draft-ietf-sipcore-sip-push-29.txt   rfc8599.txt 
SIPCORE Working Group C. Holmberg Internet Engineering Task Force (IETF) C. Holmberg
Internet-Draft Ericsson Request for Comments: 8599 Ericsson
Intended status: Standards Track M. Arnold Category: Standards Track M. Arnold
Expires: September 27, 2019 Metaswitch Networks ISSN: 2070-1721 Metaswitch Networks
March 26, 2019 May 2019
Push Notification with the Session Initiation Protocol (SIP) Push Notification with the Session Initiation Protocol (SIP)
draft-ietf-sipcore-sip-push-29
Abstract Abstract
This document describes how a Push Notification Service (PNS) can be This document describes how a Push Notification Service (PNS) can be
used to wake a suspended Session Initiation Protocol (SIP) User Agent used to wake a suspended Session Initiation Protocol (SIP) User Agent
(UA) with push notifications, and also describes how the UA can send (UA) with push notifications, and it also describes how the UA can
binding-refresh REGISTER requests and receive incoming SIP requests send binding-refresh REGISTER requests and receive incoming SIP
in an environment in which the UA may be suspended. The document requests in an environment in which the UA may be suspended. The
defines new SIP URI parameters to exchange PNS information between document defines new SIP URI parameters to exchange PNS information
the UA and the SIP entity that will then request that push between the UA and the SIP entity that will then request that push
notifications be sent to the UA, and to trigger such push notifications be sent to the UA. It also defines the parameters to
notification requests. The document also defines new feature- trigger such push notification requests. The document also defines
capability indicators that can be used to indicate support of this new feature-capability indicators that can be used to indicate
mechanism. support of this mechanism.
Status of This Memo Status of This Memo
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and how to provide feedback on it may be obtained at
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Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 7 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 8
3. Push Resource ID (PRID) . . . . . . . . . . . . . . . . . . . 7 3. Push Resource ID (PRID) . . . . . . . . . . . . . . . . . . . 8
4. SIP User Agent (UA) Behavior . . . . . . . . . . . . . . . . 7 4. SIP User Agent (UA) Behavior . . . . . . . . . . . . . . . . 9
4.1. REGISTER . . . . . . . . . . . . . . . . . . . . . . . . 7 4.1. REGISTER . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1.1. Request Push Notifications . . . . . . . . . . . . . 8 4.1.1. Request Push Notifications . . . . . . . . . . . . . 9
4.1.2. Disable Push Notifications . . . . . . . . . . . . . 9 4.1.2. Disable Push Notifications . . . . . . . . . . . . . 11
4.1.3. Receive Push Notifications . . . . . . . . . . . . . 10 4.1.3. Receive Push Notifications . . . . . . . . . . . . . 11
4.1.4. Sending Binding-Refresh Requests Using Non-Push 4.1.4. Sending Binding-Refresh Requests Using Non-push
Mechanism . . . . . . . . . . . . . . . . . . . . . . 10 Mechanism . . . . . . . . . . . . . . . . . . . . . . 11
4.1.5. Query Network PNS Capabilities . . . . . . . . . . . 12 4.1.5. Query Network PNS Capabilities . . . . . . . . . . . 13
5. SIP Proxy Behavior . . . . . . . . . . . . . . . . . . . . . 13 5. SIP Proxy Behavior . . . . . . . . . . . . . . . . . . . . . 14
5.1. PNS Provider . . . . . . . . . . . . . . . . . . . . . . 13 5.1. PNS Provider . . . . . . . . . . . . . . . . . . . . . . 14
5.2. SIP Request Push Bucket . . . . . . . . . . . . . . . . . 14 5.2. SIP Request Push Bucket . . . . . . . . . . . . . . . . . 15
5.3. SIP URI Comparison Rules . . . . . . . . . . . . . . . . 14 5.3. SIP URI Comparison Rules . . . . . . . . . . . . . . . . 15
5.4. Indicate Support of Type of PNS . . . . . . . . . . . . . 14 5.4. Indicate Support of Type of PNS . . . . . . . . . . . . . 15
5.5. Trigger Periodic Binding Refresh . . . . . . . . . . . . 15 5.5. Trigger Periodic Binding Refresh . . . . . . . . . . . . 16
5.6. SIP Requests . . . . . . . . . . . . . . . . . . . . . . 16 5.6. SIP Requests . . . . . . . . . . . . . . . . . . . . . . 17
5.6.1. REGISTER . . . . . . . . . . . . . . . . . . . . . . 16 5.6.1. REGISTER . . . . . . . . . . . . . . . . . . . . . . 17
5.6.2. Initial Request for Dialog or Stand-Alone Request . . 19 5.6.2. Initial Request for Dialog or Standalone Request . . 20
6. Support Of Longlived SIP Dialogs . . . . . . . . . . . . . . 21 6. Support of Long-Lived SIP Dialogs . . . . . . . . . . . . . . 23
6.1. SIP UA Behavior . . . . . . . . . . . . . . . . . . . . . 23 6.1. SIP UA Behavior . . . . . . . . . . . . . . . . . . . . . 25
6.1.1. Initial Request for Dialog . . . . . . . . . . . . . 23 6.1.1. Initial Request for Dialog . . . . . . . . . . . . . 25
6.2. SIP Proxy Behavior . . . . . . . . . . . . . . . . . . . 24 6.2. SIP Proxy Behavior . . . . . . . . . . . . . . . . . . . 25
6.2.1. REGISTER . . . . . . . . . . . . . . . . . . . . . . 24 6.2.1. REGISTER . . . . . . . . . . . . . . . . . . . . . . 25
6.2.2. Initial Request for Dialog . . . . . . . . . . . . . 24 6.2.2. Initial Request for Dialog . . . . . . . . . . . . . 26
6.2.3. Mid-Dialog Request . . . . . . . . . . . . . . . . . 25 6.2.3. Mid-dialog Request . . . . . . . . . . . . . . . . . 26
7. Support Of SIP Replaces . . . . . . . . . . . . . . . . . . . 26 7. Support of SIP Replaces . . . . . . . . . . . . . . . . . . . 27
8. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 8. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
8.1. 555 (Push Notification Service Not Supported) Response 8.1. 555 (Push Notification Service Not Supported) Response
Code . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Code . . . . . . . . . . . . . . . . . . . . . . . . . . 28
8.2. sip.pns Feature-Capability Indicator . . . . . . . . . . 26
8.3. sip.vapid Feature-Capability Indicator . . . . . . . . . 27 8.2. 'sip.pns' Feature-Capability Indicator . . . . . . . . . 28
8.4. sip.pnsreg Feature-Capability Indicator . . . . . . . . . 27 8.3. 'sip.vapid' Feature-Capability Indicator . . . . . . . . 28
8.5. sip.pnsreg Media Feature Tag . . . . . . . . . . . . . . 28 8.4. 'sip.pnsreg' Feature-Capability Indicator . . . . . . . . 28
8.6. sip.pnspurr Feature-Capability Indicator . . . . . . . . 28 8.5. 'sip.pnsreg' Media Feature Tag . . . . . . . . . . . . . 29
8.7. SIP URI Parameters . . . . . . . . . . . . . . . . . . . 28 8.6. 'sip.pnspurr' Feature-Capability Indicator . . . . . . . 29
9. PNS Registration Requirements . . . . . . . . . . . . . . . . 29 8.7. SIP URI Parameters . . . . . . . . . . . . . . . . . . . 29
10. pn-provider, pn-param and pn-prid URI Parameters for Apple 9. PNS Registration Requirements . . . . . . . . . . . . . . . . 30
Push Notification service . . . . . . . . . . . . . . . . . . 29 10. 'pn-provider', 'pn-param', and 'pn-prid' URI Parameters for
11. pn-provider, pn-param and pn-prid URI Parameters for Google Apple Push Notification service . . . . . . . . . . . . . . . 30
Firebase Cloud Messaging (FCM) push notification service . . 30 11. 'pn-provider', 'pn-param', and 'pn-prid' URI Parameters for
12. pn-provider, pn-param and pn-prid URI Parameters for RFC 8030 Google Firebase Cloud Messaging (FCM) Push Notification
(Generic Event Delivery Using HTTP Push) . . . . . . . . . . 30 Service . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
13. Security Considerations . . . . . . . . . . . . . . . . . . . 31 12. 'pn-provider', 'pn-param', and 'pn-prid' URI Parameters for
14. IANA considerations . . . . . . . . . . . . . . . . . . . . . 32 RFC 8030 (Generic Event Delivery Using HTTP Push) . . . . . . 31
14.1. SIP URI Parameters . . . . . . . . . . . . . . . . . . . 32 13. Security Considerations . . . . . . . . . . . . . . . . . . . 32
14.1.1. pn-provider . . . . . . . . . . . . . . . . . . . . 32 14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33
14.1.2. pn-param . . . . . . . . . . . . . . . . . . . . . . 32 14.1. SIP URI Parameters . . . . . . . . . . . . . . . . . . . 33
14.1.1. pn-provider . . . . . . . . . . . . . . . . . . . . 33
14.1.2. pn-param . . . . . . . . . . . . . . . . . . . . . . 33
14.1.3. pn-prid . . . . . . . . . . . . . . . . . . . . . . 33 14.1.3. pn-prid . . . . . . . . . . . . . . . . . . . . . . 33
14.1.4. pn-purr . . . . . . . . . . . . . . . . . . . . . . 33 14.1.4. pn-purr . . . . . . . . . . . . . . . . . . . . . . 33
14.2. SIP Response Codes . . . . . . . . . . . . . . . . . . . 33 14.2. SIP Response Codes . . . . . . . . . . . . . . . . . . . 34
14.2.1. 555 (Push Notification Service Not Supported) . . . 33 14.2.1. 555 (Push Notification Service Not Supported) . . . 34
14.3. SIP Global Feature-Capability Indicator . . . . . . . . 33 14.3. SIP Global Feature-Capability Indicator . . . . . . . . 34
14.3.1. sip.pns . . . . . . . . . . . . . . . . . . . . . . 33 14.3.1. sip.pns . . . . . . . . . . . . . . . . . . . . . . 34
14.3.2. sip.vapid . . . . . . . . . . . . . . . . . . . . . 34 14.3.2. sip.vapid . . . . . . . . . . . . . . . . . . . . . 34
14.3.3. sip.pnsreg . . . . . . . . . . . . . . . . . . . . . 34 14.3.3. sip.pnsreg . . . . . . . . . . . . . . . . . . . . . 35
14.3.4. sip.pnspurr . . . . . . . . . . . . . . . . . . . . 35 14.3.4. sip.pnspurr . . . . . . . . . . . . . . . . . . . . 35
14.4. SIP Media Feature Tag . . . . . . . . . . . . . . . . . 35 14.4. SIP Media Feature Tag . . . . . . . . . . . . . . . . . 36
14.4.1. sip.pnsreg . . . . . . . . . . . . . . . . . . . . . 36 14.4.1. sip.pnsreg . . . . . . . . . . . . . . . . . . . . . 36
14.5. PNS Sub-registry Establishment . . . . . . . . . . . . . 36 14.5. PNS Subregistry Establishment . . . . . . . . . . . . . 36
15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 37 15. References . . . . . . . . . . . . . . . . . . . . . . . . . 37
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 37 15.1. Normative References . . . . . . . . . . . . . . . . . . 37
16.1. Normative References . . . . . . . . . . . . . . . . . . 37 15.2. Informative References . . . . . . . . . . . . . . . . . 39
16.2. Informative References . . . . . . . . . . . . . . . . . 39 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 40
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 40 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 40
1. Introduction 1. Introduction
In order to save resources such as battery life, some devices In order to save resources such as battery life, some devices
(especially mobile devices) and operating systems will suspend an (especially mobile devices) and operating systems will suspend an
application that is not in use. A suspended application might not be application that is not in use. A suspended application might not be
able to wake itself with internal timers and might not be awakened by able to wake itself with internal timers and might not be awakened by
incoming network traffic. In such an environment, a Push incoming network traffic. In such an environment, a Push
Notification Service (PNS) is used to wake the application. A PNS is Notification Service (PNS) is used to wake the application. A PNS is
a service that sends messages requested by other applications to a a service that sends messages requested by other applications to a
user application in order to wake the user application. These user application in order to wake the user application. These
messages are called push notifications. Push notifications might messages are called push notifications. Push notifications might
contain payload data, depending on the application. An application contain payload data, depending on the application. An application
can request that a push notification be sent to a single user can request that a push notification be sent to a single user
application or to multiple user applications. application or to multiple user applications.
Typically each operating system uses a dedicated PNS. Different PNSs Typically, each operating system uses a dedicated PNS. Different
exist today. Some are based on the standardized mechanism defined in PNSs exist today. Some are based on the standardized mechanism
[RFC8030], while others are proprietary. For example, Apple iOS defined in [RFC8030], while others are proprietary. For example,
devices use the Apple Push Notification service (APNs) while Android Apple iOS devices use the Apple Push Notification service (APNs)
devices use the Firebase Cloud Messaging (FCM) service. Each PNS while Android devices use the Firebase Cloud Messaging (FCM) service.
uses PNS-specific terminology and function names. The terminology in Each PNS uses PNS-specific terminology and function names. The
this document is meant to be PNS-independent. If the PNS is based on terminology in this document is meant to be PNS-independent. If the
[RFC8030], the SIP proxy takes the role of the application server. PNS is based on [RFC8030], the SIP proxy takes the role of the
application server.
When a Session Initiation Protocol (SIP) User Agent (UA)[RFC3261] is When a Session Initiation Protocol (SIP) User Agent (UA)[RFC3261] is
suspended in such an environment, it is unable to send binding- suspended in such an environment, it is unable to send binding-
refresh SIP REGISTER requests, unable to receive incoming SIP refresh SIP REGISTER requests, unable to receive incoming SIP
requests, and might not be able to use internal timers to wake requests, and might not be able to use internal timers to wake
itself. A suspended UA will not be able to maintain connections itself. A suspended UA will not be able to maintain connections,
e.g., using the SIP Outbound Mechanism [RFC5626] because it cannot e.g., using the SIP Outbound Mechanism [RFC5626], because it cannot
send periodic keep-alive messages. A PNS is needed to wake the SIP send periodic keep-alive messages. A PNS is needed to wake the SIP
UA so that the UA can perform these functions. UA so that the UA can perform these functions.
This document describes how a PNS can be used to wake a suspended UA, This document describes how a PNS can be used to wake a suspended UA
using push notifications, so that the UA can be able to send binding- using push notifications, so that the UA can send binding-refresh
refresh REGISTER requests and to receive incoming SIP requests. The REGISTER requests and receive incoming SIP requests. The document
document defines new SIP URI parameters and new feature-capability defines new SIP URI parameters and new feature-capability indicators
indicators [RFC6809] that can be used in SIP messages to indicate [RFC6809] that can be used in SIP messages to indicate support of the
support of the mechanism defined in this document, to exchange PNS mechanism defined in this document; be used to exchange PNS
information between the UA and the SIP entity (realized as a SIP information between the UA and the SIP entity (realized as a SIP
proxy in this document) that will request that push notifications are proxy in this document) that will request that push notifications are
sent to the UA, and to request such push notification requests. sent to the UA; and be used to request such push notification
requests.
NOTE: Even if a UA is able to be awakened by means other than NOTE: Even if a UA is able to be awakened by means other than
receiving push notifications (e.g., by using internal timers) in receiving push notifications (e.g., by using internal timers) in
order to send periodic binding-refresh REGISTER requests, it might order to send periodic binding-refresh REGISTER requests, it might
still be useful to suspend the UA between the sending of binding- still be useful to suspend the UA between the sending of binding-
refresh requests (as it will save battery life) and use push refresh requests (as it will save battery life) and use push
notifications to wake the UA when an incoming SIP request UA arrives. notifications to wake the UA when an incoming SIP request UA arrives.
When a UA registers with a PNS (Figure 1), it will receive a unique When a UA registers with a PNS (Figure 1), it will receive a unique
Push Resource ID (PRID) associated with the push notification Push Resource ID (PRID) associated with the push notification
registration. The UA will use a REGISTER request to provide the PRID registration. The UA will use a REGISTER request to provide the PRID
to the SIP proxy, which will then request that push notifications are to the SIP proxy, which will then request that push notifications are
sent to the UA. sent to the UA.
When the SIP proxy receives a SIP request for a new dialog or a When the SIP proxy receives a SIP request for a new dialog or a
stand-alone SIP request addressed towards a UA, or when the SIP proxy standalone SIP request addressed towards a UA, or when the SIP proxy
determines that the UA needs to send a binding-refresh REGISTER determines that the UA needs to send a binding-refresh REGISTER
request, the SIP proxy will send a push request containing the PRID request, the SIP proxy will send a push request containing the PRID
of the UA to the PNS, which will then send a push notification to the of the UA to the PNS, which will then send a push notification to the
UA. Once the UA receives the push notification, it will be able to UA. Once the UA receives the push notification, it will be able to
send a binding-refresh REGISTER request. The proxy receives the send a binding-refresh REGISTER request. The proxy receives the
REGISTER request from the UA and forwards it to the SIP registrar REGISTER request from the UA and forwards it to the SIP registrar
[RFC3261]. After accepting the REGISTER request, the SIP registrar [RFC3261]. After accepting the REGISTER request, the SIP registrar
sends a 2xx response to the proxy, which forwards the response to the sends a 2xx response to the proxy, which forwards the response to the
UA. If the push notification request was triggered by a SIP request UA. If the push notification request was triggered by a SIP request
addressed towards the UA, the proxy can then forward the SIP request addressed towards the UA, the proxy can then forward the SIP request
to the UA using normal SIP routing procedures. In some cases the to the UA using normal SIP routing procedures. In some cases, the
proxy can forward the SIP request without waiting for the SIP 2xx proxy can forward the SIP request without waiting for the SIP 2xx
response to the REGISTER request from the SIP registrar. Note that response to the REGISTER request from the SIP registrar. Note that
this mechanism necessarily adds delay to responding to requests this mechanism necessarily adds delay to responding to requests
requiring push notification. The consequences of that delay are requiring push notification. The consequences of that delay are
discussed in Section 5.6.2. discussed in Section 5.6.2.
If there are Network Address Translators (NATs) between the UA and If there are Network Address Translators (NATs) between the UA and
the proxy, the REGISTER request sent by the UA will create NAT the proxy, the REGISTER request sent by the UA will create NAT
bindings that will allow the incoming SIP request that triggered the bindings that will allow the incoming SIP request that triggered the
push notification to reach the UA. push notification to reach the UA.
NOTE: The lifetime of any NAT binding created by the REGISTER request NOTE: The lifetime of any NAT binding created by the REGISTER request
only needs to be long enough in order for the SIP request that only needs to be long enough for the SIP request that triggered the
triggered the push notification to reach the UA. push notification to reach the UA.
Figure 1 shows the generic push notification architecture supported Figure 1 shows the generic push notification architecture supported
by the mechanism in this document. by the mechanism in this document.
The SIP proxy MUST be in the signalling path of REGISTER requests The SIP proxy MUST be in the signaling path of REGISTER requests sent
sent by the UA towards the registrar, and of SIP requests (for a new by the UA towards the registrar, and of SIP requests (for a new
dialog or a stand-alone) forwarded by the proxy responsible for the dialog or a standalone) forwarded by the proxy responsible for the
UA's domain (sometimes referred to as home proxy, S-CSCF, etc.) UA's domain (sometimes referred to as home proxy, Serving Call
towards the UA. The proxy can also be co-located with the proxy Session Control Function (S-CSCF), etc.) towards the UA. The proxy
responsible for the UA's domain. This will also ensure that the can also be co-located with the proxy responsible for the UA's
Request-URI of SIP requests (for a new dialog or a stand-alone) can domain. This will also ensure that the Request-URI of SIP requests
be matched against contacts in REGISTER requests. (for a new dialog or a standalone) can be matched against contacts in
REGISTER requests.
+--------+ +---------+ +-----------+ +-------------+ +--------+ +---------+ +-----------+ +-------------+
| | | | | | | SIP | | | | | | | | SIP |
| SIP UA | | Push | | SIP Proxy | | Registrar / | | SIP UA | | Push | | SIP Proxy | | Registrar / |
| | | Service | | | | Home Proxy | | | | Service | | | | Home Proxy |
+--------+ +---------+ +-----------+ +-------------+ +--------+ +---------+ +-----------+ +-------------+
| | | | | | | |
| Subscribe | | | | Subscribe | | |
|---------------->| | | |---------------->| | |
| | | | | | | |
skipping to change at page 6, line 13 skipping to change at page 7, line 27
| SIP REGISTER (PRID) | | | SIP REGISTER (PRID) | |
|===================================>| | |===================================>| |
| | |SIP REGISTER (PRID)| | | |SIP REGISTER (PRID)|
| | |==================>| | | |==================>|
| | | | | | | |
| | | SIP 200 OK | | | | SIP 200 OK |
| | |<==================| | | |<==================|
| SIP 200 OK | | | | SIP 200 OK | | |
|<===================================| | |<===================================| |
| | | | | | | |
| | | |
| | | |
| | | SIP INVITE (PRID) | | | | SIP INVITE (PRID) |
| | |<==================| | | |<==================|
| | | | | | | |
| |Push Request (PRID) | | |Push Request (PRID) |
| |<-----------------| | | |<-----------------| |
|Push Message (PRID) | | |Push Message (PRID) | |
|<----------------| | | |<----------------| | |
| | | | | | | |
| SIP REGISTER (PRID) | | | SIP REGISTER (PRID) | |
|===================================>| | |===================================>| |
skipping to change at page 7, line 27 skipping to change at page 8, line 27
pn-prid=ZTY4ZDJlMzODE1NmUgKi0K> pn-prid=ZTY4ZDJlMzODE1NmUgKi0K>
Expires: 7200 Expires: 7200
Content-Length: 0 Content-Length: 0
Figure 2: SIP REGISTER Example Figure 2: SIP REGISTER Example
2. Conventions 2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in
14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
3. Push Resource ID (PRID) 3. Push Resource ID (PRID)
When a SIP UA registers with a PNS it receives a unique Push Resource When a SIP UA registers with a PNS it receives a unique Push Resource
ID (PRID), which is a value associated with the registration that can ID (PRID), which is a value associated with the registration that can
be used to generate push notifications. be used to generate push notifications.
The format of the PRID varies depending on the PNS. The format of the PRID varies depending on the PNS.
The details regarding discovery of the PNS, and the procedures The details regarding discovery of the PNS, and the procedures
regarding the push notification registration and maintenance are regarding the push notification registration and maintenance, are
outside the scope of this document. The information needed to outside the scope of this document. The information needed to
contact the PNS is typically pre-configured in the operating system contact the PNS is typically preconfigured in the operating system of
of the device. the device.
4. SIP User Agent (UA) Behavior 4. SIP User Agent (UA) Behavior
4.1. REGISTER 4.1. REGISTER
This section describes how a SIP UA sends SIP REGISTER requests This section describes how a SIP UA sends SIP REGISTER requests
(either an initial REGISTER request for a binding or a binding- (either an initial REGISTER request for a binding or a binding-
refresh REGISTER request) in order to request and disable push refresh REGISTER request) in order to request and disable push
notifications from a SIP network, and to query the types of PNSs notifications from a SIP network, and to query the types of PNSs
supported by the SIP network. supported by the SIP network.
Unless specified otherwise, the normal SIP UA registration procedures Unless specified otherwise, the normal SIP UA registration procedures
[RFC3261] apply. The additional procedures described in this section [RFC3261] apply. The additional procedures described in this section
apply when the REGISTER request contains a pn-provider SIP URI apply when the REGISTER request contains a 'pn-provider' SIP URI
parameter in the Contact header field URI (Figure 2). parameter in the Contact header field URI (Figure 2).
The procedures in this section apply to individual bindings The procedures in this section apply to individual bindings
[RFC3261]. If a UA creates multiple bindings (e.g., one for IPv4 and [RFC3261]. If a UA creates multiple bindings (e.g., one for IPv4 and
one for IPv6) the UA needs to perform the procedures for each one for IPv6), the UA needs to perform the procedures for each
binding. binding.
NOTE: Since a push notification will trigger the UA to refresh all NOTE: Since a push notification will trigger the UA to refresh all
bindings, if a SIP UA has created multiple bindings, it is preferable bindings, if a SIP UA has created multiple bindings, it is preferable
if one can ensure that all bindings expire at the same time to help if one can ensure that all bindings expire at the same time to help
prevent some bindings from being refreshed earlier than needed. prevent some bindings from being refreshed earlier than needed.
For privacy and security reasons, a UA MUST NOT insert the SIP URI For privacy and security reasons, a UA MUST NOT insert the SIP URI
parameters (except for the pn-purr parameter) defined in this parameters (except for the 'pn-purr' parameter) defined in this
specification in non-REGISTER requests in order to prevent the PNS specification in non-REGISTER requests in order to prevent the PNS
information associated with the UA from reaching the remote peer. information associated with the UA from reaching the remote peer.
For example, the UA MUST NOT insert the pn-prid SIP URI parameter in For example, the UA MUST NOT insert the 'pn-prid' SIP URI parameter
the Contact header field URI of an INVITE request. REGISTER requests in the Contact header field URI of an INVITE request. REGISTER
will not reach the remote peer, as they will be terminated by the requests will not reach the remote peer, as they will be terminated
registrar of the UA. However, the registrar MUST still ensure that by the registrar of the UA. However, the registrar MUST still ensure
the parameters are not sent to other users, e.g., using the SIP event that the parameters are not sent to other users, e.g., using the
package for registrations mechanism [RFC3680]. See Section 13 for mechanism defined by the SIP event package for registrations
more information. [RFC3680]. See Section 13 for more information.
4.1.1. Request Push Notifications 4.1.1. Request Push Notifications
This section describes the procedures that a SIP UA follows to This section describes the procedures that a SIP UA follows to
request push notifications from the SIP network. The procedures request push notifications from the SIP network. The procedures
assume that the UA has retrieved a PRID from a PNS. The procedures assume that the UA has retrieved a PRID from a PNS. The procedures
for retrieving the PRID from the PNS are PNS-specific and outside the for retrieving the PRID from the PNS are PNS-specific and outside the
scope of this specification. See PNS-specific documentation for more scope of this specification. See PNS-specific documentation for more
details. details.
This specification does not define a mechanism to explicitly request This specification does not define a mechanism to explicitly request
push notifications from the SIP network for usages other than push notifications from the SIP network for usages other than
triggering binding-refresh REGISTER requests (e.g., for sending triggering binding-refresh REGISTER requests (e.g., for sending
periodic subscription-refresh SUBSCRIBE requests [RFC6665]), nor does periodic subscription-refresh SUBSCRIBE requests [RFC6665]), nor does
it describe how to distinguish push notifications associated with it describe how to distinguish push notifications associated with
such usages from the push notifications used to trigger binding- such usages from the push notifications used to trigger binding-
refresh REGISTER requests. If a SIP UA wants to use push refresh REGISTER requests. If a SIP UA wants to use push
notifications for other usages, the UA can perform actions associated notifications for other usages, the UA can perform actions associated
with such usages (in addition to sending a binding-refresh REGISTER with such usages (in addition to sending a binding-refresh REGISTER
request) whenever it receives a push notification by using the same request) whenever it receives a push notification by using the same
refresh interval that is used for the binding-refreshes. refresh interval that is used for the binding refreshes.
To request push notifications from the SIP network, the UA MUST To request push notifications from the SIP network, the UA MUST
insert the following SIP URI parameters in the SIP Contact header insert the following SIP URI parameters in the SIP Contact header
field URI of the REGISTER request: pn-provider, pn-prid and pn-param field URI of the REGISTER request: 'pn-provider', 'pn-prid', and
(if required for the specific PNS). The pn-provider URI parameter 'pn-param' (if required for the specific PNS). The 'pn-provider' URI
indicates the type of PNS to be used for the push notifications. parameter indicates the type of PNS to be used for the push
notifications.
If the UA receives a 2xx response to the REGISTER request that If the UA receives a 2xx response to the REGISTER request that
contains a Feature-Caps header field [RFC6809] with a 'sip.pns' contains a Feature-Caps header field [RFC6809] with a 'sip.pns'
feature-capability indicator, with an indicator value identifying the feature-capability indicator, with an indicator value identifying the
same type of PNS that was identified by the pn-provider URI parameter same type of PNS that was identified by the 'pn-provider' URI
in the REGISTER request, it indicates that another SIP Proxy in the parameter in the REGISTER request, it indicates that another SIP
SIP network will request that push notifications are sent to the UA. Proxy in the SIP network will request that push notifications are
In addition, if the same Feature-Caps header field contains a sent to the UA. In addition, if the same Feature-Caps header field
'sip.vapid' feature-capability indicator, it indicates that the proxy contains a 'sip.vapid' feature-capability indicator, it indicates
supports use of the Voluntary Application Server Identification that the proxy supports use of the Voluntary Application Server
(VAPID) mechanism [RFC8292] to restrict push notifications to the UA. Identification (VAPID) mechanism [RFC8292] to restrict push
notifications to the UA.
NOTE: The VAPID specific procedures of the SIP UA are outside the NOTE: The VAPID-specific procedures of the SIP UA are outside the
scope of this document. scope of this document.
If the UA receives a non-2xx response to the REGISTER, or if the UA If the UA receives a non-2xx response to the REGISTER, or if the UA
receives a 2xx response that does not contain a Feature-Caps header receives a 2xx response that does not contain a Feature-Caps header
field [RFC6809] with a 'sip.pns' feature-capability indicator, the UA field [RFC6809] with a 'sip.pns' feature-capability indicator, the UA
MUST NOT assume the proxy will request that push notifications are MUST NOT assume the proxy will request that push notifications are
sent to the UA. The actions taken by the UA in such cases are sent to the UA. The actions taken by the UA in such cases are
outside the scope of this document. outside the scope of this document.
If the PRID is only valid for a limited time then the UA is If the PRID is only valid for a limited time, then the UA is
responsible for retrieving a new PRID from the PNS and sending a responsible for retrieving a new PRID from the PNS and sending a
binding-refresh REGISTER request with the updated pn- parameters. If binding-refresh REGISTER request with the updated 'pn-*' parameters.
a PRID is no longer valid, and the UA is not able to retrieve a new If a PRID is no longer valid, and the UA is not able to retrieve a
PRID, the UA MUST disable the push notifications associated with the new PRID, the UA MUST disable the push notifications associated with
PRID (Section 4.1.2). the PRID (Section 4.1.2).
4.1.2. Disable Push Notifications 4.1.2. Disable Push Notifications
When a UA wants to disable previously requested push notifications, When a UA wants to disable previously requested push notifications,
the UA SHOULD remove the binding [RFC3261], unless the UA is no the UA SHOULD remove the binding [RFC3261], unless the UA is no
longer able to perform SIP procedures (e.g., due to a forced shutdown longer able to perform SIP procedures (e.g., due to a forced shutdown
of the UA) in which case the registrar will remove the binding once of the UA), in which case the registrar will remove the binding once
it expires. When the UA sends the REGISTER request for removing the it expires. When the UA sends the REGISTER request for removing the
binding, the UA MUST NOT insert the pn-prid SIP URI parameter in the binding, the UA MUST NOT insert the 'pn-prid' SIP URI parameter in
Contact header field URI of the REGISTER request, in order to inform the Contact header field URI of the REGISTER request. The lack of
the SIP network that the UA no longer wants to receive push the parameter informs the SIP network that the UA no longer wants to
notifications associated with the PRID. receive push notifications associated with the PRID.
4.1.3. Receive Push Notifications 4.1.3. Receive Push Notifications
When a UA receives a push notification, the UA MUST send a binding- When a UA receives a push notification, the UA MUST send a binding-
refresh REGISTER request. The UA MUST insert the same set of pn- SIP refresh REGISTER request. The UA MUST insert the same set of 'pn-*'
URI parameters in the SIP Contact header field URI of the REGISTER SIP URI parameters in the SIP Contact header field URI of the
request that it inserted when it requested push notifications REGISTER request that it inserted when it requested push
(Section 4.1.1). Note that, in some cases the PNS might update the notifications (Section 4.1.1). Note that, in some cases, the PNS
PRID value, in which case the UA will insert the new value in the pn- might update the PRID value, in which case the UA will insert the new
prid SIP URI parameter of the binding-refresh REGISTER request. value in the 'pn-prid' SIP URI parameter of the binding-refresh
REGISTER request.
Once the UA has received a 2xx response to the REGISTER request, the Once the UA has received a 2xx response to the REGISTER request, the
UA might receive a SIP request for a new dialog (e.g., a SIP INVITE), UA might receive a SIP request for a new dialog (e.g., a SIP INVITE)
or a stand-alone SIP request (e.g., a SIP MESSAGE), if such SIP or a standalone SIP request (e.g., a SIP MESSAGE) if such a SIP
request triggered the proxy to request that the push notification was request triggered the proxy to request that the push notification was
sent to the UA. Note that, depending on which transport protocol is sent to the UA. Note that, depending on which transport protocol is
used, the SIP request might reach the UA before the REGISTER used, the SIP request might reach the UA before the REGISTER
response. response.
If the SIP UA has created multiple bindings, the UA MUST send a If the SIP UA has created multiple bindings, the UA MUST send a
binding-refresh REGISTER request for each of those bindings when it binding-refresh REGISTER request for each of those bindings when it
receives a push notification. receives a push notification.
This specification does not define any usage of push notification This specification does not define any usage of push-notification
payload. If a SIP UA receives a push notification that contains a payload. If a SIP UA receives a push notification that contains a
payload the UA can discard the payload, but the UA will still send a payload, the UA can discard the payload but will still send a
binding-refresh REGISTER request. binding-refresh REGISTER request.
4.1.4. Sending Binding-Refresh Requests Using Non-Push Mechanism 4.1.4. Sending Binding-Refresh Requests Using Non-push Mechanism
If a UA is able to send binding-refresh REGISTER requests using a If a UA is able to send binding-refresh REGISTER requests using a
non-push mechanism (e.g., using an internal timer that periodically non-push mechanism (e.g., using an internal timer that periodically
wakes the UA) the UA MUST insert a 'sip.pnsreg' media feature tag wakes the UA), the UA MUST insert a 'sip.pnsreg' media feature tag
[RFC3840] in the Contact header field of each REGISTER request. [RFC3840] in the Contact header field of each REGISTER request.
If the UA receives a 2xx response to the REGISTER request that If the UA receives a 2xx response to the REGISTER request that
contains a Feature-Caps header field with a 'sip.pnsreq' feature- contains a Feature-Caps header field with a 'sip.pnsreq' feature-
capability indicator, the UA MUST send a binging-refresh REGISTER capability indicator, the UA MUST send a binding-refresh REGISTER
request prior to binding expiration. The indicator value indicates request prior to binding expiration. The indicator value indicates
the minimum time (given in seconds), prior to the binding expiration the minimum time (given in seconds), prior to the binding expiration
when the UA needs to send the REGISTER request. when the UA needs to send the REGISTER request.
If the UA receives a 2xx response to the REGISTER request that does If the UA receives a 2xx response to the REGISTER request that does
not contain a Feature-Caps header field with a 'sip.pnsreq' feature- not contain a Feature-Caps header field with a 'sip.pnsreq' feature-
capability indicator, the UA SHOULD only send a binding-refresh capability indicator, the UA SHOULD only send a binding-refresh
REGISTER request when it receives a push notification (even if the UA REGISTER request when it receives a push notification (even if the UA
is able to use a non-push mechanism for sending binding-refresh is able to use a non-push mechanism for sending binding-refresh
REGISTER requests), or when there are circumstances (e.g., if the UA REGISTER requests) or when there are circumstances that require an
is assigned new contact parameters due to a network configuration immediate REGISTER request to be sent (e.g., if the UA is assigned
change) that require an immediate REGISTER request to be sent. new contact parameters due to a network configuration change).
Even if the UA is able to to send binding-refresh REGISTER requests Even if the UA is able to send binding-refresh REGISTER requests
using a non-push mechanism, the UA MUST still send a binding-refresh using a non-push mechanism, the UA MUST still send a binding-refresh
REGISTER request whenever it receives a push notification REGISTER request whenever it receives a push notification
(Section 4.1.3). (Section 4.1.3).
NOTE: If the UA uses a non-push mechanism to wake and send binding- NOTE: If the UA uses a non-push mechanism to wake and send binding-
refresh REGISTER requests, such REGISTER requests will update the refresh REGISTER requests, such REGISTER requests will update the
binding expiration timer, and the proxy does not need to request that binding expiration timer, and the proxy does not need to request that
a push notification be sent to the UA in order to wake the UA. The a push notification be sent to the UA in order to wake the UA. The
proxy will still request that a push notification be sent to the UA proxy will still request that a push notification be sent to the UA
when the proxy receives a SIP request addressed towards the UA when the proxy receives a SIP request addressed towards the UA
(Section 5.6.2). This allows the UA to e.g., use timers for sending (Section 5.6.2). This allows the UA to, e.g., use timers for sending
binding-refresh REGISTER requests, but to be suspended (in order to binding-refresh REGISTER requests but be suspended (in order to save
save battery resources, etc.) between sending the REGISTER requests battery resources, etc.) between sending the REGISTER requests and
and use push notification to wake the UA to process incoming calls. using push notifications to wake the UA to process incoming calls.
Example of a SIP REGISTER request including a 'sip.pnsreg' Example of a SIP REGISTER request including a 'sip.pnsreg'
media feature tag: media feature tag:
REGISTER sip:alice@example.com SIP/2.0 REGISTER sip:alice@example.com SIP/2.0
Via: SIP/2.0/TCP alicemobile.example.com:5060;branch=z9hG4bKnashds7 Via: SIP/2.0/TCP alicemobile.example.com:5060;branch=z9hG4bKnashds7
Max-Forwards: 70 Max-Forwards: 70
To: Alice <sip:alice@example.com> To: Alice <sip:alice@example.com>
From: Alice <sip:alice@example.com>;tag=456248 From: Alice <sip:alice@example.com>;tag=456248
Call-ID: 843817637684230@998sdasdh09 Call-ID: 843817637684230@998sdasdh09
skipping to change at page 12, line 41 skipping to change at page 13, line 41
CSeq: 1826 REGISTER CSeq: 1826 REGISTER
Contact: <sip:alice@alicemobile.example.com; Contact: <sip:alice@alicemobile.example.com;
pn-provider=acme; pn-provider=acme;
pn-param=acme-param; pn-param=acme-param;
pn-prid=ZTY4ZDJlMzODE1NmUgKi0K>; pn-prid=ZTY4ZDJlMzODE1NmUgKi0K>;
+sip.pnsreg +sip.pnsreg
Feature-Caps: *;+sip.pns="acme";+sip.pnsreg="121" Feature-Caps: *;+sip.pns="acme";+sip.pnsreg="121"
Expires: 7200 Expires: 7200
Content-Length: 0 Content-Length: 0
Figure 3: SIP REGISTER When Using Non-Push Mechanism Example Figure 3: SIP REGISTER When Using Non-push Mechanism Example
4.1.5. Query Network PNS Capabilities 4.1.5. Query Network PNS Capabilities
This section describes how a SIP UA can query the types of PNSs This section describes how a SIP UA can query the types of PNSs
supported by a SIP network, and PNS-related capabilities (e.g., supported by a SIP network, and PNS-related capabilities (e.g.,
support of the VAPID mechanism). When a UA performs a query, it does support of the VAPID mechanism). When a UA performs a query, it does
not request push notifications from the SIP network. Therefore, the not request push notifications from the SIP network. Therefore, the
UA can perform the query before it has registered to a PNS and UA can perform the query before it has registered to a PNS and
received a PRID. received a PRID.
In order to perform a query, the UA MUST insert a pn-provider SIP URI In order to perform a query, the UA MUST insert a 'pn-provider' SIP
parameter in the Contact header field URI of the REGISTER request: URI parameter in the Contact header field URI of the REGISTER
request:
o If the UA inserts a pn-provider parameter value, indicating o If the UA inserts a 'pn-provider' parameter value, indicating
support of a type of PNS, the SIP network will only inform the UA support of a type of PNS, the SIP network will only inform the UA
whether that type of PNS is supported. whether that type of PNS is supported.
o If the UA does not insert a pn-provider parameter value (i.e., it
inserts an "empty" pn-provider parameter) the SIP network will
inform the UA about all types of PNSs supported by the network.
This is useful e.g., if the UA supports more than one type of PNS.
Note that it is not possible to insert multiple parameter values
in the pn-provider parameter.
The UA MUST NOT insert a pn-prid SIP URI parameter in the Contact o If the UA does not insert a 'pn-provider' parameter value (i.e.,
it inserts an "empty" 'pn-provider' parameter), the SIP network
will inform the UA about all types of PNSs supported by the
network. This is useful, e.g., if the UA supports more than one
type of PNS. Note that it is not possible to insert multiple
parameter values in the 'pn-provider' parameter.
The UA MUST NOT insert a 'pn-prid' SIP URI parameter in the Contact
header field URI of the REGISTER request. header field URI of the REGISTER request.
If the UA receives a 2xx response to the REGISTER request, the If the UA receives a 2xx response to the REGISTER request, the
response will contain one or more Feature-Caps header fields with a response will contain one or more Feature-Caps header fields with a
'sip.pns' feature-capability indicator, indicating the types of PNSs 'sip.pns' feature-capability indicator, indicating the types of PNSs
supported by the SIP network. If the UA inserted a pn-provider SIP supported by the SIP network. If the UA inserted a 'pn-provider' SIP
URI parameter value in the REGISTER request, the response will only URI parameter value in the REGISTER request, the response will only
indicate whether the SIP network supports the type of PNS supported indicate whether the SIP network supports the type of PNS supported
by the UA. by the UA.
If the UA receives a 555 (Push Notification Service Not Supported) If the UA receives a 555 (Push Notification Service Not Supported)
response to the REGISTER request, and if the UA inserted a pn- response to the REGISTER request, and if the UA inserted a
provider SIP URI parameter in the REGISTER request, the response 'pn-provider' SIP URI parameter in the REGISTER request, the response
indicates that the network does not support the type of PNS that the indicates that the network does not support the type of PNS that the
UA indicated support of. If the UA did not insert a pn-provider UA indicated support of. If the UA did not insert a 'pn-provider'
parameter in the REGISTER request, the response indicates that the parameter in the REGISTER request, the response indicates that the
network does not support any type of PNS, while still supporting the network does not support any type of PNS while still supporting the
555 (Push Notification Service Not Supported) response. 555 (Push Notification Service Not Supported) response.
NOTE: It is optional for a UA to perform a query before it requests NOTE: It is optional for a UA to perform a query before it requests
push notifications from the SIP network. push notifications from the SIP network.
5. SIP Proxy Behavior 5. SIP Proxy Behavior
5.1. PNS Provider 5.1. PNS Provider
The type of PNS is identified by the pn-provider SIP URI parameter. The type of PNS is identified by the 'pn-provider' SIP URI parameter.
In some cases there might only be one PNS provider for a given type In some cases, there might only be one PNS provider for a given type
of PNS, while in other cases there might be multiple providers. The of PNS, while in other cases there might be multiple providers. The
pn-param SIP URI parameter will provide more details associated with 'pn-param' SIP URI parameter will provide more details associated
the actual PNS provider to be used. with the actual PNS provider to be used.
The protocol and format used for the push notification requests are The protocol and format used for the push notification requests are
PNS-specific, and the details for constructing and sending a push PNS-specific, and the details for constructing and sending a push
notification request are outside the scope of this specification. notification request are outside the scope of this specification.
5.2. SIP Request Push Bucket 5.2. SIP Request Push Bucket
When a SIP proxy receives a SIP request addressed towards a UA, that When a SIP proxy receives a SIP request addressed towards a UA, that
will trigger the proxy to request that a push notification be sent to will trigger the proxy to request that a push notification be sent to
the UA. The proxy will place the request in storage referred to as the UA. The proxy will place the request in storage (referred to as
the SIP Request Push Bucket, and the proxy starts a timer (referred the SIP Request Push Bucket) and the proxy will start a timer
to as the Bucket Timer) associated with the transaction. A SIP (referred to as the Bucket Timer) associated with the transaction. A
request is removed from the bucket when one of the following has SIP request is removed from the bucket when one of the following has
occurred: the proxy forwards the request towards the UA, when the occurred: the proxy forwards the request towards the UA, the proxy
proxy sends an error response to the request, or when the Bucket sends an error response to the request, or the Bucket Timer times
Timer times out. The detailed procedures are described in the out. The detailed procedures are described in the sections below.
sections below.
Exactly how the SIP Request Push Bucket is implemented is outside the Exactly how the SIP Request Push Bucket is implemented is outside the
scope of this document. One option is to use the PRID as a key to scope of this document. One option is to use the PRID as a key to
search for SIP requests in the bucket. Note that mid-dialog requests search for SIP requests in the bucket. Note that mid-dialog requests
(Section 6) do not carry the PRID in the SIP request itself. (Section 6) do not carry the PRID in the SIP request itself.
5.3. SIP URI Comparison Rules 5.3. SIP URI Comparison Rules
By default, a SIP proxy uses the URI comparison rules defined in By default, a SIP proxy uses the URI comparison rules defined in
[RFC3261]. However, when a SIP proxy compares the Contact header [RFC3261]. However, when a SIP proxy compares the Contact header
field URI of a 2xx response to a REGISTER request with a Request-URI field URI of a 2xx response to a REGISTER request with a Request-URI
of a SIP request in the SIP Request Push Bucket (Section 5.2), the of a SIP request in the SIP Request Push Bucket (Section 5.2), the
proxy uses the URI comparison rules with the following additions: the proxy uses the URI comparison rules with the following additions: the
pn-prid, pn-provider and pn-param SIP URI parameters MUST also match. 'pn-prid', 'pn-provider', and 'pn-param' SIP URI parameters MUST also
If a pn- parameter is present in one of the compared URIs but not in match. If a 'pn-*' parameter is present in one of the compared URIs
the other URI, there is no match. but not in the other URI, there is no match.
If only the pn- SIP URI parameters listed above match, but other If only the 'pn-*' SIP URI parameters listed above match, but other
parts of the compared URIs do not match, a proxy MAY still consider parts of the compared URIs do not match, a proxy MAY still consider
the comparison successful based on local policy. This can occur in a the comparison successful based on local policy. This can occur in a
race condition when the proxy compares the Contact header field URI race condition when the proxy compares the Contact header field URI
of a 2xx response to a REGISTER request with a Request-URI of a SIP of a 2xx response to a REGISTER request with a Request-URI of a SIP
request in the SIP Request Push Bucket (Section 5.2), if the UA had request in the SIP Request Push Bucket (Section 5.2) if the UA had
modified some parts of the Contact header field URI in the REGISTER modified some parts of the Contact header field URI in the REGISTER
request but the Request-URI of the SIP request in the SIP Request request but the Request-URI of the SIP request in the SIP Request
Push Bucket still contains the old parts. Push Bucket still contains the old parts.
5.4. Indicate Support of Type of PNS 5.4. Indicate Support of Type of PNS
A SIP proxy uses feature-capability indicators [RFC6809] to indicate A SIP proxy uses feature-capability indicators [RFC6809] to indicate
support of types of PNSs and additional features (e.g., VAPID) support of types of PNSs and additional features (e.g., VAPID)
associated associated with the type of PNS. A proxy MUST use a associated with the type of PNS. A proxy MUST use a separate
separate Feature-Cap header field for each supported type of PNS. A Feature-Cap header field for each supported type of PNS. A feature-
feature-capability indicator that indicates support of an additional capability indicator that indicates support of an additional feature
feature associated with a given type of PNS MUST be inserted in the associated with a given type of PNS MUST be inserted in the same
same Feature-Caps header field that is used to indicate support of Feature-Caps header field that is used to indicate support of the
the type of PNS. type of PNS.
This specification defines the following feature-capability This specification defines the following feature-capability
indicators that a proxy can use to indicate support of additional indicators that a proxy can use to indicate support of additional
features associated with a given type of PNS: 'sip.vapid', features associated with a given type of PNS: 'sip.vapid',
'sip.pnsreg' and 'sip.pnspurr'. These feature-capability indicators 'sip.pnsreg', and 'sip.pnspurr'. These feature-capability indicators
MUST only be inserted in a Feature-Caps header field that also MUST only be inserted in a Feature-Caps header field that also
contains a 'sip.pns' feature-capability indicator. contains a 'sip.pns' feature-capability indicator.
5.5. Trigger Periodic Binding Refresh 5.5. Trigger Periodic Binding Refresh
In order to request that a push notification be sent to a SIP UA, a In order to request that a push notification be sent to a SIP UA, a
SIP proxy needs to have information about when a binding will expire. SIP proxy needs to have information about when a binding will expire.
The proxy needs to be able to retrieve the information from the The proxy needs to be able to retrieve the information from the
registrar using some mechanism, or run its own registration timers. registrar using some mechanism or run its own registration timers.
Such mechanisms are outside the scope of this document, but could be Such mechanisms are outside the scope of this document but could be
implemented e.g., using the SIP event package for registrations implemented, e.g., by using the SIP event package for registrations
mechanism [RFC3680]. mechanism [RFC3680].
When the proxy receives an indication that the UA needs to send a When the proxy receives an indication that the UA needs to send a
binding-refresh REGISTER request, the proxy will request that a push binding-refresh REGISTER request, the proxy will request that a push
notification be sent to the UA. notification be sent to the UA.
Note that the push notification needs to be requested early enough Note that the push notification needs to be requested early enough
for the associated binding-refresh REGISTER request to reach the for the associated binding-refresh REGISTER request to reach the
registrar before the binding expires. It is RECOMMENDED that the registrar before the binding expires. It is RECOMMENDED that the
proxy requests the push notification at least 120 seconds before the proxy requests the push notification at least 120 seconds before the
binding expires. binding expires.
If the UA has indicated, using the 'sip.pnsreg' media feature tag, If the UA has indicated, using the 'sip.pnsreg' media feature tag,
that it is able to wake itself using a non-push mechanism in order to that it is able to wake itself using a non-push mechanism in order to
send binding-refresh REGISTER requests, and if the proxy does not send binding-refresh REGISTER requests, and if the proxy does not
receive a REGISTER request prior to 120 seconds before the binding receive a REGISTER request prior to 120 seconds before the binding
expires, the proxy MAY request that a push notification be sent to expires, the proxy MAY request that a push notification be sent to
the UA, to trigger the UA to send a binding-refresh REGISTER request. the UA to trigger the UA to send a binding-refresh REGISTER request.
NOTE: As described in Section 4.1.5, a UA might send a REGISTER NOTE: As described in Section 4.1.5, a UA might send a REGISTER
request without including a pn-prid SIP URI parameter, in order to request without including a 'pn-prid' SIP URI parameter in order to
retrieve push notification capabilities from the network before the retrieve push notification capabilities from the network before the
UA expects to receive push notifications from the network. A proxy UA expects to receive push notifications from the network. A proxy
will not request that push notifications are sent to a UA that has will not request that push notifications are sent to a UA that has
not provided a pn-prid SIP URI parameter (Section 5.6.2). not provided a 'pn-prid' SIP URI parameter (Section 5.6.2).
If the proxy receives information that a binding associated with a If the proxy receives information that a binding associated with a
PRID has expired, or that a binding has been removed, the proxy MUST PRID has expired, or that a binding has been removed, the proxy MUST
NOT request that further push notifications are sent to the UA using NOT request that further push notifications are sent to the UA using
that PRID. that PRID.
5.6. SIP Requests 5.6. SIP Requests
5.6.1. REGISTER 5.6.1. REGISTER
This section describes how a SIP proxy processes SIP REGISTER This section describes how a SIP proxy processes SIP REGISTER
requests (initial REGISTER request for a binding, or a binding- requests (initial REGISTER request for a binding or a binding-refresh
refresh REGISTER request). REGISTER request).
The procedures in this section apply when the REGISTER request The procedures in this section apply when the REGISTER request
contains a pn-provider SIP URI parameter in the Contact header field contains a 'pn-provider' SIP URI parameter in the Contact header
URI. In other cases the proxy MUST skip the procdeures in this field URI. In other cases, the proxy MUST skip the procedures in
section, and process the REGISTER request using normal SIP this section and process the REGISTER request using normal SIP
procedures. procedures.
5.6.1.1. Request Push Notifications 5.6.1.1. Request Push Notifications
This section describes the SIP proxy procedures when a SIP UA This section describes the SIP proxy procedures when a SIP UA
requests push notifications from the SIP network. requests push notifications from the SIP network.
The procedures in this section apply when the SIP REGISTER request The procedures in this section apply when the SIP REGISTER request
contains, in addition to the pn-provider SIP URI parameter, a pn-prid contains, in addition to the 'pn-provider' SIP URI parameter, a
SIP URI parameter in the Contact header field URI of the request. 'pn-prid' SIP URI parameter in the Contact header field URI of the
request.
When a proxy receives a REGISTER request that contains a Feature-Caps When a proxy receives a REGISTER request that contains a Feature-Caps
header field with a 'sip.pns' feature-capability indicator, it header field with a 'sip.pns' feature-capability indicator, it
indicates that another proxy between this proxy and the UA supports indicates that another proxy between this proxy and the UA supports
the type of PNS supported by the UA, and will request that push the type of PNS supported by the UA, and will request that push
notifications are sent to the UA. In such case, the proxy MUST skip notifications are sent to the UA. In such case, the proxy MUST skip
the rest of the procedures in this section, and process the REGISTER the rest of the procedures in this section and process the REGISTER
request using normal SIP procedures. request using normal SIP procedures.
When a proxy receives a REGISTER request that does not contain a When a proxy receives a REGISTER request that does not contain a
Feature-Caps header field with a 'sip.pns' feature-capability Feature-Caps header field with a 'sip.pns' feature-capability
indicator, the proxy processes the request according to the indicator, the proxy processes the request according to the
procedures below: procedures below:
o If the proxy does not support the type of PNS supported by the UA, o If the proxy does not support the type of PNS supported by the UA,
or if the REGISTER request does not contain all information or if the REGISTER request does not contain all information
required for the type of PNS, the proxy SHOULD forward the request required for the type of PNS, the proxy SHOULD forward the request
skipping to change at page 18, line 8 skipping to change at page 19, line 15
* If the proxy received a 'sip.pnsreg' media feature tag in the * If the proxy received a 'sip.pnsreg' media feature tag in the
REGISTER request, the proxy SHOULD insert a 'sip.pnsreg' REGISTER request, the proxy SHOULD insert a 'sip.pnsreg'
feature-capability indicator with an indicator value bigger feature-capability indicator with an indicator value bigger
than 120 in the response, unless the proxy always wants to than 120 in the response, unless the proxy always wants to
request that push notifications are sent to the UA in order to request that push notifications are sent to the UA in order to
trigger the UA to send a binding-refresh REGISTER request. trigger the UA to send a binding-refresh REGISTER request.
5.6.1.2. Query Network PNS Capabilities 5.6.1.2. Query Network PNS Capabilities
This section describes the SIP proxy procedures when a SIP UA queries This section describes the SIP proxy procedures when a SIP UA queries
about the push notification support in the SIP network about the push-notification support in the SIP network
(Section 4.1.5). (Section 4.1.5).
The procedures in this section apply when the REGISTER request The procedures in this section apply when the REGISTER request
contains a pn-provider SIP URI parameter, but does not contain a pn- contains a 'pn-provider' SIP URI parameter, but does not contain a
prid SIP URI parameter in the Contact header field URI of the 'pn-prid' SIP URI parameter in the Contact header field URI of the
REGISTER request. REGISTER request.
When a proxy receives a REGISTER request that contains a pn-provider When a proxy receives a REGISTER request that contains a
SIP URI parameter indicating the type of PNS supported by the UA, the 'pn-provider' SIP URI parameter indicating the type of PNS supported
proxy MUST perform the following actions: by the UA, the proxy MUST perform the following actions:
o If the proxy supports the type of PNS supported by the UA, the o If the proxy supports the type of PNS supported by the UA, the
proxy MUST indicate support of that type of PNS (Section 5.4) in proxy MUST indicate support of that type of PNS (Section 5.4) in
the REGISTER request before it forwards the request towards the the REGISTER request before it forwards the request towards the
registrar. This will inform any other proxies between the proxy registrar. This will inform any other proxies between the proxy
and the registrar that the proxy supports the type of PNS and the registrar that the proxy supports the type of PNS
supported by the UA. supported by the UA.
o If the proxy does not support the type of PNS supported by the UA, o If the proxy does not support the type of PNS supported by the UA,
and if the REGISTER request contains Feature-Caps header fields and if the REGISTER request contains Feature-Caps header fields
indicating support of one or more types of PNSs, the proxy indicating support of one or more types of PNSs, the proxy
forwards the request towards the registrar. forwards the request towards the registrar.
o If the proxy does not support the type of PNS supported by the UA, o If the proxy does not support the type of PNS supported by the UA,
and if the REGISTER request does not contain Feature-Caps header and if the REGISTER request does not contain Feature-Caps header
fields indicating support of one or more types of PNSs, the proxy fields indicating support of one or more types of PNSs, the proxy
MUST either forward the request towards the registrar, or send a MUST either forward the request towards the registrar or send a
SIP 555 (Push Notification Service Not Supported) response towards SIP 555 (Push Notification Service Not Supported) response towards
the UA. The proxy MUST NOT send a SIP 555 (Push Notification the UA. The proxy MUST NOT send a SIP 555 (Push Notification
Service Not Supported) response unless it knows (by means of local Service Not Supported) response unless it knows (by means of local
configuration) that no other proxy supports any of the types of configuration) that no other proxy supports any of the types of
PNSs supported by the UA. PNSs supported by the UA.
When a proxy receives a REGISTER request, and the pn-provider SIP URI When a proxy receives a REGISTER request, and the 'pn-provider' SIP
parameter does not contain a parameter value, the proxy MUST indicate URI parameter does not contain a parameter value, the proxy MUST
support of each type of PNS supported by the proxy before it forwards indicate support of each type of PNS supported by the proxy before it
the request towards the registrar. forwards the request towards the registrar.
When a proxy receives a 2xx response to the REGISTER request, if the When a proxy receives a 2xx response to the REGISTER request, if the
proxy had indicated support of one or more types of PNSs in the proxy had indicated support of one or more types of PNSs in the
REGISTER request (see above), the proxy MUST indicate support of the REGISTER request (see above), the proxy MUST indicate support of the
same set of types of PNSs in the response. In addition, if the proxy same set of types of PNSs in the response. In addition, if the proxy
supports the VAPID mechanism for one or more types of PNSs, the proxy supports the VAPID mechanism for one or more types of PNSs, the proxy
MUST indicate support of the mechanism for those PNSs in the MUST indicate support of the mechanism for those PNSs in the
response. response.
5.6.2. Initial Request for Dialog or Stand-Alone Request 5.6.2. Initial Request for Dialog or Standalone Request
The procedures in this section apply when a SIP proxy has indicated The procedures in this section apply when a SIP proxy has indicated
that the it will request that push notifications are sent to the SIP that it will request that push notifications are sent to the SIP UA.
UA.
When the proxy receives a SIP request for a new dialog (e.g., a SIP When the proxy receives a SIP request for a new dialog (e.g., a SIP
INVITE request) or a stand-alone SIP request (e.g., a SIP MESSAGE INVITE request) or a standalone SIP request (e.g., a SIP MESSAGE
request) addressed towards a SIP UA, if the Request-URI of the request) addressed towards a SIP UA, if the Request-URI of the
request contains a pn-provider, a pn-prid and a pn-param (if required request contains a 'pn-provider', a 'pn-prid', and a 'pn-param' (if
for the specific PNS provider) SIP URI parameter, the proxy requests required for the specific PNS provider) SIP URI parameter, the proxy
that a push notification be sent to the UA using the information in requests that a push notification be sent to the UA using the
the pn- SIP URI parameters. The proxy then places the SIP request in information in the 'pn-*' SIP URI parameters. The proxy then places
the SIP Request Push Bucket. The push notification will trigger the the SIP request in the SIP Request Push Bucket. The push
UA to send a binding-refresh REGISTER request that the proxy will notification will trigger the UA to send a binding-refresh REGISTER
process as described in Section 5.6.1. In addition, the proxy MUST request that the proxy will process as described in Section 5.6.1.
store the Contact URI of the REGISTER request during the lifetime of In addition, the proxy MUST store the Contact URI of the REGISTER
the REGISTER transaction. request during the lifetime of the REGISTER transaction.
NOTE: If the proxy receives a SIP request that does not contain the NOTE: If the proxy receives a SIP request that does not contain the
pn- SIP URI parameters listed above, the proxy processing of the 'pn-*' SIP URI parameters listed above, the proxy processing of the
request is based on local policy. If the proxy also serves requests request is based on local policy. If the proxy also serves requests
for UAs that do not use the SIP push mechanism, the proxy can forward for UAs that do not use the SIP push mechanism, the proxy can forward
the request towards the UA. Otherwise the proxy can reject the the request towards the UA. Otherwise, the proxy can reject the
request. request.
When the proxy receives a 2xx response to the REGISTER request, the When the proxy receives a 2xx response to the REGISTER request, the
proxy performs the following actions: proxy performs the following actions:
o The proxy processes the REGISTER response as described in o The proxy processes the REGISTER response as described in
Section 5.6.1. Section 5.6.1.
o The proxy checks whether the SIP Request Push Bucket contains a o The proxy checks whether the SIP Request Push Bucket contains a
SIP request associated with the REGISTER transaction, by comparing SIP request associated with the REGISTER transaction by comparing
(Section 5.3) the Contact header field URI in the REGISTER (Section 5.3) the Contact header field URI in the REGISTER
response with the Request-URIs of the SIP requests in the bucket. response with the Request-URIs of the SIP requests in the bucket.
If there is a match, the proxy MUST remove the SIP request from If there is a match, the proxy MUST remove the SIP request from
the bucket and forward it towards the UA. the bucket and forward it towards the UA.
The reason the proxy needs to wait for the REGISTER response before The reason the proxy needs to wait for the REGISTER response before
forwarding a SIP request towards a UA is to make sure that the forwarding a SIP request towards a UA is to make sure that the
REGISTER request has been accepted by the registrar, and that the UA REGISTER request has been accepted by the registrar, and that the UA
that initiated the REGISTER request is authorized to receive messages that initiated the REGISTER request is authorized to receive messages
for the Request-URI. for the Request-URI.
skipping to change at page 20, line 10 skipping to change at page 21, line 21
If the proxy receives a non-2xx response to the REGISTER request, the If the proxy receives a non-2xx response to the REGISTER request, the
proxy compares the Contact URI stored from the REGISTER request (see proxy compares the Contact URI stored from the REGISTER request (see
above) with the Request-URIs of the SIP requests in the SIP Request above) with the Request-URIs of the SIP requests in the SIP Request
Push Bucket. If there is a match, the proxy SHOULD remove the Push Bucket. If there is a match, the proxy SHOULD remove the
associated request from the bucket and send an error response to the associated request from the bucket and send an error response to the
request. It is RECOMMENDED that the proxy sends either a 404 (Not request. It is RECOMMENDED that the proxy sends either a 404 (Not
Found) response or a 480 (Temporarily Unavailable) response to the Found) response or a 480 (Temporarily Unavailable) response to the
SIP request, but other response codes can be used as well. However, SIP request, but other response codes can be used as well. However,
if the REGISTER response is expected to trigger a new REGISTER if the REGISTER response is expected to trigger a new REGISTER
request from the UA (e.g., if the registrar is requesting the UA to request from the UA (e.g., if the registrar is requesting the UA to
perform authentication) the proxy MAY keep the SIP request in the perform authentication), the proxy MAY keep the SIP request in the
bucket. bucket.
If the push notification request fails (see PNS-specific If the push notification request fails (see PNS-specific
documentation for details), the proxy MUST remove the SIP request documentation for details), the proxy MUST remove the SIP request
from the bucket and send an error response to the SIP request. It is from the bucket and send an error response to the SIP request. It is
RECOMMENDED that the proxy sends either a 404 (Not Found) response or RECOMMENDED that the proxy sends either a 404 (Not Found) response or
a 480 (Temporarily Unavailable) response, but other response codes a 480 (Temporarily Unavailable) response, but other response codes
can be used as well. can be used as well.
After the proxy has requested that a push notification be sent to a After the proxy has requested that a push notification be sent to a
skipping to change at page 20, line 47 skipping to change at page 22, line 9
cause state misalignment between the endpoints (the sender considers cause state misalignment between the endpoints (the sender considers
the transaction a failure, while the receiver considers the the transaction a failure, while the receiver considers the
transaction a success). The SIP proxy needs to take this into transaction a success). The SIP proxy needs to take this into
account when it sets the value of the Bucket Timer associated with account when it sets the value of the Bucket Timer associated with
the transaction, to make sure that the error response (triggered by a the transaction, to make sure that the error response (triggered by a
Bucket Timer time out) reaches the sender before the transaction Bucket Timer time out) reaches the sender before the transaction
times out. If the accumulated delay of this mechanism combined with times out. If the accumulated delay of this mechanism combined with
any other mechanisms in the path of processing the non-INVITE any other mechanisms in the path of processing the non-INVITE
transaction cannot be kept short, this mechanism should not be used. transaction cannot be kept short, this mechanism should not be used.
For networks encountering such conditions, an alternative (left for For networks encountering such conditions, an alternative (left for
possible future work) would be for the proxy to immediately return an possible future work) would be for the proxy to immediately return a
new error code meaning "wait at least the number of seconds specified new error code meaning "wait at least the number of seconds specified
in this response, and retry your request" before initiating the push in this response and retry your request" before initiating the push
notification. notification.
NOTE: While this work on this document was ongoing, implementation NOTE: While the work on this document was ongoing, implementation
test results showed that the time it takes for a proxy to receive the test results showed that the time it takes for a proxy to receive the
REGISTER request, from when the proxy has requested a push REGISTER request, from when the proxy has requested a push
notification, is typically around 2 seconds. However, the time might notification, is typically around 2 seconds. However, the time might
vary depending on the characteristics and load of the SIP network and vary depending on the characteristics and load of the SIP network and
the PNS. the PNS.
In addition to the procedures described above there are two cases In addition to the procedures described above, there are two cases
where a proxy, as an optimization, can forward a SIP request towards where a proxy, as an optimization, can forward a SIP request towards
a UA without waiting for a 2xx response to a REGISTER request, or a UA without either waiting for a 2xx response to a REGISTER request
without even requesting that a push notification be sent to the UA: or requesting that a push notification be sent to the UA:
o If the proxy is able to authenticate the sender of the REGISTER o If the proxy is able to authenticate the sender of the REGISTER
request and verify that it is allowed by authorization policy, the request and verify that it is allowed by authorization policy, the
proxy does not need to wait for the 2xx response before it proxy does not need to wait for the 2xx response before it
forwards the SIP request towards the UA. In such cases, the proxy forwards the SIP request towards the UA. In such cases, the proxy
will use the Contact URI of the REGISTER request when comparing it will use the Contact URI of the REGISTER request when comparing it
against the Request-URIs of the SIP requests in the SIP Request against the Request-URIs of the SIP requests in the SIP Request
Push Bucket. Push Bucket.
o If the proxy has knowledge that the UA is awake, and that the UA o If the proxy has knowledge that the UA is awake, and that the UA
is able to receive the SIP request without first sending a is able to receive the SIP request without first sending a
binding-refresh REGISTER request, the proxy does not need to binding-refresh REGISTER request, the proxy does not need to
request that a push notification be sent to the UA (the UA will request that a push notification be sent to the UA (the UA will
not send a binding-refresh REGISTER request) before it forwards not send a binding-refresh REGISTER request) before it forwards
the SIP request towards the UA. The mechanisms for getting such the SIP request towards the UA. The mechanisms for getting such
knowledge might be dependent on implementation or deployment knowledge might be dependent on implementation or deployment
architecture, and are outside the scope of this document. architecture, and are outside the scope of this document.
Some PNS providers allow payload in the push notifications. This Some PNS providers allow payload in the push notifications. This
skipping to change at page 21, line 37 skipping to change at page 23, line 5
request that a push notification be sent to the UA (the UA will request that a push notification be sent to the UA (the UA will
not send a binding-refresh REGISTER request) before it forwards not send a binding-refresh REGISTER request) before it forwards
the SIP request towards the UA. The mechanisms for getting such the SIP request towards the UA. The mechanisms for getting such
knowledge might be dependent on implementation or deployment knowledge might be dependent on implementation or deployment
architecture, and are outside the scope of this document. architecture, and are outside the scope of this document.
Some PNS providers allow payload in the push notifications. This Some PNS providers allow payload in the push notifications. This
specification does not define usage of such payload (in addition to specification does not define usage of such payload (in addition to
any payload that might be required by the PNS itself). any payload that might be required by the PNS itself).
6. Support Of Longlived SIP Dialogs 6. Support of Long-Lived SIP Dialogs
Some SIP dialogs might have a long lifetime with little activity. Some SIP dialogs might have a long lifetime with little activity.
For example, when the SIP event notification mechanism [RFC6665] is For example, when the SIP event notification mechanism [RFC6665] is
used, there might be a long period between the sending of mid-dialog used, there might be a long period between the sending of mid-dialog
requests. Because of this, a SIP UA may be suspended, and may need requests. Because of this, a SIP UA may be suspended and may need to
to be awakened in order to be able to receive mid-dialog requests. be awakened in order to be able to receive mid-dialog requests.
SIP requests for a new dialog and stand-alone SIP requests addressed SIP requests for a new dialog and standalone SIP requests addressed
towards a UA will pn- SIP URI parameters that allows the proxy to towards a UA with 'pn-*' SIP URI parameters allow the proxy to
request that a push notification be sent to the UA Section 5.6.2. request that a push notification be sent to the UA (Section 5.6.2).
However, pn- SIP URI parameters will not be present in mid-dialog However, 'pn-*' SIP URI parameters will not be present in mid-dialog
requests addressed towards the UA. Instead, the proxy needs to requests addressed towards the UA. Instead, the proxy needs to
support a mechanism to store the information needed to request that a support a mechanism to store the information needed to request that a
push notification be sent to the UA, and to be able to retrieve that push notification be sent to the UA, and to be able to retrieve that
information when it receives a mid-dialog request addressed towards information when it receives a mid-dialog request addressed towards
the UA. This section defines such mechanism. The SIP UA and SIP the UA. This section defines such a mechanism. The SIP UA and SIP
proxy procedures in this section are applied in addition to the proxy procedures in this section are applied in addition to the
generic procedures defined in this specification. generic procedures defined in this specification.
+--------+ +---------+ +-----------+ +-------------+ +--------+ +---------+ +-----------+ +-------------+
| | | | | | | SIP | | | | | | | | SIP |
| SIP UA | | Push | | SIP Proxy | | Registrar / | | SIP UA | | Push | | SIP Proxy | | Registrar / |
| | | Service | | | | Home Proxy | | | | Service | | | | Home Proxy |
+--------+ +---------+ +-----------+ +-------------+ +--------+ +---------+ +-----------+ +-------------+
| | | | | | | |
| PNS Register | | | | PNS Register | | |
skipping to change at page 23, line 31 skipping to change at page 24, line 46
|<===================================| | |<===================================| |
| | | | | | | |
| SIP UPDATE | | | | SIP UPDATE | | |
|<===================================| | |<===================================| |
| | | | | | | |
------- Push Notification API ------- Push Notification API
======= SIP ======= SIP
Figure 4: SIP Push Longlived Dialog Flow Figure 4: SIP Push Long-Lived Dialog Flow
6.1. SIP UA Behavior 6.1. SIP UA Behavior
6.1.1. Initial Request for Dialog 6.1.1. Initial Request for Dialog
If the UA is willing to receive push notifications when a proxy If the UA is willing to receive push notifications when a proxy
receives a mid-dialog request addressed towards the UA, the UA MUST receives a mid-dialog request addressed towards the UA, the UA MUST
insert a 'pn-purr' SIP URI parameter (Section 6.2.1) in the Contact insert a 'pn-purr' SIP URI parameter (Section 6.2.1) in the Contact
header field URI of the initial request for a dialog or the 2xx header field URI of the initial request for a dialog or the 2xx
response to such requests. XXX The UA MUST insert a parameter value response to such requests. The UA MUST insert a parameter value
identical to the last 'sip.pnspurr' feature-capability indicator identical to the last 'sip.pnspurr' feature-capability indicator
(Section 6.2.1) that it received in a REGISTER response. If the UA (Section 6.2.1) that it received in a REGISTER response. If the UA
has not recived a 'sip.pnspurr' feature-capability indicator, the UA has not received a 'sip.pnspurr' feature-capability indicator, the UA
MUST NOT insert a 'pn-purr' SIP URI parameter in a request or MUST NOT insert a 'pn-purr' SIP URI parameter in a request or
response. response.
The UA makes the decision to receive push notifications triggered by The UA makes the decision to receive push notifications triggered by
incoming mid-dialog requests based on local policy. Such policy incoming mid-dialog requests based on local policy. Such policy
might be based on the type of SIP dialog, the type of media (if any) might be based on the type of SIP dialog, the type of media (if any)
negotiated for the dialog [RFC3264], etc. negotiated for the dialog [RFC3264], etc.
NOTE: As the 'pn-purr' SIP URI parameter only applies to a given NOTE: As the 'pn-purr' SIP URI parameter only applies to a given
dialog, the UA needs to insert a 'pn-purr' parameter in the Contact dialog, the UA needs to insert a 'pn-purr' parameter in the Contact
header field URI of the request or response for each dialog in which header field URI of the request or response for each dialog in which
the UA is willing to receive push notifications triggered by incoming the UA is willing to receive push notifications triggered by incoming
mid-dialog requests. mid-dialog requests.
6.2. SIP Proxy Behavior 6.2. SIP Proxy Behavior
6.2.1. REGISTER 6.2.1. REGISTER
If the proxy supports requesting push notifications triggered by mid- If the proxy supports requesting push notifications triggered by mid-
dialog requests being sent to the registered UA, the proxy MUST store dialog requests being sent to the registered UA, the proxy MUST store
the information (the pn- SIP URI parameters) needed to request that the information (the 'pn-*' SIP URI parameters) needed to request
push notifications are sent to the UA when a proxy receives an that push notifications are sent to the UA when a proxy receives an
initial REGISTER request for a binding from the UA. In addition, the initial REGISTER request for a binding from the UA. In addition, the
proxy MUST generate a unique (within the context of the proxy) value, proxy MUST generate a unique (within the context of the proxy) value,
referred to as the PURR (Proxy Unique Registration Reference), that referred to as the PURR (Proxy Unique Registration Reference), that
can be used as a key to retrieve the information. can be used as a key to retrieve the information.
In order to prevent client fingerprinting, the proxy MUST In order to prevent client fingerprinting, the proxy MUST
periodically generate a new PURR value (even if pn- parameters did periodically generate a new PURR value (even if 'pn-*'parameters did
not change). However, as long as there are ongoing dialogs not change). However, as long as there are ongoing dialogs
associated with the old value, the proxy MUST store it so that it can associated with the old value, the proxy MUST store it so that it can
request that push notifications are sent to the UA when it receives a request that push notifications are sent to the UA when it receives a
mid-dialog request addressed towards the UA. In addition, the PURR mid-dialog request addressed towards the UA. In addition, the PURR
value MUST be generated in such a way so that it is unforgeable, value MUST be generated in such a way so that it is unforgeable,
anonymous, and unlinkable to entities other than the proxy. It must anonymous, and unlinkable to entities other than the proxy. It must
not be possible for an attacker to generate a valid PURR, to not be possible for an attacker to generate a valid PURR, to
associate a PURR with a specific user, or to determine when two PURRs associate a PURR with a specific user, or to determine when two PURRs
correspond to the same user. It can be generated e.g., by utilizing correspond to the same user. It can be generated, e.g., by utilizing
a cryptographically secure random function with an appropriately a cryptographically secure random function with an appropriately
large output size. large output size.
Whenever the proxy receives a 2xx response to a REGISTER request, the Whenever the proxy receives a 2xx response to a REGISTER request, the
proxy MUST insert a 'sip.pnspurr' feature-capability indicator with proxy MUST insert a 'sip.pnspurr' feature-capability indicator with
the latest PURR value (see above) in the response. the latest PURR value (see above) in the response.
6.2.2. Initial Request for Dialog 6.2.2. Initial Request for Dialog
When a proxy receives an initial request for a dialog from a UA that When a proxy receives an initial request for a dialog from a UA that
contains a 'pn-purr' SIP URI parameter in the Contact header field contains a 'pn-purr' SIP URI parameter in the Contact header field
URI with a PURR value that the proxy has generated (Section 6.2.1), URI with a PURR value that the proxy has generated (Section 6.2.1),
the proxy MUST add a Record-Route header to the request to insert the proxy MUST add a Record-Route header to the request to insert
itself in the dialog route [RFC3261] before forwarding the request. itself in the dialog route [RFC3261] before forwarding the request.
When the proxy receives an initial request for a dialog addressed When the proxy receives an initial request for a dialog addressed
towards the UA, and the proxy has generated a PURR value associated towards the UA, and the proxy has generated a PURR value associated
with the pn- parameters inserted in the SIP URI of the request with the 'pn-*' parameters inserted in the SIP URI of the request
(Section 6.2.2), the proxy MUST add a Record-Route header to the (Section 6.2.2), the proxy MUST add a Record-Route header to the
request, to insert itself in the dialog route [RFC3261] before request to insert itself in the dialog route [RFC3261] before
forwarding the request. forwarding the request.
6.2.3. Mid-Dialog Request 6.2.3. Mid-dialog Request
When the proxy receives a mid-dialog SIP request addressed towards When the proxy receives a mid-dialog SIP request addressed towards
the UA that contains a 'pn-purr' SIP URI parameter, and the proxy is the UA that contains a 'pn-purr' SIP URI parameter, and the proxy is
able to retrieve the stored information needed to request that a push able to retrieve the stored information needed to request that a push
notification be sent to the UA (Section 6.2.1), the proxy MUST place notification be sent to the UA (Section 6.2.1), the proxy MUST place
the SIP request in the SIP Request Push Bucket and request that a the SIP request in the SIP Request Push Bucket and request that a
push notification be sent to the UA. push notification be sent to the UA.
NOTE: The 'pn-purr' SIP URI parameter will either be carried in the NOTE: The 'pn-purr' SIP URI parameter will either be carried in the
Request-URI or in a Route header field [RFC3261] of the SIP request, Request-URI or in a Route header field [RFC3261] of the SIP request
depending on how the route set [RFC3261] of the mid-dialog SIP depending on how the route set [RFC3261] of the mid-dialog SIP
request has been constructed. request has been constructed.
When the proxy receives a 2xx response to a REGISTER request, the When the proxy receives a 2xx response to a REGISTER request, the
proxy checks whether the SIP Request Push Bucket contains a mid- proxy checks whether the SIP Request Push Bucket contains a mid-
dialog SIP request associated with the REGISTER transaction. If the dialog SIP request associated with the REGISTER transaction. If the
bucket contains such request the proxy MUST remove the SIP request bucket contains such a request, the proxy MUST remove the SIP request
from the SIP Request Push Bucket and forward it towards the UA. from the SIP Request Push Bucket and forward it towards the UA.
Note that the proxy does not perform a URI comparison (Section 5.3) Note that the proxy does not perform a URI comparison (Section 5.3)
when processing mid-dialog requests, as a mid-dialog request will not when processing mid-dialog requests, as a mid-dialog request will not
contain the pn-prid, pn-provider and pn-param SIP URI parameters. contain the 'pn-prid', 'pn-provider', and 'pn-param' SIP URI
The proxy only checks for a mid-dialog request that contains the PURR parameters. The proxy only checks for a mid-dialog request that
value associated with the REGISTER 2xx response. contains the PURR value associated with the REGISTER 2xx response.
As described in Section 5.6.2, while waiting for the push As described in Section 5.6.2, while waiting for the push
notification request to succeed, and then for the associated REGISTER notification request to succeed, and then for the associated REGISTER
request and 2xx response, the proxy needs to take into consideration request and 2xx response, the proxy needs to take into consideration
that the transaction associated with the mid-dialog request will that the transaction associated with the mid-dialog request will
eventually time out at the sender of the request (UAC), and the eventually time out at the sender of the request (User Agent Client),
sender will consider the transaction a failure. and the sender will consider the transaction a failure.
When a proxy sends an error response to a mid-dialog request (e.g., When a proxy sends an error response to a mid-dialog request (e.g.,
due to a transaction time out), the proxy SHOULD select a response due to a transaction time out), the proxy SHOULD select a response
code that only impacts the transaction associated with the request code that only impacts the transaction associated with the request
[RFC5079]. [RFC5079].
7. Support Of SIP Replaces 7. Support of SIP Replaces
[RFC3891] defines a mechanism that allows a SIP UA to replace a [RFC3891] defines a mechanism that allows a SIP UA to replace a
dialog with another dialog. A UA that wants to replace a dialog with dialog with another dialog. A UA that wants to replace a dialog with
another one will send an initial request for the new dialog. The another one will send an initial request for the new dialog. The
Request-URI of the request will contain Contact header field URI of Request-URI of the request will contain the Contact header field URI
the peer. of the peer.
If a SIP proxy wants to be able to request that a push notification If a SIP proxy wants to be able to request that a push notification
be sent to a UA when it receives an initial request for a dialog that be sent to a UA when it receives an initial request for a dialog that
replaces an existing dialog, using the mechanism in [RFC3891], the replaces an existing dialog, using the mechanism in [RFC3891], the
proxy and the UA MUST perform the following actions: proxy and the UA MUST perform the following actions:
o The proxy MUST provide a PURR to the UA during registration o The proxy MUST provide a PURR to the UA during registration
(Section 6.2.1). (Section 6.2.1).
o The UA MUST insert a 'pn-purr' SIP URI parameter in the Contact o The UA MUST insert a 'pn-purr' SIP URI parameter in the Contact
header field URI of the initial request for a dialog, or a 2xx header field URI of either the initial request for a dialog or a
response to such requests (Section 6.1.1). This includes dialogs 2xx response to such requests (Section 6.1.1). This includes
replacing other dialogs, as those dialogs might also get replaced. dialogs replacing other dialogs, as those dialogs might also get
replaced.
o The proxy MUST apply the mechanism defined in Section 6.2.3 to o The proxy MUST apply the mechanism defined in Section 6.2.3 to
place and retrieve the request from the SIP Request Push Bucket. place and retrieve the request from the SIP Request Push Bucket.
In addition, the operator needs to make sure that the initial request In addition, the operator needs to make sure that the initial request
for dialogs, addressed towards the UA using the contact of the for dialogs, addressed towards the UA using the contact of the
replaced dialog, will be routed to the SIP proxy (in order to request replaced dialog, will be routed to the SIP proxy (in order to request
that a push notification be sent to the UA). The procedures for that a push notification be sent to the UA). The procedures for
doing that are operator specific, and are outside the scope of this doing that are operator-specific and are outside the scope of this
specification. specification.
8. Grammar 8. Grammar
8.1. 555 (Push Notification Service Not Supported) Response Code 8.1. 555 (Push Notification Service Not Supported) Response Code
The 555 response code is added to the "Server-Error" Status-Code The 555 response code is added to the "Server-Error" Status-Code
definition. 555 (Push Notification Service Not Supported) is used to definition. 555 (Push Notification Service Not Supported) is used to
indicate that the server does not support the push notification indicate that the server does not support the push notification
service identified in a 'pn-provider' SIP URI parameter. service identified in a 'pn-provider' SIP URI parameter.
The use of the SIP 555 response code is only defined for SIP REGISTER The use of the SIP 555 response code is only defined for SIP REGISTER
responses. responses.
8.2. sip.pns Feature-Capability Indicator 8.2. 'sip.pns' Feature-Capability Indicator
The sip.pns feature-capability indicator, when inserted in a Feature- The sip.pns feature-capability indicator, when inserted in a Feature-
Caps header field of a SIP REGISTER request or a SIP 2xx response to Caps header field of a SIP REGISTER request or a SIP 2xx response to
a REGISTER request, indicates that the entity associated with the a REGISTER request, indicates that the entity associated with the
indicator supports the SIP push mechanism and the type of push indicator supports the SIP push mechanism and the type of push
notification service indicated by the indicator value. The values notification service indicated by the indicator value. The values
defined for the pn-provider SIP URI parameter are used as indicator defined for the 'pn-provider' SIP URI parameter are used as indicator
values. values.
pns-fc = "+sip.pns" EQUAL LDQUOT pns RDQUOT pns-fc = "+sip.pns" EQUAL LDQUOT pns RDQUOT
pns = tag-value pns = tag-value
tag-value = <tag-value defined in [RFC3840]> tag-value = <tag-value defined in [RFC3840]>
8.3. sip.vapid Feature-Capability Indicator 8.3. 'sip.vapid' Feature-Capability Indicator
The sip.vapid feature-capability indicator, when inserted in a SIP The sip.vapid feature-capability indicator, when inserted in a SIP
2xx response to a SIP REGISTER request, denotes that the entity 2xx response to a SIP REGISTER request, denotes that the entity
associated with the indicator supports the Voluntary Application associated with the indicator supports the Voluntary Application
Server Identification (VAPID) [RFC8292] mechanism when the entity Server Identification (VAPID) [RFC8292] mechanism when the entity
requests that a push notification be sent to a SIP UA. The indicator requests that a push notification be sent to a SIP UA. The indicator
value is a public key identifying the entity that can be used by a value is a public key identifying the entity that can be used by a
SIP UA to restrict subscriptions to that entity. SIP UA to restrict subscriptions to that entity.
vapid-fc = "+sip.vapid" EQUAL LDQUOT vapid RDQUOT vapid-fc = "+sip.vapid" EQUAL LDQUOT vapid RDQUOT
vapid = tag-value vapid = tag-value
tag-value = <tag-value defined in [RFC3840]> tag-value = <tag-value defined in [RFC3840]>
8.4. sip.pnsreg Feature-Capability Indicator 8.4. 'sip.pnsreg' Feature-Capability Indicator
The sip.pnsreg feature-capability indicator, when inserted in a SIP The sip.pnsreg feature-capability indicator, when inserted in a SIP
2xx response to a SIP REGISTER request, denotes that the entity 2xx response to a SIP REGISTER request, denotes that the entity
associated with the indicator expects to receive binding-refresh associated with the indicator expects to receive binding-refresh
REGISTER requests from the SIP UA associated with the binding before REGISTER requests from the SIP UA associated with the binding before
the binding expires, even if the entity does not request that a push the binding expires, even if the entity does not request that a push
notification be sent to the SIP UA in order to trigger the binding- notification be sent to the SIP UA in order to trigger the binding-
refresh REGISTER requests. The indicator value conveys the minimum refresh REGISTER requests. The indicator value conveys the minimum
time (given in seconds), prior to the binding expiration when the UA time (given in seconds) prior to the binding expiration when the UA
MUST send the REGISTER request. MUST send the REGISTER request.
pns-fc = "+sip.pnsreg" EQUAL LDQUOT reg RDQUOT pns-fc = "+sip.pnsreg" EQUAL LDQUOT reg RDQUOT
reg = 1*DIGIT reg = 1*DIGIT
DIGIT = <DIGIT defined in [RFC3261]> DIGIT = <DIGIT defined in [RFC3261]>
8.5. sip.pnsreg Media Feature Tag 8.5. 'sip.pnsreg' Media Feature Tag
The sip.pnsreg media feature tag, when inserted in the Contact header The sip.pnsreg media feature tag, when inserted in the Contact header
field of a SIP REGISTER request, indicates that the SIP UA associated field of a SIP REGISTER request, indicates that the SIP UA associated
with the tag is able to send binding-refresh REGISTER requests for with the tag is able to send binding-refresh REGISTER requests for
the associated binding without being awakened by push notifications. the associated binding without being awakened by push notifications.
The media feature tag has no values. The media feature tag has no values.
pnsreg-mt = "+sip.pnsreg" pnsreg-mt = "+sip.pnsreg"
8.6. sip.pnspurr Feature-Capability Indicator 8.6. 'sip.pnspurr' Feature-Capability Indicator
The sip.pnspurr feature-capability indicator, when inserted in a SIP The sip.pnspurr feature-capability indicator, when inserted in a SIP
2xx response to a SIP REGISTER request, denotes that the entity 2xx response to a SIP REGISTER request, denotes that the entity
associated with the indicator will store information that can be used associated with the indicator will store information that can be used
to associate a mid-dialog SIP request with the binding information in to associate a mid-dialog SIP request with the binding information in
the REGISTER request. the REGISTER request.
pnspurr-fc = "+sip.pnspurr" EQUAL LDQUOT pnspurr RDQUOT pnspurr-fc = "+sip.pnspurr" EQUAL LDQUOT pnspurr RDQUOT
pnspurr = tag-value pnspurr = tag-value
tag-value = <tag-value defined in [RFC3840]> tag-value = <tag-value defined in [RFC3840]>
8.7. SIP URI Parameters 8.7. SIP URI Parameters
The section defines new SIP URI parameters by extending the grammar This section defines new SIP URI parameters by extending the grammar
for "uri-parameter" as defined in [RFC3261]. The ABNF is as follows: for "uri-parameter" as defined in [RFC3261]. The ABNF [RFC5234] is
as follows:
uri-parameter =/ pn-provider / pn-param / pn-prid / pn-purr uri-parameter =/ pn-provider / pn-param / pn-prid / pn-purr
pn-provider = "pn-provider" [EQUAL pvalue] pn-provider = "pn-provider" [EQUAL pvalue]
pn-param = "pn-param" EQUAL pvalue pn-param = "pn-param" EQUAL pvalue
pn-prid = "pn-prid" EQUAL pvalue pn-prid = "pn-prid" EQUAL pvalue
pn-purr = "pn-purr" EQUAL pvalue pn-purr = "pn-purr" EQUAL pvalue
pvalue = <pvalue defined in [RFC3261]> pvalue = <pvalue defined in [RFC3261]>
EQUAL = <EQUAL defined in [RFC3261]> EQUAL = <EQUAL defined in [RFC3261]>
The format and semantics of pn-prid and pn-param are The format and semantics of pn-prid and pn-param are specific to the
specific to the pn-provider value. pn-provider value.
Parameter value characters that are not part of pvalue need to be Parameter value characters that are not part of pvalue need to be
escaped, as defined in RFC 3261. escaped, as defined in RFC 3261.
9. PNS Registration Requirements 9. PNS Registration Requirements
When a new value is registered to the PNS Sub-registry, a reference When a new value is registered to the PNS subregistry, a reference to
to a specification that describes the usage of the PNS associated a specification that describes the usage of the PNS associated with
with the value is provided. That specification MUST contain the the value is provided. That specification MUST contain the following
following information: information:
o The value of the pn-provider SIP URI parameter. o The value of the 'pn-provider' SIP URI parameter.
o How the pn-prid SIP URI parameter value is retrieved and set by
o How the 'pn-prid' SIP URI parameter value is retrieved and set by
the SIP UA. the SIP UA.
o How the pn-param SIP URI parameter (if required for the specific
PNS provider) value is retrieved and set by the SIP UA.
10. pn-provider, pn-param and pn-prid URI Parameters for Apple Push o How the 'pn-param' SIP URI parameter (if required for the specific
Notification service PNS provider) value is retrieved and set by the SIP UA.
When the Apple Push Notification service (APNs) is used, the PNS- 10. 'pn-provider', 'pn-param', and 'pn-prid' URI Parameters for Apple
related SIP URI parameters are set as described below. Push Notification service
For detailed information about the parameter values: When the Apple Push Notification service (APNs) is used, the
PNS-related SIP URI parameters are set as described below.
https://developer.apple.com/library/archive/documentation/NetworkingI For detailed information about the parameter values, see
nternet/Conceptual/RemoteNotificationsPG/CommunicatingwithAPNs.html <https://developer.apple.com/library/archive/documentation/
[pns-apns]) NetworkingInternet/Conceptual/RemoteNotificationsPG/
CommunicatingwithAPNs.html> [pns-apns].
The value of the pn-provider URI parameter is "apns". The value of the 'pn-provider' URI parameter is "apns".
Example: pn-provider=apns Example: pn-provider=apns
The value of the pn-param URI parameter is a string that is composed The value of the 'pn-param' URI parameter is a string that is
of two values, separated by a period (.): Team ID and Topic. The composed of two values separated by a period (.): Team ID and Topic.
Team ID is provided by Apple and is unique to a development team. The Team ID is provided by Apple and is unique to a development team.
The Topic consists of the Bundle ID, which uniquely identifies an The Topic consists of the Bundle ID, which uniquely identifies an
application, and a service value that identifies a service associated application, and a service value that identifies a service associated
with the application, separated by a period (.). For VoIP with the application, separated by a period (.). For Voice over IP
applications the service value is "voip". (VoIP) applications, the service value is "voip".
Example: pn-param=DEF123GHIJ.com.example.yourexampleapp.voip Example: pn-param=DEF123GHIJ.com.example.yourexampleapp.voip
NOTE: The Bundle ID might contain one or more periods (.). Hence, NOTE: The Bundle ID might contain one or more periods (.). Hence,
within the pn-param value, the first period will be separating the within the 'pn-param' value, the first period will be separating the
Team ID from the Topic, and within the Topic the last period will be Team ID from the Topic, and within the Topic, the last period will be
separating the Bundle ID from the service. separating the Bundle ID from the service.
The value of the pn-prid URI parameter is the device token, which is The value of the 'pn-prid' URI parameter is the device token, which
a unique identifier assigned by Apple to a specific app on a specific is a unique identifier assigned by Apple to a specific app on a
device. specific device.
Example: pn-prid=00fc13adff78512 Example: pn-prid=00fc13adff78512
11. pn-provider, pn-param and pn-prid URI Parameters for Google 11. 'pn-provider', 'pn-param', and 'pn-prid' URI Parameters for Google
Firebase Cloud Messaging (FCM) push notification service Firebase Cloud Messaging (FCM) Push Notification Service
When Firebase Cloud Messaging (FCM) is used, the PNS related URI When Firebase Cloud Messaging (FCM) is used, the PNS-related URI
parameters are set as described below. parameters are set as described below.
For detailed information about the parameter values: For detailed information about the parameter values, see
<https://firebase.google.com/docs/cloud-messaging/concept-options>
https://firebase.google.com/docs/cloud-messaging/concept-options [pns-fcm].
[pns-fcm]
The value of the pn-provider URI parameter is "fcm". The value of the 'pn-provider' URI parameter is "fcm".
The value of the pn-param URI parameter is the Project ID. The value of the 'pn-param' URI parameter is the Project ID.
The value of the pn-prid URI parameter is the Registration token, The value of the 'pn-prid' URI parameter is the Registration token,
which is generated by the FCM SDK for each client app instance. which is generated by the FCM SDK for each client app instance.
12. pn-provider, pn-param and pn-prid URI Parameters for RFC 8030 12. 'pn-provider', 'pn-param', and 'pn-prid' URI Parameters for RFC
(Generic Event Delivery Using HTTP Push) 8030 (Generic Event Delivery Using HTTP Push)
When Generic Event Delivery Using HTTP Push is used, the PNS related When Generic Event Delivery Using HTTP Push is used, the PNS-related
URI parameters are set as described below. URI parameters are set as described below.
The value of the pn-provider URI parameter is "webpush". The value of the 'pn-provider' URI parameter is "webpush".
The value of the pn-param URI parameter MUST NOT be used. The value of the 'pn-param' URI parameter MUST NOT be used.
The value of the pn-prid URI parameter is the push subscription URI. The value of the 'pn-prid' URI parameter is the push subscription
URI.
See RFC 8030 [RFC8030] for more details. See RFC 8030 [RFC8030] for more details.
Note that encryption for web push [RFC8291] is not used, therefore Note that encryption for web push [RFC8291] is not used; therefore,
parameters for message encryption are not defined in this parameters for message encryption are not defined in this
specification. Web push permits the sending of a push message specification. Web push permits the sending of a push message
without a payload without encryption. without a payload without encryption.
13. Security Considerations 13. Security Considerations
The security considerations for the use and operation of any The security considerations for the use and operation of any
particular PNS (e.g., how users and devices are authenticated and particular PNS (e.g., how users and devices are authenticated and
authorized) is out of scope for this document. [RFC8030] documents authorized) are out of scope for this document. [RFC8030] documents
the security considerations for the PNS defined in that the security considerations for the PNS defined in that
specification. Security considerations for other PNSs are left to specification. Security considerations for other PNSs are left to
their respective specifications. their respective specifications.
Typically, the PNS requires the SIP proxy requesting push Typically, the PNS requires the SIP proxy requesting push
notifications to be authenticated and authorized by the PNS. In some notifications to be authenticated and authorized by the PNS. In some
cases the PNS also requires the SIP application (or the SIP cases, the PNS also requires the SIP application (or the SIP
application developer) to be identified in order for the application application developer) to be identified in order for the application
to request push notifications. Unless the PNS authenticates and to request push notifications. Unless the PNS authenticates and
authorizes the PNS, a malicious endpoint or network entity that authorizes the PNS, a malicious endpoint or network entity that
managed to get access to the parameters transported in the SIP managed to get access to the parameters transported in the SIP
signalling might be able to request that push notifications are sent signaling might be able to request that push notifications are sent
to a UA. Such push notifications will impact the battery life of the to a UA. Such push notifications will impact the battery life of the
UA and trigger unnecessary SIP traffic. UA and trigger unnecessary SIP traffic.
[RFC8292] defines a mechanism that allows a proxy to identity itself [RFC8292] defines a mechanism that allows a proxy to identify itself
to a PNS, by signing a JWT sent to the PNS using a key pair. The to a PNS by signing a JSON Web Token (JWT) sent to the PNS using a
public key serves as an identifier of the proxy, and can be used by key pair. The public key serves as an identifier of the proxy and
devices to restrict push notifications to the proxy associated with can be used by devices to restrict push notifications to the proxy
the key. associated with the key.
Operators MUST ensure that the SIP signalling is properly secured, Operators MUST ensure that the SIP signaling is properly secured,
e.g., using encryption, from malicious network entities. TLS MUST be e.g., using encryption, from malicious network entities. TLS MUST be
used, unless the operators know that the signalling is secured using used unless the operators know that the signaling is secured using
some other mechanism that provides strong crypto properties. some other mechanism that provides strong crypto properties.
In addition to the information that needs to be exchanged between a In addition to the information that needs to be exchanged between a
device and the PNS in order to establish a push notification device and the PNS in order to establish a push notification
subscription, the mechanism defined in this document does not require subscription, the mechanism defined in this document does not require
any additional information to be exchanged between the device and the any additional information to be exchanged between the device and the
PNS. PNS.
The mechanism defined in this document does not require a proxy to The mechanism defined in this document does not require a proxy to
insert any payload (in addition to possible payload used for the PNS insert any payload (in addition to possible payload used for the PNS
itself) when requesting push notifications. itself) when requesting push notifications.
Operators MUST ensure that the PNS-related SIP URI parameters Operators MUST ensure that the PNS-related SIP URI parameters
conveyed by a user in the Contact URI of a REGISTER request are not conveyed by a user in the Contact URI of a REGISTER request are not
sent to other users, or to non-trusted network entities. One way to sent to other users or to non-trusted network entities. One way to
convey contact information is by using the the SIP event package for convey contact information is by using the SIP event package for
registrations mechanism [RFC3680]. [RFC3680] defines generic registrations mechanism [RFC3680]. [RFC3680] defines generic
security considerations for the SIP event package for registrations. security considerations for the SIP event package for registrations.
As the PNS-related SIP URI parameters conveyed in the REGISTER As the PNS-related SIP URI parameters conveyed in the REGISTER
request contain sensitive information, operators that support the request contain sensitive information, operators that support the
event package MUST ensure that event package subscriptions are event package MUST ensure that event package subscriptions are
properly authenticated and authorized, and that the SIP URI properly authenticated and authorized, and that the SIP URI
parameters are not inserted in event notifications sent to other parameters are not inserted in event notifications sent to other
users, or to non-trusted network entities. users or to non-trusted network entities.
14. IANA considerations
[RFC EDITOR NOTE: Please replace all instances of RFCXXXX with the 14. IANA Considerations
RFC number of this document.]
14.1. SIP URI Parameters 14.1. SIP URI Parameters
This section defines new SIP URI Parameters that extend the "SIP/SIPS This section defines new SIP URI Parameters that extend the "SIP/SIPS
URI Parameters" sub-registry [RFC3969] under the sip-parameters URI Parameters" subregistry [RFC3969] under the SIP Parameters
registry: http://www.iana.org/assignments/sip-parameters. registry (https://www.iana.org/assignments/sip-parameters).
14.1.1. pn-provider 14.1.1. pn-provider
Parameter Name: pn-provider Parameter Name: pn-provider
Predefined Values: No Predefined Values: No
Reference: RFC XXXX Reference: RFC 8599
14.1.2. pn-param 14.1.2. pn-param
Parameter Name: pn-param Parameter Name: pn-param
Predefined Values: No Predefined Values: No
Reference: RFC XXXX Reference: RFC 8599
14.1.3. pn-prid 14.1.3. pn-prid
Parameter Name: pn-prid Parameter Name: pn-prid
Predefined Values: No Predefined Values: No
Reference: RFC XXXX Reference: RFC 8599
14.1.4. pn-purr 14.1.4. pn-purr
Parameter Name: pn-purr Parameter Name: pn-purr
Predefined Values: No Predefined Values: No
Reference: RFC XXXX Reference: RFC 8599
14.2. SIP Response Codes 14.2. SIP Response Codes
14.2.1. 555 (Push Notification Service Not Supported) 14.2.1. 555 (Push Notification Service Not Supported)
This section defines a new SIP response code that extends the This section defines a new SIP response code that extends the
"Response Codes" sub-registry [RFC3261] under the sip-parameters "Response Codes" subregistry [RFC3261] under the SIP Parameters
registry: http://www.iana.org/assignments/sip-parameters. registry (https://www.iana.org/assignments/sip-parameters).
Response Code Number: 555 Response Code Number: 555
Default Reason Phrase: Push Notification Service Not Supported Default Reason Phrase: Push Notification Service Not Supported
14.3. SIP Global Feature-Capability Indicator 14.3. SIP Global Feature-Capability Indicator
14.3.1. sip.pns 14.3.1. sip.pns
This section defines a new feature-capability indicator that extends This section defines a new feature-capability indicator that extends
the "SIP Feature-Capability Indicator Registration Tree" sub-registry the "SIP Feature-Capability Indicator Registration Tree" subregistry
[RFC6809] under the sip-parameters registry: [RFC6809] under the SIP Parameters registry
http://www.iana.org/assignments/sip-parameters. (https://www.iana.org/assignments/sip-parameters).
Name: sip.pns Name: sip.pns
Description: This feature-capability indicator, when inserted in a Description: This feature-capability indicator, when inserted in a
Feature-Caps header field of a SIP REGISTER request or a SIP 2xx Feature-Caps header field of a SIP REGISTER request or a SIP 2xx
response to a REGISTER request, denotes that the entity response to a REGISTER request, denotes that the entity
associated with the indicator supports the SIP push mechanism associated with the indicator supports the SIP push mechanism
and the type of push notification service conveyed by the and the type of push notification service conveyed by the
indicator value. indicator value.
Reference: [RFCXXXX] Reference: RFC 8599
Contact: IESG (iesg@ietf.org) Contact: IESG (iesg@ietf.org)
14.3.2. sip.vapid 14.3.2. sip.vapid
This section defines a new feature-capability indicator that extends This section defines a new feature-capability indicator that extends
the "SIP Feature-Capability Indicator Registration Tree" sub-registry the "SIP Feature-Capability Indicator Registration Tree" subregistry
[RFC6809] under the sip-parameters registry: [RFC6809] under the SIP Parameters registry
http://www.iana.org/assignments/sip-parameters. (https://www.iana.org/assignments/sip-parameters).
Name: sip.vapid Name: sip.vapid
Description: This feature-capability indicator, when inserted in a Description: This feature-capability indicator, when inserted in a
SIP 2xx response to a SIP REGISTER request, denotes that the SIP 2xx response to a SIP REGISTER request, denotes that the
entity associated with the indicator supports the Voluntary entity associated with the indicator supports the Voluntary
Application Server Identification (VAPID) mechanism when the Application Server Identification (VAPID) mechanism when the
entity requests that a push notifications be sent to a SIP UA. entity requests that a push notification be sent to a SIP UA.
The indicator value is a public key identifying the entity, The indicator value is a public key identifying the entity,
that can be used by a SIP UA to restrict subscriptions to that which can be used by a SIP UA to restrict subscriptions to
entity. that entity.
Reference: [RFCXXXX] Reference: RFC 8599
Contact: IESG (iesg@ietf.org) Contact: IESG (iesg@ietf.org)
14.3.3. sip.pnsreg 14.3.3. sip.pnsreg
This section defines a new feature-capability indicator that extends This section defines a new feature-capability indicator that extends
the "SIP Feature-Capability Indicator Registration Tree" sub-registry the "SIP Feature-Capability Indicator Registration Tree" subregistry
[RFC6809] under the sip-parameters registry: [RFC6809] under the SIP Parameters registry
http://www.iana.org/assignments/sip-parameters. (https://www.iana.org/assignments/sip-parameters).
Name: sip.pnsreg Name: sip.pnsreg
Description: This feature-capability indicator, when inserted in a Description: This feature-capability indicator, when inserted in a
SIP 2xx response to a SIP REGISTER request, denotes that the SIP 2xx response to a SIP REGISTER request, denotes that the
entity associated with the indicator expects to receive entity associated with the indicator expects to receive
binding-refresh REGISTER requests for the binding from the SIP binding-refresh REGISTER requests for the binding from the SIP
UA associated with the binding before the binding expires, even UA associated with the binding before the binding expires, even
if the entity does not request that a push notification be sent if the entity does not request that a push notification be sent
to the SIP UA in order to trigger the binding-refresh REGISTER to the SIP UA in order to trigger the binding-refresh REGISTER
requests. The indicator value conveys the minimum time requests. The indicator value conveys the minimum time
(given in seconds), prior to the binding expiration when the UA (given in seconds) prior to the binding expiration when the UA
MUST send the REGISTER request. MUST send the REGISTER request.
Reference: [RFCXXXX] Reference: RFC 8599
Contact: IESG (iesg@ietf.org) Contact: IESG (iesg@ietf.org)
14.3.4. sip.pnspurr 14.3.4. sip.pnspurr
This section defines a new feature-capability indicator that extends This section defines a new feature-capability indicator that extends
the "SIP Feature-Capability Indicator Registration Tree" sub-registry the "SIP Feature-Capability Indicator Registration Tree" subregistry
[RFC6809] under the sip-parameters registry: [RFC6809] under the SIP Parameters registry
http://www.iana.org/assignments/sip-parameters. (https://www.iana.org/assignments/sip-parameters).
Name: sip.pnspurr Name: sip.pnspurr
Description: This feature-capability indicator, when inserted in a Description: This feature-capability indicator, when inserted in a
SIP 2xx response to a SIP REGISTER request, conveys that SIP 2xx response to a SIP REGISTER request, conveys that
the entity associated with the indicator will store information the entity associated with the indicator will store information
that can be used to associate a mid-dialog SIP request with the that can be used to associate a mid-dialog SIP request with the
binding information in the REGISTER request. The indicator binding information in the REGISTER request. The indicator
value is an identifier that can be used a key to retrieve the value is an identifier that can be used as a key to retrieve
binding information. the binding information.
Reference: [RFCXXXX] Reference: RFC 8599
Contact: IESG (iesg@ietf.org) Contact: IESG (iesg@ietf.org)
14.4. SIP Media Feature Tag 14.4. SIP Media Feature Tag
14.4.1. sip.pnsreg 14.4.1. sip.pnsreg
This section defines a new media feature tag that extends the "SIP This section defines a new media feature tag that extends the "SIP
Media Feature Tag Registration Tree" sub-registry [RFC3840] under the Media Feature Tag Registration Tree" subregistry [RFC3840] under the
Media Feature Tag registry: https://www.iana.org/assignments/media- "Media Feature Tags" registry (https://www.iana.org/assignments/
feature-tags/media-feature-tags.xhtml. media-feature-tags).
Media feature tag name: sip.pnsreg Media feature tag name: sip.pnsreg
Summary of the media feature indicated by this feature tag: This Summary of the media feature indicated by this feature tag: This
media feature tag, when inserted in the Contact header field media feature tag, when inserted in the Contact header field
of a SIP REGISTER request, conveys that the SIP UA of a SIP REGISTER request, conveys that the SIP UA
associated with the tag is able to send binding-refresh associated with the tag is able to send binding-refresh
REGISTER requests associated with the registration without REGISTER requests associated with the registration without
being awakened by push notifications. being awakened by push notifications.
Values appropriate for use with this feature tag: none Values appropriate for use with this feature tag: none
Related standards or documents: [RFCXXXX] Related standards or documents: RFC 8599
Security considerations: This media feature tag does not introduce Security considerations: This media feature tag does not introduce
new security considerations, as it simply indicates support for new security considerations, as it simply indicates support for
a basic SIP feature. If an attacker manages to remove the media a basic SIP feature. If an attacker manages to remove the media
feature tag, push notifications will not be requested to be sent feature tag, push notifications will not be requested to be sent
to the client. to the client.
Contact: IESG (iesg@ietf.org) Contact: IESG (iesg@ietf.org)
14.5. PNS Sub-registry Establishment 14.5. PNS Subregistry Establishment
This section creates a new sub-registry, "PNS", under the sip- This section creates a new subregistry, "PNS", under the SIP
parameters registry: http://www.iana.org/assignments/sip-parameters. Parameters registry (https://www.iana.org/assignments/
sip-parameters).
The purpose of the sub-registry is to register SIP URI pn-provider The purpose of the subregistry is to register SIP URI 'pn-provider'
values. values.
When a SIP URI pn-provider value is registered in the sub-registry, When a SIP URI 'pn-provider' value is registered in the subregistry,
it needs to meet the "Specification Required" policies defined in it needs to meet the "Specification Required" policies defined in
[RFC8126]. [RFC8126].
This sub-registry is defined as a table that contains the following This subregistry is defined as a table that contains the following
three columns: three columns:
Value: The token under registration Value: The token under registration
Description: The name of the Push Notification Service (PNS) Description: The name of the Push Notification Service (PNS)
Document: A reference to the document defining the registration Document: A reference to the document defining the registration
This specification registers the following values: This specification registers the following values:
Value Description Document Value Description Document
------- -------------------------------------- ---------- ------- -------------------------------------- ----------
apns Apple Push Notification service [RFC XXXX] apns Apple Push Notification service RFC 8599
fcm Firebase Cloud Messaging [RFC XXXX] fcm Firebase Cloud Messaging RFC 8599
webpush Generic Event Delivery Using HTTP Push [RFC XXXX] webpush Generic Event Delivery Using HTTP Push RFC 8599
15. Acknowledgements
Thanks to Mickey Arnold, Paul Kyzivat, Dale Worley, Ranjit Avasarala,
Martin Thomson, Mikael Klein, Susanna Sjoholm, Kari-Pekka Perttula,
Liviu Chircu, Roman Shpount, Yehoshua Gev and Jean Mahoney for
reading the text, and providing useful feedback.
16. References 15. References
16.1. Normative References 15.1. Normative References
[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, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc- DOI 10.17487/RFC2119, March 1997,
editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E. A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261, Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002, <https://www.rfc- DOI 10.17487/RFC3261, June 2002,
editor.org/info/rfc3261>. <https://www.rfc-editor.org/info/rfc3261>.
[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, Initiation Protocol (SIP)", RFC 3840,
DOI 10.17487/RFC3840, August 2004, <https://www.rfc- DOI 10.17487/RFC3840, August 2004,
editor.org/info/rfc3840>. <https://www.rfc-editor.org/info/rfc3840>.
[RFC3891] Mahy, R., Biggs, B., and R. Dean, "The Session Initiation [RFC3891] Mahy, R., Biggs, B., and R. Dean, "The Session Initiation
Protocol (SIP) "Replaces" Header", RFC 3891, Protocol (SIP) "Replaces" Header", RFC 3891,
DOI 10.17487/RFC3891, September 2004, <https://www.rfc- DOI 10.17487/RFC3891, September 2004,
editor.org/info/rfc3891>. <https://www.rfc-editor.org/info/rfc3891>.
[RFC3969] Camarillo, G., "The Internet Assigned Number Authority [RFC3969] Camarillo, G., "The Internet Assigned Number Authority
(IANA) Uniform Resource Identifier (URI) Parameter (IANA) Uniform Resource Identifier (URI) Parameter
Registry for the Session Initiation Protocol (SIP)", Registry for the Session Initiation Protocol (SIP)",
BCP 99, RFC 3969, DOI 10.17487/RFC3969, December 2004, BCP 99, RFC 3969, DOI 10.17487/RFC3969, December 2004,
<https://www.rfc-editor.org/info/rfc3969>. <https://www.rfc-editor.org/info/rfc3969>.
[RFC5079] Rosenberg, J., "Rejecting Anonymous Requests in the [RFC5079] Rosenberg, J., "Rejecting Anonymous Requests in the
Session Initiation Protocol (SIP)", RFC 5079, Session Initiation Protocol (SIP)", RFC 5079,
DOI 10.17487/RFC5079, December 2007, <https://www.rfc- DOI 10.17487/RFC5079, December 2007,
editor.org/info/rfc5079>. <https://www.rfc-editor.org/info/rfc5079>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC6809] Holmberg, C., Sedlacek, I., and H. Kaplan, "Mechanism to [RFC6809] Holmberg, C., Sedlacek, I., and H. Kaplan, "Mechanism to
Indicate Support of Features and Capabilities in the Indicate Support of Features and Capabilities in the
Session Initiation Protocol (SIP)", RFC 6809, Session Initiation Protocol (SIP)", RFC 6809,
DOI 10.17487/RFC6809, November 2012, <https://www.rfc- DOI 10.17487/RFC6809, November 2012,
editor.org/info/rfc6809>. <https://www.rfc-editor.org/info/rfc6809>.
[RFC8030] Thomson, M., Damaggio, E., and B. Raymor, Ed., "Generic [RFC8030] Thomson, M., Damaggio, E., and B. Raymor, Ed., "Generic
Event Delivery Using HTTP Push", RFC 8030, Event Delivery Using HTTP Push", RFC 8030,
DOI 10.17487/RFC8030, December 2016, <https://www.rfc- DOI 10.17487/RFC8030, December 2016,
editor.org/info/rfc8030>. <https://www.rfc-editor.org/info/rfc8030>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8292] Thomson, M. and P. Beverloo, "Voluntary Application Server [RFC8292] Thomson, M. and P. Beverloo, "Voluntary Application Server
Identification (VAPID) for Web Push", RFC 8292, Identification (VAPID) for Web Push", RFC 8292,
DOI 10.17487/RFC8292, November 2017, <https://www.rfc- DOI 10.17487/RFC8292, November 2017,
editor.org/info/rfc8292>. <https://www.rfc-editor.org/info/rfc8292>.
[pns-apns] [pns-apns] Apple Inc., "Local and Remote Notification Programming
Apple Inc, "Apple Push Notification Service", January Guide: Communicating with APNs", <https://developer.apple.
2019, <https://developer.apple.com/library/archive/documen com/library/archive/documentation/NetworkingInternet/Conce
tation/NetworkingInternet/Conceptual/ ptual/RemoteNotificationsPG/CommunicatingwithAPNs.html>.
RemoteNotificationsPG/CommunicatingwithAPNs.html>.
[pns-fcm] Google Inc, "Firebase Cloud Messaging", January 2019, < [pns-fcm] Google Inc., "Firebase Cloud Messaging",
https://firebase.google.com/docs/cloud-messaging/concept- <https://firebase.google.com/docs/cloud-messaging/
options>. concept-options>.
16.2. Informative References 15.2. Informative References
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264, with Session Description Protocol (SDP)", RFC 3264,
DOI 10.17487/RFC3264, June 2002, <https://www.rfc- DOI 10.17487/RFC3264, June 2002,
editor.org/info/rfc3264>. <https://www.rfc-editor.org/info/rfc3264>.
[RFC3680] Rosenberg, J., "A Session Initiation Protocol (SIP) Event [RFC3680] Rosenberg, J., "A Session Initiation Protocol (SIP) Event
Package for Registrations", RFC 3680, Package for Registrations", RFC 3680,
DOI 10.17487/RFC3680, March 2004, <https://www.rfc- DOI 10.17487/RFC3680, March 2004,
editor.org/info/rfc3680>. <https://www.rfc-editor.org/info/rfc3680>.
[RFC4320] Sparks, R., "Actions Addressing Identified Issues with the [RFC4320] Sparks, R., "Actions Addressing Identified Issues with the
Session Initiation Protocol's (SIP) Non-INVITE Session Initiation Protocol's (SIP) Non-INVITE
Transaction", RFC 4320, DOI 10.17487/RFC4320, January Transaction", RFC 4320, DOI 10.17487/RFC4320, January
2006, <https://www.rfc-editor.org/info/rfc4320>. 2006, <https://www.rfc-editor.org/info/rfc4320>.
[RFC4321] Sparks, R., "Problems Identified Associated with the [RFC4321] Sparks, R., "Problems Identified Associated with the
Session Initiation Protocol's (SIP) Non-INVITE Session Initiation Protocol's (SIP) Non-INVITE
Transaction", RFC 4321, DOI 10.17487/RFC4321, January Transaction", RFC 4321, DOI 10.17487/RFC4321, January
2006, <https://www.rfc-editor.org/info/rfc4321>. 2006, <https://www.rfc-editor.org/info/rfc4321>.
[RFC5626] Jennings, C., Ed., Mahy, R., Ed., and F. Audet, Ed., [RFC5626] Jennings, C., Ed., Mahy, R., Ed., and F. Audet, Ed.,
"Managing Client-Initiated Connections in the Session "Managing Client-Initiated Connections in the Session
Initiation Protocol (SIP)", RFC 5626, Initiation Protocol (SIP)", RFC 5626,
DOI 10.17487/RFC5626, October 2009, <https://www.rfc- DOI 10.17487/RFC5626, October 2009,
editor.org/info/rfc5626>. <https://www.rfc-editor.org/info/rfc5626>.
[RFC6665] Roach, A., "SIP-Specific Event Notification", RFC 6665, [RFC6665] Roach, A., "SIP-Specific Event Notification", RFC 6665,
DOI 10.17487/RFC6665, July 2012, <https://www.rfc- DOI 10.17487/RFC6665, July 2012,
editor.org/info/rfc6665>. <https://www.rfc-editor.org/info/rfc6665>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26, Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>. <https://www.rfc-editor.org/info/rfc8126>.
[RFC8291] Thomson, M., "Message Encryption for Web Push", RFC 8291, [RFC8291] Thomson, M., "Message Encryption for Web Push", RFC 8291,
DOI 10.17487/RFC8291, November 2017, <https://www.rfc- DOI 10.17487/RFC8291, November 2017,
editor.org/info/rfc8291>. <https://www.rfc-editor.org/info/rfc8291>.
Acknowledgements
Thanks to Paul Kyzivat, Dale Worley, Ranjit Avasarala, Martin
Thomson, Mikael Klein, Susanna Sjoholm, Kari-Pekka Perttula, Liviu
Chircu, Roman Shpount, Yehoshua Gev, and Jean Mahoney for reading the
text and providing useful feedback.
Authors' Addresses Authors' Addresses
Christer Holmberg Christer Holmberg
Ericsson Ericsson
Hirsalantie 11 Hirsalantie 11
Jorvas 02420 Jorvas 02420
Finland Finland
Email: christer.holmberg@ericsson.com Email: christer.holmberg@ericsson.com
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