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Network Working Group V. Gurbani, Ed.
Request for Comments: 3910 A. Brusilovsky
Category: Standards Track I. Faynberg
Lucent Technologies, Inc.
J. Gato
Vodafone Espana
H. Lu
Bell Labs/Lucent Technologies
M. Unmehopa
Lucent Technologies, Inc.
October 2004
The SPIRITS (Services in PSTN requesting Internet Services) Protocol
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2004).
Abstract
This document describes the Services in PSTN (Public Switched
Telephone Network) requesting Internet Services (SPIRITS) protocol.
The purpose of the SPIRITS protocol is to support services that
originate in the cellular or wireline PSTN and necessitate
interactions between the PSTN and the Internet. On the PSTN side,
the SPIRITS services are most often initiated from the Intelligent
Network (IN) entities. Internet Call Waiting and Internet Caller-ID
Delivery are examples of SPIRITS services, as are location-based
services on the cellular network. The protocol defines the building
blocks from which many other services can be built.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions used in this document. . . . . . . . . . . 3
2. Overview of operations. . . . . . . . . . . . . . . . . . . . 3
2.1. Terminology. . . . . . . . . . . . . . . . . . . . . . 6
3. Using XML for subscription and notification . . . . . . . . . 7
4. XML format definition . . . . . . . . . . . . . . . . . . . . 8
Gurbani, et al. Standards Track [Page 1]
RFC 3910 SPIRITS Protocol October 2004
5. Call-related events . . . . . . . . . . . . . . . . . . . . . 10
5.1. IN-specific requirements . . . . . . . . . . . . . . . 11
5.2. Detection points and required parameters . . . . . . . 12
5.2.1. Originating-side DPs. . . . . . . . . . . . . 12
5.2.2. Terminating-side DPs. . . . . . . . . . . . . 14
5.3. Services through dynamic DPs . . . . . . . . . . . . . 15
5.3.1. Normative usage . . . . . . . . . . . . . . . 15
5.3.2. Event package name. . . . . . . . . . . . . . 16
5.3.3. Event package parameters. . . . . . . . . . . 16
5.3.4. SUBSCRIBE bodies. . . . . . . . . . . . . . . 16
5.3.5. Subscription duration . . . . . . . . . . . . 17
5.3.6. NOTIFY bodies . . . . . . . . . . . . . . . . 17
5.3.7. Notifier processing of SUBSCRIBE requests . . 18
5.3.8. Notifier generation of NOTIFY requests. . . . 18
5.3.9. Subscriber processing of NOTIFY requests. . . 19
5.3.10. Handling of forked requests . . . . . . . . . 19
5.3.11. Rate of notifications . . . . . . . . . . . . 19
5.3.12. State Agents. . . . . . . . . . . . . . . . . 20
5.3.13. Examples. . . . . . . . . . . . . . . . . . . 20
5.3.14. Use of URIs to retrieve state . . . . . . . . 25
5.4. Services through static DPs. . . . . . . . . . . . . . 25
5.4.1. Internet Call Waiting . . . . . . . . . . . . 26
5.4.2. Call disposition choices. . . . . . . . . . . 26
5.4.3. Accepting an ICW session using VoIP . . . . . 28
6. Non-call related events . . . . . . . . . . . . . . . . . . . 29
6.1. Non-call events and their required parameters. . . . . 29
6.2. Normative usage. . . . . . . . . . . . . . . . . . . . 30
6.3. Event package name . . . . . . . . . . . . . . . . . . 30
6.4. Event package parameters . . . . . . . . . . . . . . . 31
6.5. SUBSCRIBE bodies . . . . . . . . . . . . . . . . . . . 31
6.6. Subscription duration. . . . . . . . . . . . . . . . . 31
6.7. NOTIFY bodies. . . . . . . . . . . . . . . . . . . . . 32
6.8. Notifier processing of SUBSCRIBE requests. . . . . . . 32
6.9. Notifier generation of NOTIFY requests . . . . . . . . 32
6.10. Subscriber processing of NOTIFY requests . . . . . . . 33
6.11. Handling of forked requests. . . . . . . . . . . . . . 33
6.12. Rate of notifications. . . . . . . . . . . . . . . . . 33
6.13. State Agents . . . . . . . . . . . . . . . . . . . . . 33
6.14. Examples . . . . . . . . . . . . . . . . . . . . . . . 33
6.15. Use of URIs to retrieve state. . . . . . . . . . . . . 37
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38
7.1. Registering event packages . . . . . . . . . . . . . . 38
7.2. Registering MIME type. . . . . . . . . . . . . . . . . 38
7.3. Registering URN. . . . . . . . . . . . . . . . . . . . 39
7.4. Registering XML schema . . . . . . . . . . . . . . . . 40
8. Security Considerations . . . . . . . . . . . . . . . . . . . 40
9. XML schema definition . . . . . . . . . . . . . . . . . . . . 42
10. Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . 45
Gurbani, et al. Standards Track [Page 2]
RFC 3910 SPIRITS Protocol October 2004
11. Acronyms. . . . . . . . . . . . . . . . . . . . . . . . . . . 45
12. References. . . . . . . . . . . . . . . . . . . . . . . . . . 46
13. Contributors. . . . . . . . . . . . . . . . . . . . . . . . . 48
14. Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . 48
15. Full Copyright Statement. . . . . . . . . . . . . . . . . . . 50
1. Introduction
SPIRITS (Services in the PSTN Requesting Internet Services) is an
IETF architecture and an associated protocol that enables call
processing elements in the telephone network to make service requests
that are then processed on Internet hosted servers. The term Public
Switched Telephone Network (PSTN) is used here to include the
wireline circuit-switched network, as well as the wireless circuit-
switched network.
The earlier IETF work on the PSTN/Internet Interworking (PINT)
resulted in the protocol (RFC 2848) in support of the services
initiated in the reverse direction - from the Internet to PSTN.
This document has been written in response to the SPIRITS WG chairs
call for SPIRITS Protocol proposals. Among other contributions, this
document is based on:
o Informational "Pre-SPIRITS implementations" [10]
o Informational "The SPIRITS Architecture" [1]
o Informational "SPIRITS Protocol Requirements" [4]
1.1. Conventions used in this document
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 BCP 14, RFC 2119 [2].
2. Overview of operations
The purpose of the SPIRITS protocol is to enable the execution of
services in the Internet based on certain events occurring in the
PSTN. The term PSTN is used here to include all manner of switching;
i.e. wireline circuit-switched network, as well as the wireless
circuit-switched network.
In general terms, an Internet host is interested in getting
notifications of certain events occurring in the PSTN. When the
event of interest occurs, the PSTN notifies the Internet host. The
Internet host can execute appropriate services based on these
notifications.
Gurbani, et al. Standards Track [Page 3]
RFC 3910 SPIRITS Protocol October 2004
+------+
| PSTN |
|Events|
+------+
/ \
/ \
+-------+ +--------+
|Call | |Non-Call|
|Related| |Related |
+-------+ +--+-----+
/ \ |
/ \ |
+---/--+ +---\---+ +--+-----------------+
|Static| |Dynamic| |Mobility Management/|
| | | | |Registration/De- |
+------+ +-------+ |registration |
+--------------------+
Figure 1: The SPIRITS Hierarchy.
Figure 1 contains the SPIRITS events hierarchy, including their
subdivision in two discrete classes for service execution: events
related to the setup, teardown and maintenance of a call and events
un-related to call setup, teardown or maintenance. Example of the
latter class of events are geo-location mobility events that are
tracked by the cellular PSTN. SPIRITS will specify the framework to
provide services for both of these types of events.
Call-related events, its further subdivisions, and how they enable
services in the Internet is contained in Section 5. Services enabled
from events not related to call setup, teardown, or maintenance are
covered in detail in Section 6.
For reference, the SPIRITS architecture from [1] is reproduced below.
This document is focused on interfaces B and C only. Interface D is
a matter of local policy; the PSTN operator may have a functional
interface between the SPIRITS client or a message passing interface.
This document does not discuss interface D in any detail.
Gurbani, et al. Standards Track [Page 4]
RFC 3910 SPIRITS Protocol October 2004
+--------------+
| Subscriber's |
| IP Host | +--------------+
| | | |
| +----------+ | | +----------+ |
| | PINT | | A | | PINT | |
| | Client +<-------/-------->+ Gateway +<-----+
| +----------+ | | +----------+ | |
| | | | |
| +----------+ | | +----------+ | |
| | SPIRITS | | B | | SPIRITS | | |
| | Server +<-------/-------->+ Gateway | | |
| +----------+ | | +--------+-+ | |
| | | ^ | |
+--------------+ +----------|---+ |
| |
IP Network | |
------------------------------------------|--------|---
PSTN / C / E
| |
v |
+----+------+ |
| SPIRITS | |
| Client | v
+-------------------+ +---+-----D-----+-++
| Service Switching |INAP/SS7 | Service Control |
| Function +---------+ Function |
+----+--------------+ +------------------+
|
|line
+-+
[0] Subscriber's telephone
Figure 2: The SPIRITS Architecture.
(Note: The interfaces A-E are described in detail in the SPIRITS
Architecture document [1].)
The PSTN today supports service models such as the Intelligent
Network (IN), whereby some features are executed locally on switching
elements called Service Switching Points (SSPs). Other features are
executed on service elements called Service Control Points (SCPs).
The SPIRITS architecture [1] permits these SCP elements to act as
intelligent entities to leverage and use Internet hosts and
capabilities to further enhance the telephone end-user's experience.
Gurbani, et al. Standards Track [Page 5]
RFC 3910 SPIRITS Protocol October 2004
The protocol used on interfaces B and C consists of the SPIRITS
protocol, and is based on SIP and SIP event notification [3]. The
requirements of a SPIRITS protocol and the choice of using SIP as an
enabler are detailed in [4].
The SPIRITS protocol is a set of two "event packages" [3]. It
contains the procedural rules and semantic context that must be
applied to these rules for processing SIP transactions. The SPIRITS
protocol has to carry subscriptions for events from the SPIRITS
server to the SPIRITS client and notifications of these events from
the SPIRITS client to the SPIRITS server. Extensible Markup Language
(XML) [12] is used to codify the subscriptions and notifications.
Finally, in the context of ensuing discussion, the terms "SPIRITS
server" and "SPIRITS client" are somewhat confusing since the roles
appear reversed; to wit, the "SPIRITS server" issues a subscription
which is accepted by a "SPIRITS client". To mitigate such ambiguity,
from now on, we will refer to the "SPIRITS server" as a "SPIRITS
subscriber" and to the "SPIRITS client" as a "SPIRITS notifier".
This convention adheres to the nomenclature outlined in [3]; the
SPIRITS server in Figure 2 is a subscriber (issues subscriptions to
events), and the SPIRITS client in Figure 2 is a notifier (issues
notifications whenever the event of interest occurs).
2.1. Terminology
For ease of reference, we provide a terminology of the SPIRITS actors
discussed in the preceding above:
Service Control Function (SCF): A PSTN entity that executes service
logic. It provides capabilities to influence the call processing
occurring in the Service Switching Function (SSF). For more
information on how a SCF participates in the SPIRITS architecture,
please see Sections 5 and 5.1.
SPIRITS client: see SPIRITS notifier.
SPIRITS server: see SPIRITS subscriber.
SPIRITS notifier: A User Agent (UA) in the PSTN that accepts
subscriptions from SPIRITS subscribers. These subscriptions contain
events that the SPIRITS subscribers are interested in receiving a
notification for. The SPIRITS notifier interfaces with the Service
Control Function such that when the said event occurs, a notification
will be sent to the relevant SPIRITS subscriber.
Gurbani, et al. Standards Track [Page 6]
RFC 3910 SPIRITS Protocol October 2004
SPIRITS subscriber: A UA in the Internet that issues a subscription
containing events in the PSTN that it is interested in receiving a
notification for.
3. Using XML for subscription and notification
The SPIRITS protocol requirements mandate that "SPIRITS-related
parameters be carried in a manner consistent with SIP practices"
(RFC3298:Section 3). SIP already provides payload description
capabilities through the use of headers (Content-Type, Content-
Length). This document defines a new MIME type --
"application/spirits-event+xml" -- and registers it with IANA
(Section 7). This MIME type MUST be present in the "Content-Type"
header of SPIRITS requests and responses, and it describes an XML
document that contains SPIRITS-related information.
This document defines a base XML schema for subscriptions to PSTN
events. The list of events that can be subscribed to is defined in
the SPIRITS protocol requirements document [4] and this document
provides an XML schema for it. All SPIRITS subscribers (any SPIRITS
entity capable of issuing a SUBSCRIBE, REGISTER, or INVITE request)
MUST support this schema. All SPIRITS notifiers (any SPIRITS entity
capable of receiving and processing a SUBSCRIBE, REGISTER, or INVITE
request) MUST support this schema. The schema is defined in Section
9.
The support for the SIP REGISTER request is included for PINT
compatibility (RFC3298:Section 6).
The support for the SIP INVITE request is mandated because pre-
existing SPIRITS implementations did not use the SIP event
notification scheme. Instead, the initial PSTN detection point
always arrived via the SIP INVITE request.
This document also defines a base XML schema for notifications of
events (Section 9). All SPIRITS notifiers MUST generate XML
documents that correspond to the base notification schema. All
SPIRITS subscribers MUST support XML documents that correspond to
this schema.
The set of events that can be subscribed to and the amount of
notification that is returned by the PSTN entity may vary among
different PSTN operators. Some PSTN operators may have a rich set of
events that can be subscribed to, while others have only the
primitive set of events outlined in the SPIRITS protocol requirements
document [4]. This document defines a base XML schema (in Section 9)
which MUST be used for the subscription and notification of the
primitive set of events. In order to support a richer set of event
Gurbani, et al. Standards Track [Page 7]
RFC 3910 SPIRITS Protocol October 2004
subscription and notification, implementations MAY use additional XML
namespaces corresponding to alternate schemas in a SPIRITS XML
document. However, all implementations MUST support the base XML
schema defined in Section 9 of this document. Use of the base schema
ensures interoperability across implementations, and the inclusion of
additional XML namespaces allows for customization.
A logical flow of the SPIRITS protocol is depicted below (note: this
example shows a temporal flow; XML documents and related SPIRITS
protocol syntax is specified in later sections of this document). In
the flow below, S is the SPIRITS subscriber and N is the SPIRITS
notifier. The SPIRIT Gateway is presumed to have a pure proxying
functionality and thus is omitted for simplicity:
1 S->N Subscribe (events of interest in an XML document instance
using base subscription schema)
2 N->S 200 OK (Subscribe)
3 N->S Notify
4 S->N 200 OK (Notify communicating current resource state)
5 ...
6 N->S Notify (Notify communicating change in resource state;
payload is an XML document instance using
XML extensions to the base notification schema)
7 S->N 200 OK (Notify)
In line 1, the SPIRITS subscriber subscribes to certain events using
an XML document based on the base schema defined in this document.
In line 6, the SPIRITS notifier notifies the SPIRITS subscriber of
the occurrence of the event using extensions to the base notification
schema. Note that this document defines a base schema for event
notification as well; the SPIRITS notifier could have availed itself
of these. Instead, it chooses to pass to the SPIRITS subscriber an
XML document composed of extensions to the base notification schema.
The SPIRITS subscriber, if it understands the extensions, can
interpret the XML document accordingly. However, in the event that
the SPIRITS subscriber is not programmed to understand the
extensions, it MUST search the XML document for the mandatory
elements. These elements MUST be present in all notification schemas
and are detailed in Section 9.
4. XML format definition
This section defines the XML-encoded SPIRITS payload format. Such a
payload is a well formed XML document and is produced by SPIRITS
notifiers and SPIRITS subscribers.
Gurbani, et al. Standards Track [Page 8]
RFC 3910 SPIRITS Protocol October 2004
The namespace URI for elements defined in this document is a Uniform
Resource Name (URN) [14], using the namespace identifier 'ietf'
defined in [15] and extended by [16]:
urn:ietf:params:xml:ns:spirits-1.0
SPIRITS XML documents may have a default namespace, or they may be
associated with a namespace prefix following the convention
established in XML namespaces [17]. Regardless, the elements and
attributes of SPIRITS XML documents MUST conform to the SPIRITS XML
schema specified in Section 9.
The <spirits-event> element
The root of a SPIRITS XML document (characterized by a Content-
Type header of "application/spirits-event+xml">) is the <spirits-
event> element. This element MUST contain a namespace declaration
('xmlns') to indicate the namespace on which the XML document is
based. XML documents compliant to the SPIRITS protocol MUST
contain the URN "urn:ietf:params:xml:ns:spirits-1.0" in the
namespace declaration. Other namespaces may be specified as
needed.
<spirits-event> element MUST contain at least one <Event> element,
and MAY contain more than one.
The <Event> element
The <Event> element contains three attributes, two of which are
mandatory. The first mandatory attribute is a 'type' attribute
whose value is either "INDPs" or "userprof".
These types correspond, respectively, to call-related events
described in Section 5 and non-call related events described in
Section 6.
The second mandatory attribute is a 'name' attribute. Values for
this attribute MUST be limited to the SPIRITS mnemonics defined in
Section 5.2.1, Section 5.2.2, and Section 6.1.
The third attribute, which is optional, is a 'mode' attribute.
The value of 'mode' is either "N" or "R", corresponding
respectively to (N)otification or (R)equest (RFC3298:Section 4).
The default value of this attribute is "N".
If the 'type' attribute of the <Event> element is "INDPs", then it
MUST contain at least one or more of the following elements
(unknown elements MAY be ignored): <CallingPartyNumber>,
<CalledPartyNumber>, <DialledDigits>, or <Cause>. These elements
Gurbani, et al. Standards Track [Page 9]
RFC 3910 SPIRITS Protocol October 2004
are defined in Section 5.2; they MUST not contain any attributes
and MUST not be used further as parent elements. These elements
contain a string value as described in Section 5.2.1 and 5.2.2.
If the 'type' attribute of the <Event> element is "userprof", then
it MUST contain a <CalledPartyNumber> element and it MAY contain a
<Cell-ID> element. None of these elements contain any attributes
and neither must be used further as a parent element. These
elements contain a string value as described in Section 6.1. All
other elements MAY be ignored if not understood.
A SPIRITS-compliant XML document using the XML namespace defined in
this document might look like the following example:
<?xml version="1.0" encoding="UTF-8"?>
<spirits-event xmlns="urn:ietf:params:xml:ns:spirits-1.0">
<Event type="INDPs" name="OD" mode="N">
<CallingPartyNumber>5551212</CallingPartyNumber>
</Event>
<Event type="INDPs" name="OAB" mode="N">
<CallingPartyNumber>5551212</CallingPartyNumber>
</Event>
</spirits-event>
5. Call-related events
For readers who may not be familiar with the service execution
aspects of PSTN/IN, we provide a brief tutorial next. Interested
readers are urged to consult [19] for a detailed treatment of this
subject.
Services in the PSTN/IN are executed based on a call model. A call
model is a finite state machine used in SSPs and other call
processing elements that accurately and concisely reflects the
current state of a call at any given point in time. Call models
consist of states called PICs (Points In Call) and transitions
between states. Inter-state transitions pass through elements called
Detection Points or DPs. DPs house one or more triggers. Every
trigger has a firing criteria associated with it. When a trigger is
armed (made active), and its associated firing criteria are
satisfied, it fires. The particulars of firing criteria may vary
based on the call model being supported.
When a trigger fires, a message is formatted with call state
information and transmitted by the SSP to the SCP. The SCP then
reads this call related data and generates a response which the SSP
then uses in further call processing.
Gurbani, et al. Standards Track [Page 10]
RFC 3910 SPIRITS Protocol October 2004
Detection Points are of two types: TDPs (or Trigger Detection
Points), and EDPs (or Event Detection Points). TDPs are provisioned
with statically armed triggers (armed through Service Management
Tools). EDPs are dynamically armed triggers (armed by the SCP as
call processing proceeds). DPs may also be classified as "Request"
or "Notification" DPs. Thus, one can have TDP-R's, TDP-N's, EDP-R's
and EDP-N's.
The "-R" type of DPs require the SSP to suspend call processing when
communication with the SCP is initiated. Call processing resumes
when a response is received. The "-N" type of DPs enable the SSP to
continue with call processing when the trigger fires, after it sends
out the message to the SCP, notifying it that a certain event has
occurred.
Call models typically support different types of detection points.
Note that while INAP and the IN Capability Set (CS)-2 [7] call model
are used in this document as examples, and for ease of explanation,
other call models possess similar properties. For example, the
Wireless Intelligent Network (WIN) call model also supports the
dynamic arming of triggers. Thus, the essence of this discussion
applies not just to the wireline domain, but applies equally well to
the wireless domain as well.
When the SCP receives the INAP formatted message from the SSP, if the
SCP supports the SPIRITS architecture, it can encode the INAP message
contents into a SPIRITS protocol message which is then transmitted to
SPIRITS-capable elements in the IP network. Similarly, when it
receives responses back from said SPIRITS capable elements, it can
reformat the response content into the INAP format and forward these
messages back to SSPs. Thus the process of inter-conversion and/or
encoding between the INAP parameters and the SPIRITS protocol is of
primary interest.
An SCP is a physical manifestation of the Service Control Function.
An SSP is a physical manifestation of the Service Switching Function
(and the Call Control Function). To support uniformity of
nomenclature between the various SPIRITS drafts, we shall use the
terms SCP and SCF, and SSP and SSF interchangeably in this document.
5.1. IN-specific requirements
Section 4 of [4] outlines the IN-related requirements on the SPIRITS
protocol. The SUBSCRIBE request arriving at the SPIRITS notifier
MUST contain the events to be monitored (in the form of a DP list),
the mode (request or a notification, the difference being that for a
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RFC 3910 SPIRITS Protocol October 2004
request, the SPIRITS subscriber can influence subsequent call
processing and for a notification, no further influence is needed),
and any DP-related parameters.
Section 4 of [4] also enumerates a list of Capability Set 3 (CS-3)
DPs for SPIRITS services. It is a requirement (RFC3298:Section 4)
that the SPIRITS protocol specify the relevant parameters of the DPs.
These DPs and their relevant parameters to be carried in a SUBSCRIBE
request are codified in an XML schema. All SPIRITS subscribers MUST
understand this schema for subscribing to the DPs in the PSTN. The
schema is defined in Section 9.
When a DP fires, a notification -- using a SIP NOTIFY request -- is
transmitted from the SPIRITS notifier to the SPIRITS subscriber. The
NOTIFY request contains an XML document which describes the DP that
fired and any relevant parameters. The DPs and their relevant
parameters to be carried in a NOTIFY request are codified in an XML
schema. All SPIRITS notifiers MUST understand this schema; this
schema MAY be extended. The schema is defined in Section 9.
In addition, Appendices A and B of [6] contain a select subset of
CS-2 DPs that may be of interest to the reader. However, this
document will only refer to CS-3 DPs outlined in [4].
5.2. Detection points and required parameters
The IN CS-3 DPs envisioned for SPIRITS services (RFC3298:Section 4)
are described next. IN DPs are characterized by many parameters,
however, not all such parameters are required -- or even needed -- by
SPIRITS. This section, thus, serves to list the mandatory parameters
for each DP that MUST be specified in subscriptions and
notifications. Implementations can specify additional parameters as
XML extensions associated with a private (or public and standardized)
namespace.
The exhaustive list of IN CS-3 DPs and their parameters can be found
in reference [13].
Each DP is given a SPIRITS-specific mnemonic for use in the
subscriptions and notifications.
5.2.1. Originating-side DPs
Origination Attempt Authorized
SPIRITS mnemonic: OAA
Mandatory parameter in SUBSCRIBE: CallingPartyNumber
Mandatory parameters in NOTIFY: CallingPartyNumber, CalledPartyNumber
Gurbani, et al. Standards Track [Page 12]
RFC 3910 SPIRITS Protocol October 2004
CallingPartyNumber: A string used to identify the calling party for
the call. The actual length and encoding of this parameter depend on
the particulars of the dialing plan used.
CalledPartyNumber: A string containing the number (e.g., called
directory number) used to identify the called party. The actual
length and encoding of this parameter depend on the particulars of
the dialing plan used.
Collected Information
SPIRITS mnemonic: OCI
Mandatory parameter in SUBSCRIBE: CallingPartyNumber
Mandatory parameters in NOTIFY: CallingPartyNumber, DialledDigits
DialledDigits: This parameter contains non-translated address
information collected/received from the originating user/line/trunk
Analyzed Information
SPIRITS mnemonic: OAI
Mandatory parameter in SUBSCRIBE: CallingPartyNumber
Mandatory parameters in NOTIFY: CallingPartyNumber, DialledDigits
Origination Answer
SPIRITS mnemonic: OA
Mandatory parameter in SUBSCRIBE: CallingPartyNumber
Mandatory parameters in NOTIFY: CallingPartyNumber, CalledPartyNumber
Origination Term Seized
SPIRITS mnemonic: OTS
Mandatory parameter in SUBSCRIBE: CallingPartyNumber
Mandatory parameter in NOTIFY: CallingPartyNumber, CalledPartyNumber
Origination No Answer
SPIRITS mnemonic: ONA
Mandatory parameter in SUBSCRIBE: CallingPartyNumber
Mandatory parameter in NOTIFY: CallingPartyNumber, CalledPartyNumber
Origination Called Party Busy
SPIRITS mnemonic: OCPB
Mandatory parameter in SUBSCRIBE: CallingPartyNumber
Mandatory parameters in NOTIFY: CallingPartyNumber, CalledPartyNumber
Route Select Failure
SPIRITS mnemonic: ORSF
Mandatory parameter in SUBSCRIBE: CallingPartyNumber
Mandatory parameter in NOTIFY: CallingPartyNumber, CalledPartyNumber
Gurbani, et al. Standards Track [Page 13]
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Origination Mid Call
SPIRITS mnemonic: OMC
Mandatory parameter in SUBSCRIBE: CallingPartyNumber
Mandatory parameter in NOTIFY: CallingPartyNumber
Origination Abandon
SPIRITS mnemonic: OAB
Mandatory parameter in SUBSCRIBE: CallingPartyNumber
Mandatory parameter in NOTIFY: CallingPartyNumber
Origination Disconnect
SPIRITS mnemonic: OD
Mandatory parameter in SUBSCRIBE: CallingPartyNumber
Mandatory parameter in NOTIFY: CallingPartyNumber, CalledPartyNumber
5.2.2. Terminating-side DPs
Termination Answer
SPIRITS mnemonic: TA
Mandatory parameter in SUBSCRIBE: CalledPartyNumber
Mandatory parameters in NOTIFY: CallingPartyNumber, CalledPartyNumber
Termination No Answer
SPIRITS mnemonic: TNA Mandatory parameter in SUBSCRIBE:
CalledPartyNumber
Mandatory parameters in NOTIFY: CallingPartyNumber, CalledPartyNumber
Termination Mid-Call
SPIRITS mnemonic: TMC
Mandatory parameter in SUBSCRIBE: CalledPartyNumber
Mandatory parameter in NOTIFY: CalledPartyNumber
Termination Abandon
SPIRITS mnemonic: TAB
Mandatory parameter in SUBSCRIBE: CalledPartyNumber
Mandatory parameter in NOTIFY: CalledPartyNumber
Termination Disconnect
SPIRITS mnemonic: TD
Mandatory parameter in SUBSCRIBE: CalledPartyNumber
Mandatory parameters in NOTIFY: CalledPartyNumber, CallingPartyNumber
Termination Attempt Authorized
SPIRITS mnemonic: TAA
Mandatory parameter in SUBSCRIBE: CalledPartyNumber
Mandatory parameters in NOTIFY: CalledPartyNumber, CallingPartyNumber
Gurbani, et al. Standards Track [Page 14]
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Termination Facility Selected and Available
SPIRITS mnemonic: TFSA
Mandatory parameter in SUBSCRIBE: CalledPartyNumber
Mandatory parameter in NOTIFY: CalledPartyNumber
Termination Busy
SPIRITS mnemonic: TB
Mandatory parameter in SUBSCRIBE: CalledPartyNumber
Mandatory parameters in NOTIFY: CalledPartyNumber,
CallingPartyNumber, Cause
Cause: This parameter contains a string value of either "Busy" or
"Unreachable". The difference between these is translated as a
requirement (RFC3298:Section 5) to aid in the SPIRITS subscriber in
determining if the called party is indeed busy (engaged), or if the
called party is unavailable (as it would be if it were on the
cellular PSTN and the mobile subscriber was not registered with the
network).
5.3. Services through dynamic DPs
Triggers in the PSTN can be armed dynamically, often outside the
context of a call. The SIP event notification mechanism [3] is,
therefore, a convenient means to exploit in those cases where
triggers housed in EDPs fire (see section 3 of [4]). Note that [4]
uses the term "persistent" to refer to call-related DP arming and
associated interactions.
The SIP Events Package enables IP endpoints (or hosts) to subscribe
to and receive subsequent notification of events occurring in the
PSTN. With reference to Figure 2, this includes communication on the
interfaces marked "B" and "C".
5.3.1. Normative usage
A subscriber will issue a SUBSCRIBE request which identifies a set of
events (DPs) it is interested in getting the notification of. This
set MUST contain at least one DP, it MAY contain more than one. The
SUBSCRIBE request is routed to the notifier, where it is accepted,
pending a successful authentication.
When any of the DPs identified in the set of events fires, the
notifier will format a NOTIFY request and direct it towards the
subscriber. The NOTIFY request will contain information pertinent to
the event that was triggered. The un-encountered DPs MUST be
subsequently dis-armed by the SPIRITS notifier and/or the SCF.
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The dialog established by the SUBSCRIBE terminates when the event of
interest occurs and this notification is passed to the subscriber
through a NOTIFY request. If the subscriber is interested in the
future occurrence of the same event, it MUST issue a new SUBSCRIBE
request, establishing a new dialog.
When the subscriber receives a NOTIFY request, it can subsequently
choose to act in a manner appropriate to the notification.
The remaining sections fill in the specific package responsibilities
raised in RFC3265 [3], Section 4.4.
5.3.2. Event package name
This document defines two event packages; the first of these is
defined in this section and is called "spirits-INDPs". This package
MUST be used for events corresponding to IN detection points in the
cellular or wireline PSTN. All entities that implement the SPIRITS
protocol and support IN detection points MUST set the "Event" request
header [3] to "spirits-INDPs." The "Allow-Events" general header [3]
MUST include the token "spirits-INDPs" if the entity implements the
SPIRITS protocol and supports IN detection points.
Event: spirits-INDPs
Allow-Events: spirits-INDPs
The second event package is defined and discussed in Section 6.
5.3.3. Event package parameters
The "spirits-INDPs" event package does not support any additional
parameters to the Event header.
5.3.4. SUBSCRIBE bodies
SUBSCRIBE requests that serve to terminate the subscription MAY
contain an empty body; however, SUBSCRIBE requests that establish a
dialog MUST contain a body which encodes three pieces of information:
(1) The set of events (DPs) that is being subscribed to. A
subscriber MAY subscribe to multiple DPs in one SUBSCRIBE request,
or MAY issue a different SUBSCRIBE request for each DP it is
interested in receiving a notification for. The protocol allows
for both forms of representation, however, it recommends the
former manner of subscribing to DPs if the service depends on any
of the DPs being triggered.
Gurbani, et al. Standards Track [Page 16]
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(2) Because of the requirement [4] that IN be informed whether the
detection point is set as the request or notification, all events
in the "spirits-INDPs" package (but not in the "spirits-user-prof"
package) are required to provide a "mode" parameter, whose values
are "R" (for Request) and "N" for notification.
(3) A list of the values of the parameters associated with the
event detection point (Note: the term "event" here refers to the
IN usage -- a dynamically armed DP is called an Event Detection
Point). Please see Section 5.2.1 and Section 5.2.2 for a list of
parameters associated with each DP.
The default body type for SUBSCRIBEs in SPIRITS is denoted by the
MIME type "application/spirits-event+xml". The "Accept" header, if
present, MUST include this MIME type.
5.3.5. Subscription duration
For package "spirits-INDPs", the purpose of the SUBSCRIBE request is
to arm the DP, since as far as IN is concerned, being armed is the
first essential pre-requisite. A DP maybe armed either statically
(for instance, through service provisioning), or dynamically (by the
SCF). A statically armed DP remains armed until it is disarmed
proactively. A dynamically armed DP remains armed for the duration
of a call (or more appropriately, no longer than the duration of a
particular SSF-SCF relationship).
Dynamically armed DPs are automatically disarmed when the event of
interest occurs in the notifier. It is up to the subscriber to re-
arm the DPs within the context of a call, if it so desires.
Statically armed DPs are considered outside the scope of the SPIRITS
protocol requirements [4] and thus will not be considered any
further.
5.3.6. NOTIFY bodies
Bodies in NOTIFY requests for the "spirits-INDPs" package are
optional. If present, they MUST be of the MIME type
"application/spirits-event+xml". The body in a NOTIFY request
encapsulates the following pieces of information which can be used by
the subscriber:
(1) The event that resulted in the NOTIFY being generated
(typically, but not always, this will be the same event present in
the corresponding SUBSCRIBE request).
Gurbani, et al. Standards Track [Page 17]
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(2) The "mode" parameter; it is simply reflected back from the
corresponding SUBSCRIBE request.
(3) A list of values of the parameters associated with the event
that the NOTIFY is being generated for. Depending on the actual
event, the list of the parameters will vary.
If the subscriber armed multiple DPs as part of a single SUBSCRIBE
request, all the un-encountered DPs that were part of the same
SUBSCRIBE dialog MUST be dis-armed by the SPIRITS notifier and/or the
SCF/SCP.
5.3.7. Notifier processing of SUBSCRIBE requests
When the notifier receives a SUBSCRIBE request, it MUST authenticate
the request and ensure that the subscriber is authorized to access
the resource being subscribed to, in this case, PSTN/IN events on a
certain PSTN line.
Once the SUBSCRIBE request has been authenticated and authorized, the
notifier interfaces with the SCF over interface D to arm the
detection points corresponding to the PSTN line contained in the
SUBSCRIBE body. The particulars about interface D is out of scope
for this document; here we will simply assume that the notifier can
affect the arming (and disarming) of triggers in the PSTN through
interface D.
5.3.8. Notifier generation of NOTIFY requests
If the notifier expects the arming of triggers to take more than 200
ms, it MUST send a 202 response to the SUBSCRIBE request immediately,
accepting the subscription. It should then send a NOTIFY request
with an empty body. This NOTIFY request MUST have a "Subscription-
State" header with a value of "pending".
This immediate NOTIFY with an empty body is needed since the
resource identified in the SUBSCRIBE request does not have as
yet a meaningful state.
Once the notifier has successfully interfaced with the SCF, it MUST
send a subsequent NOTIFY request with an empty body and a
"Subscription-State" header with a value of "active."
When the event of interest identified in the SUBSCRIBE request
occurs, the notifier sends out a new NOTIFY request which MUST
contain a body (see Section 5.3.6). The NOTIFY request MUST have a
"Subscription-State" header and its value MUST be set to "terminated"
with a reason parameter of "fired".
Gurbani, et al. Standards Track [Page 18]
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5.3.9. Subscriber processing of NOTIFY requests
The exact steps executed at the subscriber when it gets a NOTIFY
request will depend on the service being implemented. As a
generality, the UA associated with the subscriber should somehow
impart this information to the user by visual or auditory means, if
at all possible.
If the NOTIFY request contained a "Subscription-State" header with a
value of "terminated" and a reason parameter of "fired", the UA
associated with the subscriber MAY initiate a new subscription for
the event that was just reported through the NOTIFY request.
Whether or not to initiate a new subscription when an existing
one expires is up to the context of the service that is being
implemented. For instance, a user may configure her UA to
always re-subscribe to the same event when it fires, but this
is not necessarily the normative case.
5.3.10. Handling of forked requests
Forking of SUBSCRIBE requests is prohibited. Since the SUBSCRIBE
request is targeted towards the PSTN, highly irregular behaviors
occur if the request is allowed to fork. The normal SIP DNS lookup
and routing rules [11] should result in a target set with exactly one
element: the notifier.
5.3.11. Rate of notifications
For reasons of security more than network traffic, it is RECOMMENDED
that the notifier issue two or, at most three NOTIFY requests for a
subscription. If the subscription was accepted with a 202 response,
a NOTIFY will be sent immediately towards the subscriber. This
NOTIFY serves to inform the subscriber that the request has been
accepted and is being acted on.
Once the resource (detection points) identified in the SUBSCRIBE
request have been initialized, the notifier MUST send a second NOTIFY
request. This request contains the base state of the resource.
When an event of interest occurs which leads to the firing of the
trigger associated with the detection points identified in the
SUBSCRIBE request, a final NOTIFY is sent to the subscriber. This
NOTIFY request contains more information about the event of interest.
Gurbani, et al. Standards Track [Page 19]
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If the subscription was accepted with a 200 response, the notifier
simply sends two NOTIFY requests: one containing the base state of
the resource, and the other containing information that lead to the
firing of the detection point.
5.3.12. State agents
State agents are not used in SPIRITS.
5.3.13. Examples
This section contains example call flows for a SPIRITS service called
Internet Caller-ID Delivery (ICID). One of the benchmark SPIRITS
service, as described in section 2.2 of [1] is Internet Caller-ID
delivery:
This service allows the subscriber to see the caller's number or
name or both while being connected to the Internet. If the
subscriber has only one telephone line and is using the very line
for the Internet connection, the service is a subset of the ICW
service and follows the relevant description in Section 2.1.
Otherwise, the subscriber's IP host serves as an auxiliary device
of the telephone to which the call is first sent.
We present an example of a SPIRITS call flow to realize this service.
Note that this is an example only, not a normative description of the
Internet Caller-ID service.
Further text and details of SIP messages below refer to the call flow
provided in Figure 3. Figure 3 depicts the 4 entities that are an
integral part of any SPIRITS service (the headings of the entities
refer to the names established in Figure 1 in [1]) -- the SPIRITS
subscriber, the SPIRITS notifier and the SCF. Note that the SPIRITS
gateway is not included in this figure; logically, SPIRITS messages
flow between the SPIRITS server and the SPIRITS client. A gateway,
if present, may act as a proxy.
Gurbani, et al. Standards Track [Page 20]
RFC 3910 SPIRITS Protocol October 2004
SPIRITS server SPIRITS client SCF
("subscriber") ("notifier")
S N
| | |
| F1 SUBSCRIBE | |
+--------------------->+ |
| | |
| | F2 Arm DP |
| F3 200 OK (SUBS) +--------------->|
|<---------------------| |
| | |
| F4 NOTIFY | |
|<---------------------+ |
| | |
| F5 200 OK (NOT) | |
+--------------------->| |
| | |
~ ~ ~
~ ~ ~
| | F6 Evt. Not. |
| |<---------------+
| F7 NOTIFY + |
|<---------------------| |
| | |
| F8 200 OK (NOT) | |
+--------------------->| |
| | |
| | |
\|/ \|/ \|/
v v v
Figure 3: Sample call flow
This call flow depicts an overall operation of a "subscriber"
successfully subscribing to the IN Termination_Attempt_Authorized DP
(the "subscriber" is assumed to be a user, possibly at work, who is
interested in knowing when he/she gets a phone call to his/her home
phone number) -- this interaction is captured in messages F1 through
F8 in Figure 3. The user sends (F1) a SIP SUBSCRIBE request
identifying the DP it is interested in along with zero or more
parameters relevant to that DP (in this example, the
Termination_Attempt_DP will be employed). The SPIRITS notifier in
turns interacts with the SCF to arm the Termination_Attempt_DP for
the service (F2). An immediate NOTIFY with the current state
information is send to the subscriber (F4, F5).
Gurbani, et al. Standards Track [Page 21]
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At some point after the above sequence of events has transpired, the
PSTN gets a call to the users phone. The SSF informs the SCF of this
event when it encounters an armed Termination_Attempt_DP (not shown
in Figure 3). The SCF informs the SPIRITS notifier of this event
(F6).
When the SPIRITS notifier receives this event, it forms a SIP NOTIFY
request and directs it to the SPIRITS subscriber (F7). This NOTIFY
will contain all the information elements necessary to identify the
caller to the subscriber. The subscriber, upon receiving the
notification (F8) may pop open a window with the date/time and the
number of the caller.
The rest of this section contains the details of the SIP messages in
Figure 3. The call flow details below assume that the SPIRITS
gateway is, for the purpose of this example, a SIP proxy that serves
as the default outbound proxy for the notifier and an ingress host of
the myprovider.com domain for the subscriber. The subscriber and
notifier may be in separate administrative domains.
F1: S->N
SUBSCRIBE sip:myprovider.com SIP/2.0
From: <sip:vkg@example.com>;tag=8177-afd-991
To: <sip:16302240216@myprovider.com>
CSeq: 18992 SUBSCRIBE
Call-ID: 3329as77@host.example.com
Contact: <sip:vkg@host.example.com>
Via: SIP/2.0/UDP host.example.com;branch=z9hG4bK776asdhds
Expires: 3600
Event: spirits-INDPs
Allow-Events: spirits-INDPs, spirits-user-prof
Accept: application/spirits-event+xml
Content-Type: application/spirits-event+xml
Content-Length: ...
<?xml version="1.0" encoding="UTF-8"?>
<spirits-event xmlns="urn:ietf:params:xml:ns:spirits-1.0">
<Event type="INDPs" name="TAA" mode="N">
<CalledPartyNumber>6302240216</CalledPartyNumber>
</Event>
</spirits-event>
The subscriber forms a SIP SUBSCRIBE request which identifies the DP
that it wants to subscribe to (in this case, the TAA DP) and the
actual line it wants that DP armed for (in this case, the line
Gurbani, et al. Standards Track [Page 22]
RFC 3910 SPIRITS Protocol October 2004
associated with the phone number 6302240216). This request
eventually arrives at the SIPRITS notifier, N, which authenticates it
(not shown) and sends a successful response to the subscriber:
F3: N->S
SIP/2.0 200 OK
From: <sip:vkg@example.com>;tag=8177-afd-991
To: <sip:16302240216@myprovider.com>;tag=SPIRITS-TAA-6302240216
CSeq: 18992 SUBSCRIBE
Call-ID: 3329as77@host.example.com
Contact: <sip:notifier.myprovider.com>
Via: SIP/2.0/UDP host.example.com;branch=z9hG4bK776asdhds
Expires: 3600
Accept: application/spirits-event+xml
Content-Length: 0
The notifier interacts with the SCF to arm the DP and also sends an
immediate NOTIFY towards the subscriber informing the subscriber of
the current state of the notification:
F4: N->S
NOTIFY sip:vkg@host.example.com SIP/2.0
From: <sip:16302240216@myprovider.com>;tag=SPIRITS-TAA-6302240216
To: <sip:vkg@example.com>;tag=8177-afd-991
Via: SIP/2.0/UDP gateway.myprovider.com;branch=z9hG4bK-9$0-1
Via: SIP/2.0/UDP notifier.myprovider.com;branch=z9hG4bKqo--9
Call-ID: 3329as77@host.example.com
Contact: <sip:notifier.myprovider.com>
Subscription-State: active
CSeq: 3299 NOTIFY
Accept: application/spirits-event+xml
Content-Length: 0
F5: S->N
SIP/2.0 200 OK
From: <sip:16302240216@myprovider.com>;tag=SPIRITS-TAA-6302240216
To: <sip:vkg@example.com>;tag=8177-afd-991
Via: SIP/2.0/UDP gateway.myprovider.com;branch=z9hG4bK-9$0-1
Via: SIP/2.0/UDP notifier.myprovider.com;branch=z9hG4bKqo--9
Call-ID: 3329as77@host.example.com
Contact: <sip:vkg@host.example.com>
CSeq: 3299 NOTIFY
Accept: application/spirits-event+xml
Content-Length: 0
Gurbani, et al. Standards Track [Page 23]
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At some later point in time (before the subscription established in
F1 expires at the notifier), a call arrives at the number identified
in XML-encoded body of F1 -- 6302240216. The SCF notifies the
notifier (F6). Included in this notification is the relevant
information from the PSTN, namely, the phone number of the party
attempting to call 6302240216. The notifier uses this information to
create a SIP NOTIFY request and sends it to the subscriber. The SIP
NOTIFY request has a XML-encoded body with the relevant information
from the PSTN:
F7: N->S
NOTIFY sip:vkg@host.example.com SIP/2.0
From: <sip:16302240216@myprovider.com>;tag=SPIRITS-TAA-6302240216
To: <sip:vkg@example.com>;tag=8177-afd-991
Via: SIP/2.0/UDP notifier.myprovider.com;branch=z9hG4bK9inn-=u7
Call-ID: 3329as77@host.example.com
Contact: <sip:notifier.myprovider.com>
CSeq: 3300 NOTIFY
Subscription-State: terminated;reason=fired
Accept: application/spirits-event+xml
Event: spirits-INDPs
Allow-Events: spirits-INDPs, spirits-user-prof
Content-Type: application/spirits-event+xml
Content-Length: ...
<?xml version="1.0" encoding="UTF-8"?>
<spirits-event xmlns="urn:ietf:params:xml:ns:spirits-1.0">
<Event type="INDPs" name="TAA" mode="N">
<CalledPartyNumber>6302240216</CalledPartyNumber>
<CallingPartyNumber>3125551212</CallingPartyNumber>
</Event>
</spirits-event>
There are two important issues to note in the call flows for F7:
(1) The body of the NOTIFY request contains the information passed
to the SPIRITS notifier from the SCF. In this particular
example, this is the phone number of the party (3125551212)
that attempted to call 6302240216.
(2) Since the notification occurred, the subscription established
in F1 terminated (as evident by the Subscription-State
header). The subscription terminated normally due to the DP
associated with TAA firing (hence the reason code of "fired"
in the Subscription-State header). If the subscriber
Gurbani, et al. Standards Track [Page 24]
RFC 3910 SPIRITS Protocol October 2004
wants to get notified of another attempt to call the number
6302240216, he/she should send a new SUBSCRIBE request to the
notifier.
The subscriber can take any appropriate action upon the receipt of
the NOTIFY in F7. A reasonable implementation may pop up a window
populated with the information contained in the body of F12, along
with a button asking the subscriber if they would like to re-
subscribe to the same event. Alternatively, a re-subscription could
be generated automatically by the subscriber's UA based on his/her
preferences.
To complete the protocol, the subscriber also sends a 200 OK message
towards the notifier:
F8: S->N
200 OK SIP/2.0
From: <sip:16302240216@myprovider.com>;tag=SPIRITS-TAA-6302240216
To: <sip:vkg@example.com>;tag=8177-afd-991
Via: SIP/2.0/UDP notifier.myprovider.com;z9hG4bK9inn-=u7
Call-ID: 3329as77@host.example.com
CSeq: 3300 NOTIFY
Content-Length: 0
5.3.14. Use of URIs to retrieve state
The "spirits-INDPs" package MUST NOT use URIs to retrieve state. It
is expected that most state information for this package is compact
enough to fit in a SIP message. However, to err on the side of
caution, implementations MUST follow the convention outlined in
Section 18.1.1 of [5] and use a congestion controlled transport if
the size of the request is within 200 bytes of the path MTU if known,
or if the request size is larger than 1300 bytes and the path MTU is
unknown.
5.4. Services through static DPs
We mentioned in Section 5.1 that the first trigger that fires during
call processing is typically a TDP since there isn't any pre-existing
control relationship between the SSF and the SCF. Some Internet
hosts may have expressed an interest in executing services based on
TDPs (through an a-priori arrangement, which is not a part of this
specification). Thus, the PSTN will notify such hosts. To do so, it
will send a SIP request (typically an INVITE) towards the Internet
host. The body of the SIP request MUST contain multi-part MIME with
two MIME components: the first part corresponding to the normal
payload, if any, of the request; and the second part will contain
Gurbani, et al. Standards Track [Page 25]
RFC 3910 SPIRITS Protocol October 2004
SPIRITS-specific information (e.g., the DP that fired). Responses to
the INVITE request, or subsequent SUBSCRIBE messages from the
Internet host to the PSTN within a current call context may result in
EDPs being armed.
5.4.1. Internet Call Waiting (ICW)
ICW as a benchmark SPIRITS service actually predates SPIRITS itself.
Pre-SPIRITS implementations of ICW are detailed in [10]. However, as
the document notes, while a diversity of implementations exists,
these implementations are not interoperable. At the time [10] was
published, the industry did not have the depth of experience with SIP
as is the case now. The use of SIP in [10] does not constitute
normative usage of SIP as described in [5]; for instance, no mention
is made of the SDP (if any) in the initial INVITE (especially since
this pertains to "accept the call using VoIP" case). Thus this
section serves to provide a normative description of ICW in SPIRITS.
The description of ICW is deceptively simple: it is a service most
useful for single line phone subscribers that use the line to
establish an Internet session. In a nutshell, the service enables a
subscriber engaged in an Internet dial-up session to
o be notified of an incoming call to the very same telephone line
that is being used for the Internet connection,
o specify the desirable treatment of the call, and
o have the call handled as specified.
5.4.2. Call disposition choices
Section 2 of [10] details the call disposition outcome of a ICW
session. They are reproduced here as a numbered list for further
discussion:
1. Accepting the call over the PSTN line, thus terminating the
Internet (modem) connection
2. Accepting the call over the Internet using Voice over IP (VoIP)
3. Rejecting the call
4. Playing a pre-recorded message to the calling party and
disconnecting the call
5. Forwarding the call to voice mail
Gurbani, et al. Standards Track [Page 26]
RFC 3910 SPIRITS Protocol October 2004
6. Forwarding the call to another number
7. Rejecting (or Forwarding) on no Response - If the subscriber
fails to respond within a certain period of time after the dialog
box has been displayed, the incoming call can be either rejected
or handled based on the treatment pre-defined by the subscriber.
It should be pointed out for the sake of completeness that ICW as a
SPIRITS service is not possible without making the SCP aware of the
fact that the subscriber line is being used for an Internet session.
That awareness, however, is not a part of the ICW service, but solely
a pre-requisite. One of the following three methods MUST be utilized
to impart this information to the SCP:
A. ICW subscriber based method: the ICW client on the subscriber's
PC notifies the SCP of the Internet session by issuing a SIP
REGISTER request.
B. IN based method: SCP maintains a list of Internet Service
Provider (ISP) access numbers for a geographical area; when one of
these numbers is dialed and connected to, it (the SCP) assumes
that the calling party is engaged in an Internet session.
C. Any combination of methods A and B.
ICW depends on a TDP to be provisioned in the SSP. When the said TDP
is encountered, the SSP suspends processing of the call and sends a
request to the SPIRITS-capable SCP. The SCP determines that the
subscriber line is being used for an Internet session. It instructs
the SPIRITS notifier on the SCP to create a SIP INVITE request and
send it to the SPIRITS subscriber running on the subscriber's IP
host.
The SPIRITS subscriber MUST return one of the possible call
disposition outcomes catalogued in Section 5.4.2. Note that outcomes
1 and 4 through 7 can all be coalesced into one case, namely
redirecting (using the SIP 3xx response code) the call to an
alternative SIP URI. In case of 1, the URI of the redirected call
MUST match the very same number being used by the customer to get
online. Rejecting the call implies sending a non-2xx and non-3xx
final response; the remaining outcomes result in the call being
redirected to an alternate URI which provides the desired service
(i.e., play a pre-recorded announcement, or record a voice message).
Gurbani, et al. Standards Track [Page 27]
RFC 3910 SPIRITS Protocol October 2004
Further processing of a SPIRITS notifier when it receives a final
response can be summarized by the following steps:
1. If the response is a 4xx, 5xx, or 6xx class of response,
generate and transmit an ACK request and instruct the SSP to play
a busy tone to the caller.
2. Else, for all 3xx responses, generate and transmit an ACK
request, and compare the redirected URI to the subscriber's line
number:
2a. If the comparison indicates a match, instruct the SSP to
hold onto the call for just enough time to allow the SPIRITS
subscriber to disconnect the modem, thus freeing up the line;
and then continue with normal call processing, which will
result in the subscriber's phone to ring.
2b. If the comparison fails, instruct the SSP to route the
call to the redirected URI.
3. Else, for a 2xx response, follow the steps in section 5.4.3.
5.4.3. Accepting an ICW session using VoIP
One call handling option in ICW is to "accept an incoming call using
VoIP". The SPIRITS notifier has no way of knowing a-priori if the
subscriber (callee) will be choosing this option; nonetheless, it has
to account for such a choice by adding a SDP in the body of the
INVITE request. A possible way of accomplishing this is to have the
SPIRITS notifier control a PSTN gateway and allocate appropriate
resources on it. Once this is done, the SPIRITS notifier adds
network information (IP address of the gateway and port numbers where
media will be received) and codec information as the SDP portion of
the body in the INVITE request. SPIRITS requires the DP information
to be carried in the request body as well. To that extent, the
SPIRITS notifier MUST also add the information associated with the
TDP that triggered the service. Thus, the body of the INVITE MUST
contain multi-part MIME, with two components.
The SPIRITS notifier transmits the INVITE request to the subscriber
and now waits for a final response. Further processing when the
SPIRITS subscriber returns a 200 OK MUST be handled as follows:
On the receipt of a 200 OK containing the SDP of the subscriber's
UA, the SPIRITS notifier will instruct the SSP to terminate the
call on a pre-allocated port on the gateway. This port MUST be
correlated by the gateway to the SDP that was sent in the earlier
INVITE.
Gurbani, et al. Standards Track [Page 28]
RFC 3910 SPIRITS Protocol October 2004
The end result is that the caller and callee hold a voice session
with part of the session occurring over VoIP.
6. Non-call related events
There are network events that are not related to setting up,
maintaining, or tearing down voice calls. Such events occur on the
cellular wireless network and can be used by SPIRITS to provide
services. The SPIRITS protocol requirement explicitly includes the
following events for which SPIRITS notification is needed
(RFC3298:Section 5(b)):
1. Location update in the same Visitor Location Register (VLR)
service area
2. Location update in another VLR service area
3. International Mobile Subscriber Identity (IMSI) attach
4. Mobile Subscriber (MS) initiated IMSI detach
5. Network initiated IMSI detach
6.1. Non-call events and their required parameters
Each of the five non-call related event is given a SPIRITS-specific
mnemonic for use in subscriptions and notifications.
Location update in the same VLR area
SPIRITS mnemonic: LUSV
Mandatory parameter in SUBSCRIBE: CalledPartyNumber
Mandatory parameter in NOTIFY: CalledPartyNumber, Cell-ID
Cell-ID: A string used to identify the serving Cell-ID. The actual
length and representation of this parameter depend on the particulars
of the cellular provider's network.
Location update in different VLR area
SPIRITS mnemonic: LUDV
Mandatory parameter in SUBSCRIBE: CalledPartyNumber
Mandatory parameter in NOTIFY: CalledPartyNumber, Cell-ID
IMSI attach
SPIRITS mnemonic: REG
Mandatory parameter in SUBSCRIBE: CalledPartyNumber
Mandatory parameter in NOTIFY: CalledPartyNumber, Cell-ID
Gurbani, et al. Standards Track [Page 29]
RFC 3910 SPIRITS Protocol October 2004
MS initiated IMSI detach
SPIRITS mnemonic: UNREGMS
Mandatory parameter in SUBSCRIBE: CalledPartyNumber
Mandatory parameter in NOTIFY: CalledPartyNumber
Network initiated IMSI detach
SPIRITS mnemonic: UNREGNTWK
Mandatory parameter in SUBSCRIBE: CalledPartyNumber
Mandatory parameter in NOTIFY: CalledPartyNumber
6.2. Normative usage
A subscriber will issue a SUBSCRIBE request which identifies a set of
non-call related PSTN events it is interested in getting the
notification of. This set MAY contain exactly one event, or it MAY
contain multiple events. The SUBSCRIBE request is routed to the
notifier where it is accepted, pending a successful authentication.
When any of the events identified in the set occurs, the notifier
will format a NOTIFY request and direct it towards the subscriber.
The NOTIFY request will contain information pertinent to the one of
the event whose notification was requested.
The dialog established by the SUBSCRIBE persists until it expires
normally, or is explicitly expired by the subscriber. This behavior
is different than the behavior for subscriptions associated with the
"spirits-INDPs" package. In the cellular network, the events
subscribed for may occur at a far greater frequency than those
compared to the wireline network (consider location updates as a
cellular user moves around). Thus it is far more expedient to allow
the subscription to expire normally.
When a subscriber receives a NOTIFY request, it can subsequently
choose to act in a manner appropriate to the notification.
The remaining sections fill in the specific package responsibilities
raised in RFC3265 [3], Section 4.4.
6.3. Event package name
This document defines two event packages; the first was defined in
Section 5.3. The second package, defined in this section is called
"spirits-user-prof". This package MUST be used for events
corresponding to non-call related events in the cellular network.
All entities that implement the SPIRITS protocol and support the
non-call related events outlined in the SPIRITS protocol requirements
Gurbani, et al. Standards Track [Page 30]
RFC 3910 SPIRITS Protocol October 2004
(RFC3298:Section 5(b)) MUST set the "Event" header request header[3]
to "spirits-user-prof." The "Allow-Events" general header [3] MUST
include the token "spirits-user-prof" as well.
Example:
Event: spirits-user-prof
Allow-Events: spirits-user-prof, spirits-INDPs
6.4. Event package parameters
The "spirits-user-prof" event package does not support any additional
parameters to the Event header
6.5. SUBSCRIBE bodies
SUBSCRIBE requests that serve to terminate the subscriptions MAY
contain an empty body; however, SUBSCRIBE requests that establish a
dialog MUST contain a body which encodes two pieces of information:
(1) The set of events that is being subscribed to. A subscriber
MAY subscribe to multiple events in one SUBSCRIBE request, or MAY
issue a different SUBSCRIBE request for each event it is
interested in receiving a notification for. The protocol allows
for both forms of representation. However, note that if one
SUBSCRIBE is used to subscribe to multiple events, then an expiry
for the dialog associated with that subscription affects all such
events.
(2) A list of values of the parameters associated with the event.
Please see Section 6.1 for a list of parameters associated with
each event.
The default body type for SUBSCRIBEs in SPIRITS is denoted by the
MIME type "application/spirits-event+xml". The "Accept" header, if
present, MUST include this MIME type.
6.6. Subscription duration
The duration of a dialog established by a SUBSCRIBE request is
limited to the expiration time negotiated between the subscriber and
notifier when the dialog was established. The subscriber MUST send a
new SUBSCRIBE to refresh the dialog if it is interested in keeping it
alive. A dialog can be terminated by sending a new SUBSCRIBE request
with an "Expires" header value of 0, as outlined in [3].
Gurbani, et al. Standards Track [Page 31]
RFC 3910 SPIRITS Protocol October 2004
6.7. NOTIFY bodies
Bodies in NOTIFY requests for the "spirits-user-prof" package are
optional. If present, they MUST be of the MIME type
"application/spirits-event+xml". The body in a NOTIFY request
encapsulates the following pieces of information which can be used by
the subscriber:
(1) The event that resulted in the NOTIFY being generated
(typically, but not always, this will be the same event present in
the corresponding SUBSCRIBE request).
(2) A list of values of the parameters associated with the event
that the NOTIFY is being generated for. Depending on the actual
event, the list of the parameters will vary.
6.8. Notifier processing of SUBSCRIBE requests
When the notifier receives a SUBSCRIBE request, it MUST authenticate
the request and ensure that the subscriber is authorized to access
the resource being subscribed to, in this case, non-call related
cellular events for a mobile phone.
Once the SUBSCRIBE request has been authenticated and authorized, the
notifier interfaces with the SCF over interface D to set marks in the
HLR corresponding to the mobile phone number contained in the
SUBSCRIBE body. The particulars of interface D are outside the scope
of this document; here we simply assume that the notifier is able to
set the appropriate marks in the HLR.
6.9. Notifier generation of NOTIFY requests
If the notifier expects the setting of marks in the HLR to take more
than 200 ms, it MUST send a 202 response to the SUBSCRIBE request
immediately, accepting the subscription. It should then send a
NOTIFY request with an empty body. This NOTIFY request MUST have a
"Subscription-State" header with a value of "pending".
This immediate NOTIFY with an empty body is needed since the
resource identified in the SUBSCRIBE request does not have as yet
a meaningful state.
Once the notifier has successfully interfaced with the SCF, it MUST
send a subsequent NOTIFY request with an empty body and a
"Subscription-State" header with a value of "active."
Gurbani, et al. Standards Track [Page 32]
RFC 3910 SPIRITS Protocol October 2004
When the event of interest identified in the SUBSCRIBE request
occurs, the notifier sends out a new NOTIFY request which MUST
contain a body as described in Section 6.7.
6.10. Subscriber processing of NOTIFY requests
The exact steps executed at the subscriber when it receives a NOTIFY
request depend on the nature of the service that is being
implemented. As a generality, the UA associated with the subscriber
should somehow impart this information to the user by visual or
auditory means, if at all possible.
6.11. Handling of forked requests
Forking of SUBSCRIBE requests is prohibited. Since the SUBSCRIBE
request is targeted towards the PSTN, highly irregular behaviors
occur if the request is allowed to fork. The normal SIP DNS lookup
and routing rules [11] should result in a target set with exactly one
element: the notifier.
6.12. Rate of notifications
For reasons of congestion control, it is important that the rate of
notifications not become excessive. For instance, if a subscriber
subscribes to the location update event for a notifier moving through
the cellular network at a high enough velocity, it is entirely
conceivable that the notifier may generate many NOTIFY requests in a
small time frame. Thus, within this package, the location update
event needs an appropriate throttling mechanism.
Whenever a SPIRITS notifier sends a location update NOTIFY, it MUST
start a timer (Tn) with a value of 15 seconds. If a subsequent
location update NOTIFY request needs to be sent out before the timer
has expired, it MUST be discarded. Any future location update NOTIFY
requests MUST be transmitted only if Tn has expired (i.e. 15 seconds
have passed since the last NOTIFY request was send out). If a
location update NOTIFY is send out, Tn should be reset to go off
again in 15 seconds.
6.13. State agents
State agents are not used in SPIRITS.
6.14. Examples
This section contains an example of a SPIRITS service that may be
used to update the presence status of a mobile user. The call flow
is depicted in Figure 4 below.
Gurbani, et al. Standards Track [Page 33]
RFC 3910 SPIRITS Protocol October 2004
SPIRITS server SPIRITS client SCF
("subscriber") ("notifier")
S N
| | |
| F1 SUBSCRIBE | |
+--------------------->+ |
| | |
| | F2 Set HLR mark|
| F3 200 OK (SUBS) +--------------->|
|<---------------------| |
| | |
| F4 NOTIFY | |
|<---------------------+ |
| | |
| F5 200 OK (NOT) | |
+--------------------->| |
| | |
~ ~ ~
~ ~ ~
| | F6 Evt. Not. |
| |<---------------+
| F7 NOTIFY + |
|<---------------------| |
| | |
| F8 200 OK (NOT) | |
+--------------------->| |
| | |
| | |
\|/ \|/ \|/
v v v
Figure 4: Sample call flow
In F1 of Figure 4, the subscriber indicates an interest in receiving
a notification when a mobile user registers with the cellular
network. The cellular network notes this event (F2) and confirms the
subscription (F3-F5). When the mobile user turns on her cell phone
and registers with the network, this event is detected (F6). The
cellular network then sends out a notification to the subscriber
informing it of this event (F7-F8).
We present the details of the call flow next.
In F1, the subscriber subscribes to the registration event (REG) of a
cellular phone number.
Gurbani, et al. Standards Track [Page 34]
RFC 3910 SPIRITS Protocol October 2004
F1: S->N
SUBSCRIBE sip:myprovider.com SIP/2.0
From: <sip:vkg@example.com>;tag=8177-afd-991
To: <sip:16302240216@myprovider.com>
CSeq: 18992 SUBSCRIBE
Call-ID: 3329as77@host.example.com
Contact: <sip:vkg@host.example.com>
Via: SIP/2.0/UDP host.example.com;branch=z9hG4bK776asdhdsa8
Expires: 3600
Event: spirits-user-prof
Allow-Events: spirits-INDPs, spirits-user-prof
Accept: application/spirits-event+xml
Content-Type: application/spirits-event+xml
Content-Length: ...
<?xml version="1.0" encoding="UTF-8"?>
<spirits-event xmlns="urn:ietf:params:xml:ns:spirits-1.0">
<Event type="userprof" name="REG">
<CalledPartyNumber>6302240216</CalledPartyNumber>
</Event>
</spirits-event>
The subscription reaches the notifier which authenticates the request
(not shown) and interacts with the SCF to update the subscribers
database for this event. The notifier sends out a successful
response to the subscription:
F3: N->S
SIP/2.0 200 OK
From: <sip:vkg@example.com>;tag=8177-afd-991
To: <sip:16302240216@myprovider.com>;tag=SPIRITS-REG-16302240216
CSeq: 18992 SUBSCRIBE
Call-ID: 3329as77@host.example.com
Contact: <sip:notifier.myprovider.com>
Via: SIP/2.0/UDP host.example.com;branch=z9hG4bK776asdhdsa8
Expires: 3600
Allow-Events: spirits-INDPs, spirits-user-prof
Accept: application/spirits-event+xml
Content-Length: 0
The notifier also sends out a NOTIFY request confirming the
subscription:
F4: N->S
NOTIFY sip:vkg@host.example.com SIP/2.0
To: <sip:vkg@example.com>;tag=8177-afd-991
From: <sip:16302240216@myprovider.com>;tag=SPIRITS-REG-16302240216
CSeq: 9121 NOTIFY
Gurbani, et al. Standards Track [Page 35]
RFC 3910 SPIRITS Protocol October 2004
Call-ID: 3329as77@host.example.com
Contact: <sip:notifier.myprovider.com>
Subscription-State: active
Via: SIP/2.0/UDP notifier.myprovider.com;branch=z9hG4bK7007-091a
Allow-Events: spirits-INDPs, spirits-user-prof
Accept: application/spirits-event+xml
Content-Length: 0
The subscriber confirms the receipt of the NOTIFY request:
F5: S->N
SIP/2.0 200 OK
To: <sip:vkg@example.com>;tag=8177-afd-991
From: <sip:16302240216@myprovider.com>;tag=SPIRITS-REG-16302240216
CSeq: 9121 NOTIFY
Call-ID: 3329as77@host.example.com
Contact: <sip:vkg@host.example.com>
Via: SIP/2.0/UDP notifier.myprovider.com;branch=z9hG4bK7007-091a
Content-Length: 0
In F6, the mobile user identified by the PSTN number "6302240216"
turns the mobile phone on, thus causing it to register with the
cellular network. The cellular network detects this event, and since
a subscriber has indicated an interest in receiving a notification of
this event, a SIP NOTIFY request is transmitted towards the
subscriber:
F7: N->S
NOTIFY sip:vkg@host.example.com SIP/2.0
To: <sip:vkg@example.com>;tag=8177-afd-991
From: <sip:16302240216@myprovider.com>;tag=SPIRITS-REG-16302240216
CSeq: 9122 NOTIFY
Call-ID: 3329as77@host.example.com
Contact: <sip:notifier.myprovider.com>
Subscription-State: terminated;reason=fired
Via: SIP/2.0/UDP notifier.myprovider.com;branch=z9hG4bK7yi-p12
Event: spirits-user-prof
Allow-Events: spirits-INDPs, spirits-user-prof
Accept: application/spirits-event+xml
Content-Type: application/spirits-event+xml
Content-Length: ...
Gurbani, et al. Standards Track [Page 36]
RFC 3910 SPIRITS Protocol October 2004
<?xml version="1.0" encoding="UTF-8"?>
<spirits-event xmlns="urn:ietf:params:xml:ns:spirits-1.0">
<Event type="userprof" name="REG">
<CalledPartyNumber>6302240216</CalledPartyNumber>
<Cell-ID>45987</Cell-ID>
</Event>
</spirits-event>
The subscriber receives the notification and acknowledges it by
sending a response:
F8: S->N
SIP/2.0 200 OK
To: <sip:vkg@example.com>;tag=8177-afd-991
From: <sip:16302240216@myprovider.com>;tag=SPIRITS-REG-16302240216
CSeq: 9122 NOTIFY
Call-ID: 3329as77@host.example.com
Via: SIP/2.0/UDP notifier.myprovider.com;branch=z9hG4bK7yi-p12
Content-Length: 0
Note that once the subscriber has received this notification, it can
execute appropriate services. In this particular instance, an
appropriate service may consist of the subscriber acting as a
composer of a presence service and turning the presence status of the
user associated with the phone number "6302240216" to "on". Also
note in F7 that the notifier included a Cell ID in the notification.
The Cell ID can be used as a basis for location specific services;
however, a discussion of such services is out of the scope of this
document.
6.15. Use of URIs to retrieve state
The "spirits-user-prof" package MUST NOT use URIs to retrieve state.
It is expected that most state information for this package is
compact enough to fit in a SIP message. However, to err on the side
of caution, implementations MUST follow the convention outlined in
Section 18.1.1 of [5] and use a congestion controlled transport if
the size of the request is within 200 bytes of the path MTU if known,
or if the request size is larger than 1300 bytes and the path MTU is
unknown.
Gurbani, et al. Standards Track [Page 37]
RFC 3910 SPIRITS Protocol October 2004
7. IANA Considerations
This document calls for IANA to:
o register two new SIP Event Packages per [3].
o register a new MIME type per [20].
o register a new namespace URN per [16].
o register a new XML schema per [16].
7.1. Registering event packages
Package Name: spirits-INDPs
Type: package
Contact: Vijay K. Gurbani, vkg@lucent.com
Reference: RFC 3910
Package Name: spirits-user-prof
Type: package
Contact: Vijay K. Gurbani, vkg@lucent.com
Reference: RFC 3910
7.2. Registering MIME type
MIME media type name: application
MIME subtype name: spirits-event+xml
Mandatory parameters: none
Optional parameters: charset (same semantics of charset parameter in
application/xml [9])
Encoding considerations: same as considerations outlined for
application/xml in [9].
Security considerations: Section 10 of [9] and Section 8 of this
document.
Interoperability considerations: none.
Gurbani, et al. Standards Track [Page 38]
RFC 3910 SPIRITS Protocol October 2004
Published specifications: this document.
Applications which use this media type: SPIRITS aware entities which
adhere to this document.
Additional information:
Magic number(s): none.
File extension(s): none.
Macintosh file type code(s): none.
Object Identifier(s) or OID(s): none.
Person and email address for further information: Vijay K. Gurbani,
<vkg@lucent.com>
Intended usage: Common
Author/Change controller: The IETF
7.3. Registering URN
URI
urn:ietf:params:xml:ns:spirits-1.0
Description
This is the XML namespace URI for XML elements defined by this
document. Such elements describe the SPIRITS information in the
"application/ spirits-event+xml" content type.
Registrant Contact
IESG.
XML
BEGIN
<?xml version="1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
"http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="content-type"
content="text/html;charset=utf-8"/>
<title>Namespace for SPIRITS-related information</title>
</head>
<body>
<h1>Namespace for SPIRITS-related information</h1>
Gurbani, et al. Standards Track [Page 39]
RFC 3910 SPIRITS Protocol October 2004
<h2>application/spirits-event+xml</h2>
<p>See <a href="[[[URL of published RFC]]]">RFC3910</a>.</p>
</body>
</html>
END
7.4. Registering XML schema
URI
urn:ietf:params:xml:schema:spirits-1.0
Description
XML base schema for SPIRITS entities.
Registrant Contact
IESG.
XML
Please see XML schema definition in Section 9 of this document.
8. Security Considerations
This section focuses on security considerations which are unique to
SPIRITS. SIP security mechanisms are discussed in detail in the core
SIP specification [5] and are outside the scope of this document.
SPIRITS security mechanisms are based on and strengthen SIP security
[5], for example, SPIRITS mandates the support of S/MIME. Beyond
that, any other security solutions specified in [5], i.e., TLS or
HTTP Digest authentication, may be utilized by SPIRITS operators.
As outlined in Chapter 9 (Security Consideration) of RFC3298 [4], the
following security aspects are applicable to the SPIRITS protocol:
Authentication
Integrity
Confidentiality
Non-repudiation
The SPIRITS architecture in Figure 1 contains 5 interfaces -- A, B,
C, D, and E. Of these, only two -- B and C -- are of interest to
SPIRITS. Interfaces A and E are PINT interfaces and are thus assumed
secured by the PINT RFC [8]. Security for interface D is out of
scope in this document since it deals primarily with the PSTN
infrastructure. We will discuss security aspects on interfaces B and
C predicated on certain assumptions.
Gurbani, et al. Standards Track [Page 40]
RFC 3910 SPIRITS Protocol October 2004
A driving assumption for SPIRITS security is that the SPIRITS gateway
is owned by the same PSTN operator that owns the SPIRITS notifier.
Thus, it is attractive to simply relegate security of interface C to
the PSTN operator, and in fact, there are merits to doing just that
since interface C crosses the IP Network and PSTN boundaries.
However, a closer inspection reveals that both interfaces B and C
transmit the SPIRITS protocol; thus, any security arrangement we
arrive at for interface B can be suitably applied to interface C as
well. This makes it possible to secure interface C in case the
SPIRITS gateway is not owned by the same PSTN operator that owns the
SPIRITS notifier.
The ensuing security discussion assumes that the SPIRITS subscriber
is communicating directly to the SPIRITS notifier (and vice-versa)
and specifies a security apparatus for this arrangement. However,
the same apparatus can be used to secure the communication between a
SPIRITS subscriber and an intermediary (like the SPIRITS gateway),
and the same intermediary and the SPIRITS notifier.
Confidentiality of the SPIRITS protocol is essential since the
information carried in the protocol data units is of a sensitive
nature and may lead to privacy concerns if revealed to non-authorized
parties. The communication path between the SPIRITS notifier and the
SPIRITS subscriber should be secured through S/MIME [18] to alleviate
privacy concerns, as is described in the Security Consideration
section of the core SIP specification [5].
S/MIME is an end-to-end security mechanism which encrypts the
SPIRITS bodies for transit across an open network. Intermediaries
need not be cognizant of S/MIME in order to route the messages
(routing headers travel in the clear).
S/MIME provides all the security aspects for SPIRITS outlined at the
beginning of this section: authentication, message integrity,
confidentiality, and non-repudiation. Authentication properties
provided by S/MIME would allow the recipient of a SPIRITS message to
ensure that the SPIRITS payload was generated by an authorized
entity. Encryption would ensure that only those SPIRITS entities
possessing a particular decryption key are capable of inspecting
encapsulated SPIRITS bodies in a SIP request.
All SPIRITS endpoints MUST support S/MIME signatures (CMS SignedData)
and MUST support encryption (CMS EnvelopedData).
If the B and C interfaces are owned by the same PSTN operator, it is
possible that public keys will be installed in the SPIRITS endpoints.
Gurbani, et al. Standards Track [Page 41]
RFC 3910 SPIRITS Protocol October 2004
S/MIME supports two methods -- issuerAndSerialNumber and
subjectKeyIdentifier -- of naming the public key needed to validate a
signature. Between these, subjectKeyIdentifier works with X.509
certificates and other schemes as well, while issuerAndSerialNumber
works with X.509 certificates only. If the administrator configures
the necessary public keys, providing integrity through procedural
means, then S/MIME can be used without X.509 certificates.
All requests (and responses) between SPIRITS entities MUST be
encrypted.
When a request arrives at a SPIRITS notifier from a SPIRITS
subscriber, the SPIRITS notifier MUST authenticate the request. The
subscription (or registration) from a SPIRITS subscriber MUST be
rejected if the authentication fails. If the SPIRITS subscriber
successfully authenticated itself to the SPIRITS notifier, the
SPIRITS notifier MUST, at the very least, ensure that the SPIRITS
subscriber is indeed allowed to receive notifications of the events
it is subscribing to.
Note that this document does not proscribe how the SPIRITS
notifier achieves this. In practice, it could be through access
control lists (ACL) that are populated by a service management
system in the PSTN, or through a web interface of some sort.
Requests from the SPIRITS notifier to the SPIRITS subscribers MUST
also be authenticated, lest a malicious party attempts to
fraudulently pose as a SPIRITS notifier to hijack a session.
9. XML schema definition
The SPIRITS payload is specified in XML; this section defines the
base XML schema for documents that make up the SPIRITS payload. All
SPIRITS entities that transport a payload characterized by the MIME
type "application/spirits-event+xml" MUST support documents
corresponding to the base schema below.
Multiple versions of the base schema are not expected; rather, any
additional functionality (e.g., conveying new PSTN events) must be
accomplished through the definition of a new XML namespace and a
corresponding schema. Elements from the new XML namespace will then
co-exist with elements from the base schema in a document.
Gurbani, et al. Standards Track [Page 42]
RFC 3910 SPIRITS Protocol October 2004
<xs:schema targetNamespace="urn:ietf:params:xml:ns:spirits-1.0"
xmlns:tns="urn:ietf:params:xml:ns:spirits-1.0"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified"
attributeFormDefault="unqualified">
<!-- This import brings in the XML language attribute xml:lang-->
<xs:import namespace="http://www.w3.org/XML/1998/namespace"
schemaLocation="http://www.w3.org/2001/xml.xsd"/>
<xs:annotation>
<xs:documentation xml:lang="en">
Describes SPIRITS events.
</xs:documentation>
</xs:annotation>
<xs:element name="spirits-event" type="tns:SpiritsEventType"/>
<xs:complexType name="SpiritsEventType">
<xs:sequence>
<xs:element name="Event" type="tns:EventType" minOccurs="1"
maxOccurs="unbounded"/>
<xs:any namespace="##other" processContents="lax"
maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
<xs:complexType name="EventType">
<xs:sequence>
<xs:element name="CalledPartyNumber" type="xs:token"
minOccurs="0" maxOccurs="1"/>
<xs:element name="CallingPartyNumber" type="xs:token"
minOccurs="0" maxOccurs="1"/>
<xs:element name="DialledDigits" type="xs:token"
minOccurs="0" maxOccurs="1"/>
<xs:element name="Cell-ID" type="xs:token"
minOccurs="0" maxOccurs="1"/>
<xs:element name="Cause" type="tns:CauseType"
minOccurs="0" maxOccurs="1"/>
</xs:sequence>
<xs:attribute name="type" type="tns:PayloadType"
use="required"/>
<xs:attribute name="name" type="tns:EventNameType"
use="required"/>
<xs:attribute name="mode" type="tns:ModeType"
use="optional" default="N"/>
</xs:complexType>
Gurbani, et al. Standards Track [Page 43]
RFC 3910 SPIRITS Protocol October 2004
<xs:simpleType name="PayloadType">
<!-- The <spirits-event> will contain either a list of -->
<!-- INDPs events or a list of userprof events -->
<xs:restriction base="xs:string">
<xs:enumeration value="INDPs"/>
<xs:enumeration value="userprof"/>
</xs:restriction>
</xs:simpleType>
<xs:simpleType name="EventNameType">
<xs:restriction base="xs:string">
<!-- These are the call related events (DPs). If the -->
<!-- PaylaodType is "INDPs", then the value of the "name" -->
<!-- attribute is one of these; example -->
<!-- <spirits-event type="INDPs" name="OCI"> -->
<xs:enumeration value="OAA"/>
<xs:enumeration value="OCI"/>
<xs:enumeration value="OAI"/>
<xs:enumeration value="OA"/>
<xs:enumeration value="OTS"/>
<xs:enumeration value="ONA"/>
<xs:enumeration value="OCPB"/>
<xs:enumeration value="ORSF"/>
<xs:enumeration value="OMC"/>
<xs:enumeration value="OAB"/>
<xs:enumeration value="OD"/>
<xs:enumeration value="TA"/>
<xs:enumeration value="TMC"/>
<xs:enumeration value="TAB"/>
<xs:enumeration value="TD"/>
<xs:enumeration value="TAA"/>
<xs:enumeration value="TFSA"/>
<xs:enumeration value="TB"/>
<!-- These are the non-call related events. If the -->
<!-- PayloadType is "user-prof", then the value of the -->
<!-- "name" attribute is one of these; example -->
<!-- <spirits-event type="userprof" name="LUDV"> -->
<xs:enumeration value="LUSV"/>
<xs:enumeration value="LUDV"/>
<xs:enumeration value="REG"/>
<xs:enumeration value="UNREGMS"/>
<xs:enumeration value="UNREGNTWK"/>
</xs:restriction>
</xs:simpleType>
<xs:simpleType name="ModeType">
<!-- One of two values: "N"otification or "R"equest -->
<xs:restriction base="xs:string">
Gurbani, et al. Standards Track [Page 44]
RFC 3910 SPIRITS Protocol October 2004
<xs:enumeration value="N"/>
<xs:enumeration value="R"/>
</xs:restriction>
</xs:simpleType>
<xs:simpleType name="CauseType">
<xs:restriction base="xs:string">
<xs:enumeration value="Busy"/>
<xs:enumeration value="Unreachable"/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
10. Acknowledgements
The authors are grateful to participants in the SPIRITS WG for the
discussion that contributed to this work. These include J-L. Bakker,
J. Bjorkner, J. Buller, J-E. Chapron, B. Chatras, O. Cleuziou,
L. Conroy, R. Forbes, F. Haerens, J. Humphrey, J. Kozik,
W. Montgomery, S. Nyckelgard, M. O'Doherty, A. Roach, J. Rosenberg,
H. Sinnreich, L. Slutsman, D. Varney, and W. Zeuch. The authors also
acknowledge Steve Bellovin, Allison Mankin and Jon Peterson for help
provided on the Security section.
11. Acronyms
ACL Access Control List
CS Capability Set
DP Detection Point
DTD Document Type Definition
EDP Event Detection Point
EDP-N Event Detection Point "Notification"
EDP-R Event Detection Point "Request"
IANA Internet Assigned Numbers Authority
ICW Internet Call Waiting
IMSI International Mobile Subscriber Identity
IN Intelligent Network
INAP Intelligent Network Application Protocol
IP Internet Protocol
ISP Internet Service Provider
ITU International Telecommunications Union
MIME Multipurpose Internet Mail Extensions
MS Mobile Station (or Mobile Subscriber)
OBCSM Originating Basic Call State Model
PIC Point In Call
PINT PSTN/Internet Interworking
PSTN Public Switched Telephone Network
SCF Service Control Function
Gurbani, et al. Standards Track [Page 45]
RFC 3910 SPIRITS Protocol October 2004
SCP Service Control Point
SDP Session Description Protocol
SIP Session Initiation Protocol
SIP-T SIP for Telephones
SPIRITS Services in the PSTN/IN Requesting InTernet
Services
SSF Service Switching Function
SSP Service Switching Point
STD State Transition Diagram
TBCSM Terminating Basic Call State Model
TDP Trigger Detection Point
TDP-N Trigger Detection Point "Notification"
TDP-R Trigger Detection Point "Request"
TLS Transport Layer Security
UA User Agent
VLR Visitor Location Register
WIN Wireless Intelligent Network
XML Extensible Markup Language
12. References
12.1. Normative References
[1] Slutsman, L., Faynberg, I., Lu, H., and M. Weissman, "The
SPIRITS Architecture", RFC 3136, June 2001.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[3] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.
[4] Faynberg, I., Gato, J., Lu, H., and L. Slutsman, "Service in the
Public Switched Telephone Network/Intelligent Network (PSTN/IN)
Requesting InTernet Service (SPIRITS) Protocol Requirements",
RFC 3298, August 2002.
[5] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002.
12.2. Informative References
[6] M. Unmehopa, K. Vemuri, A. Brusilovsky, E. Dacloush, A. Zaki, F.
Haerens, J-L. Bakker, B. Chatras, and J. Dobrowolski, "On
selection of IN parameters to be carried by the SPIRITS
Protocol", Work In Progress, January 2003.
Gurbani, et al. Standards Track [Page 46]
RFC 3910 SPIRITS Protocol October 2004
[7] Intelligent Network Capability Set 2. ITU-T, Recommendation
Q.1228.
[8] Petrack, S. and L. Conroy, "The PINT Service Protocol:
Extensions to SIP and SDP for IP Access to Telephone Call
Services", RFC 2848, June 2000.
[9] Murata, M., St.Laurent, S., and D. Kohn, "XML Media Types", RFC
3023, January 2001.
[10] Lu, H., Faynberg, I., Voelker, J., Weissman, M., Zhang, W.,
Rhim, S., Hwang, J., Ago, S., Moeenuddin, S., Hadvani, S.,
Nyckelgard, S., Yoakum, J., and L. Robart, "Pre-Spirits
Implementations of PSTN-initiated Services", RFC 2995, November
2000.
[11] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol
(SIP): Locating SIP Servers", RFC 3263, June 2002.
[12] Thompson, H., Beech, D., Maloney, M. and N. Mendelsohn, "XML
Schema Part 1: Structures", W3C REC REC-xmlschema-1-20010502,
May 2001. <http://www.w3c.org/XML/>.
[13] "Interface recommendations for intelligent network capability
set 3: SCF-SSF interface", ITU-T Recommendation Q.1238.2, June
2000.
[14] Moats, R., "URN Syntax", RFC 2141, May 1997.
[15] Moats, R., "A URN Namespace for IETF Documents", RFC 2648,
August 1999.
[16] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January
2004.
[17] Tim Bray, Dave Hollander, and Andrew Layman, "Namespaces in
XML", W3C recommendation: xml-names, 14th January 1999,
<http://www.w3.org/ TR/REC-xml-names>.
[18] Ramsdell, B., "Secure/Multipurpose Internet Mail Extensions
(S/MIME) Version 3.1 Message Specification", RFC 3851, July
2004.
[19] Faynberg, I., L. Gabuzda, M. Kaplan, and N.Shah, "The
Intelligent Network Standards: Their Application to Services",
McGraw-Hill, 1997.
Gurbani, et al. Standards Track [Page 47]
RFC 3910 SPIRITS Protocol October 2004
[20] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies",
RFC 2045, November 1996.
Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046, November
1996.
Moore, K., "MIME (Multipurpose Internet Mail Extensions) Part
Three: Message Header Extensions for Non-ASCII Text ", RFC
2047, November 1996.
Freed, N., Klensin, J., and J. Postel, "Multipurpose Internet
Mail Extensions (MIME) Part Four: Registration Procedures", BCP
13, RFC 2048, November 1996.
Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Five: Conformance Criteria and Examples",
RFC 2049, November 1996.
13. Contributors
Kumar Vemuri
Lucent Technologies, Inc.
2000 Naperville Rd.
Naperville, IL 60566
USA
EMail: vvkumar@lucent.com
14. Authors' Addresses
Vijay K. Gurbani, Editor
2000 Lucent Lane
Rm 6G-440
Naperville, IL 60566
USA
EMail: vkg@lucent.com
Alec Brusilovsky
2601 Lucent Lane
Lisle, IL 60532-3640
USA
EMail: abrusilovsky@lucent.com
Gurbani, et al. Standards Track [Page 48]
RFC 3910 SPIRITS Protocol October 2004
Igor Faynberg
Lucent Technologies, Inc.
101 Crawfords Corner Rd.
Holmdel, NJ 07733
USA
EMail: faynberg@lucent.com
Jorge Gato
Vodafone Espana
Isabel Colbrand, 22
28050 Madrid
Spain
EMail: jorge.gato@vodafone.com
Hui-Lan Lu
Bell Labs/Lucent Technologies
Room 4C-607A, 101 Crawfords Corner Road
Holmdel, New Jersey, 07733
Phone: (732) 949-0321
EMail: huilanlu@lucent.com
Musa Unmehopa
Lucent Technologies, Inc.
Larenseweg 50,
Postbus 1168
1200 BD, Hilversum,
The Netherlands
EMail: unmehopa@lucent.com
Gurbani, et al. Standards Track [Page 49]
RFC 3910 SPIRITS Protocol October 2004
15. Full Copyright Statement
Copyright (C) The Internet Society (2004).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/S HE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE
INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Gurbani, et al. Standards Track [Page 50]