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rfc:rfc3298

Network Working Group I. Faynberg, Editor Request for Comments: 3298 Lucent Technologies Category: Informational J. Gato

                                                             Vodaphone
                                                                 H. Lu
                                                   Lucent Technologies
                                                           L. Slutsman
                                                                  AT&T
                                                           August 2002
Service in the Public Switched Telephone Network/Intelligent Network

(PSTN/IN) Requesting InTernet Service (SPIRITS) Protocol Requirements

Status of this Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

 This document describes the SPIRITS protocol requirements, based on
 the architecture presented in RFC 3136.  (SPIRITS stands for "Service
 in the PSTN/IN Requesting InTernet Service".)  The purpose of the
 protocol is to support services that originate in the Public Switched
 Telephone Network (PSTN) and necessitate the interactions between the
 PSTN and the Internet.  Similarly, such services are called SPIRITS
 services.  (Internet Call Waiting, Internet Caller-ID Delivery, and
 Internet Call Forwarding are examples of SPIRIT services, but the
 protocol is to define the building blocks from which many other
 services can be built.)  On the PSTN side, the SPIRITS services are
 initiated from the Intelligent Network (IN) entities; the earlier
 IETF work on the PSTN/Internet Interworking (PINT) resulted in the
 protocol (RFC 2848) in support of the services initiated the other
 way around--from the Internet to PSTN.
 To this end, this document lists general requirements for the SPIRITS
 protocol as well as those pertinent to IN, Wireless IN, and PINT
 building blocks.  The document also presents the SPIRITS WG consensus
 on the choice of the SPIRITS signaling protocol.

Faynberg, et al. Informational [Page 1] RFC 3298 SPIRITS Protocol Requirements August 2002

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.
 Unless otherwise qualified, the term PINT is used here not to refer
 to the present PINT services and protocol, but in reference to the
 scope of the generic PINT (vs. SPIRITS) service characteristics--
 services being invoked from an IP network (vs. PSTN).

2. Introduction

 This document describes the SPIRITS protocol requirements, based on
 the architecture presented in RFC 3136.  (SPIRITS stands for "Service
 in the PSTN/IN Requesting InTernet Service.")  The purpose of the
 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.
 (Internet Call Waiting, Internet Caller-ID Delivery, and Internet
 Call Forwarding are examples of SPIRIT services, but the protocol is
 to define the building blocks from which many other services can be
 built.)  On the PSTN side, the SPIRITS services are initiated from
 the Intelligent Network (IN) entities; the earlier IETF work on the
 PSTN/Internet Interworking (PINT) resulted in the protocol (RFC 2848)
 in support of the services initiated the other way around--from the
 Internet to PSTN.
 To this end, this document lists general requirements for the SPIRITS
 protocol as well as those pertinent to IN, Wireless IN, and PINT
 building blocks.  The document also presents the SPIRITS WG consensus
 on the choice of the SPIRITS signaling protocol.  The joint
 PINT/SPIRITS architecture (described in [1]) is depicted in Figure 1.
 It is assumed that the Spirits Client is either co-located with the
 IN Service Control Function (SCF) or communicates with it (over the
 PSTN-specific interface D) in such a way so as to act on behalf of
 the PSTN/IN.  (This assumption is confirmed by current
 implementations, as reported in [2].)
 The SPIRITS services are invoked (and, subsequently, the SPIRITS
 protocol is initiated) when a message from a SPIRITS Client (located
 in the IN Service Control Point [SCP] or Service Node [SN]) arrives
 on interface C to the SPIRITS gateway.  The Spirits gateway processes
 the message and, in turn, passes it on over the Interface B to the
 SPIRITS server.  In most practically important cases, the request
 from a SPIRITS client is ultimately caused by a request from a
 Central Office (i.e., a telephone switch) sent to either the SCP or

Faynberg, et al. Informational [Page 2] RFC 3298 SPIRITS Protocol Requirements August 2002

 SN, although the Internet-based service initiation by these elements
 that had not been triggered by the Central Office is theoretically
 possible.  (Definitely, none of the SPIRITS benchmark services are
 initiated in such a way, so, for the purposes of the SPIRITS protocol
 development, it should be assumed that the service invocation was a
 direct result of an earlier action by the Service Switching
 Function.)

Faynberg, et al. Informational [Page 3] RFC 3298 SPIRITS Protocol Requirements August 2002

                                    ......................
    +----------------+              .                    .
    | +------------+ |              .   +------------+   .
    | |            | |       A      .   |            |   .
    | | PINT Client|********************|PINT Server/|********
    | |            | |              .   |  Gateway   |       *
    | +------------+ |              .   +------------+   .   *
    |                |              .                    .   *
    |  Subscriber's  |              .                    .   *
    |                |              .                    .   *
    |  IP Host       |              .                    .   *
    |                |              .   +------------+   .   *
    | +------------+ |              .   | SPIRITS    |   .   *
    | | SPIRITS    | |       B      .   | Gateway    |   .   *
    | | Server     |********************|            |   .   * E
    | |            | |              .   +------------+   .   *
    | +------------+ |              .          *         .   *
    +----------------+              .          *         .   *
                                    ...........*..........   *
                                               *             *
                                               *             *
         Subscriber's                          *  C          *
         Telephone                             *             *
                                               *             *
           (---)                               *             *
             *                                 *             *
            * *                                *             *
   ++++++++++++++++++++++++++  PSTN   ++++++++++++++++++++++++++
             *                                 *             *
             *                                 *             *
             *                          +------------------+ *
             * Line                     | SPIRITS Client   | *
             *                          |                  | *
    +--------------------+          +---+----- D  ---------+-*+
    |                    | INAP/SS7 |                         |
    |Service Switching   ************Service Control Function |
    |    Function        |          |                         |
    |                    |          +-------------------------+
    |                    |
    |                    |
    +--------------------+
           Figure 1. Joint PINT/SPIRITS Architecture

Faynberg, et al. Informational [Page 4] RFC 3298 SPIRITS Protocol Requirements August 2002

 With PINT (and that also applies to the PINT architecture and
 protocol as described in [3]), the service request to the PINT Server
 is always initiated by the PINT Client over the interface A.  The PINT
 Server can either be co-located with the IN Service Control or a
 similar entity (referred to as "Executive System" by [3]) or
 communicate with it over the PSTN-specific interface E.
 As Figure 1 shows, the PINT Client and SPIRITS Server are co-located
 in Subscriber's IP Host.  In fact, both can be implemented to run as
 one process.  No provision is made for interactions between the PINT
 Client and Spirits Server.  Similarly, the PINT Server/PINT Gateway
 and SPIRITS gateway are assumed to be co-located, too.  This
 assumption is convenient but not essential; the PINT Server could
 also be co-located with the SPIRITS Client.  In either case, no
 specific provision is made to define interworking between either the
 PINT Server and Spirits Gateway or PINT Server and SPIRITS Client
 other than by listing the overall PINT-related requirements.
 Since the currently deployed worldwide wireless networks are based on
 circuit switching, they are considered PSTN networks for the SPIRITS
 purposes.  Adding SPIRITS type of services to wireless networks can
 allow new services to be developed (for example geolocation
 information can be handled in the IP network).
 Nevertheless, there are certain peculiarities of wireless networks,
 which force considerations to be made in the protocol
 requirements and in the SPIRITS architecture.
 A particular Wireless IN standard development being considered here
 is CAMEL phase 3, standardized by the Third Generation Partnership
 group (3GPP).  The relevant service and architectural considerations
 and protocol requirements are presented later in this document.  As
 far as the architecture is concerned, certain wireless events are
 generated by Home Location Register (HLR), which may, but does not
 have to, be part of the Mobile Switching Center (MSC) (a wireless
 equivalent of the SSP).  These events are communicated to Service
 Control, at which point they use the same mechanism for invoking
 SPIRITS services that the IN would.
 The rest of this document addresses the general requirements,
 IN Requirements, specific Wireless IN requirements, PINT
 Requirements, the protocol development methodology, and security
 issues, in that order.

Faynberg, et al. Informational [Page 5] RFC 3298 SPIRITS Protocol Requirements August 2002

3. General Requirements

 Based on the success of extending SIP for PINT ([3]) and, especially,
 the results of pre-SPIRITS implementations reported in [2], the
 Session Initiation Protocol (SIP) [7] has been chosen as the
 signaling base protocol for SPIRITS.
 Thus, it is a requirement that specific SPIRITS-related parameters be
 carried in a manner consistent with SIP practices.  In particular,
 either Session Description Protocol (SDP) [8] or Multi-purpose
 Internet Mail Extensions MIME [5-6] may be used for this purpose.
 Except for the proposed new SUBSCRIBE/NOTIFY mechanism [4], and
 extensions already defined in PINT, no new SIP extensions are
 foreseen; instead the SPIRITS protocol is to rely on the above
 extension mechanisms.
 It is by no means a requirement that any SPIRITS implementation
 automatically support PINT services.  The SPIRITS protocol must be
 defined in a manner where, as the minimum, it can support only the
 basic notification mechanism without relying on PINT services or
 otherwise relying on persistent interactions with PSTN.
 Nevertheless, it has been demonstrated [2] that combining PINT
 building blocks with those of SPIRITS is beneficial to building rich,
 enhanced PSTN/Internet services, so the SPIRITS protocol must meet
 the PINT-related requirements listed in section 7 of this document.
 One specific example demonstrating the application of the latter
 requirement, which is elaborated on further in this document, is as
 follows: Implementation of SUBSCRIBE/NOTIFY is not mandatory as far
 as the minimum SPIRITS protocol is concerned.  Thus, the initial PSTN
 (Detection Point) notification will always arrive via the SIP INVITE
 method; however, to implement persistent interactions with the PSTN,
 the SUBSCRIBE method may be used to obtain further notifications of
 the PSTN events.  Subsequently, these events will be reported on by
 means of the NOTIFY method.

4. IN Requirements

 The interface immediately relevant to IN is that between the SPIRITS
 Client and SPIRITS Gateway (interface C).  A typical message (which
 starts a SPIRITS service) looks like this:
 C -> G: <Event Notification>, <Parameter-List (DP)>
 The relevant events correspond to the detection points (DPs) of the
 IN Basic Call State Model (BCSM).  The <Parameter-List> is a function
 of a specific DP; it contains the parameters relevant to it.  The
 following requirements apply:

Faynberg, et al. Informational [Page 6] RFC 3298 SPIRITS Protocol Requirements August 2002

 1) The list of the DPs to be covered encompasses those defined in the
    IN Capability Set 3 BCSM as well as those which relate to the
    Wireless IN (WIN) specified by the IMT 2000 project in ITU-T.
 2) Not all parameters associated with such DPs are needed by the
    SPIRITS benchmark services, nor may all the parameters be needed
    in SPIRITS.  The selection of the relevant parameters is part of
    the SPIRITS protocol definition.
 3) It is desirable to avoid semantic overload of protocol messages.
    (One way to achieve that is to match each type of an event with a
    message that corresponds to it.)  As the SPIRITS protocol is
    designed as a set of extensions to another (existing) protocol
    with the defined message set, the syntax and semantics of the
    extensions should be defined with this requirement in mind.
 4) The ITU-T Recommendations use the abstract syntax notation (ASN.1)
    to specify the semantics of the IN Application Protocol (INAP)
    parameters, which are expected to be binary-encoded.  Neither the
    use of the ASN.1, nor the requirement for binary encoding are the
    typical requirements for the IETF application protocols.
    Recognizing that, provisions must be made for careful
    specification of the conversion of the INAP parameters to text,
    which must preserve their original semantics.  The actual
    conversion of the parameters is the function of the SPIRITS
    Client.
    In order to issue an initial query (or a notification) to service
    control, a switch must have such a DP set.  This can be done
    statically via service management (this particular action should
    be left to implementation and thus is considered outside of the
    scope of SPIRITS Protocol) or dynamically--but only for the
    purpose of a particular call--from the service control.  In the
    latter case, it is part of the SPIRITS (or PINT) protocol to
    request the event notification from the service control.  The SIP
    specific event notification scheme [4] should be specifically
    considered.  This function can be performed by either the Spirits
    Client or PINT Server, the distinction being further discussed in
    the next section.  Assuming that it is performed by the SPIRITS
    Client, the relevant message should look like:
    G->C: SUBSCRIBE <Event> <Mode> <DP-specific parameters>,
    where <Event> refers to a particular DP; <Mode> determines whether
    the Event Detection Point (EDP) is to be armed as EDP Request
    (EDP-R), EDP Notification (EDP-N), or TDP-R (the need for TDP-N is
    not foreseen because it would not provide any additional
    capability for SPIRITS); and the <DP-specific parameters> is the

Faynberg, et al. Informational [Page 7] RFC 3298 SPIRITS Protocol Requirements August 2002

    list of the values of the parameters associated with the EDP (for
    example, if the DP in question is O_No_Answer, then the value of
    the appropriate timer should be included in the list).  Note that
    such a subscription may also originate at a) PINT Client or b)
    SPIRITS Gateway, either of which may (but does not have to) have a
    locally significant definition of the <Event>.  In either case, it
    is the function of the SPIRITS Client to translate the definition
    of the Event into a particular DP (or set of DPs) when passing the
    message to Service Control.  To summarize, for the case when PINT
    and SPIRITS events are defined in a way where they do not refer to
    the BCSM DPs, it is the function of the SPIRITS Client to define a
    mapping:
    Event -> DP List,
    for each event for which the PSTN notification is needed.
    The list of CS-3 DPs envisioned in SPIRITS is:
  1. origination_attempt_authorized (the SPIRITS service can control

call attempts, (for example, to limit calls during specific

       time periods)
  1. collected_information and analyzed_information (for SPIRITS

outgoing call screening)

  1. o_answer, o_term_seized, and t_answer (to release SPIRITS

resources after the call is complete and perform relevant OA&M

       actions such as creating a record of attempts to reach a party
       via various means like land-line phone, cell phone, SMS, or
       paging.)
  1. o_no_answer, route_select_failure, and t_no_answer (to re-route

a call)

  1. o_called_party_busy (to re-route a call and for Internet Call

Waiting)

  1. o_mid_call and t_mid_call (to assist a midcall action)
  1. o_abandon, o_disconnect, t_abandon, and t_disconnect (to

terminate a SPIRITS service and release the resources and

       perform relevant OA&M actions such as creating a record of
       attempts to reach a party via various means like land-line
       phone, cell phone, SMS, or paging.)

Faynberg, et al. Informational [Page 8] RFC 3298 SPIRITS Protocol Requirements August 2002

 In addition, the following DPs are relevant to the present SPIRITS
 milestone services:
  1. termination_attempt_authorized
  1. facility_selected_and_available (could be used in SPIRITS

Internet Caller-ID)

  1. t_busy (for Internet Call Waiting and Call Forwarding).

5. Wireless-IN-related Requirements

 Wireless IN covers several types of "calls," which are neither
 circuit switched nor have an effect on circuit switched calls.  For
 this reason, those are not considered in SPIRITS requirements.  To
 further clarify this point, the types of "calls" not considered are:
  1. USSD (Unstructured Supplementary Service Data)
  1. GPRS (General Packet Radio System)
  1. SMS (Short Message System)
       The types of calls relevant to SPIRITS are as follows:
    a) Voice Calls.  In this case no new DP is needed since CAMEL DPs
       are included in CS2.  The only special case is "Not Reachable"
       (when it is detected that the mobile user is out of coverage or
       has switched off), which is mapped as a special cause in the
       Busy DP.  Since the Busy DP parameters would be received (if a
       SPIRITS service has subscribed to Busy), it would be possible
       to distinguish a "busy" from a "not reachable" situation.
       This translates into the requirement that one of the parameters
       in the Event Notification message (from SPIRITS Client to
       SPIRITS Gateway, over the interface C) denotes the "cause" for
       the Busy Detection Point.
       Another aspect of difference, when compared to PSTN, is setting
       of static DPs.  In CAMEL networks, this is done in the Home
       Location Register (HLR) (and copied to the VLR during location
       update).  It is important to note this difference, even though
       it has no effect on  SPIRITS protocol.

Faynberg, et al. Informational [Page 9] RFC 3298 SPIRITS Protocol Requirements August 2002

    b) Mobility Management events.  This allows a SPIRITS server to be
       notified of changes of location of a mobile user.  The events
       would only be applicable to mobile users reachable through a
       Circuit-Switched network.  To provide for this function, the
       subscription marks must be set in the subscriber's HLR.  This
       is equivalent to setting TDPs in the SSP.  In this case, the
       marks in the HLR (which are copied to the Visitor Location
       Register [VLR] on location update) are not mapped into Trigger
       Detection Points.
       As with TDP setting, this is outside of the scope of SPIRITS
       protocol.
       In order to support this function in SPIRITS, the SPIRITS
       protocol should be able to map the CAMEL specific operations
       into events notification to the SPIRITS client.  Since the SCP
       receives the information about the mobility state, this
       involves the C interface.  (This is just an extension of the DP
       notification mechanism from the SPIRITS client to the SPIRITS
       gateway).
       The events (which are not DP-related) which need notifications
       are:
  1. Location Update in the same VLR service area
  1. Location Update in another VLR service area
  1. IMSI attach
  1. MS initiated IMSI detach
  1. Network initiated IMSI detach.
       With this mechanism, the SPIRITS services can use the user-
       profile-based location information.  For example, the Internet
       Call Waiting service can re-direct the call to a mobile phone.
    c) Supplementary Services Notification.
       This mechanism makes a SPIRITS server aware of a subscriber
       having invoked one of the following supplementary services:
       Explicit Call Transfer, Call Deflection, Call Completion on
       Busy Subscriber, or Multi-Party.

Faynberg, et al. Informational [Page 10] RFC 3298 SPIRITS Protocol Requirements August 2002

6. PINT-related Requirements

 Before a SPIRITS service can be invoked, the relevant IP Host must be
 registered.  Thus, Registration is an essential service, which is
 initiated from the IP side.  The registration information is
 ultimately used by the PSTN to authenticate the subscriber.
 Depending on the model, this can be done in two ways with the present
 architecture:
 1) The PINT Client issues the appropriate Register message over the
 interface A, which is then passed by the PINT server to the SPIRITS
 Gateway and SPIRITS Client:
 PINT C.: -- Register --> PINT S. [--> SPIRITS Gateway --> SPIRITS
 C.].  In this case the SPIRITS Client (co-located with the service
 control) is responsible for record keeping and the authentication.
 2) The PINT Client issues the appropriate Register message to the
 PINT Server, which then passes this information to the PSTN service
 control "by magic".
 The second model is much easier to handle, because it involves only
 one relevant interface ("A"); however it assumes no interworking
 between PINT and SPIRITS except that the SPIRITS Client finds "by
 magic" that a friendly and expecting IP Host is alive and well.
 Finally, in the event PINT is not implemented, the SIP SUBSCRIBE
 mechanism can be used.
 As noted in the previous section, the existing SUBSCRIBE/NOTIFY PINT
 building blocks [3] must be extended for their use in SPIRITS for the
 purposes of setting DPs/getting DP event notifications.  (A more
 general SIP mechanism for the same PINT-introduced block is described
 in [4]; it provides the necessary mechanism for specifying relevant
 events.)  Conversely, the same building blocks for the functional
 capabilities can be used in both PINT and SPIRITS protocols.  Note,
 however, that in SPIRITS the PSTN notification may arrive without a
 particular subscription to an event (in the case of a statically set
 DP).

7. Follow-up on Event Notifications

 The requirements of this section are neither PINT-specific, nor IN-
 specific; their role is to outline the remaining element necessary
 for the delivery of the SPIRITS service, which is the reaction to the
 notification received.

Faynberg, et al. Informational [Page 11] RFC 3298 SPIRITS Protocol Requirements August 2002

 In a particular scenario where:
    a)  The IP subscriber registers a SPIRITS service;
    b)  A call triggering the SPIRITS service is received (and
       notification is sent); and
    c) The call disposition is performed by the end user, the
       signalling flow is demonstrated in Figure 2.
                    |---->  Registration  ----->|
            SPIRITS |<-- Event Notification <-- | SPIRITS
            Gateway |---> Call Disposition ---->| Client
                    |                   |
                                        |
                                        |
                                        |
                                        V
                                  Service Control
                                        |
                                        |
                                        V
                                       SSP
               Figure 2: Sequence of SPIRITS actions
 One of the following actions is required by benchmark services:
    a) Accept the incoming call
    b) Reject the incoming call
    c) Redirect the incoming call
    d) Accept the call via VoIP (this particular item is outside of
       the scope of SPIRITS WG).
 Accordingly, the SPIRITS protocol should define the following message
 types:
    a) S->G: <Accept Call>
    b) S->G: <[Reject Call],[Cause]>
    c) S->G: <[Redirect Call],[Redirection Destination]>

Faynberg, et al. Informational [Page 12] RFC 3298 SPIRITS Protocol Requirements August 2002

8. Methodology

 To determine the MINIMUM SPIRITS protocol vocabulary (i.e., the set
 of messages), the PSTN events associated with each detection point of
 the Basic Call State Model should be examined.  To date, the CS-3
 BSCM has the richest set of DPs, although not all switching exchanges
 have implemented it.
 To determine the MINIMUM information available to the SPIRITS client
 (this information is to be carried by the SPIRITS protocol from
 SPIRITS client to SPIRITS server), each DP-specific information
 elements needs to be examined.
 Parameters should be event-specific, the following generic types of
 parameters are expected to be mandatory:
  1. timer (for no answer)
  1. midcall control info (for mid_call)
  1. number of digits (for collected_information)

9. Security Considerations

 Overall, the basic aspects of security apply to SPIRITS protocol:
  1. Authentication:

In the communications between the SPIRITS Client and SPIRITS

    Gateway as well as the SPIRITS Gateway and SPIRITS Server, it is
    required that the information be sent between known and trusted
    partners.
  1. Integrity:

It is a requirement that no exchanged data be modified in transit.

  1. Confidentiality:

It is a requirement that any private user information or

    confidential network data be protected by the protocol (typically
    through encryption, for which the protocol should allow a choice
    in the algorithm selection.
  1. Availability:

It is a requirement that the communicating endpoints remain in

    service for authorized use only.

Faynberg, et al. Informational [Page 13] RFC 3298 SPIRITS Protocol Requirements August 2002

 In addition, the protocol should support non-repudiation for those
 control messages pertinent to charging the PSTN subscriber.
 As Figure 1 demonstrates, there are two distinct communications
 interfaces, B and C.  The B interface is, in general, across the
 public Internet and is thus most vulnerable to security attacks
 resulting in theft or denial of service.  The C interface, on the
 other hand is likely to be implemented across a service providers
 intranet, where the security measures should be applied at the
 discretion of the service provider.  Even then, because at least one
 IP host (the PINT gateway) is connected to the Internet, special
 measures (e.g., installation of firewalls, although this particular
 measure alone may be insufficient) need to be taken to protect the
 interface C and the rest of the network from security attacks.
 The assumption that the PINT Client and SPIRITS server are co-
 located, dictates that the security considerations for the A and B
 interfaces are exactly same.  Detailed security requirements and
 solutions for interface A (and, consequently, B) can be found in RFC
 2848 [3].
 Possible security attacks can result in both theft and denial of
 services.  In addition, such attacks may violate the privacy of a
 PSTN subscriber.  For example, with Internet Call Waiting, a
 fraudulent registration (or a manipulation of integrity of a valid
 registration) may force a network operator to provide to an
 authorized party a full log of attempted telephone calls (accompanied
 by the identification of callers).  Furthermore, the calls may be
 diverted to wrong recipients (who may further defraud the
 unsuspecting calling party).  In this case, the calling party is
 using only the PSTN and thus expecting the security of communications
 that are typical of the PSTN.  The PSTN service providers may be
 liable for the consequences of establishing wrong connections.  In
 addition, the PSTN service providers may be liable for inadvertent
 divulging of the private information of the subscriber.
 The service and network providers need to review the possibilities of
 the security attacks and prepare the means of protection from them.
 Some of this may be achieved by using the means outside of those
 provided by the protocol itself.  For example, administrative
 information (such as statistics collected by PINT MIB or SPIRITS MIB)
 can help in determining violations and thwarting them.  As far as the
 protocol is concerned, it must provide the means for authenticating a
 subscriber as well as a session.  It must also provide a capability
 to carry encrypted information in its body.

Faynberg, et al. Informational [Page 14] RFC 3298 SPIRITS Protocol Requirements August 2002

10. Acknowledgements

 The authors are grateful to all participants in the SPIRITS group for
 the discussion that has been shaping this work.  Many thanks go to
 Jorgen Bjorkner, Alec Brusilovsky, Jim Buller, Lawrence Conroy, Soren
 Nyckelgard, and John Voelker for their incisive comments.  Special
 thanks are to Vijay Gurbani, Dave Hewins, and Kumar Vemuri, whose
 careful, detailed reviews of several versions of this document have
 been particularly helpful in improving its quality.

11. References

 [1] Slutsman, L., Faynberg, I., Lu, H. and M. Weissman, "The Spirits
     Architecture", RFC 3136, June 2001.
 [2] Lu, H. (Editor), 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.
 [3] 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.
 [4] Roach, A.B., "Session Initiation Protocol (SIP)-Specific Event
     Notification", RFC 3265, June 2002.
 [5] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
     Extensions (MIME) Part One: Format of Internet Message Bodies",
     RFC 2045, November 1996.
 [6] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
     Extensions (MIME) Part Two: Media Types", RFC 2046, November
     1996.
 [7] Handley, M., Schooler, E., Schulzrinne, H. and J. Rosenberg,
     "SIP: Session Initiation Protocol", RFC 2543, March 1999.
 [8] Handley, M. and  V. Jacobsen, "SDP: Session Description
     Protocol", RFC 2327, April 1998.

Faynberg, et al. Informational [Page 15] RFC 3298 SPIRITS Protocol Requirements August 2002

12. Authors' Addresses

 Lev Slutsman
 AT&T Laboratories
 200 Laurel Ave.
 Middletown, New Jersey, 07748
 Phone: (732) 420-3752
 EMail: lslutsman@att.com
 Igor Faynberg
 Bell Labs/Lucent Technologies
 Room 4D-601A, 101 Crawfords Corner Road
 Holmdel, New Jersey, 07733
 Phone: (732) 949-0137
 EMail: faynberg@lucent.com
 Jorge Gato
 Vodaphone
 Avda de Europa, 1.
 28108 Alcobendas (Madrid). Spain
 Phone: +34 607 13 31 10
 Fax:   +34 607 13 30 57
 EMail: jgato@airtel.es
 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

Faynberg, et al. Informational [Page 16] RFC 3298 SPIRITS Protocol Requirements August 2002

13. Full Copyright Statement

 Copyright (C) The Internet Society (2002).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS 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.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Faynberg, et al. Informational [Page 17]

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