SIPCORE Working Group C. Holmberg
Internet-Draft Ericsson
Intended status: Standards Track M. Arnold
Expires: February 15, 2019 Metaswitch Networks
August 14, 2018
Push Notification with the Session Initiation Protocol (SIP)
draft-ietf-sipcore-sip-push-12
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
binding refresh 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 February 15, 2019.
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
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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 . . . . . . 9
5. SIP Proxy Behavior . . . . . . . . . . . . . . . . . . . . . 9
5.1. PNS Provider . . . . . . . . . . . . . . . . . . . . . . 9
5.2. Trigger Periodic Binding Refresh . . . . . . . . . . . . 9
5.3. SIP Requests . . . . . . . . . . . . . . . . . . . . . . 10
5.3.1. REGISTER . . . . . . . . . . . . . . . . . . . . . . 10
5.3.2. Initial Request for Dialog or Stand-Alone Request . . 12
6. Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.1. 555 (Push Notification Service Not Supported) Response
Code . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.2. 556 (Push Notification Failed) Response Code . . . . . . 15
6.3. sip.pns Feature-Capability Indicator . . . . . . . . . . 15
6.4. sip.vapid Feature-Capability Indicator . . . . . . . . . 15
6.5. sip.pnsreg Feature-Capability Indicator . . . . . . . . . 16
6.6. sip.pnsreg Media Feature Tag . . . . . . . . . . . . . . 16
6.7. SIP URI Parameters . . . . . . . . . . . . . . . . . . . 16
7. PNS Registration Requirements . . . . . . . . . . . . . . . . 17
8. pn-provider, pn-param and pn-prid URI Parameters for Apple
Push Notification service . . . . . . . . . . . . . . . . . . 17
9. pn-provider, pn-param and pn-prid URI Parameters for Google
Firebase Cloud Messaging (FCM) push notification service . . 18
10. pn-provider, pn-param and pn-prid URI Parameters for RFC 8030
(Generic Event Delivery Using HTTP Push) . . . . . . . . . . 18
11. Security Considerations . . . . . . . . . . . . . . . . . . . 19
12. IANA considerations . . . . . . . . . . . . . . . . . . . . . 19
12.1. SIP URI Parameters . . . . . . . . . . . . . . . . . . . 19
12.1.1. pn-provider . . . . . . . . . . . . . . . . . . . . 20
12.1.2. pn-param . . . . . . . . . . . . . . . . . . . . . . 20
12.1.3. pn-prid . . . . . . . . . . . . . . . . . . . . . . 20
12.2. SIP Response Codes . . . . . . . . . . . . . . . . . . . 20
12.2.1. 555 (Push Notification Service Not Supported) . . . 20
12.2.2. 556 (Push Notification Failed) . . . . . . . . . . . 21
12.3. SIP Global Feature-Capability Indicator . . . . . . . . 21
12.3.1. sip.pns . . . . . . . . . . . . . . . . . . . . . . 21
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12.3.2. sip.vapid . . . . . . . . . . . . . . . . . . . . . 21
12.3.3. sip.pnsreg . . . . . . . . . . . . . . . . . . . . . 22
12.4. SIP Media Feature Tag . . . . . . . . . . . . . . . . . 22
12.4.1. sip.pnsreg . . . . . . . . . . . . . . . . . . . . . 23
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 . . . . . . . . . . . . . . . . . . . . . . . 26
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, one 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
binding refresh 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 binding refresh 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 binding refresh REGISTER requests, it might still be useful
to suspend the application between the sending of binding refresh
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requests (as it will save battery life) 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 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 binding refresh 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 binding refresh REGISTER request and
receive the incoming SIP request. The proxy will receive 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 SIP registrar [RFC3261], 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. In some cases the proxy can forward
the SIP request without waiting for the SIP 2xx response to the
REGISTER request.
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.
The proxy MUST be in the signalling path of REGISTER requests sent by
the UA towards the registrar, and of SIP requests (for a new dialog
or a stand-alone) forwarded by the proxy responsible for the UA's
domain (sometimes referred to as home proxy, S-CSCF, etc) towards the
UA. The proxy can also be co-located with the proxy responsible for
the UA's domain.
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+--------+ +--------------+ +-----------------+
| SIP UA | | Push Service | | SIP Proxy |
+--------+ +--------------+ +-----------------+
| | |
| Subscribe | |
|--------------------->| |
| | |
| Push Resource ID | |
|<---------------------| |
| | |
| SIP REGISTER (Push Resource ID) |
|===============================================>|
| | | SIP REGISTER
| | |============>
| | |
| | | SIP 200 OK
| | |<============
| SIP 200 OK | |
|<===============================================|
| | |
| | |
| | |
| | | SIP INVITE
| | Push Message |<============
| | (Push Resource ID) |
| Push Message |<------------------------|
| (Push Resource ID) | |
|<---------------------| |
| | |
| SIP REGISTER (Push Resource ID) |
|===============================================>|
| | | SIP REGISTER
| | |============>
| | |
| | | SIP 200 OK
| | |<============
| SIP 200 OK | |
|<===============================================|
| | |
| SIP INVITE | |
|<===============================================|
| | |
------- Push Notification API
======= SIP
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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", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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
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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 [RFC6809] 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.
When the UA receives a push notification, it MUST send a binding
refresh 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 binding refresh 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 binding refresh
REGISTER request when it receives a push notification (even if the UA
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is able to use a non-push mechanism for sending binding refresh
REGISTER requests).
NOTE: In some cases the UA might be able to use a non-push mechanism
to awake and send binding refresh 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 binding refresh 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 binding refresh
REGISTER request.
NOTE: If the SIP UA application wants to use push notifications for
other purposes than to trigger binding refresh 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
binding refresh 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 binding refresh
REGISTER request.
If the UA no longer wants to receive push notifications (requested by
the proxy), the UA MUST send a binding refresh 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
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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 binding refresh
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 Provider
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 Binding Refresh
In order to request push notifications towards a SIP UA that will
trigger the UA to send binding refresh SIP REGISTER requests, the SIP
proxy needs to have information about when a registration will
expire. The proxy needs to be able 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
binding refresh REGISTER request, the proxy requests a push
notification towards the UA.
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Note that the push notification needs to be requested early enough,
in order for the associated binding refresh REGISTER request to reach
the 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
binding refresh 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.
5.3. SIP Requests
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 binding refresh 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
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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.
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 towards the registrar. 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
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the proxy receives 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
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 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 binding refresh
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
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the REGISTER response towards the UA, if one of the contacts in the
REGISTER response matches the Request-URI of the SIP request to be
forwarded, and if the contact binding has not expired, 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
binding refresh 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.
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 registrar, and that the UA which initiated
the REGISTER request is authorized to receive messages for the
Request-URI. However, if the proxy is able to authorize the sender
of the REGISTER request, it does not need to wait for the associated
2xx response before it forwards the SIP request towards the UA. The
mechanism for authorizing the UA is outside the scope of this
document.
As both the SIP request to be forwarded towards the UA, and the
binding refresh 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
binding refresh REGISTER request (even if the most recent contact and
the Request-URI of the SIP request do not match).
NOTE: The proxy 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, and the proxy
has not yet forwarded the SIP request towards the UA, 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.
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.
As describe above, there are cases where the proxy will reject the
SIP request with an error response. While waiting for the push
notification request to succeed, and the associated REGISTER request
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to arrive from the SIP UA, the proxy needs to take into consideration
that the transaction associated with the SIP request will eventually
time out at the sender of the request (UAC), and the sender will
consider the transaction a failure. If the proxy forwards the SIP
request towards the SIP UA, the SIP UA accepts the request and the
transaction times out at the sender before it receives the successful
response, this will cause state misalignment between the endpoints
(the sender will consider the transaction a failure, while the
receiver will consider the transaction a success). The SIP proxy
needs to take this into account when deciding for how long to wait
before it considers the transaction associated with the SIP request a
failure, to make sure that the error response reaches the sender
before the transaction times out.
NOTE: While this work on this document was ongoing, implementation
test results showed that the time it takes for a proxy to receive the
REGISTER request, from when the proxy has requested a push
notification, is typically around 2 seconds.
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
indicate that the server did not support the push notification
service identified in a 'pn-provider' SIP URI parameter.
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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
the entity, that can be used by a SIP UA to restrict subscriptions to
that entity.
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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 binding refresh
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 binding refresh REGISTER
requests associated with the registration without being awaken by
push notifications. The media feature tag has no values.
pnsreg-mt = "+sip.pnsreg"
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:
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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 characters 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
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
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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".
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:
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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 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.
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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.
Response Code Number: 555
Default Reason Phrase: Push Notification Service Not Supported
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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)
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.
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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.
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
binding refresh 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
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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.
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 binding refresh
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].
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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
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>.
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[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>.
[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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[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>.
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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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