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Versions: (draft-holmberg-sipcore-sip-push) 00 01 02 03 04 08

SIPCORE Working Group                                        C. Holmberg
Internet-Draft                                                  Ericsson
Intended status: Standards Track                               M. Arnold
Expires: September 1, 2018                           Metaswitch Networks
                                                       February 28, 2018


      Push Notification with the Session Initiation Protocol (SIP)
                     draft-ietf-sipcore-sip-push-08

Abstract

   This document describes how a Push Notification Service (PNS) can be
   used to awake suspended Session Initiation Protocol (SIP) User Agents
   (UAs), for the UA to be able to receive and send SIP requests.  The
   document defines new SIP URI parameters and new feature-capability
   indicators that can be used in SIP messages to indicate support of
   the mechanism defined in this document, to exchange PNS information
   between the SIP User Agent (UA) and the SIP entity that will request
   push notifications towards the UA, and to trigger such push
   notification requests.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 1, 2018.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Push Resource ID (PRID) . . . . . . . . . . . . . . . . . . .   5
   4.  SIP User Agent (UA) Behavior  . . . . . . . . . . . . . . . .   6
   5.  SIP Proxy Behavior  . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  PNS Identifier  . . . . . . . . . . . . . . . . . . . . .   8
     5.2.  Trigger Periodic Re-registration  . . . . . . . . . . . .   8
     5.3.  SIP Request . . . . . . . . . . . . . . . . . . . . . . .   9
       5.3.1.  REGISTER Request  . . . . . . . . . . . . . . . . . .   9
       5.3.2.  Initial Request for Dialog or Stand-Alone Request . .  10
   6.  Network Address Translator (NAT) Considerations . . . . . . .  11
   7.  Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . .  12
     7.1.  555 (Push Notification Service Not Supported) Response
           Code  . . . . . . . . . . . . . . . . . . . . . . . . . .  12
     7.2.  sip.pns Feature-Capability Indicator  . . . . . . . . . .  12
     7.3.  sip.vapid Feature-Capability Indicator  . . . . . . . . .  12
     7.4.  sip.pnsreg Feature-Capability Indicator . . . . . . . . .  13
     7.5.  sip.pnsreg Media Feature Tag  . . . . . . . . . . . . . .  13
     7.6.  SIP URI Parameters  . . . . . . . . . . . . . . . . . . .  14
   8.  PNS Registration Requirements . . . . . . . . . . . . . . . .  14
   9.  pn-provider, pn-param and pn-prid URI Parameters for Apple
       Push Notification service . . . . . . . . . . . . . . . . . .  14
   10. pn-provider, pn-param and pn-prid URI Parameters for Google
       Firebase Cloud Messaging (FCM) push notification service  . .  15
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  15
   12. IANA considerations . . . . . . . . . . . . . . . . . . . . .  16
     12.1.  SIP URI Parameters . . . . . . . . . . . . . . . . . . .  16
       12.1.1.  pn-provider  . . . . . . . . . . . . . . . . . . . .  16
       12.1.2.  pn-param . . . . . . . . . . . . . . . . . . . . . .  16
       12.1.3.  pn-prid  . . . . . . . . . . . . . . . . . . . . . .  17
     12.2.  SIP Response Code  . . . . . . . . . . . . . . . . . . .  17
     12.3.  SIP Global Feature-Capability Indicator  . . . . . . . .  17
       12.3.1.  sip.pns  . . . . . . . . . . . . . . . . . . . . . .  17
       12.3.2.  sip.vapid  . . . . . . . . . . . . . . . . . . . . .  18
       12.3.3.  sip.pnsreg . . . . . . . . . . . . . . . . . . . . .  18
     12.4.  SIP Media Feature Tag  . . . . . . . . . . . . . . . . .  19
       12.4.1.  sip.pnsreg . . . . . . . . . . . . . . . . . . . . .  19
     12.5.  PNS Sub-registry Establishment . . . . . . . . . . . . .  20
   13. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  21
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  21



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     14.1.  Normative References . . . . . . . . . . . . . . . . . .  21
     14.2.  Informative References . . . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22

1.  Introduction

   In order to save resources (e.g., battery life) some devices
   (especially mobile devices) and operating systems will suspend
   applications when not used.  In some cases, internal timers cannot be
   used to awake such applications, nor will incoming network traffic
   awake the application.  Instead, the only way to awake the
   application is by using a Push Notification Service (PNS).  Typically
   each operating system uses a dedicated PNS.  For example, Apple iOS
   devices use the Apple Push Notification service (APNs) while Android
   devices use the Firebase Cloud Messaging (FCM) service.

   Because of the restrictions above, Session Initiation Protocol (SIP)
   User Agents (UAs) [RFC3261] can not be awoken, in order to send re-
   registration SIP REGISTER requests and to receive incoming SIP
   requests, without using a PNS to awake the UA in order to perform
   those functions.

   Also, without being able to use internal timers in order to awake
   applications, a UA will not be able to maintain connections e.g.,
   using the SIP Outbound Mechanism [RFC5626], as it requires the UA to
   send periodic keep-alive messages.

   This document describes how PNSs can be used to awake suspended UAs,
   to be able to send re-registration REGISTER requests and to receive
   incoming SIP requests.  The document defines new SIP URI parameters
   and new feature-capability indicators [RFC6809] that can be used in
   SIP messages to indicate support of the mechanism defined in this
   document, to exchange PNS information between the UA and the SIP
   entity (realized as a SIP proxy in this document) that will request
   push notifications towards the UA, and to trigger such push
   notification requests.

   NOTE: Even if a UA is able to awake (e.g., using internal timers) in
   order to send periodic re-registration REGISTER requests, it might
   still be useful to suspend the application between the sending of re-
   registration requests (as it will save battery life etc) and use a
   PNS to awake the UA when a SIP request addressed towards the UA
   arrives.

   When a UA registers to a PNS, it will receive a unique Push Resource
   ID (PRID) associated with the push notification registration.  The UA
   will provide the PRID to the SIP proxy that will request push
   notifications towards the UA in a REGISTER request.



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   When the proxy receives (or, if the proxy is the SIP registrar
   [RFC3261], initiates) a SIP request for a new dialog, or a stand-
   alone SIP request, addressed towards a UA, or when the proxy
   determines that the UA needs to send a re-registration REGISTER
   request, the proxy will request a push notification towards the UA,
   using the PNS of the UA.  Once the UA receives the push notification,
   it will be able to send a re-registration REGISTER request and
   receive the incoming SIP request.  The proxy will receive and forward
   (or, if the proxy is the registrar, process) the REGISTER request.
   If the push notification request was triggered by a SIP request
   addressed towards the UA (see above), once the REGISTER request has
   been accepted by the registrar, and the associated SIP 2xx response
   has been forwarded by the proxy towards the UA, the proxy can forward
   the SIP request towards the UA using normal SIP routing procedures.

   Different PNSs exist today.  Some are based on the standardized
   mechanism defined in [RFC8030], while others are proprietary (e.g.,
   the Apple Push Notification service).  Figure 1 shows the generic
   push notification architecture supported by the mechanism in this
   document.

   Each PNS uses PNS-specific terminology and function names.  The
   terminology in this document is meant to be PNS-independent.  If the
   PNS is based on [RFC8030], the SIP proxy takes the role of the
   application server.



     +--------+           +--------------+       +-----------------+
     | SIP UA |           | Push Service |       |    SIP Proxy    |
     +--------+           +--------------+       +-----------------+
         |                      |                         |
         |      Subscribe       |                         |
         |--------------------->|                         |
         |                      |                         |
         |    Push Resource ID  |                         |
         |<---------------------|                         |
         |                      |                         |
         |          SIP REGISTER (Push Resource ID)       |
         |===============================================>|
         |          SIP 200 OK  |                         |
         |<===============================================|
         |                      |                         |
         |                      |                         |
         |                      |                         |
         |                      |                         |  SIP INVITE
         |                      |     Push Message        |<============
         |                      |   (Push Resource ID)    |



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         |    Push Message      |<------------------------|
         |  (Push Resource ID)  |                         |
         |<---------------------|                         |
         |                      |                         |
         |          SIP REGISTER (Push Resource ID)       |
         |===============================================>|
         |          SIP 200 OK  |                         |
         |<===============================================|
         |                      |                         |
         |          SIP INVITE  |                         |
         |<===============================================|
         |                      |                         |


         ------- Push Notification API

         ======= SIP

     REGISTER sip:alice@example.com SIP/2.0
     Via: SIP/2.0/TCP alicemobile.example.com:5060;branch=z9hG4bKnashds7
     Max-Forwards: 70
     To: Alice <sip:alice@example.com>
     From: Alice <sip:alice@example.com>;tag=456248
     Call-ID: 843817637684230@998sdasdh09
     CSeq: 1826 REGISTER
     Contact: <sip:alice@alicemobile.example.com;
       pn-provider=acme;
       pn-param=acme-param;
       pn-prid=ZTY4ZDJlMzODE1NmUgKi0K>
     Expires: 7200
     Content-Length: 0


               Figure 1: SIP Push Notification Architecture

2.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

3.  Push Resource ID (PRID)

   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
   be used to generate push notifications.

   The format of the PRID may vary depending on the PNS.



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   The details regarding discovery of the PNS, and the procedures
   regarding the push notification registration and maintenance are
   outside the scope of this document.  The information needed to
   contact the PNS is typically pre-configured in the operating system
   of the device.

4.  SIP User Agent (UA) Behavior

   Once the SIP UA has registered with the PNS, has received the PRID
   (using the protocol and procedures associated with the PNS), and when
   the UA wants to receive push notifications, the UA MUST send a SIP
   REGISTER request using normal SIP procedures.  The UA MUST include
   the following SIP URI parameters in the SIP Contact header field URI
   of the REGISTER request: pn-provider, pn-prid and pn-param (if
   required for the specific PNS).  The pn-provider URI parameter
   identifies the PNS, the pn-prid URI parameter contains the PRID value
   and the pn-param URI parameter contains additional PNS-specific
   information.

   When the UA receives a 2xx response to the REGISTER request, if the
   response contains a Feature-Caps header field with a 'sip.pns'
   feature-capability indicator with a parameter value identifying the
   same PNS that was identified by the pn-provider URI parameter in the
   REGISTER request, the UA can assume that a SIP proxy will request
   push notifications towards the UA.  In other cases, the UA MUST NOT
   assume that push notifications will be requested, and the actions
   taken by the UA might be dependent on implementation or deployment
   architecture, and are outside the scope of this document.

   In addition, if the response contains a Feature-Caps header field
   with a 'sip.vapid' feature-capability indicator, the UA can use the
   Voluntary Application Server Identification VAPID) mechanism
   [RFC8292] to restrict push notifications to the proxy (assuming that
   the PNS supports VAPID).

   When the UA receives a push notification, it MUST send a re-
   registration REGISTER request, using normal SIP procedures.  If there
   are Network Address Translators (NATs) between the UA and the proxy,
   the REGISTER request will create NAT bindings that will allow
   incoming SIP requests to reach the UA.  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), or a stand-alone SIP
   request (e.g., a SIP MESSAGE), if such SIP request triggered the push
   notification request.  Note that, depending on which transport
   protocol is used, the SIP request might reach the UA before the
   REGISTER response.





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   If the UA is able to generate re-registration REGISTER requests
   without recieving push notifications (e.g., using a timer), the UA
   MUST insert a 'sip.pnsreg' media feature tag [RFC3840] in the Contact
   header field of each REGISTER request.  Then, if the response to the
   REGISTER request contains a 'sip.pnsreg' feature-capability indicator
   with an indicator value, the UA MUST send REGISTER requests prior to
   the registration expires.  The indicator value indicates a minimum
   time (given in seconds), prior to the registration expires when the
   UA MUST send the REGISTER request.  If the REGISTER response does not
   contain a a 'sip.pnsreg' feature-capability indicator, the UA only
   sends REGISTER requests when it receives a push notification.

   Note that even if the UA is able to send re-registration REGISTER
   requests without receiving push notifications, the UA MUST still send
   a REGISTER request whenever it receives a push notification,
   according to the procedures in this section.

   NOTE: As described above, in some cases the UA might be able to use a
   non-push mechanism (e.g., a timer) to awake and send re-registration
   REGISTER requests.  This allows the UA to e.g., use timers for
   sending REGISTER requests, but to be suspended (in order to save
   battery resources etc) between sending the REGISTER requests and use
   push notification to awaken the UA to process incoming calls.

   As long as the UA wants to receive push notifications (requested by
   the proxy), the UA MUST include a pn-provider, pn-prid and a pn-param
   (if required for the specific PNS provider) SIP URI parameter in each
   re-registration REGISTER request.  Note that, in some cases, the PNS
   might update the PRID value, in which case the UA will include the
   new value in the pn-prid SIP URI parameter in the re-registration
   REGISTER request.

   If the UA no longer wants to receive push notifications (requested by
   the proxy), the UA MUST send a re-registration REGISTER request
   without including the SIP URI parameters described above, or the UA
   MUST remove the registration.

   If a UA's subscription to a PNS (and the associated PRID) is only
   valid for a limited time then the UA is responsible for retrieving
   new subscription details from the PNS and sending a REGISTER request
   with the updated pn parameters to the proxy prior to the expiry of
   the existing subscription.  If a UA's subscription to a PNS expires
   then the UA MUST send a REGISTER without the pn parameters (to tell
   the proxy that it no longer wants push notifications) or terminate
   the registration.  The exact mechanisms for expiry and renewal of
   PRIDs will be PNS-specific and are outside the scope of this
   document.




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   For privacy and security reasons, the UA MUST NOT include the SIP URI
   parameters defined in this document in non-REGISTER request, to
   prevent the PNS information associated with the UA from reaching the
   remote peer.  For example, the UA MUST NOT include the SIP URI
   parameters in the Contact header field of an INVITE request.

5.  SIP Proxy Behavior

5.1.  PNS Identifier

   The PNS is identified by the pn-provider SIP URI parameter.

   The protocol and format used for the push notification requests are
   PNS-specific, and the details for constructing and sending a push
   notification request are outside the scope of this specification.

5.2.  Trigger Periodic Re-registration

   In order to request push notifications towards a SIP UA that will
   trigger the UA to send re-registration SIP REGISTER requests, the SIP
   proxy MUST have information about when a registration will expire.
   The proxy either needs to be the SIP registrar, or the proxy needs to
   retrieve the information from the registrar using some other
   mechanism.  Such mechanisms are outside the scope of this document.

   When the proxy receives an indication that the UA needs to send a re-
   registration REGISTER request, the proxy requests a push notification
   towards the UA.

   Note that the push notification needs to be requested early enough,
   in order for the associated re-registration REGISTER request to reach
   the SIP registrar before the registration expires.  It is RECOMMENDED
   that the proxy requests the push notification at least 120 seconds
   before the registration expires.

   If the UA has indicated, using the 'sip.pnsreg' media feature tag,
   that it is able to sending re-registration REGISTER requests without
   receiving push notifications, if the proxy does not receive a
   REGISTER request prior to 120 seconds before the registration
   expires, the proxy SHOULD request a push notification towards the UA,
   to trigger the UA to send a REGISTER request.

   NOTE: In some cases the UA might be able to use a non-push mechanism
   (e.g., a timer) to awake and send re-registration REGISTER requests.
   Such REGISTER request will update the registration expiration timer,
   and the proxy does not need to request a push notification towards
   the UA in order to awake the UA.  The proxy will still request a push
   notification towards the UA when the proxy receives a SIP request



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   addressed towards the UA (Section 5.3.2).  This allows the UA to
   e.g., use timers for sending re-registration REGISTER requests, but
   to be suspended (in order to save battery resources etc) between
   sending the REGISTER requests and use push notification to awaken the
   UA to process incoming calls.

5.3.  SIP Request

5.3.1.  REGISTER Request

   The procedures in this section apply when the SIP proxy receives a
   SIP REGISTER request (initial REGISTER request for a registration, or
   a re-registration REGISTER request) that contains a pn-provider SIP
   URI parameter identifying a PNS.  If the proxy receives a REGISTER
   request that does not contain a pn-provider SIP URI parameter, or
   that removes the registration, the proxy MUST NOT request push
   notifications towards the UA associated with the REGISTER request, or
   perform any other procedures in this section.

   When the proxy receives a REGISTER request, if the REGISTER request
   contains a Feature-Caps header field with a 'sip.pns' feature-
   capability indicator, it indicates that an upstream proxy supports,
   and will request, push notifications towards the UA.  The proxy MUST
   skip the rest of the procedures in this section, and process the
   REGISTER request using normal SIP procedures.

   Otherwise, if the pn-provider SIP URI parameter identifies a PNS that
   the proxy does not support, or if the REGISTER request does not
   contain all additional information required for the specific PNS, the
   proxy MUST either forward the request (e.g., if the proxy knows that
   a downstream proxy supports the PNS) or send a SIP 555 (Push
   Notification Service Not Supported) response to the REGISTER request.
   If the proxy sends a SIP 555 (Push Notification Service Not
   Supported) response, the proxy SHOULD insert a Feature-Caps header
   field with a 'sip.pns' feature-capability indicator in the response,
   identifying each PNS that the proxy supports.

   If the proxy supports the PNS identified by the pn-provider SIP URI
   parameter, the proxy MUST insert a Feature-Caps header field with a
   'sip.pns' feature-capability indicator, identifying the PNS, in the
   REGISTER request before forwarding the REGISTER request (unless the
   proxy is the registrar, in which case the proxy will terminate the
   REGISTER request).  This will inform downstream proxies that the
   proxy supports, and will request, push notifications towards the UA.

   If the proxy inserted a Feature-Caps header field with a 'sip.pns'
   feature-capability indicator in the REGISTER request (see above),
   when the proxy receives (or, in case the proxy is the SIP registrar,



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   creates) a 2xx response to the REGISTER request, the proxy MUST
   insert a Feature-Caps header field with a 'sip.pns' feature-
   capability indicator in the response, identifying the PNS.  This will
   inform the UA that the proxy supports, and will request, push
   notifications towards the UA.  The proxy MUST only indicate support
   of the same PNS that was identified in the pn-provider SIP URI
   parameter in the REGISTER request.

   In addition, if the proxy supports, and will use, the VAPID
   mechanism, the proxy MUST insert a Feature-Caps header field with a
   'sip.vapid' feature-capability indicator in the response.  The header
   field parameter contains the public key identifying the proxy
   [RFC8292].

   In addition, if the proxy received a 'sip.pnsreg' media feature tag
   in the REGISTER request, the proxy SHOULD include a 'sip.pnsreg'
   feature-capability indicator with an indicator value bigger than 120
   in the response, unless the proxy always want to request push
   notifications to trigger the UA to send a REGISTER request.

5.3.2.  Initial Request for Dialog or Stand-Alone Request

   The procedures in this section apply when the SIP proxy has indicated
   that it supports, and will request, push notifications towards the
   SIP UA.

   When the proxy receives (or, in case the proxy is the registrar,
   creates) a SIP request for a new dialog (e.g., a SIP INVITE request)
   or a stand-alone SIP request (e.g., a SIP MESSAGE 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 for the specific PNS
   provider) SIP URI parameter, the proxy requests a push notification
   towards the UA, using the PRID included in the pn-prid SIP URI
   parameter and the PNS identified by the pn-provider SIP URI
   parameter.

   The push notification will trigger the UA to send a re-registration
   REGISTER request.  The proxy will process the REGISTER request and
   the associated response as described in Section 5.3.1.  In case of a
   2xx response to the REGISTER request, once the proxy has forwarded
   the REGISTER response towards the UA, if the contact in the REGISTER
   response matches the Request-URI of the SIP request to be forwarded,
   the proxy can also forward the SIP request towards the UA, using
   normal SIP procedures.  If the contact of the most recent REGISTER
   2xx response and Request-URI do not match, the proxy MUST reject the
   SIP request with a 404 (Not Found) response.





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   NOTE: If the proxy is not the registrar, it needs to store (or be
   able to retrieve) the contact of the most recent REGISTER 2xx
   response, to be able to compare it with the Request-URI of the
   request to be forwarded towards the UA.

   In case of non-2xx response to the REGISTER request, the proxy MUST
   reject the SIP request with a 404 (Not Found) response.

   If the push notification request fails (see PNS-specific
   documentation for details), the proxy MUST reject the SIP request
   with a 555 (Push Notification Service Not Supported) response.

   NOTE: As described above, the reason the proxy needs to wait for the
   REGISTER response before forwarding the SIP request is to make sure
   that the REGISTER request has been accepted by the SIP registrar, and
   that the registered contact matches the Request-URI of the SIP
   request to be forwarded.

   If the proxy does not receive the REGISTER request from the UA within
   a given time after the proxy has requested the push notification, the
   proxy MUST reject the request with a 404 (Not Found) response.  The
   time value is set based on local policy.

   The proxy MUST NOT include the SIP request as payload in the
   requested push message.

   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 REGISTER
   request, the proxy MAY choose to not request a push notification
   towards the UA (and wait for the associated REGISTER request and 2xx
   response) before it tries to forward the SIP request towards the UA.
   The mechanisms for getting such knowledge might be dependent on
   implementation or deployment architecture, and are outside the scope
   of this document.

6.  Network Address Translator (NAT) Considerations

   Whenever the SIP UA receives a push notification, if the UA is
   located behind a Network Address Translator (NAT), the UA might need
   to take actions in order to establish a binding in the NAT, in order
   for an incoming SIP request to reach the UA.  By sending the re-
   registration SIP REQUEST the UA will establish such a NAT binding.

   If the UA and the SIP proxy are operating in an environment where one
   or more NATs might be located between the UA and the proxy, when the
   proxy receives a REGISTER request from the UA it can store the IP
   address and port information from where it received the request.
   Then, when the proxy forwards a SIP request towards the UA, it uses



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   that IP address and port, instead of the IP address and port
   associated with the Request-URI of the request.  If the REGISTER
   request created one or more NAT bindings, this will ensure that the
   SIP request reaches the UA.

7.  Grammar

7.1.  555 (Push Notification Service Not Supported) Response Code

   The 555 response code is added to the "Server-Error" Status-Code
   definition. 555 (Push Notification Service Not Supported) is used to
   indicate that the server did not support the push notification
   service identified in a 'pn-provider' SIP URI parameter, or that the
   server failed to request a push notification from the push
   notification service.

   The use of the SIP 555 response code is defined for SIP REGISTER
   responses, responses to SIP requests initiating dialogs and responses
   to stand-alone SIP requests.

7.2.  sip.pns Feature-Capability Indicator

   The sip.pns feature-capability indicator, when included in a Feature-
   Caps header field of a SIP REGISTER request or a SIP 2xx response to
   a REGISTER request, indicates that the entity associated with the
   indicator supports, and will use, the SIP push mechanism and the push
   notification service identified by the indicator value.  When
   included in a 555 (Push Notification Service Not Supported) response
   to a REGISTER request, the the indicator indicates that the entity
   associated with the indicator supports the SIP push mechanism, and
   the push notification service(s) identified by the indicator value.
   The values defined for the pn-provider SIP URI parameter are used as
   indicator values.



     pns-fc          = "+sip.pns" EQUAL LDQUOT pns-list RDQUOT
     pns-list        = pns *(COMMA pns)
     pns             = tag-value

     ; tag-value as defined in RFC 3840


7.3.  sip.vapid Feature-Capability Indicator

   The sip.vapid feature-capability indicator, when included in a SIP
   2xx response to a SIP REGISTER request, indicates that the entity
   associated with the indicator supports, and will use, the Voluntary



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   Application Server Identification (VAPID) [RFC8292] mechanism when
   requesting push notifications towards the SIP UA associated with the
   SIP registration.  The indicator value is a public key identifying
   the entity, that can be used by a SIP UA to restrict subscriptions to
   that entity.



     vapid-fc          = "+sip.vapid" EQUAL LDQUOT vapid RDQUOT
     vapid             = tag-value

     ; tag-value as defined in RFC 3840


7.4.  sip.pnsreg Feature-Capability Indicator

   The sip.pnsreg feature-capability indicator, when included in a SIP
   2xx response to a SIP REGISTER request, indicates that the entity
   associated with the indicator expects to receive re-registration
   REGISTER requests from the SIP UA associated with the registration
   before the registration expires, without the entity having to request
   push notifications towards the SIP UA in order to trigger the
   REGISTER requests.  The indicator value is the minimum value (given
   in seconds) before the registration expireation when the entity
   expects to receive the REGISTER request.



     pns-fc          = "+sip.pnsreg" EQUAL LDQUOT reg RDQUOT
     reg             = 1*DIGIT

     ; DIGIT as defined in RFC 3261


7.5.  sip.pnsreg Media Feature Tag

   The sip.pnsreg media feature tag, when included in the SIP Contact
   header field of a SIP REGISTER request, indciates that the SIP UA
   associated with the tag is able to send re-registration REGISTER
   requests associated with the registration without being awaken by
   push notifications.  The media feature tag has no values.



     pns-mt          = "+sip.pnsreg"






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7.6.  SIP URI Parameters

   The section defines new SIP URI parameters, by extending the grammar
   for "uri-parameter" as defined in [RFC3261].  The ABNF is as follows:



     uri-parameter   =/ pn-provider / pn-param / pn-prid
     pn-provider     = "pn-provider" EQUAL pvalue
     pn-param        = "pn-param" EQUAL pvalue
     pn-prid         = "pn-prid" EQUAL pvalue

     ; pvalue as defined in RFC 3261
     ; EQUAL as defined in RFC 3261
     ; COLON as defined in RFC 3261

     The format and semantics of pn-prid and pn-param are
     specific to the pn-provider value.

     Parameter value chapters that are not part of pvalue needs to be
     escaped, as defined in RFC 3261.


8.  PNS Registration Requirements

   When a new value is registered to the PNS Sub-registry, a reference
   to a specification which describes the PNS associated with the value
   is provided.  That specification MUST contain the following
   information:

   o  The value of the pn-provider SIP URI parameter.
   o  How the pn-prid SIP URI parameter value is retrieved and set by
      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.

9.  pn-provider, pn-param and pn-prid URI Parameters for Apple Push
    Notification service

   When the Apple Push Notification service (APNs) is used, the PNS-
   related SIP URI parameters are set as described below.

   The value of the pn-provider URI parameter is "apns".

   Example: pn-provider = apns

   The value of the pn-param URI parameter is the APNs App ID, which is
   encoded by two values, separated by a period (.): Team ID and Bundle



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   ID.  The Team ID is provided by Apple and is unique to a development
   team.  The Bundle ID is unique to a development team, and is a string
   that will match a single application or a group of applications.

   Example: pn-param = DEF123GHIJ.com.yourcompany.yourexampleapp

   The value of the pn-prid URI parameter is the device token, which is
   a unique identifier assigned by Apple to a specific app on a specific
   device.

   Example: pn-prid = 00fc13adff78512

   For more information on the APNs App ID:

   https://developer.apple.com/library/content/documentation/General/
   Conceptual/DevPedia-CocoaCore/AppID.html

   For more information on the APNs device token:

   https://developer.apple.com/library/content/documentation/NetworkingI
   nternet/Conceptual/RemoteNotificationsPG/APNSOverview.html#//apple_re
   f/doc/uid/TP40008194-CH8-SW13

10.  pn-provider, pn-param and pn-prid URI Parameters for Google
     Firebase Cloud Messaging (FCM) push notification service

   When Firebase Cloud Messaging (FCM) is used, the PNS related URI
   parameters are set as described below.

   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-prid URI parameter is the Registration token,
   which is generated by the FCM SDK for each client app instance.

   For more information on the Project ID and Registration token:

   https://firebase.google.com/docs/cloud-messaging/concept-options

11.  Security Considerations

   Different mechanisms exist for authenticating and authorizing devices
   and users registering with a PNS.  The mechanisms for authorizing and
   authenticating the users are PNS-specific, and are outside the scope
   of this document.  In addition to the information that needs to be
   exchanged between a device and the PNS in order to establish a push
   notification subscription, the mechanism defined in this document



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   does not require any additional information to be exchanged between
   the device and the PNS.

   Typically, the PNS also requires the SIP proxy requesting push
   notifications to be authenticated and authorized by the PNS.  In some
   cases the PNS also require the SIP application (or the SIP
   application developer) to be identified in order for the application
   to request push notifications.

   If the push notification related information carried in SIP could be
   used by a malicious middleman to trigger push notifications towards a
   device, operators MUST ensure that the SIP signalling is properly
   secured from malicious middlemen, e.g., using encryption.

   [RFC8292] defines a mechanism which allows a proxy to create a
   identity itself to a PNS, by signing a JWT sent to the PNS using a
   key pair.  The public key serves as an identifier of the proxy, and
   can be used by devices to restrict push notifications to the proxy
   associated with the key.

   The mechanism in this document does not require a proxy to include
   any payload (in addition to possible payload used for the PNS itself)
   when requesting push notifications.

12.  IANA considerations

12.1.  SIP URI Parameters

   This section defines new SIP URI Parameters that extend the "SIP/SIPS
   URI Parameters" sub-registry [RFC3969] under the sip-parameters
   registry: http://www.iana.org/assignments/sip-parameters.

12.1.1.  pn-provider



     Parameter Name: pn-provider

     Predefined Values:  No

     Reference:  RFC XXXX


12.1.2.  pn-param







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     Parameter Name: pn-param

     Predefined Values:  No

     Reference:  RFC XXXX


12.1.3.  pn-prid



     Parameter Name: pn-prid

     Predefined Values:  No

     Reference:  RFC XXXX


12.2.  SIP Response Code

   This section defines a new SIP response code that extends the
   "Response Codes" sub-registry [RFC3261] under the sip-parameters
   registry: http://www.iana.org/assignments/sip-parameters.



      Response Code Number:   555

      Default Reason Phrase:  Push Notification Service Not Supported


12.3.  SIP Global Feature-Capability Indicator

12.3.1.  sip.pns

   This section defines a new feature-capability indicator that extends
   the "SIP Feature-Capability Indicator Registration Tree" sub-registry
   [RFC6809] under the sip-parameters registry:
   http://www.iana.org/assignments/sip-parameters.












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    Name: sip.pns

    Description: This feature-capability indicator, when included in a
        Feature-Caps header field of a SIP REGISTER request or a SIP 2xx
        response to a REGISTER request, indicates that the entity
        associated with the indicator supports, and will use, the SIP
        push mechanism and the push notification service identified by
        the indicator value. When included in a 555 (Push Notification
        Service Not Supported) response to a REGISTER request, the the
        indicator indicates that the entity associated with the
        indicator supports the SIP push mechanism, and the push
        notification service(s) identified by the indicator value.

    Reference: [RFCXXXX]

    Contact: IESG (iesg@ietf.org)


12.3.2.  sip.vapid

   This section defines a new feature-capability indicator that extends
   the "SIP Feature-Capability Indicator Registration Tree" sub-registry
   [RFC6809] under the sip-parameters registry:
   http://www.iana.org/assignments/sip-parameters.



    Name: sip.vapid

    Description: This feature-capability indicator, when included in a
         SIP 2xx response to a SIP REGISTER request, indicates that the
         entity associated with the indicator supports, and will use,
         the Voluntary Application Server Identification (VAPID)
         mechanism when requesting push notifications towards the SIP UA
         associated with the SIP registration. The indicator value is a
         public key identifying the entity, that can be used by a SIP UA
         to restrict subscriptions to that entity.

    Reference: [RFCXXXX]

    Contact: IESG (iesg@ietf.org)


12.3.3.  sip.pnsreg

   This section defines a new feature-capability indicator that extends
   the "SIP Feature-Capability Indicator Registration Tree" sub-registry




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   [RFC6809] under the sip-parameters registry:
   http://www.iana.org/assignments/sip-parameters.



    Name: sip.pnsreg

    Description: This feature-capability indicator, when included in a
         SIP 2xx response to a SIP REGISTER request, indicates that the
         entity associated with the indicator expects to receive
         re-registration REGISTER requests from the SIP UA associated
         with the registration before the registration expires, without
         the entity having to request push notifications towards the SIP
         UA in order to trigger the REGISTER requests. The indicator
         value is the minimum value (given in seconds) before the
         registration expireation when the entity expects to receive the
         REGISTER request.

    Reference: [RFCXXXX]

    Contact: IESG (iesg@ietf.org)


12.4.  SIP Media Feature Tag

12.4.1.  sip.pnsreg

   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 registry: https://www.iana.org/assignments/media-
   feature-tags/media-feature-tags.xhtml.




















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      Media feature tag name: sip.pnsreg

      Summary of the media feature indicated by this feature tag: This
           media feature tag, when included in the SIP Contact header
           field of a SIP REGISTER request, indciates that the SIP UA
           associated with the tag is able to send re-registration
           REGISTER requests associated with the registration without
           being awaken by push notifications.

      Values appropriate for use with this feature tag: none

      Related standards or documents: [RFCXXXX]

      Security considerations: This media feature tag does not introduce
         new security considerations, as it simply indicates support for
         a basic SIP feature. If an attacker manages to remove the media
         feature tag, push notifications towards the client will be
         requested.

      Contact: IESG (iesg@ietf.org)


12.5.  PNS Sub-registry Establishment

   This section creates a new sub-registry, "PNS", under the sip-
   parameters registry: http://www.iana.org/assignments/sip-parameters.

   The purpose of the sub-registry is to register SIP URI pn-provider
   values.

   When a SIP URI pn-provider value is registered in the sub-registry,
   it needs to meet the "Expert Review" policies defined in [RFC8126].



     This sub-registry is defined as a table that contains the following
     three columns:

     Value:        The token under registration

     Description:  The name of the Push Notification Service (PNS)

     Document:     A reference to the document defining the registration








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     This specification registers the following values:

     Value         Description                         Document
     -------       ----------------------------------  ----------

     apns          Apple Push Notification service     [RFC XXXX]
     fcm           Firebase Cloud Messaging            [RFC XXXX]



13.  Acknowledgements

   Thanks to Mickey Arnold, Paul Kyzivat, Dale Worley, Ranjit Avasarala,
   Martin Thomson, Mikael Klein, Susanna Sjoholm, Kari-Pekka Perttula,
   Liviu Chircu, Roman Shpount and Yehoshua Gev for reading the text,
   and providing useful feedback.

14.  References

14.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
              editor.org/info/rfc2119>.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002, <https://www.rfc-
              editor.org/info/rfc3261>.

   [RFC3840]  Rosenberg, J., Schulzrinne, H., and P. Kyzivat,
              "Indicating User Agent Capabilities in the Session
              Initiation Protocol (SIP)", RFC 3840,
              DOI 10.17487/RFC3840, August 2004, <https://www.rfc-
              editor.org/info/rfc3840>.

   [RFC3969]  Camarillo, G., "The Internet Assigned Number Authority
              (IANA) Uniform Resource Identifier (URI) Parameter
              Registry for the Session Initiation Protocol (SIP)",
              BCP 99, RFC 3969, DOI 10.17487/RFC3969, December 2004,
              <https://www.rfc-editor.org/info/rfc3969>.








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   [RFC6809]  Holmberg, C., Sedlacek, I., and H. Kaplan, "Mechanism to
              Indicate Support of Features and Capabilities in the
              Session Initiation Protocol (SIP)", RFC 6809,
              DOI 10.17487/RFC6809, November 2012, <https://www.rfc-
              editor.org/info/rfc6809>.

   [RFC8030]  Thomson, M., Damaggio, E., and B. Raymor, Ed., "Generic
              Event Delivery Using HTTP Push", RFC 8030,
              DOI 10.17487/RFC8030, December 2016, <https://www.rfc-
              editor.org/info/rfc8030>.

   [RFC8292]  Thomson, M. and P. Beverloo, "Voluntary Application Server
              Identification (VAPID) for Web Push", RFC 8292,
              DOI 10.17487/RFC8292, November 2017, <https://www.rfc-
              editor.org/info/rfc8292>.

14.2.  Informative References

   [RFC5626]  Jennings, C., Ed., Mahy, R., Ed., and F. Audet, Ed.,
              "Managing Client-Initiated Connections in the Session
              Initiation Protocol (SIP)", RFC 5626,
              DOI 10.17487/RFC5626, October 2009, <https://www.rfc-
              editor.org/info/rfc5626>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

Authors' Addresses

   Christer Holmberg
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: christer.holmberg@ericsson.com


   Michael Arnold
   Metaswitch Networks
   100 Church Street
   Enfield  EN2 6BQ
   United Kingdom

   Email: Michael.Arnold@metaswitch.com




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