INTERNET-DRAFT Vijay K. Gurbani (Editor)
November 2002 Alec Brusilovsky
Expires: May 2003 Igor Faynberg
Hui-Lan Lu
Musa Unmehopa
Kumar Vemuri
Lucent Technologies, Inc.
Jorge Gato
Vodafone
Document: draft-ietf-spirits-protocol-03.txt
Category: Standards Track
The SPIRITS (Services in PSTN requesting Internet services) Protocol
STATUS OF THIS MEMO
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
This document describes SPIRITS protocol. The purpose of the SPIRITS
protocol is to support services that originate in the Public Switched
Telephone Network (PSTN) and necessitate the interactions between the
PSTN and the Internet. Such services are called SPIRITS services.
On the PSTN side, the SPIRITS services are most often initiated from
the Intelligent Network (IN) entities. Internet Call Waiting,
Internet Caller-ID Delivery, are examples of SPIRITS services; as are
location-based services or application-specific ones. The protocol
is to define the building blocks from which many other services can
be built.
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Table of Contents
1. INTRODUCTION...............................................2
1.1 Conventions used in this document .....................3
2. OVERVIEW OF OPERATIONS.....................................3
3. CALL-RELATED EVENTS........................................
3.1 Background.............................................
3.2 IN-specific details....................................
3.3 Services through dynamic DPs...........................
3.3.1 Normative usage.................................
3.3.2 Event package name..............................
3.3.3 Event package parameters........................
3.3.4 SUBSCRIBE bodies................................
3.3.5 Subscription duration...........................
3.3.6 NOTIFY bodies...................................
3.3.7 Notifier processing of SUBSCRIBE requests.......
3.3.8 Notifier generation of NOTIFY requests..........
3.3.9 Subscriber processing of NOTIFY requests........
3.3.10 Handling of forked requests.....................
3.3.11 Rate of notifications...........................
3.3.12 State Agents....................................
3.3.13 Examples........................................
3.3.14 Use of URIs to retrieve state...................
3.4 Services through static DPs............................
3.4.1 Internet Call Waiting............................
3.4.2 Call disposition choices.........................
3.4.3 Accepting an ICW session using VoIP..............
4. NON-CALL RELATED EVENTS....................................
4.1 Background............................................
4.2 Normative usage.......................................
4.3 Event package name....................................
4.4 Event package parameters..............................
4.5 SUBSCRIBE bodies......................................
4.6 Subscription duration.................................
4.7 NOTIFY bodies.........................................
4.8 Notifier processing of SUBSCRIBE requests.............
4.9 Notifier generation of NOTIFY requests................
4.10 Subscriber processing of NOTIFY requests..............
4.11 Handling of forked requests...........................
4.12 Rate of notifications.................................
4.13 State Agents..........................................
4.14 Examples..............................................
4.15 Use of URIs to retrieve state.........................
5. IANA CONSIDERATIONS..... ..................................
5.1 Registering event packages.............................
5.2 Registering MIME type..................................
6. SECURITY CONSIDERATIONS....................................
ACKNOWLEDGMENTS............................................
CHANGES....................................................
AUTHORS' ADDRESS...........................................
ACRONYMS...................................................
NORMATIVE REFERENCE........................................
INFORMATIVE REFERENCE......................................
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1. Introduction
SPIRITS (Services in the PSTN Requesting InTernet Services) is an
IETF architecture and associated protocol that enables call
processing elements in the telephone network such as the PSTN to make
service requests that are then processed on Internet hosted servers.
The term PSTN is used here to include all manner of access; i.e.
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 Internet-Draft has been written in response to the SPIRITS WG
chairs call for SPIRITS Protocol proposals. Among other
contributions, this I-D is based on:
o Informational RFC2995, "Pre-SPIRITS implementations"
o Informational RFC3136, "The SPIRITS Architecture"
o Informational RFC3298, "SPIRITS Protocol Requirements"
The rest of this document is organized as follows: section 2 provides
an overview of SPIRITS operations; sections 3 and 4 discusses the
mechanisms for an Internet host expressing an interest in PSTN
events, and the PSTN propagating such events to the Internet host.
Section 5 is concerned with the tokens defined in this document with
IANA. Finally, section 6 discusses the important aspect of securing
the communications between the PSTN and the Internet.
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 RFC 2119.
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 will express an interest 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 approrpiate services based on the
notification.
+------+
| PSTN |
|Events|
+------+
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/ \
/ \
+-------+ +--------+
|Call | |Non-Call|
|Related| |Related |
+-------+ +--------+
/ \ / \
/ \ / \
+---/--+ +---\--+ +--/-----+ +-------------+
|Static| |Dynamic| |Location| |App. Specific| ...
+------+ +-------+ +--------+ +-------------+
Figure 1: The SPIRITS hierarchy.
Figure 1 contains a very the SPIRITS events heirarchy including their
subdivision in two discrete classes for service execution: events
related to the setup, teardown, and maintenence 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 these types of events.
Call-related events, its further subdivisions and how they enable
services in the Internet is contained in section {X-Ref 3}. Services
enabled from events not related to call setup, teardown, or
maintenance are covered in detail in section {X-Ref 4}.
For reference, the SPIRITS architecture from [1] is reproduced below.
This document is primarily focused on interfaces B and C. 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.
+--------------+
| Subscriber's |
| IP Host | +--------------+
| | | |
| +----------+ | | +----------+ |
| | PINT | | A | | PINT | |
| | Client +<-------/-------->+ Gateway +<-----+
| +----------+ | | +----------+ | |
| | | | |
| +----------+ | | +----------+ | |
| | SPIRITS | | B | | SPIRITS | | |
| | Server +<-------/-------->+ Gateway | | |
| +----------+ | | +--------+-+ | |
| | | ^ | |
+--------------+ +----------|---+ |
| |
IP Network | |
------------------------------------------|--------|---
PSTN / C / E
| |
v |
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+----+------+ |
| SPIRITS | |
| Client | v
+-------------------+ +---+-----D-----+-++
| Service Switching |INAP/SS7 | Service Control |
| Function +---------+ Function |
+----+--------------+ +------------------+
|
|line
+-+
[0] Subscriber's
Figure 2: The SPIRITS Architecture.
(Note: The interfaces A-E are described in detail in the SPIRITS
Architecture document [1])
The requirements of a SPIRITS protocol are detailed in [5]. For the
sake of completeness, we simply re-iterate the decisions that lead to
the selection of SIP as a SPIRITS protocol: Most of the pre-SPIRITS
implementations [11] of a benchmark SPIRITS service, Internet Call
Waiting (ICW), were realized in SIP. Furthermore, a companion
protocol, PINT [9], successfully used SIP for its operations. SIP
also provides the notification capabilities needed by SPIRITS through
the SIP event notification framework [4]. Based on all of these
factors, the protocol used on interfaces B and C is SIP.
3. Call-related events
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), and other features
are executed on service elements called Service Control Points
(SCPs). The SPIRITS architecture [1] permits these SCP elements to
act as intelligent proxies to leverage and use Internet hosts and
capabilities to further enhance the telephone end-user's experience.
3.1 Background
A call model (CM) 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.
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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 [3],
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 [8] call model
are used in this draft as examples, and for ease of explanation,
other call models possess similar properties. For example, the 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.
3.2 IN-specific details
IN-specific details in relation to SPIRITS, namely, how to extract
common data types, parameters and response codes information, with
their associated descriptions, for particular DPs and triggers of
interest to SPIRITS and their associated data elements are captured
in [7]. Appendix B of [7] also includes an example XML DTD that may
be used to support the XML-encoding for SPIRITS messages.
Appendices A and B of [7] contain a select subset of IN CS-2
detection points and information flows that we believe will be useful
in the context of SPIRITS services. Admittedly, this list may not be
exhaustive. Note that INAP and similar protocols support a large
number of optional parameters in each message. Not all such
parameters may be useful in the SPIRITS context, thus, only a subset
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of available information elements are of direct interest.
Note also, that depending on what kinds of SPIRITS services are
supported, and how they are implemented, the "thickness" of the
SPIRITS implementation may drive exactly what subset of parameters
received by the SCP are forwarded on towards the SPIRITS server for
processing. An SCP could thus function in one of three modes for
every incoming request:
(1) process the request locally (as is traditionally done today,
no SPIRITS involvement)
(2) process part of the request locally and forward some
parameters to a SPIRITS-entity for further processing, and
formulate a response based on both the local processing and
the SPIRITS response
(3) forward all the received data in a SPIRITS protocol-
compliant format to a SPIRITS entity for processing, and
forward back the appropriately formatted response to the
entity that originated the request.
We do not here preclude operation in any of the modes above.
As mentioned previously, the first trigger that fires during call
processing is typically a TDP (since there is no pre-existing control
relationship between the SSF and the SCF prior to this). TDPs are
provisioned through a management system interface on the switching
element (SSP). In the future, other mechanisms (such as PINT) may be
used to provision this data as well, but in this document we limit
our discussion to pure SPIRITS implementations.
3.3 Services through dynamic DPs
Triggers in the PSTN can be armed dynamically, often outside the
context of a call. The SIP event notification mechanism [4] is,
therefore, a convenient means to exploit in those cases where
triggers housed in EDPs fire (see section 3 of [5]). Note that [5]
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".
Following the nomenclature outlined in [4], the SPIRITS server in
Figure 2 is a "Subscriber" and the SPIRITS client in Figure 2 is a
"Notifier". These terms will be used to refer to the SPIRITS server
and SPIRITS clients respectively in the remaining of this section.
Please refer to [4] for detailed workings of the SUBSCRIBE/NOTIFY
mechanism.
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3.3.1 Normative usage
A subscriber, under the effect of the user controlling it, may issue
a SUBSCRIBE request which identifies the events it is interested in
getting the notification of. The SUBSCRIBE request is routed to the
notifier, where it is authenticated and may be accepted.
When an event of the nature requested for in the earlier SUBSCRIBE
request occurs in the notifier, the notifier will format a NOTIFY
request and direct it towards the subscriber. The NOTIFY request
will contain the relevant information requested by the subscriber.
The subscriber can then choose to act in a manner appropriate to the
notification.
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.
The remaining sections fill in the template that is needed in order
to fully specify a SIP Event package for the SPIRITS protocol.
3.3.2 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. All
entities that implement the SPIRITS protocol and support IN detection
points MUST set the "Event" request header [4] to "spirits-INDPs."
The "Allow-Events" general header [4] 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
3.3.3 Event package parameters
The "spirits-INDPs" event package does not support any additional
parameters to the Event header.
3.3.4 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 particular event that is being subscribed to.
(2) Because of the requirement [5] 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 require to provide a "mode" parameter, whose values
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are "R" (for report) 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)
The default body type for SUBSCRIBEs in SPIRITS is denoted by the
MIME type "application/spirits-event". The "Accept" header, if
present, MUST include this MIME type.
3.3.5 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 [5] and thus will not be considered any further.
3.3.6 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". 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) 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.
3.3.7 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.
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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 draft; here we will simply assume that the notifier can
effect the arming (and disarming) of triggers in the PSTN through
interface D.
3.3.8 Notifier generation of NOTIFY requests
If the notifier expects the arming of triggers to take more than 200
ms (NOTE: is this too small, too large, okay?), 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 X-Ref 3.3.6). The NOTIFY request MUST have a
"Subscription-State" header and its value MUST be set to "terminated"
with a reason parameter of "fired".
3.3.9 Subscriber processing of NOTIFY requests
The exact steps executed at the subscriber when it gets a NOTIFY
request will depend on the nature of the information contained in the
request. 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 upto 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.
3.3.10 Handling of forked requests
Forking of SUBSCRIBE requests is prohibited. Since the SUBSCRIBE
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request is targetted towards the PSTN, highly irregular behaviors
occur if the request is allowed to fork. The normal SIP DNS lookup
and routing rules [7b] should result in a target set with exactly one
element: the notifier.
3.3.11 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 interst occurs which leads to the firing of 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.
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.
3.3.12 State agents
<To fill in>
3.3.13 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 2. Figure 2 depicts the 4 entities that are an
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integral part of any SPIRITS service (the headings of the entities
refer to the names established in Figure 1 in [1]) -- the SPIRITS
server (also termed as a "subscriber" as per section 4.0), the
SPIRITS gateway (also termed as a "notifier" as per section 4.0), the
SPIRITS client, and the SCF.
SPIRITS server SPIRITS gateway SPIRITS client SCF
("subscriber") ("notifier")
S G N
| | | |
| F1 SUBSCRIBE | | |
+--------------------->| F2 SUBSCRIBE | |
| +----------------->| |
| | F3 200 OK (SUBS) | |
| F4 200 OK (SUBS) |<-----------------+ F5 Arm DP |
|<---------------------+ +--------------->|
| | F6 NOTIFY | |
| F7 NOTIFY |<-----------------+ |
|<---------------------+ | |
| | | |
| F8 200 OK (NOT) | | |
+--------------------->| F9 200 OK (NOT) | |
| +----------------->| |
| | | |
~ ~ ~ ~
~ ~ ~ ~
| | | F10 Evt. Not. |
| | F11 NOTIFY |<---------------+
| F12 NOTIFY |<-----------------+ |
|<---------------------+ | |
| | | |
| F13 200 OK (NOT) | | |
+--------------------->| F14 200 OK (NOT) | |
| +----------------->| |
| | | |
| | | |
\|/ \|/ \|/ \|/
v v v v
Figure 2: Sample call flow
This call flow depicts an overall operation of a "subscriber"
successfully subscribing to the IN Termination_Attempt 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
F9 in Figure 2. 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 gateway
authorizes the user (F2) and propagates the request to the SPIRITS
client (F2). The SPIRITS client in turns interacts with the SCF to
arm the Termination_Attempt_DP for the service (F5). An immediate
NOTIFY with the current state information is send to the subscriber
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(F6 through F9).
At some later point in time 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 2). The SCF informs the
SPIRITS client of this event (F10).
When the SPIRITS client receives this event, it forms a SIP NOTIFY
request and directs it to the SPIRITS gateway (F11). This NOTIFY
will contain all the information elements necessary to identify the
caller to the subscriber. The subscriber, upon receiving the
notification (F12) 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 2. 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->G
SUBSCRIBE sip:myprovider.com SIP/2.0
From: <sip:vkg@lucent.com>;tag=8177-afd-991
To: <sip:16302240216@myprovider.com>
CSeq: 18992 SUBSCRIBE
Call-ID: 3329as77@host.lucent.com
Contact: <sip:vkg@host.lucent.com>
Via: SIP/2.0/UDP host.lucent.com
Expires: 3600
Event: spirits-INDPs
Allow-Events: spirits-INDPs, spirits-user-prof
Accept: application/spirits-event
Content-Type: application/spirits-event
Content-Length: ...
<spirits-event>
<DP INDPs="TAA" Mode="N"/>
<Termination_Attempt_Authorized>
<CallingPartySubaddress>6302240216</CallingPartySubaddress>
</Termination_Attempt_Authorized>
</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
associated with the phone number 6302240216). This request
eventually arrives at the SPIRITS gateway, G, which forwards it to
the SIPRITS client, N:
F2: G->N
draft-ietf-spirits-protocol-03.txt [Page 13]
The SPIRITS Protocol June 2002
SUBSCRIBE sip:notifier.myprovider.com SIP/2.0
From: <sip:vkg@lucent.com>;tag=8177-afd-991
To: <sip:16302240216@myprovider.com>
CSeq: 18992 SUBSCRIBE
Call-ID: 3329as77@host.lucent.com
Contact: <sip:vkg@host.lucent.com>
Via: SIP/2.0/UDP gateway.myprovider.com
Via: SIP/2.0/UDP host.lucent.com
Expires: 3600
Event: spirits-INDPs
Accept: application/spirits-event
Content-Type: application/spirits-event
Content-Length: ...
<spirits-event>
<DP INDPs="TAA" Mode="N"/>
<Termination_Attempt_Authorized>
<CallingPartySubaddress>6302240216</CallingPartySubaddress>
</Termination_Attempt_Authorized>
</spirits-event>
A 200 OK is sent by the notifier when it gets the SUBSCRIBE request
and understands the contents in it. The notifier also interfaces
with the SCF to arm the DP (F5, not shown in the SIP messages below):
F3: N->G
SIP/2.0 200 OK
From: <sip:vkg@lucent.com>;tag=8177-afd-991
To: <sip:16302240216@myprovider.com>;tag=SPIRITS-TAA-6302240216
CSeq: 18992 SUBSCRIBE
Call-ID: 3329as77@host.lucent.com
Contact: <sip:notifier.myprovider.com>
Via: SIP/2.0/UDP gateway.myprovider.com
Via: SIP/2.0/UDP host.lucent.com
Expires: 3600
Accept: application/spirits-event
Content-Length: 0
The 200 OK arrives at the subscriber, thus creating a dialog between
the subscriber and the notifier:
F4: G->S
SIP/2.0 200 OK
From: <sip:vkg@lucent.com>;tag=8177-afd-991
To: <sip:16302240216@myprovider.com>;tag=SPIRITS-TAA-6302240216
CSeq: 18992 SUBSCRIBE
Call-ID: 3329as77@host.lucent.com
Contact: <sip:notifier.myprovider.com>
Via: SIP/2.0/UDP host.lucent.com
Expires: 3600
Accept: application/spirits-event
Content-Length: 0
draft-ietf-spirits-protocol-03.txt [Page 14]
The SPIRITS Protocol June 2002
The notifier also sends an immediate NOTIFY towards the subscriber
informing the subscriber of the current state of the notification:
F6: N->G
NOTIFY sip:vkg@host.lucent.com SIP/2.0
From: <sip:16302240216@myprovider.com>;tag=SPIRITS-TAA-6302240216
To: <sip:vkg@lucent.com>;tag=8177-afd-991
Via: SIP/2.0/UDP notifier.myprovider.com
Call-ID: 3329as77@host.lucent.com
Contact: <sip:notifier.myprovider.com>
CSeq: 3299 NOTIFY
Event: spirits-INDPs
Allow-Events: spirits-INDPs, spirits-user-prof
Subscription-State: active
Accept: application/spirits-event
Content-Length: 0
The SPIRITS gateway routes the SIP request towards the subscriber:
F7: G->S
NOTIFY sip:vkg@host.lucent.com SIP/2.0
From: <sip:16302240216@myprovider.com>;tag=SPIRITS-TAA-6302240216
To: <sip:vkg@lucent.com>;tag=8177-afd-991
Via: SIP/2.0/UDP gateway.myprovider.com
Via: SIP/2.0/UDP notifier.myprovider.com
Call-ID: 3329as77@host.lucent.com
Contact: <sip:notifier.myprovider.com>
Subscription-State: active
CSeq: 3299 NOTIFY
Accept: application/spirits-event
Content-Length: 0
And finally, the 200 OK to the NOTIFY reaches the notifier:
F8: S->G
SIP/2.0 200 OK
From: <sip:16302240216@myprovider.com>;tag=SPIRITS-TAA-6302240216
To: <sip:vkg@lucent.com>;tag=8177-afd-991
Via: SIP/2.0/UDP gateway.myprovider.com
Via: SIP/2.0/UDP notifier.myprovider.com
Call-ID: 3329as77@host.lucent.com
Contact: <sip:vkg@host.lucent.com>
CSeq: 3299 NOTIFY
Accept: application/spirits-event
Content-Length: 0
F9: G->N
SIP/2.0 200 OK
From: <sip:16302240216@myprovider.com>;tag=SPIRITS-TAA-6302240216
To: <sip:vkg@lucent.com>;tag=8177-afd-991
draft-ietf-spirits-protocol-03.txt [Page 15]
The SPIRITS Protocol June 2002
Via: SIP/2.0/UDP notifier.myprovider.com
Call-ID: 3329as77@host.lucent.com
Contact: <sip:vkg@host.lucent.com>
CSeq: 3299 NOTIFY
Accept: application/spirits-event
Content-Length: 0
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 (F10, not shown in the SIP messages below). 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 default outbound proxy. The SIP NOTIFY request has a
XML-encoded body with the relevant information from the PSTN:
F11: N->G
NOTIFY sip:vkg@host.lucent.com SIP/2.0
From: <sip:16302240216@myprovider.com>;tag=SPIRITS-TAA-6302240216
To: <sip:vkg@lucent.com>;tag=8177-afd-991
Via: SIP/2.0/UDP notifier.myprovider.com
Call-ID: 3329as77@host.lucent.com
Contact: <sip:notifier.myprovider.com>
CSeq: 3300 NOTIFY
Subscription-State: terminated;reason=fired
Accept: application/spirits-event
Event: spirits-INDPs
Allow-Events: spirits-INDPs, spirits-user-prof
Content-Type: application/spirits-event
Content-Length: ...
<spirits-event>
<DP INDPs="TAA" Mode="N"/>
<Termination_Attempt_Authorized>
<CallingPartySubaddress>6302240216</CallingPartySubaddress>
<CalledPartySubaddress>3125675000</CalledPartySubaddress>
</Termination_Attempt_Authorized>
</spirits-event>
The default outbound proxy delivers the SIP NOTIFY request to the
subscriber:
F12: G->S
NOTIFY sip:vkg@host.lucent.com SIP/2.0
From: <sip:16302240216@myprovider.com>;tag=SPIRITS-TAA-6302240216
To: <sip:vkg@lucent.com>;tag=8177-afd-991
Via: SIP/2.0/UDP gateway.myprovider.com
Via: SIP/2.0/UDP notifier.myprovider.com
Call-ID: 3329as77@host.lucent.com
Contact: <sip:notifier.myprovider.com>
CSeq: 3300 NOTIFY
draft-ietf-spirits-protocol-03.txt [Page 16]
The SPIRITS Protocol June 2002
Subscription-State: terminated;reason=fired
Accept: application/spirits-event
Event: spirits-INDPs
Allow-Events: spirits-INDPs, spirits-user-prof
Content-Type: application/spirits-event
Content-Length: ...
<spirits-event>
<DP INDPs="TAA" Mode="N"/>
<Termination_Attempt_Authorized>
<CallingPartySubaddress>6302240216</CallingPartySubaddress>
<CalledPartySubaddress>3125675000</CalledPartySubaddress>
</Termination_Attempt_Authorized>
</spirits-event>
There are a couple of important issues to note in the call flows for
F11 or F12:
(1) The body of the NOTIFY request contains the information
passed to the SPIRITS client from the SCF. In this particular
example, this is the phone number of the party (3125675000)
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
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 F12. 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:
F13: S->G
200 OK SIP/2.0
From: <sip:16302240216@myprovider.com>;tag=SPIRITS-TAA-6302240216
To: <sip:vkg@lucent.com>;tag=8177-afd-991
Via: SIP/2.0/UDP gateway.myprovider.com
Via: SIP/2.0/UDP notifier.myprovider.com
Call-ID: 3329as77@host.lucent.com
CSeq: 3300 NOTIFY
Content-Length: 0
draft-ietf-spirits-protocol-03.txt [Page 17]
The SPIRITS Protocol June 2002
F14: G->N
200 OK SIP/2.0
From: <sip:16302240216@myprovider.com>;tag=SPIRITS-TAA-6302240216
To: <sip:vkg@lucent.com>;tag=8177-afd-991
Via: SIP/2.0/UDP notifier.myprovider.com
Call-ID: 3329as77@host.lucent.com
CSeq: 3300 NOTIFY
Content-Length: 0
3.3.14 Use of URIs to retrieve state
The "spirits-INDPs" package MUST not use URIs to retrieve state. All
state information for this package is compact enough to fit in a SIP
message body.
3.4 Services through static DPs
We mentioned in section {X-Ref 3.2} 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 specificiation). 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 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.
3.4.1 Internet Call Waiting (ICW)
ICW as a benchmark SPIRITS service actually predates SPIRITS itself.
Pre- SPIRITS implementations of ICW are detailed in [11]. However,
as the draft notes, while a diversity of implementations exists,
these implementations are not interoperable. At the time [11] was
published, the industry did not have the depth of experience with SIP
as is the case now. The use of SIP in [11] does not constitute
normative usage of SIP as described in [6]; 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;
draft-ietf-spirits-protocol-03.txt [Page 18]
The SPIRITS Protocol June 2002
o specify the desirable treatment of the call; and
o have the call handled as specified.
3.4.2 Call disposition choices
Section 2 of [11] 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
6. Forwarding the call to another number
7. Rejecting (or Forwarding) on no Response - If the
subscriber fails to respond within a certain period 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:
1. 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.
2. IN based method: SCP maintains a list of 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.
3. Any combination of methods 1 and 2.
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 client on the SCP to create a SIP INVITE request and send
draft-ietf-spirits-protocol-03.txt [Page 19]
The SPIRITS Protocol June 2002
it to the SPIRITS server running on the subscriber's IP host.
The SPIRITS server MUST return one of the possible call disposition
outcomes cataloged section 3.1. 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).
Further processing of a SPIRITS client when it receives a final non-
2xx 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 server 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
3.2.
3.4.3 Accepting an ICW session using VoIP
One call handling option in ICW is to "accept an incoming call using
VoIP". The SPIRITS client 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 client control a PSTN gateway and allocate appropriate
resources on it. Once this is done, the SPIRITS client 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
client 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.
draft-ietf-spirits-protocol-03.txt [Page 20]
The SPIRITS Protocol June 2002
The SPIRITS client transmits the INVITE request to the subscriber and
now waits for a final response. Further processing when the SPIRITS
server 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 client 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.
The end result is that the caller and callee hold a voice session
with part of the session occurring over VoIP.
4. Non-call related events
<To fill in>
4.1 Background
<To fill in>
4.2 Normative usage
<To fill in>
4.3 Event package name
<To fill in>
4.4 Event package parameters
<To fill in>
4.5 SUBSCRIBE bodies
<To fill in>
4.6 Subscription duration
<To fill in>
4.7 NOTIFY bodies
<To fill in>
4.8 Notifier processing of SUBSCRIBE requests
<To fill in>
4.9 Notifier generation of NOTIFY requests
<To fill in>
4.10 Subscriber processing of NOTIFY requests
draft-ietf-spirits-protocol-03.txt [Page 21]
The SPIRITS Protocol June 2002
<To fill in>
4.11 Handling of forked requests
<To fill in>
4.12 Rate of notifications
<To fill in>
4.13 State agents
<To fill in>
4.14 Examples
<To fill in>
4.15 Use of URIs to retrieve state
<To fill in>
5. IANA considerations
5.1 Registering event packages
Package Name: spirits-INDPs
Type: package
Contact: Vijay K. Gurbani, vkg@lucent.com
Reference: RFC XXXX [Note to RFC Editor: please replace with RFC
number for this draft].
Package Name: spirits-user-prof
Type: package
Contact: Vijay K. Gurbani, vkg@lucent.com
Reference: RFC XXXX [Note to RFC Editor: please replace with RFC
number for this draft].
Package Name: spirits-user-prof
Type: package
Contact: Vijay K. Gurbani, vkg@lucent.com
Reference: RFC XXXX [Note to RFC Editor: please replace with RFC
number for this draft].
5.2 Registering MIME type
draft-ietf-spirits-protocol-03.txt [Page 22]
The SPIRITS Protocol June 2002
MIME media type name: application
MIME subtype name: spirits-event
Mandatory parameters: none
Optional parameters: charset (same semantics of charset parameter in
application/xml [10])
Encoding considerations: same as considerations outlined for
application/xml in [10].
Security considerations: section 10 of [10] and section 7 of this
document.
Interoperability considerations: none.
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
6. Security considerations
Security concerns are listed here as a starting point; this list is
by no means exhaustive and will be updated as this I-D progresses.
As outlined in Chapter 10 of [5], the following security aspects are
applicable to the SPIRITS protocol:
Authentication
Integrity
Confidentiality
draft-ietf-spirits-protocol-03.txt [Page 23]
The SPIRITS Protocol June 2002
Availability
Non-repudiation
For the most part, the SPIRITS protocol will leverage the security
infrastructure defined in SIP [6] as well as XML security [12]. In
addition, there are other issues of concern to SPIRITS, most of which
have to do with the trust relationship between SPIRITS entities. For
example, in Figure 1, interface C straddles the boundary between the
two networks -- PSTN and the Internet. Thus it crosses both the
administrative as well as the network domains. As such, issues like
authentication, message integrity, and confidentiality take on a
deeper meaning.
These issues are being discussed in a separate I-D [7a] and the
results of that discussion will be merged into this specification
upon their conclusion.
ACKNOWLEDGMENTS
The authors are grateful to participants in the SPIRITS WG for the
discussion that has 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.
CHANGES
Changes in -03
(1) Re-organized much of the I-D to better reflect the nature of
SPIRITS services; specifically, divided the services in two classes:
call-related events and non-call related events.
Changes in -02
(1) Added section on the ICW service and its realization in SPIRITS
(2) Added 'Mode' parameter to SUBSCRIBE/NOTIFY call flow examples
(3) Took out Appendix A and B; the information contained in them
is now in a new I-D.
(4) Filled out IANA consideration section.
Changes in -01
(1) Changed the name of the I-D to draft-ietf-spirits-protocol-01.txt
to reflect the WG decision of making it an agenda item
Changes since draft-gurbani-spirits-protocol-00
draft-ietf-spirits-protocol-03.txt [Page 24]
The SPIRITS Protocol June 2002
(1) Updated section 8.0 (Acknowledgments)
(2) Fleshed out the call flow in section 4.0 (Example SPIRITS
service call flow)
AUTHORS' ADDRESSES
Alec Brusilovsky Igor Faynberg
Lucent Technologies, Inc. Lucent Technologies, Inc.
2000 Naperville Rd., 101 Crawfords Corner Rd.,
Naperville, IL 60566 Holmdel, NJ 07733
USA USA
abrusilovsky@lucent.com faynberg@lucent.com
Jorge Gato Vijay K. Gurbani
Airtel Movil, S.A. 2000 Lucent Lane
Avda de Europa, 1 Rm 6G-440
28108 Alcobendas (Madrid) Naperville, IL 60566
Spain USA
jgato@airtel.es vkg@lucent.com
Musa Unmehopa Kumar Vemuri
Lucent Technologies, Inc. Lucent Technologies, Inc.
Larenseweg 50, 2000 Naperville Rd.,
Postbus 1168 Naperville, IL 60566
1200 BD, Hilversum, USA
The Netherlands vvkumar@lucent.com
unmehopa@lucent.com
ACRONYMS
CM Call Model
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
IN Intelligent Network
INAP Intelligent Network Application Protocol
IP Internet Protocol
ITU International Telecommunications Union
MIME Multipurpose Internet Mail Extensions
OBCSM Originating Basic Call State Model
PIC Point In Call
PINT PSTN/Internet Interworking
PSTN Public Switched Telephone Network
SCF Service Control Function
SCP Service Control Point
SDP Session Description Protocol
SIP Session Initiation Protocol
SIP-T SIP for Telephones
draft-ietf-spirits-protocol-03.txt [Page 25]
The SPIRITS Protocol June 2002
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"
XML Extensible Markup Language
Normative references
[1] L. Slutsman (Ed.), I. Faynberg, H. Lu, M. Weissman, "The SPIRITS
Architecture", IETF RFC 3136, June 2001,
<http://www.ietf.org/rfc/rfc3136.txt>
[2] <Void>
[3] Faynberg, I., L. Gabuzda, M. Kaplan, and N.Shah, "The Intelligent
Network Standards: Their Application to Services", McGraw-Hill, 1997.
[4] Adam Roach, "SIP-Specific Event Notification", IETF RFC 3265,
June 2002, <http://www.ietf.org/rfc/rfc3265.txt>
[5] I.Faynberg, J. Gato, H. Lu, and L. Slutsman, "SPIRITS Protocol
Requirements", IETF RFC 3298, August 2002,
<http://www.ietf.org/rfc/rfc3298.txt>
[6] J. Rosenberg, H. Schulzrinne, G. Camarillo, J. Peterson, R.
Sparks, A. Johnston, M. Handley, and E. Schooler, "SIP: Session
Initiation Protocol" IETF RFC 3261, June 2002,
<http://www.ietf.org/rfc/rfc3261.txt>
[7] 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", IETF I-D,
Expires January 2003, Work In Progress.
[7a] Vijay K. Gurbani, "Security for SPIRITS services", IETF
Internet-Draft, Work in Progress.
[7b] J. Rosenberg, H. Schulzrinne, "Session Initiation Protocol
(SIP): Locating SIP Servers", IETF RFC 3263, June 2002,
<http://www.ietf.org/rfc/ rfc3263.txt>
Informative references
[8] Intelligent Network Capability Set 2. ITU-T, Recommendation
Q.1228
[9] S. Petrack, L. Conroy, "The PINT Service Protocol: Extensions to
SIP and SDP for IP Access to Telephone Call Services", IETF RFC 2848,
June 2000, <ftp://ftp.isi.edu/in-notes/rfc2848.txt>
draft-ietf-spirits-protocol-03.txt [Page 26]
The SPIRITS Protocol June 2002
[10] M. Murata, S. St. Laurent, D. Kohn, "XML Media Types", IETF RFC
3023, January 2001, <ftp://ftp.isi.edu/in-notes/rfc3023.txt>
[11] H. Lu (Ed.), I. Faynberg, J. Voelker, M. Weissman, W. Zhang, S.
Rhim, J. Hwang, S. Ago, S. Moeenuddin, S. Hadvani, S. Nyckelgard, J.
Yoakum, and L. Robart, "Pre-SPIRITS Implementations of PSTN-initiated
Services", IETF RFC 2995, November 2000,
<http://www.ietf.org/rfc/rfc2995.txt>
[12] Donald Eastlake, Joseph Reagle, David Solo at al., "XML-
Signature Syntax and Processing", W3C Recommendation 12 February
2002, <http://www.w3.org/TR/2002/REC-xmldsig-core-20020212/>
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draft-ietf-spirits-protocol-03.txt [Page 27]
