbound Registrations
A User Agent MUST NOT include a reg-id header parameter in the In an initial registration, a User Agent MUST NOT include a reg-id
Contact header field of a registration with a non-zero expiration, if header parameter in the Contact header field if the registering UA is
the registering UA is not the same instance as the UA referred to by not the same instance as the UA referred to by the target Contact
the target Contact header field. (This practice is occasionally used header field. (This practice is occasionally used to install
to install forwarding policy into registrars.) 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 UAC 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.
UAs that support this specification SHOULD include the outbound UAs that support this specification SHOULD include the outbound
option tag in a Supported header field in a non-Register REGISTER option tag in a Supported header field in a non-Register request.
request.
The UA performs normal DNS resolution on the next hop URI (as The UAC performs normal DNS resolution on the next hop URI (as
described in RFC 3263 [RFC3263]) to find a protocol, IP address, and described in [RFC3263]) to find a protocol, IP address, and port.
port. For protocols that don't use TLS, if the UA has an existing For protocols that don't use TLS, if the UAC 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 UAC
UA MUST use the existing connection. For TLS protocols, there MUST MUST use the existing connection. For TLS protocols, there MUST also
also be a match between the host production in the next hop and one be a match between the host production in the next hop and one of the
of the URIs contained in the subjectAltName in the peer certificate. URIs contained in the subjectAltName in the peer certificate. If the
If the UA cannot use one of the existing flows, then it SHOULD form a UAC cannot use one of the existing flows, then it SHOULD form a new
new flow by sending a datagram or opening a new connection to the flow by sending a datagram or opening a new connection to the next
next hop, as appropriate for the transport protocol. hop, as appropriate for the transport protocol.
If the UA is sending a dialog-forming request, and wants all If the UAC 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 UAC 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 [I-D.ietf-sip-gruu]. The flow used for the request is typically GRUU [I-D.ietf-sip-gruu]. The flow used for the request is typically
the same flow the UA registered over, but it could be a new flow, for the same flow the UA registered over, but it could be a new flow, for
example the initial subcription dialog for the configuration example the initial subcription dialog for the configuration
framework [I-D.ietf-sipping-config-framework] needs to exist before framework [I-D.ietf-sipping-config-framework] needs to exist before
registration. registration.
Note that if the UA wants a UDP flow to work through NATs or Note that if the UAC wants a UDP flow to work through NATs or
firewalls it still needs to put the 'rport' parameter [RFC3581] in firewalls it still needs to put the 'rport' parameter [RFC3581] in
its Via header field value, and send from the port it is prepared its Via header field value, and send from the port it is prepared
to receive on. More general information about NAT traversal in to receive on. More general information about NAT traversal in
SIP is described in [I-D.ietf-sipping-nat-scenarios]. SIP is described in [I-D.ietf-sipping-nat-scenarios].
4.4. Keep-alives and Detecting Flow Failure 4.4. Keep-alives and Detecting Flow Failure
Keepalives are used for refreshing NAT/firewall bindings and
detecting flow failure. Flows can fail for many reasons including
NATs rebooting and Edge Proxies crashing.
As described in Section 4.2, a UA that registers will begin sending
keepalives after an appropriate registration response. A UA that
does not register (for example, a PSTN gateway behind a firewall) can
also send keepalives under certain circumstances.
Under specific circumstances, a UAC might be allowed to send STUN
keep alives even if the procedures in Section 4.2 were not completed,
provided that there is an explicit indication that the target first
hop SIP note supports STUN keep alives. This applies for example to
a non-registering UA or to a case where the UA registration
succeeded, but the response did not include the outbound option-tag
in the Require header field.
Note that a UA can "always" send a double CRLF (a "ping") over
connection-oriented transports as this is already allowed by
[RFC3261]. Section 7.5, however a UA that did not register using
outbound registration cannot expect a CRLF in response (a "pong")
unless the UA has an explicit indication that CRLF keepalives are
supported as described in this section. Likewise, a UA that did not
successfully register with outbound procedures needs explicit
indication that the target first hop SIP node supports STUN
keepalives before it can send any STUN messages.
Configuration indicating keepalive support for a specific target is
considered an explicit indication. If these conditions are
satisfied, the UA sends its keepalives according to the same
guidelines described in the rest of this section as UAs which
register.
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 keep alive messages tries to detect failure by periodically sending keep alive 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 with a registration has failed, the UA
in Section 4.2 to form a new flow to replace the failed one. follows the procedures in Section 4.2 to form a new flow to replace
the failed one.
When a successful registration response contains the Flow-Timer When a successful registration response contains the Flow-Timer
header field, the value of this header field is the number of seconds header field, the value of this header field is the number of seconds
the server is prepared to wait without seeing keepalives before it the server is prepared to wait without seeing keepalives before it
considers the corresponding flow dead. The UA MUST send keepalives considers the corresponding flow dead. The UA MUST send keepalives
at least as often as this number of seconds. If the UA uses the at least as often as this number of seconds. If the UA uses the
server recommended keepalive frequency it SHOULD send its keepalives server recommended keepalive frequency it SHOULD send its keepalives
so that the interval between each keepalive is randomly distributed so that the interval between each keepalive is randomly distributed
between 80% and 100% of the server provided time. For example, it between 80% and 100% of the server provided time. For example, if
the server suggests 120 seconds, the UA would send each keepalive the server suggests 120 seconds, the UA would send each keepalive
with a different frequency between 95 and 120 seconds. with a different frequency between 95 and 120 seconds.
If no Flow-Timer header field was present in a register response for If no Flow-Timer header field was present in a register response for
this flow, the UA can send keepalives at its discretion. The rest of this flow, the UA can send keepalives at its discretion. The
this paragraph provides RECOMMENDED default values for these sections below provide RECOMMENDED default values for these
keepalives. The time between each keep alive request when using non keepalives.
connection based transports such as UDP SHOULD be a random number
between 24 and 29 seconds. For connection based transports such as
TCP, correct selection of keepalive frequency is primarily a trade-
off between battery usage and availability. For devices where power
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
seconds was selected, as many NATs have UDP timeouts as low as 30
seconds. The 24 second lower bound was selected so that after 10
minutes the jitter introduced by different timers will make the
keep alive requests unsynchronized to evenly spread the load on
the servers. For TCP, the 120 seconds upper bound was chosen
based on the idea that for a good user experience, failures
normally will be detected in this amount of time and a new
connection set up. The 14 minute upper-bound for battery-powered
devices was selected based on NATs with TCP timeouts as low as 15
minutes. Operators that wish to change the relationship between
load on servers and the expected time that a user might not
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 [RFC3263] SIP DNS The client needs to perform normal [RFC3263] SIP DNS resolution on
resolution on the URI from the outbound-proxy-set to pick a the URI from the outbound-proxy-set to pick a transport. Once a
transport. Once a transport is selected, the UA selects the keep transport is selected, the UA selects the keep alive approach that is
alive approach that is recommended for that transport. recommended for that transport.
4.4.1. Keep alive with CRLF 4.4.1. Keep alive 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 TLS over TCP).
skipping to change at page 19, line 5 skipping to change at page 19, line 12
are sent inside the TLS protected channel. If sending over a SigComp are sent inside the TLS protected channel. If sending over a SigComp
[RFC3320] compressed data stream, the CRLF keep alives are sent [RFC3320] compressed data stream, the CRLF keep alives are sent
inside the compressed stream. The double CRLF is considered a single inside the compressed stream. The double CRLF is considered a single
SigComp message. The specific mechanism for representing these SigComp message. The specific mechanism for representing these
characters is an implementation specific matter to be handled by the characters is an implementation specific matter to be handled by the
SigComp 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 keep alive. treat the flow as failed. Clients MUST support this CRLF keep alive.
The proper selection of keepalive frequency is primarily a trade-off
between battery usage and availability. For devices where power 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: the 120 seconds upper bound was
chosen based on the idea that for a good user experience, failures
normally will be detected in this amount of time and a new
connection set up. The 14 minute upper-bound for battery-powered
devices was selected based on NATs with TCP timeouts as low as 15
minutes. Operators that wish to change the relationship between
load on servers and the expected time that a user might not
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.
4.4.2. Keep alive with STUN 4.4.2. Keep alive 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. The UA can the UA is connecting resolves to use the UDP transport. The UA can
periodically perform keep alive checks by sending STUN periodically perform keep alive checks by sending STUN
[I-D.ietf-behave-rfc3489bis] Binding Requests over the flow as [I-D.ietf-behave-rfc3489bis] Binding Requests over the flow as
described in Section 8. Clients MUST support STUN based keep alives. described in Section 8. Clients MUST support STUN based keep alives.
The time between each keep alive request SHOULD be a random number
between 24 and 29 seconds.
Note on selection of time values: the upper bound of 29 seconds
was selected, as many NATs have UDP timeouts as low as 30 seconds.
The 24 second lower bound was selected so that after 10 minutes
the jitter introduced by different timers will make the keep alive
requests unsynchronized to evenly spread the load on the servers.
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 used for registration (through a particular URI in the When a flow used for registration (through a particular URI in the
outbound-proxy-set) fails, the UA needs to form a new flow to replace outbound-proxy-set) fails, the UA needs to form a new flow to replace
skipping to change at page 20, line 32 skipping to change at page 21, line 18
attempt. attempt.
5. Edge Proxy Mechanisms 5. Edge Proxy Mechanisms
5.1. Processing Register Requests 5.1. Processing Register Requests
When an Edge Proxy receives a registration request with a reg-id When an Edge Proxy receives a registration request with a reg-id
header parameter in the Contact header field, it needs to determine header parameter in the Contact header field, it needs to determine
if it (the edge proxy) will have to be visited for any subsequent if it (the edge proxy) will have to be visited for any subsequent
requests sent to the user agent identified in the Contact header requests sent to the user agent identified in the Contact header
field, or not. If the Edge Proxy determines that this is the case, field, or not. If the edge proxy is the first hop, as indicated by
it inserts its URI in a Path header field value as described in RFC the Via header field, it always inserts its URI in a Path header
3327 [RFC3327]. If the Edge Proxy is the first SIP node after the field value as described in [RFC3327]. If it is not the first hop,
UAC, it either MUST store a "flow token" (containing information it might still decide to add itself to the Path header based on local
about the flow from the previous hop) in its Path URI or reject the policy. In addition, if the Edge Proxy is the first SIP node after
request. The flow token MUST be an identifier that is unique to this the UAC, the edge proxy either MUST store a "flow token" (containing
network flow. The flow token MAY be placed in the userpart of the information about the flow from the previous hop) in its Path URI or
URI. In addition, the first node MUST include an 'ob' URI parameter reject the request. The flow token MUST be an identifier that is
in its Path header field value. If the Edge Proxy is not the first unique to this network flow. The flow token MAY be placed in the
SIP node after the UAC it MUST NOT place an 'ob' URI parameter in a userpart of the URI. In addition, the first node MUST include an
Path header field value. The Edge Proxy can determine if it is the 'ob' URI parameter in its Path header field value. If the Edge Proxy
first hop by examining the Via header field. is not the first SIP node after the UAC it MUST NOT place an 'ob' URI
parameter in a Path header field value. The Edge Proxy can determine
if it is the first 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 infeasible 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
skipping to change at page 21, line 26 skipping to change at page 22, line 15
the HMAC and S are base64 encoded, as defined in [RFC4648], and the HMAC and S are base64 encoded, as defined in [RFC4648], and
used as the flow identifier. When using IPv4 addresses, this will used as the flow identifier. When using IPv4 addresses, this will
result in a 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 additions. If the Edge Proxy receives procedures with the following additions. If the Edge Proxy receives
a request where the edge proxy is the host in the topmost Route a request where the edge proxy is the host in the topmost Route
header field value, and the Route header field value contains a flow header field value, and the Route header field value contains a flow
token, the proxy may need to do additional processing. token, the proxy may need to do additional processing described in
the rest of this section. Otherwise the edge proxy skips the
procedures in this section, removes itself from the Route header
field, and continues processing the request.
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 identified by the topmost Route header
field value matches the source IP address and port of the request,
the request is an "outgoing" request, otherwise, it is an "incoming"
request.
5.3.1. Processing Incoming Requests
If the Route header value contains an 'ob' parameter, the Route If the Route header value contains an 'ob' parameter, the Route
header was probably copied from the Path header in a registration. 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, If the Route header value contains an 'ob' parameter, and the request
the proxy needs to adjust the route set to insure that subsequent is a new dialog-forming request, the proxy needs to adjust the route
requests in the dialog can be delivered over a valid flow to the UA set to insure that subsequent requests in the dialog can be delivered
instance identified by the flow token. 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 A simple approach to satisfy this requirement is for the proxy to
add a Record-Route header field value that contains the flow- add a Record-Route header field value that contains the flow-
token, by copying the URI in the Route header minus the 'ob' token, by copying the URI in the Route header minus the 'ob'
parameter. parameter.
Whether the Route header contained an 'ob' parameter or not, next the Next, whether the Route header field contained an 'ob' parameter or
proxy decodes the flow token and compares the flow in the flow token not, the proxy removes the Route header field value and forwards the
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
matches the source IP address and port of the request, the request is
an "outgoing" request. For an "outgoing" request, the edge proxy
just removes the Route header and continues processing the request.
Otherwise, this is an "incoming" request. For an incoming request,
the proxy removes the Route header field value and forwards the
request over the 'logical flow' identified by the flow token, that is request over the 'logical flow' identified by the flow token, that is
known to deliver data to the specific target UA instance. For known to deliver data to the specific target UA instance. If the
connection-oriented transports, if the flow no longer exists the flow token has been tampered with, the proxy SHOULD send a 403
proxy SHOULD send a 430 (Flow Failed) response to the request. (Forbidden) response. If the flow no longer exists the 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 Section 5.2 to
to form a flow token follow the procedures below to determine the form a flow token follow the procedures below to determine the
correct flow. correct flow. To decode the flow token, take the flow identifier in
the user portion of the URI and base64 decode it, then verify the
HMAC is correct by recomputing the HMAC and checking that it matches.
If the HMAC is not correct, the request has been tampered with.
Example Algorithm: To decode the flow token, take the flow 5.3.2. Processing Outgoing Requests
identifier in the user portion of the URI and base64 decode it,
then verify the HMAC is correct by recomputing the HMAC and
checking that it matches. If the HMAC is not correct, the proxy
SHOULD send a 403 (Forbidden) response. (The proxy could ignore
such requests for prevention of denial of service attacks.) If
the HMAC is correct then the proxy SHOULD forward the request on
the flow that was specified by the information in the flow
identifier. If this flow no longer exists, the proxy SHOULD send
a 430 (Flow Failed) response to the request.
Note that this specification needs mid-dialog requests to be routed For mid-dialog requests to work with outbound UAs, the requests need
over the same flows as those stored in the Path vector from the to be forwarded over some valid flow to the appropriate UA instance.
initial registration, but specific procedures at the edge proxy to If the Edge Proxy receives an outgoing dialog-forming request, the
ensure that mid-dialog requests are routed over an existing flow are Edge Proxy can use the presence of the "ob" parameter in the UAC's
not part of this specification. However, an approach such as having Contact URI (or topmost Route header field) to determine if the Edge
the Edge Proxy add a Record-Route header with a flow token is one way Proxy needs to assist in mid-dialog request routing.
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- Implementation note: Specific procedures at the edge proxy to ensure
forming requests in the UAC's Contact URI (or topmost Route header that mid-dialog requests are routed over an existing flow are not
field) to determine if it should add a flow token. 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 to ensure that mid-dialog requests are routed over the correct
flow.
5.4. Edge Proxy Keep alive Handling 5.4. Edge Proxy Keep alive Handling
All edge proxies compliant with this specification MUST implement All edge proxies compliant with this specification MUST implement
support for STUN NAT Keep alives on its SIP UDP ports as described in support for STUN NAT Keep alives 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 between SIP messages on
oriented transport such as TCP or SCTP, it MUST immediately respond a connection oriented transport such as TCP or SCTP, it MUST
with a single CRLF over the same connection. immediately respond with a single CRLF over the same connection.
The last proxy to forward a successful registration response to a UA The last proxy to forward a successful registration response to a UA
MAY include a Flow-Timer header field if the response contains the MAY include a Flow-Timer header field if the response contains the
outbound option-tag in a Require header field value in the response. outbound option-tag in a Require header field value in the response.
6. Registrar Mechanisms: Processing REGISTER Requests 6. Registrar Mechanisms
This specification updates the definition of a binding in RFC 3261 This specification updates the definition of a binding in [RFC3261]
[RFC3261] Section 10 and RFC 3327 [RFC3327] Section 5.3. Section 10 and [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 [RFC3327]. header mechanism [RFC3327].
When receiving a REGISTER request, the registrar first checks from When receiving a REGISTER request, the registrar MUST check from its
its Via header field if the registrar is the first hop or not. If Via header field if the registrar is the first hop or not. If the
the registrar is not the first hop, it examines the Path header of registrar is not the first hop, it MUST examine 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, then outbound the first URI does not have an 'ob' URI parameter, then outbound
processing cannot be applied to the registration. In this case, the processing MUST NOT be applied to the registration. In this case,
following processing applies: if the REGISTER request contains the the following processing applies: if the REGISTER request contains
"outbound" option tag in a "Require" header field, then the registrar the "outbound" option tag in a "Require" header field, then the
MUST respond to the REGISTER request with a 439 (First Hop Lacks registrar MUST respond to the REGISTER request with a 439 (First Hop
Outbound Support) response; otherwise, the registrar MUST ignore the Lacks Outbound Support) response; otherwise, the registrar MUST
reg-id parameter of the Contact header. See Section 11.2 for more ignore the reg-id parameter of the Contact header. See Section 11.6
information on the 439 response code. 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 [I-D.ietf-sip-gruu] valid (this combination can be used in the GRUU [I-D.ietf-sip-gruu]
specification), but one with a reg-id but no instance-id is not. If specification), but one with a reg-id but no instance-id is not. If
the registrar processes a Contact header field value with a reg-id the registrar processes a Contact header field value with a reg-id
but no instance-id, it simply ignores the reg-id parameter. If the but no instance-id, it simply ignores the reg-id parameter.
Contact header contains more than one header field value with a non-
zero expiration and a 'reg-id' parameter, the entire registration A registration containing a reg-id parameter and a non-zero
SHOULD be rejected with a 400 Bad Request response. If the Contact expiration is used to register a single UA instance over a single
header did not contain a 'reg-id' parameter or if that parameter flow, and can also de-register any Contact header fields with zero
became ignored (as described above) the registrar MUST NOT include expiration. Therefore if the Contact header field contains more than
the 'outbound' option-tag in the Require header field of its one header field value with a non-zero expiration and any of these
header field values contain a 'reg-id' parameter, the entire
registration SHOULD be rejected with a 400 (Bad Request) response.
The justification for recommending rejection versus making it
mandatory is that the receiver is allowed by [RFC3261] to squelch
(not respond to) excessively malformed or malicious messages.
If the Contact header did not contain a 'reg-id' parameter or if that
parameter was ignored (as described above) the registrar MUST NOT
include the 'outbound' option-tag in the Require header field of its
response. 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 [RFC3261].
[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. (Even though the Contact URI is not used for binding values. (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 12.2) in a Require header field value in its tag (defined in Section 11.2) 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 24, line 30 skipping to change at page 25, line 30
If the registrar receives a re-registration for a specific If the registrar receives a re-registration for a specific
combination of AOR, instance-id and reg-id values, the registrar MUST combination of AOR, instance-id and reg-id values, the registrar MUST
update any information that uniquely identifies the network flow over update any information that uniquely identifies the network flow over
which the request arrived if that information has changed, and SHOULD which the request arrived if that information has changed, and SHOULD
update the time the binding was last updated. update the time the binding was last updated.
To be compliant with this specification, registrars which can receive To be compliant with this specification, registrars which can receive
SIP requests directly from a UAC without intervening edge proxies SIP requests directly from a UAC without intervening edge proxies
MUST implement the same keep alive mechanisms as Edge Proxies MUST implement the same keep alive mechanisms as Edge Proxies
(Section 5.4). (Section 5.4). Registrars with a direct flow with a UA MAY include a
Flow-Timer header in a 200-class registration response which includes
the outbound option-tag in the Require header.
7. Authoritative Proxy Mechanisms: Forwarding Requests 7. Authoritative Proxy Mechanisms: Forwarding Requests
When a proxy uses the location service to look up a registration When a proxy uses the location service to look up a registration
binding and then proxies a request to a particular contact, it binding and then proxies a request to a particular contact, it
selects a contact to use normally, with a few additional rules: selects a contact to use normally, with a few additional rules:
o The proxy MUST NOT populate the target set with more than one o The proxy MUST NOT populate the target set with more than one
contact with the same AOR and instance-id at a time. contact with the same AOR and instance-id at a time.
o If a request for a particular AOR and instance-id fails with a 430 o If a request for a particular AOR and instance-id fails with a 430
skipping to change at page 25, line 12 skipping to change at page 26, line 14
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 is colocated with the registrar and stored information If the proxy is colocated with the registrar and stored information
about the flow to the UA that created the binding, then the proxy about the flow to the UA that created the binding, then the proxy
MUST send the request over the same 'logical flow' saved with the MUST send the request over the same 'logical flow' saved with the
binding, since that flow is known to deliver data to the specific binding, since that flow is known to deliver data to the specific
target UA instance's network 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 Implementation Note: Typically this means that for TCP, the request
TCP socket that received the REGISTER request. For UDP, the is sent on the same TCP socket that received the REGISTER request.
request is sent from the same local IP address and port over which For UDP, the request is sent from the same local IP address and
the registration was received, to the same IP address and port port over which the registration was received, to the same IP
from which the REGISTER was received. address and port 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.
skipping to change at page 26, line 20 skipping to change at page 27, line 20
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 this specification. Note that UACs MUST NOT use an ambiguous support this specification. Note that UACs MUST NOT use an ambiguous
configuration option such as "Work through NATs?" or "Do Keep configuration option such as "Work through NATs?" or "Do Keep
alives?" to imply next hop STUN support. alives?" to imply next hop STUN support. A UAC MAY use the presence
of an 'ob' parameter in the Path header in a registration response as
an indication that its first edge proxy supports the keep alives
defined in this document.
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 keep alive STUN usage requires no backwards compatibility The SIP keep alive STUN usage requires no backwards compatibility
with RFC 3489 [RFC3489]. with [RFC3489].
8.1. Use with Sigcomp 8.1. Use with Sigcomp
When STUN is used together with SigComp [RFC3320] compressed SIP When STUN is used together with SigComp [RFC3320] compressed SIP
messages over the same flow,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.
skipping to change at page 27, line 16 skipping to change at page 28, line 17
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
Below is an example message flow illustrating most of the concepts Below is an example message flow illustrating most of the concepts
discussed in this specification. In many cases, Via, Content-Length discussed in this specification. In many cases, Via, Content-Length
and Max-Forwards headers are omitted for brevity and readability. and Max-Forwards headers are omitted for brevity and readability.
In the first part of this example message flow, Bob's UA sends a The section is subdivided into independent calls flows: however,
SUBSCRIBE request for the UA profile configuration package. This they are structured in sequential order of an hypothetical sequence
request is a poll (Expires is zero). After receiving the NOTIFY of call flows.
request, Bob's UA fetches the external configuration using HTTPS (not
shown) and obtains a configuration file which contains the outbound- 9.1. Subscription to configuration package
proxy-set "sip:ep1.example.com;lr" and "sip:ep2.example.com;lr.
If the outbound proxy set is already configured on Bob's UA, then
this subsection can be skipped. Otherwise, if the outbound proxy set
is learned through the configuration package, Bob's UA sends a
SUBSCRIBE request for the UA profile configuration package
[I-D.ietf-sipping-config-framework]. 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-------------------------] [----example.com domain-------------------------]
Bob EP1 EP2 Proxy Config Bob EP1 EP2 Proxy Config
| | | | | | | | | |
1)|SUBSCRIBE->| | | | 1)|SUBSCRIBE->| | | |
2)| |---SUBSCRIBE Event: ua-profile ->| 2)| |---SUBSCRIBE Event: ua-profile ->|
3)| |<--200 OK -----------------------| 3)| |<--200 OK -----------------------|
4)|<--200 OK--| | | | 4)|<--200 OK--| | | |
5)| |<--NOTIFY------------------------| 5)| |<--NOTIFY------------------------|
6)|<--NOTIFY--| | | | 6)|<--NOTIFY--| | | |
skipping to change at page 28, line 35 skipping to change at page 30, line 26
Content-Type: message/external-body; access-type="URL" Content-Type: message/external-body; access-type="URL"
;expiration="Thu, 01 Jan 2009 09:00:00 UTC" ;expiration="Thu, 01 Jan 2009 09:00:00 UTC"
;URL="http://example.com/uPhone.cfg" ;URL="http://example.com/uPhone.cfg"
;size=9999;hash=10AB568E91245681AC1B ;size=9999;hash=10AB568E91245681AC1B
Content-Length: 0 Content-Length: 0
EP1 receives this NOTIFY request, strips off the Route header, EP1 receives this NOTIFY request, strips off the Route header,
extracts the flow-token, calculates the correct flow and forwards the extracts the flow-token, calculates the correct flow and forwards the
request (Message #6) over that flow to Bob. request (Message #6) over that flow to Bob.
Bob's UA fetches the configuration file. Now that Bob's UA is Bob's UA fetches the configuration file and learns the outbound proxy
configured with the outbound-proxy-set, Bob's UA sends REGISTER set.
requests through each edge proxy in the set. Once the registrations
succeed, Bob's UA begins sending CRLF keepalives about every 2 9.2. Registration
minutes.
Now that Bob's UA is configured with the outbound-proxy-set whether
through configuration or using the configuration framework procedures
of the previous section, 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 Bob EP1 EP2 Proxy Alice
| | | | | | | | | |
9)|-REGISTER->| | | | 9)|-REGISTER->| | | |
10)| |---REGISTER-->| | 10)| |---REGISTER-->| |
11)| |<----200 OK---| | 11)| |<----200 OK---| |
12)|<-200 OK---| | | | 12)|<-200 OK---| | | |
13)|----REGISTER---->| | | 13)|----REGISTER---->| | |
14)| | |--REG-->| | 14)| | |--REG-->| |
15)| | |<-200---| | 15)| | |<-200---| |
skipping to change at page 30, line 18 skipping to change at page 32, line 18
Via: SIP/2.0/TCP 192.0.2.15;branch=z9hG4bKnuiqisi Via: SIP/2.0/TCP 192.0.2.15;branch=z9hG4bKnuiqisi
Via: SIP/2.0/TCP 192.168.1.2;branch=z9hG4bKnashds7 Via: SIP/2.0/TCP 192.168.1.2;branch=z9hG4bKnashds7
From: Bob <sip:bob@example.com>;tag=7F94778B653B From: Bob <sip:bob@example.com>;tag=7F94778B653B
To: Bob <sip:bob@example.com>;tag=6AF99445E44A To: Bob <sip:bob@example.com>;tag=6AF99445E44A
Call-ID: 16CB75F21C70 Call-ID: 16CB75F21C70
CSeq: 1 REGISTER CSeq: 1 REGISTER
Supported: path, outbound Supported: path, outbound
Require: outbound Require: outbound
Contact: <sip:bob@192.168.1.2;transport=tcp>;reg-id=1;expires=3600 Contact: <sip:bob@192.168.1.2;transport=tcp>;reg-id=1;expires=3600
;+sip.instance="<urn:uuid:00000000-0000-1000-8000-AABBCCDDEEFF>" ;+sip.instance="<urn:uuid:00000000-0000-1000-8000-AABBCCDDEEFF>"
Path: <sip:VskztcQ-S8p4WPbOnHbuyh5iJvJIW3ib@ep1.example.com;lr;ob> Path: <sip:VskztcQ/S8p4WPbOnHbuyh5iJvJIW3ib@ep1.example.com;lr;ob>
Content-Length: 0 Content-Length: 0
The second registration through EP2 (message #13) is similar other The second registration through EP2 (message #13) is similar other
than the Call-ID has changed, the reg-id is 2, and the Route header than the Call-ID has changed, the reg-id is 2, and the Route header
goes through EP2. goes through EP2.
REGISTER sip:example.com SIP/2.0 REGISTER sip:example.com SIP/2.0
Via: SIP/2.0/TCP 192.168.1.2;branch=z9hG4bKnqr9bym Via: SIP/2.0/TCP 192.168.1.2;branch=z9hG4bKnqr9bym
Max-Forwards: 70 Max-Forwards: 70
From: Bob <sip:bob@example.com>;tag=755285EABDE2 From: Bob <sip:bob@example.com>;tag=755285EABDE2
skipping to change at page 31, line 20 skipping to change at page 33, line 20
Supported: path, outbound Supported: path, outbound
Require: outbound Require: outbound
CSeq: 1 REGISTER CSeq: 1 REGISTER
Contact: <sip:bob@192.168.1.2;transport=tcp>;reg-id=1;expires=3600 Contact: <sip:bob@192.168.1.2;transport=tcp>;reg-id=1;expires=3600
;+sip.instance="<urn:uuid:00000000-0000-1000-8000-AABBCCDDEEFF>" ;+sip.instance="<urn:uuid:00000000-0000-1000-8000-AABBCCDDEEFF>"
Contact: <sip:bob@192.168.1.2;transport=tcp>;reg-id=2;expires=3600 Contact: <sip:bob@192.168.1.2;transport=tcp>;reg-id=2;expires=3600
;+sip.instance="<urn:uuid:00000000-0000-1000-8000-AABBCCDDEEFF>" ;+sip.instance="<urn:uuid:00000000-0000-1000-8000-AABBCCDDEEFF>"
Path: <sip:wazHDLdIMtUg6r0I/oRZ15zx3zHE1w1Z@ep2.example.com;lr;ob> Path: <sip:wazHDLdIMtUg6r0I/oRZ15zx3zHE1w1Z@ep2.example.com;lr;ob>
Content-Length: 0 Content-Length: 0
A bit later, EP1 crashes and reboots. Before Bob's UA notices that 9.3. Incoming call and proxy crash
its flow to EP1 is no longer responding, Alice calls Bob. Bob's
authoritative proxy first tries the flow to EP1, but EP1 no longer In this example, after registration, EP1 crashes and reboots. Before
has a flow to Bob so it responds with a 430 Flow Failed response. Bob's UA notices that its flow to EP1 is no longer responding, Alice
The proxy removes the stale registration and tries the next binding calls Bob. Bob's authoritative proxy first tries the flow to EP1, but
for the same instance. 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.
Bob EP1 EP2 Proxy Alice Bob EP1 EP2 Proxy Alice
| | | | | | | | | |
| CRASH X | | | | CRASH X | | |
| Reboot | | | | Reboot | | |
| | | | | | | | | |
21)| | | |<-INVITE-| 21)| | | |<-INVITE-|
22)| |<---INVITE----| | 22)| |<---INVITE----| |
23)| |----430------>| | 23)| |----430------>| |
24)| | |<-INVITE| | 24)| | |<-INVITE| |
skipping to change at page 33, line 42 skipping to change at page 35, line 42
Route: <sip:wazHDLdIMtUg6r0I/oRZ15zx3zHE1w1Z@ep2.example.com;lr> Route: <sip:wazHDLdIMtUg6r0I/oRZ15zx3zHE1w1Z@ep2.example.com;lr>
Message #31 Message #31
BYE sip:bob@192.168.1.2;transport=tcp SIP/2.0 BYE sip:bob@192.168.1.2;transport=tcp SIP/2.0
To: Bob <sip:bob@example.com>;tag=skduk2 To: Bob <sip:bob@example.com>;tag=skduk2
From: Alice <sip:alice@a.example>;tag=02935 From: Alice <sip:alice@a.example>;tag=02935
Call-ID: klmvCxVWGp6MxJp2T2mb Call-ID: klmvCxVWGp6MxJp2T2mb
CSeq: 2 BYE CSeq: 2 BYE
Route: <sip:wazHDLdIMtUg6r0I/oRZ15zx3zHE1w1Z@ep2.example.com;lr> Route: <sip:wazHDLdIMtUg6r0I/oRZ15zx3zHE1w1Z@ep2.example.com;lr>
9.4. Re-registration
Somewhat later, Bob's UA sends keepalives to both its edge proxies, 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- 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 registers through EP1 using the same reg-id and Call-ID it previously
used. used.
Bob EP1 EP2 Proxy Alice Bob EP1 EP2 Proxy Alice
| | | | | | | | | |
35)|------2CRLF----->| | | 35)|------2CRLF----->| | |
36)|<------CRLF------| | | 36)|<------CRLF------| | |
37)|--2CRLF->X | | | | 37)|--2CRLF->X | | | |
skipping to change at page 34, line 32 skipping to change at page 36, line 32
CSeq: 2 REGISTER CSeq: 2 REGISTER
Supported: path, outbound Supported: path, outbound
Route: <sip:ep1.example.com;lr> Route: <sip:ep1.example.com;lr>
Contact: <sip:bob@192.168.1.2;transport=tcp>;reg-id=1 Contact: <sip:bob@192.168.1.2;transport=tcp>;reg-id=1
;+sip.instance="<urn:uuid:00000000-0000-1000-8000-AABBCCDDEEFF>" ;+sip.instance="<urn:uuid:00000000-0000-1000-8000-AABBCCDDEEFF>"
In message #39, EP1 inserts a Path header with a new flow token: In message #39, EP1 inserts a Path header with a new flow token:
Path: <sip:3yJEbr1GYZK9cPYk5Snocez6DzO7w+AX@ep1.example.com;lr;ob> Path: <sip:3yJEbr1GYZK9cPYk5Snocez6DzO7w+AX@ep1.example.com;lr;ob>
9.5. Outgoing call
Finally, Bob makes an outgoing call to Alice. Bob's UA includes an 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- '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 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 Bob in the response (messages #45, 46, and 47) and either Bob or
Alice can send in-dialog requests. Alice can send in-dialog requests.
Bob EP1 EP2 Proxy Alice Bob EP1 EP2 Proxy Alice
| | | | | | | | | |
42)|--INVITE-->| | | | 42)|--INVITE-->| | | |
43)| |---INVITE---->| | 43)| |---INVITE---->| |
skipping to change at page 36, line 32 skipping to change at page 38, line 32
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. New Response Codes 11. IANA Considerations
11.1. Definition of 430 Flow Failed response code
This specification defines a new SIP response code '430 Flow Failed'.
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.
Other flows to the same instance could still succeed. The
Authoritative Proxy SHOULD attempt to forward to another target
(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
12.1. Flow-Timer Header Field 11.1. Flow-Timer Header Field
This specification defines a new SIP header field "Flow-Timer". This specification defines a new SIP header field "Flow-Timer" whose
syntax is defined in Section 10.
RFC Number: RFC XXXX RFC Number: RFC XXXX
Header Field Name: Flow-Timer Header Field Name: Flow-Timer
Compact Form: none Compact Form: none
[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. 'reg-id' Contact Header Field Parameter 11.2. '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 [RFC3968]. The required sub-registry as per the registry created by [RFC3968]. The syntax is
information is: defined in Section 10. The required 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.]
12.3. SIP/SIPS URI Parameters 11.3. 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 [RFC3969]. 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
____________________________________________ ____________________________________________
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.]
12.4. SIP Option Tag 11.4. 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 UA which support extensions for Client Initiated Connections. A UA
places this option in a Supported header to communicate its places this option in a Supported header to communicate its
support for this extension. A Registrar places this option-tag in support for this extension. A Registrar places this option-tag in
a Require header to indicate to the registering User Agent that a Require header to indicate to the registering User Agent that
the Registrar used registrations using the binding rules defined the Registrar used registrations using the binding rules defined
in this extension. in this extension.
12.5. Response Codes 11.5. 430 (Flow Failed) Response Code
This section registers two new SIP Response Codes, as per the
guidelines in Section 27.4 of RFC 3261.
12.5.1. 430 Response Code
Code: 430 This document registers a new SIP response code (430 Flow Failed), as
per the guidelines in Section 27.4 of [RFC3261]. 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. Other flows to the same
instance could still succeed. The Authoritative Proxy SHOULD attempt
to forward to another target (flow) with the same instance-id and
AOR. This response code is defined by the following information,
which has been added to the method and response-code sub-registry
under http://www.iana.org/assignments/sip-parameters.
Response Code Number: 430
Default Reason Phrase: Flow Failed Default Reason Phrase: Flow Failed
Reference: This document
12.5.2. 439 Response Code 11.6. 439 (First Hop Lacks Outbound Support) Response Code
Code: 439 This document registers a new SIP response code (439 First Hop Lacks
Outbound Support), as per the guidelines in Section 27.4 of
[RFC3261]. 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. This response code is defined by the
following information, which has been added to the method and
response-code sub-registry under
http://www.iana.org/assignments/sip-parameters.
Response Code Number: 439
Default Reason Phrase: First Hop Lacks Outbound Support Default Reason Phrase: First Hop Lacks Outbound Support
Reference: This document
12.6. Media Feature Tag 11.7. Media Feature Tag
This section registers a new media feature tag, per the procedures This section registers a new media feature tag, per the procedures
defined in RFC 2506 [RFC2506]. The tag is placed into the sip tree, defined in [RFC2506]. The tag is placed into the sip tree, which is
which is defined in RFC 3840 [RFC3840]. defined in [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 39, line 27 skipping to change at page 41, line 24
preferences extension [RFC3841] allows for call routing decisions to preferences extension [RFC3841] allows for call routing decisions to
be based on the values of these parameters. Therefore, if an be based on the values of these parameters. Therefore, if an
attacker can modify the values of this tag, they might be able to attacker can modify the values of this tag, they might be able to
affect the behavior of applications. As a result, applications which affect the behavior of applications. As a result, applications which
utilize this media feature tag SHOULD provide a means for ensuring utilize this media feature tag SHOULD provide a means for ensuring
its 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 12. 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
TCP traffic, but to insure that no new attacks are added by TCP traffic, but to insure that no new attacks are added by
introducing the outbound mechanism. introducing the outbound mechanism.
The simple case is when there are no edge proxies. In this case, the The simple case is when there are no edge proxies. In this case, the
only time an entry can be added to the routing for a given AOR is only time an entry can be added to the routing for a given AOR is
skipping to change at page 40, line 30 skipping to change at page 42, line 26
The Security Considerations discussed in [RFC3261] and [RFC3327] are The Security Considerations discussed in [RFC3261] and [RFC3327] are
also 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 13. Operational Notes on Transports
This entire section is non-normative. This entire section is non-normative.
RFC 3261 requires proxies, registrars, and User Agents to implement RFC 3261 requires proxies, registrars, and User Agents to implement
both TCP and UDP but deployments can chose which transport protocols both TCP and UDP but deployments can chose which transport protocols
they want to use. Deployments need to be careful in choosing what they want to use. Deployments need to be careful in choosing what
transports to use. Many SIP features and extensions, such as large transports to use. Many SIP features and extensions, such as large
presence notification bodies, result in SIP requests that can be too presence notification bodies, result in SIP requests that can be too
large to be reasonably transported over UDP. RFC 3261 states that large to be reasonably transported over UDP. RFC 3261 states that
when a request is too large for UDP, the device sending the request when a request is too large for UDP, the device sending the request
skipping to change at page 41, line 8 skipping to change at page 43, line 5
it will probably make more sense for the UA to form a TCP outbound it will probably make more sense for the UA to form a TCP outbound
connection only, rather than forming both UDP and TCP flows. One of connection only, rather than forming both UDP and TCP flows. One of
the key reasons that many deployments choose not to use TCP has to do the key reasons that many deployments choose not to use TCP has to do
with the difficulty of building proxies that can maintain a very with the difficulty of building proxies that can maintain a very
large number of active TCP connections. Many deployments today use large number of active TCP connections. Many deployments today use
SIP in such a way that the messages are small enough that they work SIP in such a way that the messages are small enough that they work
over UDP but they can not take advantage of all the functionality SIP over UDP but they can not take advantage of all the functionality SIP
offers. Deployments that use only UDP outbound connections are going offers. Deployments that use only UDP outbound connections are going
to fail with sufficiently large SIP messages. to fail with sufficiently large SIP messages.
15. Requirements 14. Requirements
This specification was developed to meet the following requirements: This specification was developed to meet the following requirements:
1. Must be able to detect that a UA supports these mechanisms. 1. Must be able to detect that a UA supports these mechanisms.
2. Support UAs behind NATs. 2. Support UAs behind NATs.
3. Support TLS to a UA without a stable DNS name or IP address. 3. Support TLS to a UA without a stable DNS name or IP address.
4. Detect failure of a connection and be able to correct for this. 4. Detect failure of a connection and be able to correct for this.
5. Support many UAs simultaneously rebooting. 5. Support many UAs simultaneously rebooting.
6. Support a NAT rebooting or resetting. 6. Support a NAT rebooting or resetting.
7. Minimize initial startup load on a proxy. 7. Minimize initial startup load on a proxy.
8. Support architectures with edge proxies. 8. Support architectures with edge proxies.
16. Changes 15. Changes
Note to RFC Editor: Please remove this whole section. Note to RFC Editor: Please remove this whole section.
16.1. Changes from 11 Version 15.1. Changes from 12 Version
Lots of editorials comments. Allows for sending keep-alive based on
presence of ob parameter and/or through explicit configuration.
Clarified treatment of recoverable error responses to REGISTER
regarding keeping flows active.
15.2. Changes from 11 Version
Added 439 response code to handle "Require: outbound" with first Added 439 response code to handle "Require: outbound" with first
outbound proxy that doesn't insert ";ob". outbound proxy that doesn't insert ";ob".
16.2. Changes from 09 Version 15.3. 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.
16.3. Changes from 08 Version 15.4. 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 42, line 16 skipping to change at page 44, line 17
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
16.4. Changes from 07 Version 15.5. 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.
16.5. Changes from 06 Version 15.6. 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.
16.6. Changes from 05 Version 15.7. 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 43, line 13 skipping to change at page 45, line 15
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.
16.7. Changes from 04 Version 15.8. 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 44, line 19 skipping to change at page 46, line 22
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.
16.8. Changes from 03 Version 15.9. 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 45, line 5 skipping to change at page 47, 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.
16.9. Changes from 02 Version 15.10. 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.
16.10. Changes from 01 Version 15.11. Changes from 01 Version
Moved definition of instance-id from GRUU[I-D.ietf-sip-gruu] draft to Moved definition of instance-id from GRUU[I-D.ietf-sip-gruu] draft to
this draft. this draft.
Added tentative text about Double CRLF Keepalive Added tentative text about Double CRLF Keepalive
Removed pin-route stuff Removed pin-route stuff
Changed the name of "flow-id" to "reg-id" Changed the name of "flow-id" to "reg-id"
Reorganized document flow Reorganized document flow
Described the use of STUN as a proper STUN usage Described the use of STUN as a proper STUN usage
Added 'outbound' option-tag to detect if registrar supports outbound Added 'outbound' option-tag to detect if registrar supports outbound
16.11. Changes from 00 Version 15.12. 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 16. Acknowledgments
Francois Audet acted as document shepherd for this draft, tracking Francois Audet acted as document shepherd for this draft, tracking
hundreds of comments and incorporating many grammatical fixes as well hundreds of comments and incorporating many grammatical fixes as well
as prodding the editors to "get on with it". Jonathan Rosenberg, as prodding the editors to "get on with it". Jonathan Rosenberg,
Erkki Koivusalo, and Byron Campben provided many comments and useful Erkki Koivusalo, and Byron Campben provided many comments and useful
text. Dave Oran came up with the idea of using the most recent text. Dave Oran came up with the idea of using the most recent
registration first in the proxy. Alan Hawrylyshen co-authored the registration first in the proxy. Alan Hawrylyshen co-authored the
draft that formed the initial text of this specification. draft that formed the initial text of this specification.
Additionally, many of the concepts here originated at a connection Additionally, many of the concepts here originated at a connection
reuse meeting at IETF 60 that included the authors, Jon Peterson, reuse meeting at IETF 60 that included the authors, Jon Peterson,
Jonathan Rosenberg, Alan Hawrylyshen, and Paul Kyzivat. The TCP Jonathan Rosenberg, Alan Hawrylyshen, and Paul Kyzivat. The TCP
design team consisting of Chris Boulton, Scott Lawrence, Rajnish design team consisting of Chris Boulton, Scott Lawrence, Rajnish
Jain, Vijay K. Gurbani, and Ganesh Jayadevan provided input and text. Jain, Vijay K. Gurbani, and Ganesh Jayadevan provided input and text.
Nils Ohlmeier provided many fixes and initial implementation Nils Ohlmeier provided many fixes and initial implementation
experience. In addition, thanks to the following folks for useful experience. In addition, thanks to the following folks for useful
comments: Francois Audet, Flemming Andreasen, Mike Hammer, Dan Wing, comments: Francois Audet, Flemming Andreasen, Mike Hammer, Dan Wing,
Srivatsa Srinivasan, Dale Worely, Juha Heinanen, Eric Rescorla, Srivatsa Srinivasan, Dale Worely, Juha Heinanen, Eric Rescorla,
Lyndsay Campbell, Christer Holmberg, Kevin Johns, Jeroen van Bemmel, Lyndsay Campbell, Christer Holmberg, Kevin Johns, Jeroen van Bemmel,
and Derek MacDonald. and Derek MacDonald.
18. References 17. References
18.1. Normative References 17.1. Normative References
[I-D.ietf-behave-rfc3489bis] [I-D.ietf-behave-rfc3489bis]
Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for (NAT) (STUN)", "Session Traversal Utilities for (NAT) (STUN)",
draft-ietf-behave-rfc3489bis-15 (work in progress), draft-ietf-behave-rfc3489bis-15 (work in progress),
February 2008. February 2008.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
skipping to change at page 47, line 38 skipping to change at page 49, line 38
Resource Identifier (URI): Generic Syntax", STD 66, Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005. RFC 3986, January 2005.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122, Unique IDentifier (UUID) URN Namespace", RFC 4122,
July 2005. July 2005.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008. Specifications: ABNF", STD 68, RFC 5234, January 2008.
18.2. Informational References 17.2. Informational References
[I-D.ietf-sip-gruu] [I-D.ietf-sip-gruu]
Rosenberg, J., "Obtaining and Using Globally Routable User Rosenberg, J., "Obtaining and Using Globally Routable User
Agent (UA) URIs (GRUU) in the Session Initiation Protocol Agent (UA) URIs (GRUU) in the Session Initiation Protocol
(SIP)", draft-ietf-sip-gruu-15 (work in progress), (SIP)", draft-ietf-sip-gruu-15 (work in progress),
October 2007. October 2007.
[I-D.ietf-sipping-config-framework] [I-D.ietf-sipping-config-framework]
Channabasappa, S., "A Framework for Session Initiation Channabasappa, S., "A Framework for Session Initiation
Protocol User Agent Profile Delivery", Protocol User Agent Profile Delivery",
draft-ietf-sipping-config-framework-15 (work in progress), draft-ietf-sipping-config-framework-15 (work in progress),
February 2008. February 2008.
[I-D.ietf-sipping-nat-scenarios] [I-D.ietf-sipping-nat-scenarios]
Boulton, C., "Best Current Practices for NAT Traversal for Boulton, C., "Best Current Practices for NAT Traversal for
SIP", draft-ietf-sipping-nat-scenarios-07 (work in SIP", draft-ietf-sipping-nat-scenarios-07 (work in
progress), July 2007. progress), July 2007.
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104, Hashing for Message Authentication", RFC 2104,
February 1997. February 1997.
[RFC2782] 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.
[RFC3320] Price, R., Bormann, C., Christoffersson, J., Hannu, H., [RFC3320] Price, R., Bormann, C., Christoffersson, J., Hannu, H.,
Liu, Z., and J. Rosenberg, "Signaling Compression Liu, Z., and J. Rosenberg, "Signaling Compression
(SigComp)", RFC 3320, January 2003. (SigComp)", RFC 3320, January 2003.
[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346, April 2006. (TLS) Protocol Version 1.1", RFC 4346, April 2006.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, October 2006. Encodings", RFC 4648, October 2006.
[RFC4966] Aoun, C. and E. Davies, "Reasons to Move the Network
Address Translator - Protocol Translator (NAT-PT) to
Historic Status", RFC 4966, July 2007.
Appendix A. Default Flow Registration Backoff Times Appendix A. Default Flow Registration Backoff Times
The base-time used for the flow re-registration backoff times The base-time used for the flow re-registration backoff times
described in Section 4.5 are configurable. If the base-time-all-fail described in Section 4.5 are configurable. If the base-time-all-fail
value is set to the default of 30 seconds and the base-time-not- value is set to the default of 30 seconds and the base-time-not-
failed value is set to the default of 90 seconds, the following table failed value is set to the default of 90 seconds, the following table
shows the resulting delay values. shows the resulting delay values.
+-------------------+--------------------+--------------------+ +-------------------+--------------------+--------------------+
| # of reg failures | all flows unusable | >1 non-failed flow | | # of reg failures | all flows unusable | >1 non-failed flow |
 End of changes. 117 change blocks. 
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