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SIPCORE Working Group                                        C. Holmberg
Internet-Draft                                                  Ericsson
Intended status: Standards Track                       November 23, 2017
Expires: May 27, 2018


      Push Notification with the Session Initiation Protocol (SIP)
                   draft-holmberg-sipcore-sip-push-03

Abstract

   This document describes how push notification mechanisms can be used
   to wake up suspended Session Initiation Protocol (SIP) User Agents
   (UAs), in order to be able to receive and generate SIP requests.  The
   document defines new SIP URI parameters, that can be used in a SIP
   REGISTER request to provide push notification information from the
   SIP User Agent (UA) to the SIP entity (realized as a SIP proxy in
   this document) that will send a push request to the push server in
   order to trigger a push notification towards the SIP UA.

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 May 27, 2018.

Copyright Notice

   Copyright (c) 2017 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
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Push Resource ID (PRID) . . . . . . . . . . . . . . . . . . .   5
   4.  SIP User Agent (UA) Behavior  . . . . . . . . . . . . . . . .   5
   5.  SIP Proxy Behavior  . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Push Notification Provider Information  . . . . . . . . .   6
     5.2.  Trigger Periodic Re-registration  . . . . . . . . . . . .   6
     5.3.  SIP Request . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Network Address Translator (NAT) Considerations . . . . . . .   7
   7.  Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   8.  PNS Registration Requirements . . . . . . . . . . . . . . . .   8
   9.  pn-prid and pn-type URI parameters for Apple Push
       Notification service  . . . . . . . . . . . . . . . . . . . .   8
   10. pn-prid and pn-type URI parameters for Google Firebase Cloud
       Messaging (FCM) push notification service . . . . . . . . . .   9
   11. Security considerations . . . . . . . . . . . . . . . . . . .   9
   12. IANA considerations . . . . . . . . . . . . . . . . . . . . .  10
     12.1.  pn-prid  . . . . . . . . . . . . . . . . . . . . . . . .  10
     12.2.  pn-type  . . . . . . . . . . . . . . . . . . . . . . . .  10
     12.3.  pn-enckey  . . . . . . . . . . . . . . . . . . . . . . .  10
     12.4.  pn-enccode . . . . . . . . . . . . . . . . . . . . . . .  10
     12.5.  PNS Sub-registry Establishment . . . . . . . . . . . . .  11
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     13.1.  Normative references . . . . . . . . . . . . . . . . . .  11
     13.2.  Informative references . . . . . . . . . . . . . . . . .  12
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   In order to save resources (e.g, battery life) some devices and
   operating systems require suspended Session Initiation Protocol (SIP)
   User Agents (UAs) [RFC3261] to be woken up using a push notification
   service.  Typically each operating system uses a dedicated push
   notification service.  For example, Apple iOS devices use the Apple
   Push Notification service (APNs).

   Due to the restriction above, applications can not be woken up by
   non-push notification traffic.  This means that a suspended SIP UA
   will not be able to receive an incoming SIP request (e.g., a SIP
   INVITE request), or to send periodic re-registration requests.





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   This document describes how push notification mechanisms can be used
   to wake up suspended SIP UAs, in order to be able to receive and
   generate SIP requests.  The document defines new SIP URI parameters,
   that can be used in a SIP REGISTER request to provide push
   notification information from the SIP UA to the SIP entity (realized
   as a SIP proxy in this document) that will send a push request to the
   push server in order to trigger a push notification towards the SIP
   UA.

   When a SIP UA registers to a push service, it will receive a unique
   Push Resource ID (PRID) associated to that registration.  The SIP UA
   will provide the PRID to the SIP network in a SIP REGISTER request.
   A SIP proxy (e.g., the SIP registrar) will store a mapping between
   the registered contact and the PRID.

   When the SIP proxy receives a SIP request for a new session, or a
   stand-alone SIP request, addressed towards a SIP UA, or when the SIP
   proxy determines that the SIP UA needs to perform a re-registration,
   the SIP proxy will send a push request to the push notification
   service used by the SIP UA, using the push resource ID associated
   with the registered contact of the SIP UA, in order to trigger a push
   notification towards the SIP UA.  The SIP proxy will then forward the
   SIP request towards the SIP UA using normal SIP routing procedures.
   Once the SIP UA receives the push notification, it will be to receive
   the SIP request, and to generate a SIP request (e.g., a SIP REGISTER)
   itself.

   Different push notification mechanisms exist today.  Some are based
   on there 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.



















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

         ------- 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-type=acme: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].






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3.  Push Resource ID (PRID)

   When an entity registers with a Push Notification Server (PNS) is
   receives a unique Push Resource ID (PRID), which is a value
   associated with the registration.

   The format of the PRID may vary depending on the PNS provider.  The
   PRID may be part of a URI that can be used to retrieve the address
   and port of the PNS when sending push requests to the PNS.  The PRID
   may also be a token value, in which case the address and port of the
   PNS needs to be provided using other means.

   The details regarding discovery of the PNS, and the procedures for
   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 (OS) of the device.

4.  SIP User Agent (UA) Behavior

   Once the SIP UA has registered with the PNS and received the PRID,
   and when the UA wants to receive push notifications triggered by the
   SIP proxy, the UA MUST send a SIP REGISTER using normal SIP
   registration procedures.  The UA MUST add a pn-prid URI parameter and
   a pn-type URI parameter to the SIP Contact header field URI of the
   request.  The pn-prid URI parameter contains the PRID value.  The pn-
   type contains additional, PNS-specific, information.

   When the SIP UA receives a push notification, it MUST perform a SIP
   re-registration [RFC3261] by sending a SIP REGISTER request.  If
   there are Network Address Translators (NATs) between the SIP UA and
   the SIP proxy, the SIP REGISTER request will create NAT bindings
   allowing incoming SIP requests to reach the SIP UA.  If the SIP proxy
   triggered the push notification because it wants to forward a SIP
   request towards the SIP UA, the receival of the SIP REGISTER request
   can be used by the SIP proxy as a trigger to forward the SIP request.

   As long as the UA wants the SIP proxy to continue sending push
   requests, the UA MUST include the pn-prid and pn-type URI parameters
   in every re-registration SIP REGISTER request sent towards the SIP
   proxy.  Note that, in some cases, the PNS might update the PRID
   value, in which case the re-registration SIP REGISTER request will
   contain the new value.

   If the SIP UA at some point wants to stop the SIP proxy from sending
   push requests, the SIP UA MUST send a SIP REGISTER request without
   the pn-prid and pn-type URI parameters.





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   If the SIP UA expects to receive payload in the push notification,
   the SIP UA MAY add a pn-enckey and a pn-encsec Contact header field
   URI parameter, in order to allow encryption of the data using the
   mechanism in [I-D.ietf-webpush-encryption].  The pn-enckey URI
   parameter contains the public key, and the pn-encsec URI parameter
   contains the authentication secret [I-D.ietf-webpush-encryption].

   NOTE: End-to-end encryption of the payload between the SIP proxy and
   the SIP UA cannot be used if the push notification request payload
   contains information that needs to be accessible by the push
   notification server.

5.  SIP Proxy Behavior

5.1.  Push Notification Provider Information

   In some cases the push notification provider can be retrieved from
   the pn-prid URI parameter.  In other cases the pn-type URI parameter
   is used to identity the push notification provider.

   The protocol and format used for the push request depends on the push
   notification provider, and the details for constructing and sending
   the messages are outside the scope of this specification.

5.2.  Trigger Periodic Re-registration

   If the SIP UA needs to perform periodic re-registrations, the SIP
   proxy needs to have information about when those re-registrations are
   to be performed.  The SIP proxy either needs to contain the SIP
   registrar functionality, or the SIP proxy needs to retreive the
   information from the registrar using some other mechanism.

   When the SIP proxy receives an indication that the SIP UA needs to
   perform a re-registration, the SIP proxy triggers a push request
   towards the push notification server associated with the PRID.

5.3.  SIP Request

   When the SIP proxy receives a SIP request for a new dialog (e.g., a
   SIP INVITE request) or a non-dialog SIP request (e.g., a SIP MESSAGE
   request) aimed for a SIP UA, if the Request-URI of the request
   contains a pn-prid URI parameter, the SIP proxy triggers a push
   request towards the push notification server associated with the
   PRID.  After that, the SIP proxy forwards the SIP request towards the
   SIP UA using normal SIP procedures.






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   As the push notification will trigger the SIP UA to perform a re-
   registration, the SIP proxy can use the receival of the SIP REGISTER
   request as a trigger to forward SIP request towards the SIP UA.

   The SIP proxy MUST NOT transport the SIP request as push request
   payload, instead of forwarding the request using normal SIP
   procedures.

   If the proxy is not able to contact the push notification provider,
   or even determine which push notification provider to contact, it
   SHOULD reject the SIP request.

   If the SIP proxy is able to assume that the SIP UA is awake, and that
   the SIP UA is able to receive the SIP request, the SIP proxy MAY
   choose to not trigger a push notification request before trying to
   forward the SIP request towards the SIP UA.  The SIP proxy can make
   such assumption e.g., if a TLS connection previously established by
   the SIP UA is still open.

6.  Network Address Translator (NAT) Considerations

   Whenever the UA receives a push notification, if the SIP 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 performing the re-
   registration the SIP UA will establish such NAT binding.

7.  Grammar

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




















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     uri-parameter   =/ pn-prid / pn-type / pn-enccode / pn-enckey
     pn-prid         = "pn-prid" EQUAL pvalue
     pn-type         = "pn-type" EQUAL pns-provider COLON pns-param
     pn-enccode      = "pn-enccode" EQUAL pvalue
     pn-enckey       = "pn-enckey" EQUAL pvalue

     pns-provider    = pvalue ; Colon (":") characters MUST be escaped
     pns-param       = pvalue ; Colon (":") characters MUST be escaped

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

     The format and semantics of pns-param is specific to a given
     pns-provider value.


8.  PNS Registration Requirements

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

   o  How the values for the pn-prid parameter is retrieved and set by
      the SIP UA.
   o  The format of the pns-param part of the pns-type parameter, and
      how the value of the pns-param part is retrieved and set by the
      SIP UA.
   o  Whether there are any restrictions regarding usage of payload
      encryption [I-D.ietf-webpush-encryption] with the associated push
      notification service.

9.  pn-prid and pn-type URI parameters for Apple Push Notification
    service

   When the Apple Push Notification service (APNs) is used, the value of
   the pn-type URI parameter pns-provider parameter part is "apns".  The
   pns-param part contains the APNs App ID, which is encoded by two
   values, separated by a period (.): Team ID and Bundle 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
   can match a single application or a group of applications.

   Example: pn-type = apns:DEF123GHIJ.com.yourcompany.yourexampleapp

   When the Apple Push Notification service (APNs) is used, pn-type URI
   parameter pns-prid parameter part contains the device token, which is



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   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-prid and pn-type URI parameters for Google Firebase Cloud
     Messaging (FCM) push notification service

   When Firebase Cloud Messaging (FCM) is used, the value of the pn-type
   URI parameter pns-provider parameter part is "fcm".  The pns-param
   part contains the Sender ID.

   When Firebase Cloud Messaging (FCM) is used, pn-type URI parameter
   pns-prid parameter part contains the Registration token, which
   generated by the FCM SDK for each client app instance.

   For more information on the Sender ID and Registration token:

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

11.  Security considerations

   In addition to the information exchanged between a device and its PNS
   in order to establish a push notification subscription, the mechanism
   in this document does not require entities to provide any additional
   information to the PNS.

   Push notification mechanisms provide different methods to ensure that
   malicious user cannot trigger push notifications to a device.  Users
   of the mechanism in this document MUST take measures to prevent push
   notifications from being sent to a device from a malicious user.

   In case entities do want to include payload in the push
   notifications, this document defines the means for using end-to-end
   payload encryption between the entity sending the push request and
   the entity receiving the associated push notification.




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12.  IANA considerations

   This specification defines new SIP URI parameters that extend the
   registry created by [RFC3969]:

12.1.  pn-prid



     Parameter Name: pn-prid

     Predefined Values:  No

     Reference:  RFC XXXX


12.2.  pn-type



     Parameter Name: pn-type

     Predefined Values:  No

     Reference:  RFC XXXX


12.3.  pn-enckey



     Parameter Name: pn-enckey

     Predefined Values:  No

     Reference:  RFC XXXX


12.4.  pn-enccode



     Parameter Name: pn-enccode

     Predefined Values:  No

     Reference:  RFC XXXX




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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-type
   values.



     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

     Document:     A reference to the document defining the registration




     This specification registers the following values:

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

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



13.  References

13.1.  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>.





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   [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>.

   [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>.

13.2.  Informative references

   [I-D.ietf-webpush-encryption]
              Thomson, M., "Message Encryption for Web Push", draft-
              ietf-webpush-encryption-09 (work in progress), September
              2017.

Author's Address

   Christer Holmberg
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: christer.holmberg@ericsson.com
























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