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Versions: (draft-holmberg-sipcore-sip-push) 00 01 02 03 04 05 06 07 08 09 10 11

SIPCORE Working Group                                        C. Holmberg
Internet-Draft                                                  Ericsson
Intended status: Standards Track                               M. Arnold
Expires: October 13, 2018                            Metaswitch Networks
                                                          April 11, 2018


      Push Notification with the Session Initiation Protocol (SIP)
                     draft-ietf-sipcore-sip-push-11

Abstract

   This document describes how a Push Notification Service (PNS) can be
   used to awake suspended Session Initiation Protocol (SIP) User Agents
   (UAs), using push notifications, for the UA to be able to send re-
   registration REGISTER requests and to receive receive incoming 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 October 13, 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



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   publication of this document.  Please review these documents
   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 . . . . . . . . . . . . . . . . . . . . . . . . .   6
   3.  Push Resource ID (PRID) . . . . . . . . . . . . . . . . . . .   6
   4.  SIP User Agent (UA) Behavior  . . . . . . . . . . . . . . . .   6
     4.1.  Request Push Notifications from Network . . . . . . . . .   6
     4.2.  Query Network Push Notification Capabilities  . . . . . .   8
   5.  SIP Proxy Behavior  . . . . . . . . . . . . . . . . . . . . .   9
     5.1.  PNS Identifier  . . . . . . . . . . . . . . . . . . . . .   9
     5.2.  Trigger Periodic Re-registration  . . . . . . . . . . . .   9
     5.3.  SIP Request . . . . . . . . . . . . . . . . . . . . . . .  10
       5.3.1.  REGISTER  . . . . . . . . . . . . . . . . . . . . . .  10
       5.3.2.  Initial Request for Dialog or Stand-Alone Request . .  12
   6.  Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
     6.1.  555 (Push Notification Service Not Supported) Response
           Code  . . . . . . . . . . . . . . . . . . . . . . . . . .  13
     6.2.  556 (Push Notification Failed) Response Code  . . . . . .  14
     6.3.  sip.pns Feature-Capability Indicator  . . . . . . . . . .  14
     6.4.  sip.vapid Feature-Capability Indicator  . . . . . . . . .  14
     6.5.  sip.pnsreg Feature-Capability Indicator . . . . . . . . .  15
     6.6.  sip.pnsreg Media Feature Tag  . . . . . . . . . . . . . .  15
     6.7.  SIP URI Parameters  . . . . . . . . . . . . . . . . . . .  16
   7.  PNS Registration Requirements . . . . . . . . . . . . . . . .  16
   8.  pn-provider, pn-param and pn-prid URI Parameters for Apple
       Push Notification service . . . . . . . . . . . . . . . . . .  16
   9.  pn-provider, pn-param and pn-prid URI Parameters for Google
       Firebase Cloud Messaging (FCM) push notification service  . .  17
   10. pn-provider, pn-param and pn-prid URI Parameters for RFC 8030
       (Generic Event Delivery Using HTTP Push)  . . . . . . . . . .  17
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  18
   12. IANA considerations . . . . . . . . . . . . . . . . . . . . .  18
     12.1.  SIP URI Parameters . . . . . . . . . . . . . . . . . . .  19
       12.1.1.  pn-provider  . . . . . . . . . . . . . . . . . . . .  19
       12.1.2.  pn-param . . . . . . . . . . . . . . . . . . . . . .  19
       12.1.3.  pn-prid  . . . . . . . . . . . . . . . . . . . . . .  19
     12.2.  SIP Response Codes . . . . . . . . . . . . . . . . . . .  19
       12.2.1.  555 (Push Notification Service Not Supported)  . . .  19
       12.2.2.  556 (Push Notification Failed) . . . . . . . . . . .  20
     12.3.  SIP Global Feature-Capability Indicator  . . . . . . . .  20
       12.3.1.  sip.pns  . . . . . . . . . . . . . . . . . . . . . .  20



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       12.3.2.  sip.vapid  . . . . . . . . . . . . . . . . . . . . .  21
       12.3.3.  sip.pnsreg . . . . . . . . . . . . . . . . . . . . .  21
     12.4.  SIP Media Feature Tag  . . . . . . . . . . . . . . . . .  22
       12.4.1.  sip.pnsreg . . . . . . . . . . . . . . . . . . . . .  22
     12.5.  PNS Sub-registry Establishment . . . . . . . . . . . . .  23
   13. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  24
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  24
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  24
     14.2.  Informative References . . . . . . . . . . . . . . . . .  25
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  25

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,
   using push notifications, 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
   request such push notification requests.

   NOTE: Even if a UA is able to awake by other means than receiving
   push notifications (e.g., by 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



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   requests (as it will save battery life etc) and use push
   notifications to awake the UA when an incoming SIP request 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 use a REGISTER request to provide the PRID to the SIP proxy that
   will request push notifications towards the UA.

   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)       |



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








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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.

   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

4.1.  Request Push Notifications from Network

   Once the SIP UA has registered with the PNS, has received the PRID
   (using the protocol and procedures associated with the PNS), if the
   UA wants to receive push notifications (requested by the proxy), 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 type of 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 type of 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 proxy supports
   use of the Voluntary Application Server Identification (VAPID)
   mechanism [RFC8292] to restrict push notifications to the proxy.



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   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.

   If the UA is able to send re-registration REGISTER requests using a
   non-push mechanism (e.g., using an internal timer that periodically
   awakes the UA), the UA MUST insert a 'sip.pnsreg' media feature tag
   [RFC3840] in the Contact header field URI 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.
   Even if the UA is able to to send REGISTER requests using a non-push
   mechanism, the UA MUST still send a REGISTER request when it receives
   a push notification, following the procedures in this section.  If
   the REGISTER response does not contain a a 'sip.pnsreg' feature-
   capability indicator, the UA SHOULD only send a re-registration
   REGISTER request when it receives a push notification (even if the UA
   is able to use a non-push mechanism for sending re-registration
   REGISTER requests).

   NOTE: In some cases the UA might be able to use a non-push mechanism
   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 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.

   NOTE: This specification does not define any usage of a push
   notification payload.  As defined in Section 5.3.2, a proxy must not
   include any payload in the push notification request.  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 re-registration
   REGISTER request.



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   NOTE: If the SIP UA application wants to use push notifications for
   other purposes than to trigger re-registration requests, it needs to
   be able to distinguish between the different purposes when receiving
   push notifications.  Mechanisms for doing that are outside the scope
   of this specification.

   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.

   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.

4.2.  Query Network Push Notification Capabilities

   A SIP UA might need to query the network for push notification
   capabilities (e.g., related to VAPID) before it registers with the
   PNS, and before it indicates that it wants to receive push
   notifications.  The UA can do so by only including the pn-provider
   SIP URI parameter in the SIP Contact header field URI of the REGISTER
   request, but without including the pn-prid SIP URI parameter.  Later,
   once the UA has received a response to the REGISTER request, with the
   push notification information from the network, if the UA wants to
   receive push notifications, the UA will send a re-registration




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   REGISTER request, including all pn- SIP URI parameters required by
   the specific PNS, following the procedures in Section 4.1.

5.  SIP Proxy Behavior

5.1.  PNS Identifier

   The type of 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 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 awake using a non-push mechanism for sending re-
   registration REGISTER requests, if the proxy does not receive a
   REGISTER request prior to 120 seconds before the registration
   expires, the proxy MAY request a push notification towards the UA, to
   trigger the UA to send a REGISTER request.

   NOTE: As described in Section 4.2, a SIP UA might send a REGISTER
   request without including a pn-prid SIP URI parameter, in order to
   retrieve push notification capabilities from the network before the
   UA expects to receive push notifications from the network.  A proxy
   will not request push notifications towards a UA that has not
   provided a pn-prid SIP URI parameter.

   If the proxy receives information that a registration has expired,
   the proxy MUST NOT request further push notifications towards the UA.



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5.3.  SIP Request

5.3.1.  REGISTER

   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 type of 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.

   As described in Section 4.2, a SIP UA might send a REGISTER request
   without including a pn-prid SIP URI parameter in the Contact header
   field URI, in order to retrieve push notification capabilities from
   the network before the UA the proxy will request push notifications
   towards the UA.  The procedures in this section apply to both the
   case when the REGISTER request contains a pn-prid SIP URI parameter,
   and when it does not.

   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 (if the Contact header field URI of the REGISTER
   request contains a pn-prid SIP URI parameter), 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.

   If the proxy considers the requested registration expiration interval
   [RFC3261] to be too short, the proxy MUST either send a 423 (Interval
   Too Brief) response to the REGISTER request, or skip the rest of the
   procedures in this section and process the REGISTER request using
   normal SIP procedures.  If the proxy sends a 423 (Interval Too Brief)
   response, the proxy SHOULD insert a Feature-Caps header field with a
   'sip.pns' feature-capability indicator in the response, identifying
   each type of PNS that the proxy supports.  Similarly, when the proxy
   receives a 2xx response to the REGISTER request (see below), if the
   proxy considers the registration expiration interval indicated by the
   registrar too short, the proxy MUST NOT insert a Feature-Caps header
   field with a 'sip.pns' feature-capability indicator in the response,
   and the proxy MUST NOT request push notifications associated with the
   registration.  A registration expiration interval MUST be considered
   too short if the interval is smaller than the time prior to
   expiration that the proxy would request a push notification.  The
   proxy MAY consider the interval too small based on its own policy so
   as to reduce load on the system.



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   Otherwise, if the pn-provider SIP URI parameter identifies a type of
   PNS that the proxy does not support, or if the REGISTER request does
   not contain all additional information required for the specific type
   of PNS, the proxy MUST either forward the request (e.g., if the proxy
   knows that a downstream proxy supports the type of 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 the type of each PNS that the proxy
   supports.  The decision whether to forward the request, or to send a
   response, is done based on local policy.

   If the proxy supports the type of 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 type
   of 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 (if the Contact
   header field URI of the REGISTER request contains a pn-prid SIP URI
   parameter), 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), if
   the proxy receives (or, in case the proxy is the SIP registrar,
   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 type of PNS.
   This will inform the UA that the proxy supports, and will request (if
   the Contact header field URI of the REGISTER request contained a pn-
   prid SIP URI parameter), 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.  If the
   proxy receives a receives 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 the type of each PNS that the proxy supports.

   In addition, if the proxy receives a 2xx response to the REGISTER
   request:

   o  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].
      The proxy MUST be able to determine whether the PNS supports the




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      VAPID mechanism before it inserts the feature-capability
      indicator.
   o  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.  This can happen if the
   UA sends a re-registration REGISTER request with a new contact at the
   same time the registrar forwards a SIP request towards a UA using the
   previously registered contact in the Request-URI.

   As both the SIP request to be forwarded towards the UA, and the re-
   registration REGISTER request triggered by the push notification
   request, will convey pn- SIP URI parameters associated with the SIP
   registration, those can be used to match the SIP request with the re-
   registration REGISTER request (even if the most recent contact and
   the Request-URI of the SIP request do not match).

   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




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   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 556 (Push Notification Failed) 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.  Similarly, if the Request-URI of the SIP request
   only contains any pn-provider SIP URI parameter, but no other pn- SIP
   URI parameters, e.g., because the SIP UA has not included them in a
   REGISTER request (Section 4.2), the proxy is not able to request a
   push notification towards the UA.  If the proxy has knowledge that
   the UA is awake, and that the UA is able to receive the SIP request,
   the proxy MAY forwards the request towards the UA.  Otherwise the
   proxy MUST reject the SIP request with a 556 (Push Notification
   Failed) response.

6.  Grammar

6.1.  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




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   indicate that the server did not support the push notification
   service identified in a 'pn-provider' SIP URI parameter.

   The use of the SIP 555 response code is defined for SIP REGISTER
   responses.

6.2.  556 (Push Notification Failed) Response Code

   The 556 response code is added to the "Server-Error" Status-Code
   definition. 556 (Push Notification Failed) is used to indicate that
   the server failed to request a push notification from the push
   notification service identified in a 'pn-provider' SIP URI parameter.

   The use of the SIP 556 response code is defined for responses to SIP
   requests initiating dialogs, and responses to stand-alone SIP
   requests.

6.3.  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


6.4.  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
   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



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   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


6.5.  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 expiration 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


6.6.  sip.pnsreg Media Feature Tag

   The sip.pnsreg media feature tag, when included in the SIP Contact
   header field of a SIP REGISTER request, indicates 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.



     pnsreg-mt          = "+sip.pnsreg"









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6.7.  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.


7.  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.

8.  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

9.  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

10.  pn-provider, pn-param and pn-prid URI Parameters for RFC 8030
     (Generic Event Delivery Using HTTP Push)

   When Generic Event Delivery Using HTTP Push is used, the PNS related
   URI parameters are set as described below.

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




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   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.

   See RFC 8030 for more details:

   Note that encryption for web push [RFC8291] is not used, therefore
   parameters for message encryption are not defined in this
   specification.  Web push permits the sending of a push message
   without a payload without encryption.

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
   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







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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



     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 Codes

12.2.1.  555 (Push Notification Service Not Supported)

   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.





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      Response Code Number:   555

      Default Reason Phrase:  Push Notification Service Not Supported


12.2.2.  556 (Push Notification Failed)

   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:   556

      Default Reason Phrase:  Push Notififcation Failed


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.



    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)






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




















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    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, indicates 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]
     webpush       Generic Event Delivery Using HTTP Push  [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>.

   [RFC8291]  Thomson, M., "Message Encryption for Web Push", RFC 8291,
              DOI 10.17487/RFC8291, November 2017, <https://www.rfc-
              editor.org/info/rfc8291>.

Authors' Addresses

   Christer Holmberg
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: christer.holmberg@ericsson.com









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

   Email: Michael.Arnold@metaswitch.com












































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