draft-ietf-sip-outbound-05.txt   draft-ietf-sip-outbound-06.txt 
Network Working Group C. Jennings, Ed. Network Working Group C. Jennings, Ed.
Internet-Draft Cisco Systems Internet-Draft Cisco Systems
Updates: 3261,3327 (if approved) R. Mahy, Ed. Updates: 3261,3327 (if approved) R. Mahy, Ed.
Expires: April 25, 2007 Plantronics Expires: May 26, 2007 Plantronics
October 22, 2006 November 22, 2006
Managing Client Initiated Connections in the Session Initiation Protocol Managing Client Initiated Connections in the Session Initiation Protocol
(SIP) (SIP)
draft-ietf-sip-outbound-05 draft-ietf-sip-outbound-06
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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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on April 25, 2007. This Internet-Draft will expire on May 26, 2007.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
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
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2.1 Definitions . . . . . . . . . . . . . . . . . . . . . . . 4 2.1 Definitions . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1 Summary of Mechanism . . . . . . . . . . . . . . . . . . . 5 3.1 Summary of Mechanism . . . . . . . . . . . . . . . . . . . 5
3.2 Single Registrar and UA . . . . . . . . . . . . . . . . . 6 3.2 Single Registrar and UA . . . . . . . . . . . . . . . . . 6
3.3 Multiple Connections from a User Agent . . . . . . . . . . 7 3.3 Multiple Connections from a User Agent . . . . . . . . . . 7
3.4 Edge Proxies . . . . . . . . . . . . . . . . . . . . . . . 9 3.4 Edge Proxies . . . . . . . . . . . . . . . . . . . . . . . 9
3.5 Keepalive Technique . . . . . . . . . . . . . . . . . . . 10 3.5 Keepalive Technique . . . . . . . . . . . . . . . . . . . 10
4. User Agent Mechanisms . . . . . . . . . . . . . . . . . . . . 12 4. User Agent Mechanisms . . . . . . . . . . . . . . . . . . . . 12
4.1 Instance ID Creation . . . . . . . . . . . . . . . . . . . 12 4.1 Instance ID Creation . . . . . . . . . . . . . . . . . . . 12
4.2 Initial Registrations . . . . . . . . . . . . . . . . . . 13 4.2 Initial Registrations . . . . . . . . . . . . . . . . . . 13
4.2.1 Registration by Other Instances . . . . . . . . . . . 14 4.2.1 Registration by Other Instances . . . . . . . . . . . 15
4.3 Sending Requests . . . . . . . . . . . . . . . . . . . . . 15 4.3 Sending Requests . . . . . . . . . . . . . . . . . . . . . 15
4.4 Detecting Flow Failure . . . . . . . . . . . . . . . . . . 15 4.4 Detecting Flow Failure . . . . . . . . . . . . . . . . . . 15
4.4.1 Keepalive with TCP KEEPALIVE . . . . . . . . . . . . . 16 4.4.1 Keepalive with TCP KEEPALIVE . . . . . . . . . . . . . 16
4.4.2 Keepalive with STUN . . . . . . . . . . . . . . . . . 16 4.4.2 Keepalive with STUN . . . . . . . . . . . . . . . . . 16
4.4.3 Flow Recovery . . . . . . . . . . . . . . . . . . . . 16 4.4.3 Flow Recovery . . . . . . . . . . . . . . . . . . . . 16
5. Edge Proxy Mechanisms . . . . . . . . . . . . . . . . . . . . 17 5. Edge Proxy Mechanisms . . . . . . . . . . . . . . . . . . . . 18
5.1 Processing Register Requests . . . . . . . . . . . . . . . 17 5.1 Processing Register Requests . . . . . . . . . . . . . . . 18
5.2 Generating Flow Tokens . . . . . . . . . . . . . . . . . . 18 5.2 Generating Flow Tokens . . . . . . . . . . . . . . . . . . 18
5.3 Forwarding Requests . . . . . . . . . . . . . . . . . . . 18 5.3 Forwarding Requests . . . . . . . . . . . . . . . . . . . 19
5.4 Edge Proxy Keepalive Handling . . . . . . . . . . . . . . 19 5.4 Edge Proxy Keepalive Handling . . . . . . . . . . . . . . 20
6. Registrar Mechanisms: Processing REGISTER Requests . . . . . . 20 6. Registrar Mechanisms: Processing REGISTER Requests . . . . . . 20
7. Authoritative Proxy Mechansims: Forwarding Requests . . . . . 21 7. Authoritative Proxy Mechansims: Forwarding Requests . . . . . 22
8. STUN Keepalive Processing . . . . . . . . . . . . . . . . . . 22 8. STUN Keepalive Processing . . . . . . . . . . . . . . . . . . 23
8.1 Explicit Probes . . . . . . . . . . . . . . . . . . . . . 24 8.1 Explicit Probes . . . . . . . . . . . . . . . . . . . . . 25
8.2 Use with Sigcomp . . . . . . . . . . . . . . . . . . . . . 24 8.2 Use with Sigcomp . . . . . . . . . . . . . . . . . . . . . 25
9. Example Message Flow . . . . . . . . . . . . . . . . . . . . . 25 9. Example Message Flow . . . . . . . . . . . . . . . . . . . . . 26
10. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . 28 10. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . 29
11. Definition of 430 Flow Failed response code . . . . . . . . 29 11. Definition of 430 Flow Failed response code . . . . . . . . 30
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . 29 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . 30
12.1 Contact Header Field . . . . . . . . . . . . . . . . . . . 29 12.1 Contact Header Field . . . . . . . . . . . . . . . . . . . 30
12.2 SIP/SIPS URI Parameters . . . . . . . . . . . . . . . . . 30 12.2 SIP/SIPS URI Parameters . . . . . . . . . . . . . . . . . 31
12.3 SIP Option Tag . . . . . . . . . . . . . . . . . . . . . . 30 12.3 SIP Option Tag . . . . . . . . . . . . . . . . . . . . . . 31
12.4 Response Code . . . . . . . . . . . . . . . . . . . . . . 30 12.4 Response Code . . . . . . . . . . . . . . . . . . . . . . 31
12.5 Media Feature Tag . . . . . . . . . . . . . . . . . . . . 30 12.5 Media Feature Tag . . . . . . . . . . . . . . . . . . . . 31
13. Security Considerations . . . . . . . . . . . . . . . . . . 31 13. Security Considerations . . . . . . . . . . . . . . . . . . 32
14. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 32 14. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 33
15. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . 32 15. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . 33
15.1 Changes from 04 Version . . . . . . . . . . . . . . . . . 32 15.1 Changes from 05 Version . . . . . . . . . . . . . . . . . 33
15.2 Changes from 03 Version . . . . . . . . . . . . . . . . . 33 15.2 Changes from 04 Version . . . . . . . . . . . . . . . . . 34
15.3 Changes from 02 Version . . . . . . . . . . . . . . . . . 34 15.3 Changes from 03 Version . . . . . . . . . . . . . . . . . 35
15.4 Changes from 01 Version . . . . . . . . . . . . . . . . . 34 15.4 Changes from 02 Version . . . . . . . . . . . . . . . . . 36
15.5 Changes from 00 Version . . . . . . . . . . . . . . . . . 35 15.5 Changes from 01 Version . . . . . . . . . . . . . . . . . 36
16. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 35 15.6 Changes from 00 Version . . . . . . . . . . . . . . . . . 36
A. Default Flow Registration Backoff Times . . . . . . . . . . . 35 16. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 36
17. References . . . . . . . . . . . . . . . . . . . . . . . . . 36 A. Default Flow Registration Backoff Times . . . . . . . . . . . 37
17.1 Normative References . . . . . . . . . . . . . . . . . . . 36 17. References . . . . . . . . . . . . . . . . . . . . . . . . . 37
17.2 Informative References . . . . . . . . . . . . . . . . . . 37 17.1 Normative References . . . . . . . . . . . . . . . . . . . 37
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 38 17.2 Informative References . . . . . . . . . . . . . . . . . . 39
Intellectual Property and Copyright Statements . . . . . . . . 39 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 40
Intellectual Property and Copyright Statements . . . . . . . . 41
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. Connections to the
UA can be blocked by a firewall device between the UA and the proxy UA can be blocked by a firewall device between the UA and the proxy
or registrar, which will only allow new connections in the direction or registrar, which will only allow new connections in the direction
of the UA to the Proxy. Similarly there may be a NAT, which are only of the UA to the Proxy. Similarly there a NAT could be present,
capable of allowing new connections from the private address side to which is only capable of allowing new connections from the private
the public side. This specification allows SIP registration when the address side to the public side. This specification allows SIP
UA is behind such a firewall or NAT. registration when the UA is behind such a firewall or NAT.
Most IP phones and personal computers get their network Most IP phones and personal computers get their network
configurations dynamically via a protocol such as DHCP (Dynamic Host configurations dynamically via a protocol such as DHCP (Dynamic Host
Configuration Protocol). These systems typically do not have a Configuration Protocol). These systems typically do not have a
useful name in the Domain Name System (DNS), and they definitely do useful name in the Domain Name System (DNS), and they almost never
not have a long-term, stable DNS name that is appropriate for use in have a long-term, stable DNS name that is appropriate for use in the
the subjectAltName of a certificate, as required by [RFC3261]. subjectAltName of a certificate, as required by [RFC3261]. However,
However, these systems can still act as a TLS client and form these systems can still act as a TLS client and form connections to a
connections to a proxy or registrar which authenticates with a server proxy or registrar which authenticates with a server certificate.
certificate. The server can authenticate the UA using a shared The server can authenticate the UA using a shared secret in a digest
secret in a digest challenge over that TLS connection. challenge over that TLS connection.
The key idea of this specification is that when a UA sends a REGISTER The key idea of this specification is that when a UA sends a REGISTER
request, the proxy can later use this same network "flow", whether request, the proxy can later use this same network "flow"--whether
this is a bidirectional stream of UDP datagrams, a TCP connection, or this is a bidirectional stream of UDP datagrams, a TCP connection, or
an analogous concept of another transport protocol to forward any an analogous concept of another transport protocol--to forward any
requests that need to go to this UA. For a UA to receive incoming requests that need to go to this UA. For a UA to receive incoming
requests, the UA has to connect to a server. Since the server can't requests, the UA has to connect to a server. Since the server can't
connect to the UA, the UA has to make sure that a flow is always connect to the UA, the UA has to make sure that a flow is always
active. This requires the UA to detect when a flow fails. Since active. This requires the UA to detect when a flow fails. Since
such detection takes time and leaves a window of opportunity for such detection takes time and leaves a window of opportunity for
missed incoming requests, this mechanism allows the UA to use missed incoming requests, this mechanism allows the UA to use
multiple flows to the proxy or registrar. This mechanism also uses a multiple flows to the proxy or registrar. This specification also
keep alive mechanism over each flow so that the UA can detect when a defines how SIP implements the STUN keepalive usage. The keepalive
flow has failed. mechanism is used to keep NAT bindings fresh, and to allow the 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 RFC 2119 [RFC2119].
2.1 Definitions 2.1 Definitions
Authoritative Proxy: A proxy that handles non-REGISTER requests for a Authoritative Proxy: A proxy that handles non-REGISTER requests for a
specific Address-of-Record (AOR), performs the logical Location specific Address-of-Record (AOR), performs the logical Location
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restart. If a UA has multiple flows, and one of the servers fails, restart. If a UA has multiple flows, and one of the servers fails,
the UA delays the specified time before trying to form a new the UA delays the specified time before trying to form a new
connection to replace the flow to the server that failed. By connection to replace the flow to the server that failed. By
spreading out the time used for all the UAs to reconnect to a server, spreading out the time used for all the UAs to reconnect to a server,
the load on the server farm is reduced. the load on the server farm is reduced.
When used in this fashion to achieve high reliability, the operator When used in this fashion to achieve high reliability, the operator
will need to configure DNS such that the various URIs in the outbound will need to configure DNS such that the various URIs in the outbound
proxy set do not resolve to the same host. proxy set do not resolve to the same host.
Another motivation for maintaining multiple flows between the UA and
its registrar is related to multihomed UAs. Such UAs can benefit
from multiple connections from different interfaces to protect
against the failure of an individual access link.
3.4 Edge Proxies 3.4 Edge Proxies
Some SIP deployments use edge proxies such that the UA sends the Some SIP deployments use edge proxies such that the UA sends the
REGISTER to an Edge Proxy that then forwards the REGISTER to the REGISTER to an Edge Proxy that then forwards the REGISTER to the
Registrar. The Edge Proxy includes a Path header [RFC3327] so that Registrar. The Edge Proxy includes a Path header [RFC3327] so that
when the registrar later forwards a request to this UA, the request when the registrar later forwards a request to this UA, the request
is routed through the Edge Proxy. There could be a NAT or firewall is routed through the Edge Proxy. There could be a NAT or firewall
between the UA and the Edge Proxy. between the UA and the Edge Proxy.
+---------+ +---------+
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4.1 Instance ID Creation 4.1 Instance ID Creation
Each UA MUST have an Instance Identifier URN that uniquely identifies Each UA MUST have an Instance Identifier URN that uniquely identifies
the device. Usage of a URN provides a persistent and unique name for the device. Usage of a URN provides a persistent and unique name for
the UA instance. It also provides an easy way to guarantee the UA instance. It also provides an easy way to guarantee
uniqueness within the AOR. This URN MUST be persistent across power uniqueness within the AOR. This URN MUST be persistent across power
cycles of the device. The Instance ID MUST NOT change as the device cycles of the device. The Instance ID MUST NOT change as the device
moves from one network to another. moves from one network to another.
A UA SHOULD use a UUID URN [RFC4122]. The UUID URN allows for non- A UA SHOULD use a UUID URN [RFC4122] as its instance-id. The UUID
centralized computation of a URN based on time, unique names (such as URN allows for non-centralized computation of a URN based on time,
a MAC address), or a random number generator. unique names (such as a MAC address), or a random number generator.
A device like a soft-phone, when first installed, can generate a A device like a soft-phone, when first installed, can generate a
UUID [RFC4122] and then save this in persistent storage for all UUID [RFC4122] and then save this in persistent storage for all
future use. For a device such as a hard phone, which will only future use. For a device such as a hard phone, which will only
ever have a single SIP UA present, the UUID can include the MAC ever have a single SIP UA present, the UUID can include the MAC
address and be generated at any time because it is guaranteed that address and be generated at any time because it is guaranteed that
no other UUID is being generated at the same time on that physical no other UUID is being generated at the same time on that physical
device. This means the value of the time component of the UUID device. This means the value of the time component of the UUID
can be arbitrarily selected to be any time less than the time when can be arbitrarily selected to be any time less than the time when
the device was manufactured. A time of 0 (as shown in the example the device was manufactured. A time of 0 (as shown in the example
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within the quoted string value of the +sip.instance Contact header within the quoted string value of the +sip.instance Contact header
field parameter. The case-sensitive matching rules apply only to field parameter. The case-sensitive matching rules apply only to
the generic usages defined in RFC 3840 [RFC3840] and in the caller the generic usages defined in RFC 3840 [RFC3840] and in the caller
preferences specification [RFC3841]. When the instance ID is used preferences specification [RFC3841]. When the instance ID is used
in this specification, it is effectively "extracted" from the in this specification, it is effectively "extracted" from the
value in the "sip.instance" media feature tag. Thus, equality value in the "sip.instance" media feature tag. Thus, equality
comparisons are performed using the rules for URN equality that comparisons are performed using the rules for URN equality that
are specific to the scheme in the URN. If the element performing are specific to the scheme in the URN. If the element performing
the comparisons does not understand the URN scheme, it performs the comparisons does not understand the URN scheme, it performs
the comparisons using the lexical equality rules defined in RFC the comparisons using the lexical equality rules defined in RFC
2141 [RFC2141]. Lexical equality may result in two URNs being 2141 [RFC2141]. Lexical equality could result in two URNs being
considered unequal when they are actually equal. In this specific considered unequal when they are actually equal. In this specific
usage of URNs, the only element which provides the URN is the SIP usage of URNs, the only element which provides the URN is the SIP
UA instance identified by that URN. As a result, the UA instance UA instance identified by that URN. As a result, the UA instance
SHOULD provide lexically equivalent URNs in each registration it SHOULD provide lexically equivalent URNs in each registration it
generates. This is likely to be normal behavior in any case; generates. This is likely to be normal behavior in any case;
clients are not likely to modify the value of the instance ID so clients are not likely to modify the value of the instance ID so
that it remains functionally equivalent yet lexigraphically that it remains functionally equivalent yet lexigraphically
different from previous registrations. different from previous registrations.
4.2 Initial Registrations 4.2 Initial Registrations
UAs obtain at configuration time 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 may define additional mechanisms such as using future specifications can define additional mechanisms such as using
DNS to discover this set. How the UA is configured is outside the DNS to discover this set. How the UA is configured is outside the
scope of this specification. However, a UA MUST support sets with at scope of this specification. However, a UA MUST support sets with at
least two outbound proxy URIs and SHOULD support sets with up to four least two outbound proxy URIs and SHOULD support sets with up to four
URIs. For each outbound proxy URI in the set, the UA SHOULD send a URIs. For each outbound proxy URI in the set, the UA SHOULD send a
REGISTER in the normal way using this URI as the default outbound REGISTER in the normal way using this URI as the default outbound
proxy. Forming the route set for the request is outside the scope of proxy. Forming the route set for the request is outside the scope of
this document, but typically results in sending the REGISTER such this document, but typically results in sending the REGISTER such
that the topmost Route header field contains a loose route to the that the topmost Route header field contains a loose route to the
outbound proxy URI. Other issues related to outbound route outbound proxy URI. Other issues related to outbound route
construction are discussed in [I-D.rosenberg-sip-route-construct]. construction are discussed in [I-D.rosenberg-sip-route-construct].
Registration requests, other than those described in Section 4.2.1, Registration requests, other than those described in Section 4.2.1,
MUST include 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 MUST also add a distinct reg-id These ordinary registration requests include a distinct reg-id
parameter to the Contact header field. Each one of these parameter to the Contact header field. Each one of these
registrations will form a new flow from the UA to the proxy. The registrations will form a new flow from the UA to the proxy. The
reg-id sequence does not have to be sequential but MUST be exactly sequence of reg-id values does not have to be sequential but MUST be
the same reg-id sequence each time the device power cycles or reboots exactly the same sequence of reg-id values each time the UA instance
so that the reg-id values will collide with the previously used power cycles or reboots so that the reg-id values will collide with
reg-id values. This is so the registrar can replace the older the previously used reg-id values. This is so the registrar can
registration. replace the older registration.
The UAC can situationally decide whether to request outbound
behavior by including or omitting the 'reg-id' parameter. For
example, imagine the outbound-proxy-set contains two proxies in
different domains, EP1 and EP2. If an outbound-style registration
succeeded for a flow through EP1, the UA might decide to include
'outbound' in its option-tag when registering with EP2, in order
to insure consistency. Similarly, if the registration through EP1
did not support outbound, the UA might decide to omit the 'reg-id'
parameter when registering with EP2.
The UAC MUST indicate that it supports the Path header [RFC3327] The UAC MUST indicate that it supports the Path header [RFC3327]
mechanism, by including the 'path' option-tag in a Supported header mechanism, by including the 'path' option-tag in a Supported header
field value in its REGISTER requests. Other than optionally field value in its REGISTER requests. Other than optionally
examining the Path vector in the response, this is all that is examining the Path vector in the response, this is all that is
required of the UAC to support Path. required of the UAC to support Path.
The UAC MAY examine successful registrations for the presence of an The UAC MAY examine successful registrations for the presence of an
'outbound' option-tag in a Supported header field value. Presence of 'outbound' option-tag in a Supported header field value. Presence of
this option-tag indicates that the registrar is compliant with this this option-tag indicates that the registrar is compliant with this
specification, and that any edge proxies which need to partcipate are specification, and that any edge proxies which need to partcipate are
also compliant. also compliant.
Note that the UA needs to honor 503 responses to registrations as Note that the UA needs to honor 503 (Service Unavailable) responses
described in RFC 3261 and RFC 3263 [RFC3263]. In particular, to registrations as described in RFC 3261 and RFC 3263 [RFC3263]. In
implementors should note that when receiving a 503 response with a particular, implementors should note that when receiving a 503
Retry-After header field, the UA should wait the indicated amount of (Service Unavailable) response with a Retry-After header field, the
time and retry the registration. A Retry-After header field value of UA is expected to wait the indicated amount of time and retry the
0 is valid and indicates the UA should retry the REGISTER registration. A Retry-After header field value of 0 is valid and
immediately. Implementations need to ensure that when retrying the indicates the UA is expected to retry the REGISTER immediately.
REGISTER, they revisit the DNS resolution results such that the UA Implementations need to ensure that when retrying the REGISTER, they
can select an alternate host from the one chosen the previous time revisit the DNS resolution results such that the UA can select an
the URI was resolved. alternate host from the one chosen the previous time the URI was
resolved.
Use of outbound with UDP flows typically prevents messages larger
than 1300 bytes from being delivered using TCP as described in
Section 18.1.1 RFC 3261. Use of outbound in conjunction with UDP
flows in environments where requests are expected to be larger than
this size is therefore NOT RECOMMENDED.
Finally, re-registrations which merely refresh an existing valid Finally, re-registrations which merely refresh an existing valid
registration SHOULD be sent over the same flow as the original registration SHOULD be sent over the same flow as the original
registration. registration.
4.2.1 Registration by Other Instances 4.2.1 Registration by Other Instances
A User Agent MUST NOT include a reg-id header parameter in the A User Agent MUST NOT include a reg-id header parameter in the
Contact header field of a registration if the registering UA is not Contact header field of a registration if the registering UA is not
the same instance as the UA referred to by the target Contact header the same instance as the UA referred to by the target Contact header
skipping to change at page 15, line 18 skipping to change at page 15, line 32
processing to select the next hop URI. The UA can use a variety of processing to select the next hop URI. The UA can use a variety of
techniques to compute the route set and accordingly the next hop URI. techniques to compute the route set and accordingly the next hop URI.
Discussion of these techniques is outside the scope of this document Discussion of these techniques is outside the scope of this document
but could include mechanisms specified in RFC 3608 [RFC3608] (Service but could include mechanisms specified in RFC 3608 [RFC3608] (Service
Route) and [I-D.rosenberg-sip-route-construct]. Route) and [I-D.rosenberg-sip-route-construct].
The UA performs normal DNS resolution on the next hop URI (as The UA performs normal DNS resolution on the next hop URI (as
described in RFC 3263 [RFC3263]) to find a protocol, IP address, and described in RFC 3263 [RFC3263]) to find a protocol, IP address, and
port. For non-TLS protocols, if the UA has an existing flow to this port. For non-TLS protocols, if the UA has an existing flow to this
IP address, and port with the correct protocol, then the UA MUST use IP address, and port with the correct protocol, then the UA MUST use
the existing connection. For TLS protocols, there must also be a the existing connection. For TLS protocols, there MUST also be a
match between the host production in the next hop and one of the URIs match between the host production in the next hop and one of the URIs
contained in the subjectAltName in the peer certificate. If the UA contained in the subjectAltName in the peer certificate. If the UA
cannot use one of the existing flows, then it SHOULD form a new flow cannot use one of the existing flows, then it SHOULD form a new flow
by sending a datagram or opening a new connection to the next hop, as by sending a datagram or opening a new connection to the next hop, as
appropriate for the transport protocol. appropriate for the transport protocol.
Note that if the UA wants its flow to work through NATs or
firewalls it still needs to put the 'rport' parameter [RFC3581] in
its Via header field value, and send from the port it is prepared
to receive on. More general information about NAT traversal in
SIP is described in [I-D.ietf-sipping-nat-scenarios].
4.4 Detecting Flow Failure 4.4 Detecting Flow Failure
The UA needs to detect when a specific flow fails. The UA actively The UA needs to detect when a specific flow fails. The UA actively
tries to detect failure by periodically sending keepalive messages tries to detect failure by periodically sending keepalive messages
using one of the techniques described in this section. If a flow has using one of the techniques described in Section 4.4.1 or
failed, the UA follows the procedures in Section 4.2 to form a new Section 4.4.2. If a flow has failed, the UA follows the procedures
flow to replace the failed one. in Section 4.2 to form a new flow to replace the failed one.
The time between keepalive requests when using UDP-based transports The time between keepalive requests when using UDP-based transports
SHOULD be a random number between 24 and 29 seconds while for TCP- SHOULD be a random number between 24 and 29 seconds while for TCP-
based transports it SHOULD be a random number between 95 and 120 based transports it SHOULD be a random number between 95 and 120
seconds. These times MAY be configurable. seconds. These times MAY be configurable. Issues such as battery
consumption might motivate longer keepalive intervals.
o Note on selection of time values: For UDP, the upper bound of 29 Note on selection of time values: For UDP, the upper bound of 29
seconds was selected so that multiple STUN packets could be sent seconds was selected so that multiple STUN packets could be sent
before 30 seconds based on information that many NATs have UDP before 30 seconds based on information that many NATs have UDP
timeouts as low as 30 seconds. The 24 second lower bound was timeouts as low as 30 seconds. The 24 second lower bound was
selected so that after 10 minutes the jitter introduced by selected so that after 10 minutes the jitter introduced by
different timers will make the keepalive requests unsynchronized different timers will make the keepalive requests unsynchronized
to evenly spread the load on the servers. For TCP, the 120 to evenly spread the load on the servers. For TCP, the 120
seconds upper bound was chosen based on the idea that for a good seconds upper bound was chosen based on the idea that for a good
user experience, failures should be detected in this amount of user experience, failures normally will be detected in this amount
time and a new connection set up. Operators that wish to change of time and a new connection set up. Operators that wish to
the relationship between load on servers and the expected time change the relationship between load on servers and the expected
that a user may not receive inbound communications will probably time that a user might not receive inbound communications will
adjust this time. The 95 seconds lower bound was chosen so that probably adjust this time. The 95 seconds lower bound was chosen
the jitter introduced will result in a relatively even load on the so that the jitter introduced will result in a relatively even
servers after 30 minutes. load on the servers after 30 minutes.
4.4.1 Keepalive with TCP KEEPALIVE 4.4.1 Keepalive with TCP KEEPALIVE
User Agents that are capable of generating per-connection TCP User Agents that are capable of generating per-connection TCP
keepalives with timer values consistent with those in this section keepalives with timer values consistent with those in this section
MAY use TCP keepalives instead of using STUN keepalives for TCP-based MAY use TCP keepalives instead of using STUN keepalives for TCP-based
flows. flows.
4.4.2 Keepalive with STUN 4.4.2 Keepalive with STUN
skipping to change at page 17, line 37 skipping to change at page 18, line 11
If the number of consecutive-failures is large enough that the If the number of consecutive-failures is large enough that the
maximum of 1800 seconds is reached, the UA will keep trying maximum of 1800 seconds is reached, the UA will keep trying
indefinitely with a random time of 15 to 30 minutes (900 to 1800 indefinitely with a random time of 15 to 30 minutes (900 to 1800
seconds) between each attempt. seconds) between each 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 typically needs to header parameter in the Contact header field, it needs to determine
store a "flow token", containing information about the flow from the if it (the edge proxy) will have to be visited for any subsequent
previous hop, in a Path header field value as described in RFC 3327 requests sent to the user agent identified in the Contact header
[RFC3327]. The token MAY be placed in the userpart of the URI. If field, or not. If the Edge Proxy determines that this is the case,
the edge proxy is the first SIP node after the UAC, it either MUST it inserts its URI in a Path header field value as described in RFC
store a flow token in a Path header, or reject the request. In 3327 [RFC3327]. If the Edge Proxy is the first SIP node after the
addition, the first node MUST include an 'ob' URI parameter in its UAC, it either MUST store a "flow token"--containing information
Path header field value. about the flow from the previous hop--in its Path URI, or reject the
request. The flow token MAY be placed in the userpart of the URI.
Each subsequent edge proxy examines the first Path header field In addition, the first node MUST include an 'ob' URI parameter in its
value. If this URI does not contain an 'ob' parameter, the edge Path header field value. If the Edge Proxy is not the first SIP node
proxy MUST ignore the reg-id parameter and MUST NOT include an 'ob' after the UAC it MUST NOT place an 'ob' URI parameter in a Path
parameter if it adds a Path header field value. If the first Path header field value. The Edge Proxy can determine if it is the first
header field value contains an 'ob' parameter, this indicates that hop by examining the Via header field
the first edge proxy performed outbound processing. In this case the
edge proxy MUST store a flow token in a Path header, unless it has
positive knowledge that the URI in previous Path header is reachable
from any node on the public Internet, and that the next hop SIP node
can reach any node on the public Internet. This insures that there
is a reachable path from the authoritative proxy back to the User
Agent. Regardless if the proxy includes a flow token, if it adds a
Path header field value, it MUST include the 'ob' parameter in its
Path URI.
5.2 Generating Flow Tokens 5.2 Generating Flow Tokens
A trivial but impractical way to satisfy the flow token requirement A trivial but impractical way to satisfy the flow token requirement
in Section 5.1 involves storing a mapping between an incrementing in Section 5.1 involves storing a mapping between an incrementing
counter and the connection information; however this would require counter and the connection information; however this would require
the Edge Proxy to keep an impractical amount of state. It is unclear the Edge Proxy to keep an impractical amount of state. It is unclear
when this state could be removed and the approach would have problems when this state could be removed and the approach would have problems
if the proxy crashed and lost the value of the counter. Two if the proxy crashed and lost the value of the counter. Two
stateless examples are provided below. A proxy can use any algorithm stateless examples are provided below. A proxy can use any algorithm
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5.3 Forwarding Requests 5.3 Forwarding Requests
When an Edge Proxy receives a request, it applies normal routing When an Edge Proxy receives a request, it applies normal routing
procedures with the following addition. If the Edge Proxy receives a procedures with the following addition. If the Edge Proxy receives a
request where the edge proxy is the host in the topmost Route header request where the edge proxy is the host in the topmost Route header
field value, and the Route header contains a flow token, the proxy field value, and the Route header contains a flow token, the proxy
compares the flow in the flow token with the source of the request. compares the flow in the flow token with the source of the request.
If these refer to the same flow, the Edge Proxy removes the Route If these refer to the same flow, the Edge Proxy removes the Route
header and continues processing the request. Otherwise, if the top- header and continues processing the request. Otherwise, if the top-
most Route header refers to the Edge Proxy and contains a valid flow most Route header refers to the Edge Proxy and contains a valid flow
identifier token created by this proxy, the proxy MUST remove the the identifier token created by this proxy, the proxy MUST remove the
Route header and forward the request over the flow that received the Route header and forward the request over the 'logical flow'
REGISTER request that caused the flow identifier token to be created. identified by the flow token, that is known to deliver data to the
For connection-oriented transports, if the flow no longer exists the specific target UA instance. For connection-oriented transports, if
proxy SHOULD send a 430 Flow Failed response to the request. the flow no longer exists the proxy SHOULD send a 430 (Flow Failed)
response to the request.
The advantage to a stateless approach to managing the flow The advantage to a stateless approach to managing the flow
information is that there is no state on the Edge Proxy that information is that there is no state on the Edge Proxy that
requires clean up or that has to be synchronized with the requires clean up or that has to be synchronized with the
registrar. registrar.
Proxies which used one of the two algorithms described in this Proxies which used one of the two algorithms described in this
document to form a flow token follow the procedures below to document to form a flow token follow the procedures below to
determine the correct flow. determine the correct flow.
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document to form a flow token follow the procedures below to document to form a flow token follow the procedures below to
determine the correct flow. determine the correct flow.
Algorithm 1: The proxy base64 decodes the user part of the Route Algorithm 1: The proxy base64 decodes the user part of the Route
header. For a TCP-based transport, if a connection specified by header. For a TCP-based transport, if a connection specified by
the file descriptor is present and the creation time of the file the file descriptor is present and the creation time of the file
descriptor matches the creation time encoded in the Route header, descriptor matches the creation time encoded in the Route header,
the proxy forwards the request over that connection. For a UDP- the proxy forwards the request over that connection. For a UDP-
based transport, the proxy forwards the request from the encoded based transport, the proxy forwards the request from the encoded
file descriptor to the source IP address and port. file descriptor to the source IP address and port.
Algorithm 2: To decode the flow token, take the flow identifier in Algorithm 2: To decode the flow token, take the flow identifier in
the user portion of the URI and base64 decode it, then verify the the user portion of the URI and base64 decode it, then verify the
HMAC is correct by recomputing the HMAC and checking it matches. HMAC is correct by recomputing the HMAC and checking it matches.
If the HMAC is not correct, the proxy SHOULD send a 403 response. If the HMAC is not correct, the proxy SHOULD send a 403
If the HMAC is correct then the proxy SHOULD forward the request (Forbidden) response. If the HMAC is correct then the proxy
on the flow that was specified by the information in the flow SHOULD forward the request on the flow that was specified by the
identifier. If this flow no longer exists, the proxy SHOULD send information in the flow identifier. If this flow no longer
a 430 Flow Failed response to the request. exists, the proxy SHOULD send a 430 (Flow Failed) response to the
request.
Note that this specification needs mid-dialog requests to be routed Note that this specification needs mid-dialog requests to be routed
over the same flows as those stored in the Path vector from the over the same flows as those stored in the Path vector from the
initial registration, but techniques to ensure that mid-dialog initial registration, but techniques to ensure that mid-dialog
requests are routed over an existing flow are not part of this requests are routed over an existing flow are not part of this
specification. However, an approach such as having the Edge Proxy specification. However, an approach such as having the Edge Proxy
Record-Route with a flow token is one way to ensure that mid-dialog Record-Route with a flow token is one way to ensure that mid-dialog
requests are routed over the correct flow. requests are routed over the correct flow.
5.4 Edge Proxy Keepalive Handling 5.4 Edge Proxy Keepalive Handling
skipping to change at page 20, line 35 skipping to change at page 21, line 8
field value with a reg-id but no instance-id, it simply ignores the field value with a reg-id but no instance-id, it simply ignores the
reg-id parameter. The registrar MUST be prepared to receive, reg-id parameter. The registrar MUST be prepared to receive,
simultaneously for the same AOR, some registrations that use simultaneously for the same AOR, some registrations that use
instance-id and reg-id and some registrations that do not. instance-id and reg-id and some registrations that do not.
Registrars which implement this specification MUST support the Path Registrars which implement this specification MUST support the Path
header mechanism [RFC3327]. header mechanism [RFC3327].
In addition to the normal information stored in the binding record, In addition to the normal information stored in the binding record,
some additional information needs to be stored for any registration some additional information needs to be stored for any registration
that contains a reg-id header parameter in the Contact header field that contains an instance-id and a reg-id header parameter in the
value. First the registrar examines all Path header field values, if Contact header field value. First the registrar examines the first
any. If any of these does not have an 'ob' URI parameter, the Path header field value, if any. If the Path header field exists and
registrar MUST ignore the reg-id parameter and continue processing the first URI does not have an 'ob' URI parameter, the registrar MUST
the request as if it did not support this specification. Likewise if ignore the reg-id parameter and continue processing the request as if
the REGISTER request visited an edge proxy, but no Path header field it did not support this specification. Likewise if the REGISTER
values are present, the registrar MUST ignore the reg-id parameter. request visited an edge proxy, but no Path header field values are
present, the registrar MUST ignore the reg-id parameter.
Specifically, the registrar MUST use RFC 3261 Contact binding rules, Specifically, the registrar MUST use RFC 3261 Contact binding rules,
and MUST NOT include the 'outbound' option-tag in its Supported and MUST NOT include the 'outbound' option-tag in its Supported
header field. header field. The registrar can determine if it is the first hop by
examining the Via header field.
If the UAC has a direct flow with the registrar, the registrar MUST If the UAC has a direct flow with the registrar, the registrar MUST
store enough information to uniquely identify the network flow over store enough information to uniquely identify the network flow over
which the request arrived. For common operating systems with TCP, which the request arrived. For common operating systems with TCP,
this would typically just be the file descriptor and the time the this would typically just be the file descriptor and the time the
file descriptor was opened. For common operating systems with UDP file descriptor was opened. For common operating systems with UDP
this would typically be the file descriptor for the local socket that this would typically be the file descriptor for the local socket that
received the request, the local interface, and the IP address and received the request, the local interface, and the IP address and
port number of the remote side that sent the request. port number of the remote side that sent the request. The registrar
In addition, unless the registrar has positive knowledge that the
topmost Path header URI is reachable from the authoritative proxy, it
must store the flow information for the previous hop. The registrar
MAY store this information by adding itself to the Path header field MAY store this information by adding itself to the Path header field
with an appropriate flow token. with an appropriate flow token.
The registrar MUST also store all the Contact header field The registrar MUST also store all the Contact header field
information including the reg-id and instance-id parameters and information including the reg-id and instance-id parameters and
SHOULD also store the time at which the binding was last updated. If SHOULD also store the time at which the binding was last updated. If
a Path header field is present, RFC 3327 [RFC3327] requires the a Path header field is present, RFC 3327 [RFC3327] requires the
registrar to store this information as well. If the registrar registrar to store this information as well. If the registrar
receives a re-registration, it MUST update any information that receives a re-registration, it MUST update any information that
uniquely identifies the network flow over which the request arrived uniquely identifies the network flow over which the request arrived
skipping to change at page 21, line 34 skipping to change at page 22, line 5
Section (Section 12.1)) in a Supported header field value in its Section (Section 12.1)) in a Supported header field value in its
responses to REGISTER requests for which it has performed outbound responses to REGISTER requests for which it has performed outbound
processing. The Registrar MAY be configured with local policy to processing. The Registrar MAY be configured with local policy to
reject any registrations that do not include the instance-id and reject any registrations that do not include the instance-id and
reg-id. Note that the requirements in this section applies to both reg-id. Note that the requirements in this section applies to both
REGISTER requests received from an Edge Proxy as well as requests REGISTER requests received from an Edge Proxy as well as requests
received directly from the UAC. received directly from the UAC.
To be compliant with this specification, registrars which can receive To be compliant with this specification, registrars which can receive
SIP requests directly from a UAC without intervening edge proxies SIP requests directly from a UAC without intervening edge proxies
MUST implement support the STUN NAT Keepalive usage on its SIP ports MUST implement the STUN NAT Keepalive usage on its SIP ports as
as described in Section 8. described in Section 8.
7. Authoritative Proxy Mechansims: Forwarding Requests 7. Authoritative Proxy Mechansims: Forwarding Requests
When a proxy uses the location service to look up a registration When a proxy uses the location service to look up a registration
binding and then proxies a request to a particular contact, it binding and then proxies a request to a particular contact, it
selects a contact to use normally, with a few additional rules: selects a contact to use normally, with a few additional rules:
o The proxy MUST NOT populate the target set with more than one o The proxy MUST NOT populate the target set with more than one
contact with the same AOR and instance-id at a time. If a request contact with the same AOR and instance-id at a time. If a request
for a particular AOR and instance-id fails with a 430 Flow Failed for a particular AOR and instance-id fails with a 430 (Flow
response, the proxy SHOULD replace the failed branch with another Failed) response, the proxy SHOULD replace the failed branch with
target (if one is available) with the same AOR and instance-id, another target (if one is available) with the same AOR and
but a different reg-id. instance-id, but a different reg-id.
o If the proxy receives a final response from a branch other than a o If the proxy receives a final response from a branch other than a
408 or a 430 response, the proxy MUST NOT forward the same request 408 (Request Timeout) or a 430 (Flow Failed) response, the proxy
to another target representing the same AOR and instance-id. The MUST NOT forward the same request to another target representing
targetted instance has already provided its response. the same AOR and instance-id. The targetted instance has already
provided its response.
The proxy uses normal forwarding rules looking at the next-hop target The proxy uses normal forwarding rules looking at the next-hop target
of the message and the value of any stored Path header field vector of the message and the value of any stored Path header field vector
in the registration binding to decide how to forward the request and in the registration binding to decide how to forward the request and
populate the Route header in the request. Additionally, when the populate the Route header in the request. If the proxy stored
proxy forwards a request to a binding that contains a reg-id, if the information about the flow over which it received the REGISTER for
binding has a previous hop flow associated with it, the proxy MUST the binding, then the proxy MUST send the request over the same
send the request over the same network flow that was saved with the 'logical flow' saved with the binding that is known to deliver data
binding. This means that for TCP, the request MUST be sent on the to the specific target UA instance.
same TCP socket that received the REGISTER request. For UDP, the
request MUST be sent from the same local IP address and port over Typically this means that for TCP, the request is sent on the same
which the registration was received, to the same IP address and port TCP socket that received the REGISTER request. For UDP, the
request is sent from the same local IP address and port over which
the registration was received, to the same IP address and port
from which the REGISTER was received. from which the REGISTER was received.
If a proxy or registrar receives information from the network that If a proxy or registrar receives information from the network that
indicates that no future messages will be delivered on a specific indicates that no future messages will be delivered on a specific
flow, then the proxy MUST invalidate all the bindings 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.
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given interface and port, it MUST also provide a limited version of a given interface and port, it MUST also provide a limited version of a
STUN server on the same interface and port as described in Section STUN server on the same interface and port as described in Section
12.3 of [I-D.ietf-behave-rfc3489bis]. When STUN messages are sent 12.3 of [I-D.ietf-behave-rfc3489bis]. When STUN messages are sent
with a SIP over TLS over TCP flow, the STUN messages are sent inside with a SIP over TLS over TCP flow, the STUN messages are sent inside
the TLS-protected channel. the TLS-protected channel.
It is easy to distinguish STUN and SIP packets sent over UDP, It is easy to distinguish STUN and SIP packets sent over UDP,
because the first octet of a STUN packet has a value of 0 or 1 because the first octet of a STUN packet has a value of 0 or 1
while the first octet of a SIP message is never a 0 or 1. For TCP while the first octet of a SIP message is never a 0 or 1. For TCP
or TLS over TCP flows, determining if the first octet of the next or TLS over TCP flows, determining if the first octet of the next
message in a stream is SIP or STUN is still straightforward, message in a stream is SIP or STUN is still straightforward. As
however implementations need to be preared to receive STUN with any stream-based protocol, implementations need to be preared
messages which cross a stream buffer boundary, and SIP and STUN to receive STUN messages which cross a stream buffer boundary, and
messages which share the same stream buffer. SIP and STUN messages which share the same stream buffer.
Because sending and receiving binary STUN data on the same ports used Because sending and receiving binary STUN data on the same ports used
for SIP is a significant and non-backwards compatible change to RFC for SIP is a significant and non-backwards compatible change to RFC
3261, this section requires a number of checks before sending STUN 3261, this section requires a number of checks before sending STUN
messages to a SIP node. If a SIP node sends STUN requests (for messages to a SIP node. If a SIP node sends STUN requests (for
example due to misconfiguration) despite these warnings, the node may example due to misconfiguration) despite these warnings, the node
be blacklisted for UDP traffic, or cause its TCP server to loose could be blacklisted for UDP traffic, or cause its TCP server to
framing over its connection. For each target node (as determined by loose framing over its connection. For each target node (as
IP address, address family, and port number), the sender needs to determined by IP address, address family, and port number), the
determine if that destination is validated to support STUN, that it sender needs to determine if that destination is validated to support
does not support STUN, or that it needs to be validated. STUN, that it does not support STUN, or that it needs to be
validated.
When a URI is created that refers to a SIP device that supports STUN When a URI is created that refers to a SIP node that supports STUN as
as described in this section, the 'keepalive' URI parameter, as described in this section, the 'keepalive' URI parameter, as defined
defined in Section 12 SHOULD be added to the URI, with a value of in Section 12 SHOULD be added to the URI, with a value of 'stun'.
'stun'. This allows a UA to inspect the URI to decide if it should This allows a UA to inspect the URI to decide if it should attempt to
attempt to send STUN requests to this location. send STUN requests to this location. For example, an edge proxy
could insert this parameter into its Path URI so that the registering
UA can discover the edge proxy supports STUN keepalives.
A SIP node MUST NOT send STUN requests over a flow unless it has an A SIP node MUST NOT send STUN requests over a flow unless it has an
explicit indication that the target next hop SIP server claims to explicit indication that the target next hop SIP server claims to
support STUN. For example, automatic or manual configuration of an support STUN. For example, automatic or manual configuration of an
outbound-proxy-set which contains the keepalive=stun parameter is outbound-proxy-set which contains the keepalive=stun parameter is
considered sufficient explicit indication. Note that UACs MUST NOT considered sufficient explicit indication. Note that UACs MUST NOT
use an ambiguous configuration option such as "Work through NATs?" or use an ambiguous configuration option such as "Work through NATs?" or
"Do Keepalives?" to imply next hop STUN support. A SIP node MAY also "Do Keepalives?" to imply next hop STUN support. A SIP node MAY also
probe the next hop using a SIP OPTIONS request to check for support probe the next hop using a SIP OPTIONS request to check for support
of the 'sip-stun' option tag in a Supported header field. of the 'sip-stun' option tag in a Supported header field.
skipping to change at page 25, line 25 skipping to change at page 26, line 5
uncompressed application messages and SigComp messages on the same uncompressed application messages and SigComp messages on the same
UDP port. UDP port.
The most significant two bits of every STUN message are both The most significant two bits of every STUN message are both
zeroes. This, combined with the magic cookie, aids in zeroes. This, combined with the magic cookie, aids in
differentiating STUN packets from other protocols when STUN is differentiating STUN packets from other protocols when STUN is
multiplexed with other protocols on the same port. multiplexed with other protocols on the same port.
For TCP-based flows, SigComp requires that all messages are processed For TCP-based flows, SigComp requires that all messages are processed
by the SigComp compressor to facilitate framing. For these by the SigComp compressor to facilitate framing. For these
transports, STUN messages are sent encapsulated in the SigComp "well- transports, STUN messages are sent encapsulated in the SigComp "well-
known shim header" as described in Appendix A of RFC 3320 [RFC3320]. known shim header" as described in Section 11 of [I-D.ietf-rohc-
sigcomp-impl-guide].
Because the bytecodes expressed in the well-known shim header do
not store any state, correlation of such SigComp requests to a
compartment is not necessary. To avoid ambiguity, we add the
following requirement: any SigComp state that might result from a
message that, once decompressed, turns out to be a STUN message,
MUST be discarded.
9. Example Message Flow 9. Example Message Flow
The following call flow shows a basic registration and an incoming The following call flow shows a basic registration and an incoming
call. At some point, the flow to the Primary proxy is lost. An call. At some point, the flow to the Primary proxy is lost. An
incoming INVITE tries to reach the Callee through the Primary flow, incoming INVITE tries to reach the Callee through the Primary flow,
but receives an ICMP Unreachable message. The Caller retries using but receives an ICMP Unreachable message. The Caller retries using
the Secondary Edge Proxy, which uses a separate flow. Later, after the Secondary Edge Proxy, which uses a separate flow. Later, after
the Primary reboots, The Callee discovers the flow failure and the Primary reboots, The Callee discovers the flow failure and
reestablishes a new flow to the Primary. reestablishes a new flow to the Primary.
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instance-val = *uric ; defined in RFC 2396 instance-val = *uric ; defined in RFC 2396
The value of the reg-id MUST NOT be 0 and MUST be less than 2**31. The value of the reg-id MUST NOT be 0 and MUST be less than 2**31.
11. Definition of 430 Flow Failed response code 11. Definition of 430 Flow Failed response code
This specification defines a new SIP response code '430 Flow Failed'. This specification defines a new SIP response code '430 Flow Failed'.
This response code is used by an Edge Proxy to indicate to the This response code is used by an Edge Proxy to indicate to the
Authoritative Proxy that a specific flow to a UA instance has failed. Authoritative Proxy that a specific flow to a UA instance has failed.
Other flows to the same instance may still succeed. The Other flows to the same instance could still succeed. The
Authoritative Proxy SHOULD attempt to forward to another target Authoritative Proxy SHOULD attempt to forward to another target
(flow) with the same instance-id and AOR. (flow) with the same instance-id and AOR.
12. IANA Considerations 12. IANA Considerations
12.1 Contact Header Field 12.1 Contact Header Field
This specification defines a new Contact header field parameter This specification defines a new Contact header field parameter
called reg-id in the "Header Field Parameters and Parameter Values" called reg-id in the "Header Field Parameters and Parameter Values"
sub-registry as per the registry created by [RFC3968]. The required sub-registry as per the registry created by [RFC3968]. The required
skipping to change at page 31, line 28 skipping to change at page 32, line 28
Related standards or documents: RFC XXXX Related standards or documents: RFC XXXX
[[Note to IANA: Please replace XXXX with the RFC number of this [[Note to IANA: Please replace XXXX with the RFC number of this
specification.]] specification.]]
Security Considerations: This media feature tag can be used in ways Security Considerations: This media feature tag can be used in ways
which affect application behaviors. For example, the SIP caller which affect application behaviors. For example, the SIP caller
preferences extension [RFC3841] allows for call routing decisions to preferences extension [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 may 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 13. Security Considerations
One of the key security concerns in this work is making sure that an One of the key security concerns in this work is making sure that an
skipping to change at page 32, line 42 skipping to change at page 33, line 42
4. Detect failure of a connection and be able to correct for this. 4. Detect failure of a connection and be able to correct for this.
5. Support many UAs simultaneously rebooting. 5. Support many UAs simultaneously rebooting.
6. Support a NAT rebooting or resetting. 6. Support a NAT rebooting or resetting.
7. Minimize initial startup load on a proxy. 7. Minimize initial startup load on a proxy.
8. Support architectures with edge proxies. 8. Support architectures with edge proxies.
15. Changes 15. Changes
Note to RFC Editor: Please remove this whole section. Note to RFC Editor: Please remove this whole section.
15.1 Changes from 04 Version 15.1 Changes from 05 Version
Mention the relevance of the 'rport' parameter.
Change registrar verification so that only first-hop proxy and the
registrar need to support outbound. Other intermediaries in between
do not any more.
Relaxed flow-token language slightly. Instead of flow-token saving
specific UDP address/port tuples over which the request arrived, make
language fuzzy to save token which points to a 'logical flow' that is
known to deliver data to that specific UA instance.
Added comment that keepalive=stun could be added to Path.
Added comment that battery concerns could motivate longer TCP
keepalive intervals than the defaults.
Scrubbed document for avoidable lowercase mays, shoulds, and musts.
Added text about how Edge Proxies could determine they are the first
hop.
15.2 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 33, line 49 skipping to change at page 35, line 25
Added text about the 'ob' parameter which is used in Path header Added text about the 'ob' parameter which is used in Path header
field URIs to make sure that the previous proxy that added a Path field URIs to make sure that the previous proxy that added a Path
understood outbound processing. The registrar doesn't include understood outbound processing. The registrar doesn't include
Supported: outbound unless it could actually do outbound processing Supported: outbound unless it could actually do outbound processing
(ex: any Path headers have to have the 'ob' parameter). (ex: any Path headers have to have the 'ob' parameter).
Added some text describing what a registration means when there is an Added some text describing what a registration means when there is an
instance-id, but no reg-id. instance-id, but no reg-id.
15.2 Changes from 03 Version 15.3 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 34, line 32 skipping to change at page 36, line 8
by Bill Fenner. by Bill Fenner.
Added a table in an appendix expanding the default flow recovery Added a table in an appendix expanding the default flow recovery
timers. timers.
Incorporated numerous clarifications and rewordings for better Incorporated numerous clarifications and rewordings for better
comprehension. comprehension.
Fixed many typos and spelling misteaks. Fixed many typos and spelling misteaks.
15.3 Changes from 02 Version 15.4 Changes from 02 Version
Removed Double CRLF Keepalive Removed Double CRLF Keepalive
Changed ;sip-stun syntax to ;keepalive=stun Changed ;sip-stun syntax to ;keepalive=stun
Fixed incorrect text about TCP keepalives. Fixed incorrect text about TCP keepalives.
15.4 Changes from 01 Version 15.5 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"
skipping to change at page 35, line 4 skipping to change at page 36, line 28
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
15.5 Changes from 00 Version 15.6 Changes from 00 Version
Moved TCP keepalive to be STUN. Moved TCP keepalive to be STUN.
Allowed SUBSCRIBE to create flow mappings. Added pin-route option Allowed SUBSCRIBE to create flow mappings. Added pin-route option
tags to support this. tags to support this.
Added text about updating dialog state on each usage after a Added text about updating dialog state on each usage after a
connection failure. connection failure.
16. Acknowledgments 16. Acknowledgments
skipping to change at page 36, line 22 skipping to change at page 37, line 37
| 4 | 4-8 mins | 12-24 mins | | 4 | 4-8 mins | 12-24 mins |
| 5 | 8-16 mins | 15-30 mins | | 5 | 8-16 mins | 15-30 mins |
| 6 or more | 15-30 mins | 15-30 mins | | 6 or more | 15-30 mins | 15-30 mins |
+-------------------+--------------------+--------------------+ +-------------------+--------------------+--------------------+
17. References 17. References
17.1 Normative References 17.1 Normative References
[I-D.ietf-behave-rfc3489bis] [I-D.ietf-behave-rfc3489bis]
Rosenberg, J., "Simple Traversal of UDP Through Network Rosenberg, J., "Simple Traversal Underneath Network
Address Translators (NAT) (STUN)", Address Translators (NAT) (STUN)",
draft-ietf-behave-rfc3489bis-02 (work in progress), draft-ietf-behave-rfc3489bis-05 (work in progress),
July 2005. October 2006.
[I-D.ietf-rohc-sigcomp-impl-guide]
Surtees, A., "Implementer's Guide for SigComp",
draft-ietf-rohc-sigcomp-impl-guide-08 (work in progress),
October 2006.
[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.
[RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997. [RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997.
[RFC2396] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC2396] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396, Resource Identifiers (URI): Generic Syntax", RFC 2396,
August 1998. August 1998.
skipping to change at page 37, line 9 skipping to change at page 38, line 29
June 2002. June 2002.
[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.
[RFC3327] Willis, D. and B. Hoeneisen, "Session Initiation Protocol [RFC3327] Willis, D. and B. Hoeneisen, "Session Initiation Protocol
(SIP) Extension Header Field for Registering Non-Adjacent (SIP) Extension Header Field for Registering Non-Adjacent
Contacts", RFC 3327, December 2002. Contacts", RFC 3327, December 2002.
[RFC3581] Rosenberg, J. and H. Schulzrinne, "An Extension to the
Session Initiation Protocol (SIP) for Symmetric Response
Routing", RFC 3581, August 2003.
[RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat,
"Indicating User Agent Capabilities in the Session "Indicating User Agent Capabilities in the Session
Initiation Protocol (SIP)", RFC 3840, August 2004. Initiation Protocol (SIP)", RFC 3840, August 2004.
[RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller [RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller
Preferences for the Session Initiation Protocol (SIP)", Preferences for the Session Initiation Protocol (SIP)",
RFC 3841, August 2004. RFC 3841, August 2004.
[RFC3968] Camarillo, G., "The Internet Assigned Number Authority [RFC3968] Camarillo, G., "The Internet Assigned Number Authority
(IANA) Header Field Parameter Registry for the Session (IANA) Header Field Parameter Registry for the Session
skipping to change at page 37, line 39 skipping to change at page 39, line 14
July 2005. July 2005.
[RFC4234] Crocker, D. and P. Overell, "Augmented BNF for Syntax [RFC4234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005. Specifications: ABNF", RFC 4234, October 2005.
17.2 Informative References 17.2 Informative 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-04 (work in progress), (SIP)", draft-ietf-sip-gruu-11 (work in progress),
July 2005. October 2006.
[I-D.ietf-sipping-config-framework] [I-D.ietf-sipping-config-framework]
Petrie, D., "A Framework for Session Initiation Protocol Petrie, D., "A Framework for Session Initiation Protocol
User Agent Profile Delivery", User Agent Profile Delivery",
draft-ietf-sipping-config-framework-08 (work in progress), draft-ietf-sipping-config-framework-09 (work in progress),
Mar 2006. October 2006.
[I-D.ietf-sipping-nat-scenarios]
Boulton, C., "Best Current Practices for NAT Traversal for
SIP", draft-ietf-sipping-nat-scenarios-05 (work in
progress), June 2006.
[I-D.rosenberg-sip-route-construct] [I-D.rosenberg-sip-route-construct]
Rosenberg, J., "Clarifying Construction of the Route Rosenberg, J., "Construction of the Route Header Field in
Header Field in the Session Initiation Protocol (SIP)", the Session Initiation Protocol (SIP)",
draft-rosenberg-sip-route-construct-00 (work in progress), draft-rosenberg-sip-route-construct-02 (work in progress),
July 2005. October 2006.
[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.
[RFC3188] Hakala, J., "Using National Bibliography Numbers as [RFC3188] Hakala, J., "Using National Bibliography Numbers as
Uniform Resource Names", RFC 3188, October 2001. Uniform Resource Names", RFC 3188, October 2001.
[RFC3548] Josefsson, S., "The Base16, Base32, and Base64 Data [RFC3548] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 3548, July 2003. Encodings", RFC 3548, July 2003.
 End of changes. 55 change blocks. 
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