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Versions: 00 01 02                                                      
SIP Working Group                                           W. Marshall
Internet Draft                                          K. Ramakrishnan
Document: <draft-dcsgroup-sip-call-auth-02.txt>                    AT&T

                                                              E. Miller
                                                             G. Russell
                                                              CableLabs

                                                               B. Beser
                                                            M. Mannette
                                                        K. Steinbrenner
                                                                   3Com

                                                                D. Oran
                                                           F. Andreasen
                                                                  Cisco

                                                             J. Pickens
                                                                  Com21

                                                            P. Lalwaney
                                                                  Nokia

                                                             J. Fellows
                                                               Motorola

                                                               D. Evans
                                                 Secure Cable Solutions

                                                               K. Kelly
                                                               NetSpeak

                                                             June, 2000


                   SIP Extensions for Media Authorization


Status of this Memo

   This document is an Internet-Draft and is in full conformance with all
   provisions of Section 10 of RFC2026 [1].

   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.
                SIP Extensions for Media Authorization       June 2000


   The distribution of this memo is unlimited.  It is filed as <draft-
   dcsgroup-sip-call-auth-02.txt>, and expires December 31, 2000. Please
   send comments to the authors.

1. Abstract

   This document describes the need for call authorization and offers a
   mechanism for call authorization that can be used for admission control
   and against denial of service attacks.

2. 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].

3. Background and Motivation

   The current IP Telephony systems consider a perfect world in which there
   is unlimited amount of bandwidth and network layer QoS comes free.  The
   reality is that bandwidth is neither unlimited nor free. Enhanced quality
   of service, as required for high-grade voice communication, needs special
   authorization for better than `best-effort' service.  Without such a
   capability, it is possible that a single berserk IP telephony device can
   cause denial of service to a significant number of others.

4. Overview

   Integration of Media Authorization and Call Signaling architecture
   consists of User Agents (UAs) which are considered untrusted, and SIP-
   Proxy which authorizes the call that is initiated by UA.

   The SIP-Proxy authorizes the Media data flow to/from the UA and returns
   to the UA a Media-Authorization-Token, which is to be used for
   authorization when bandwidth is requested for the data-stream.

   When the UA is ready to send the media data-stream to the other end-
   point, it first requests bandwidth, using the Authorization-Token it
   received from its SIP-Proxy.

5. Changes to SIP to Support Media Authorization

   This document extends SIP in support of an authorization scheme. In this
   architecture the SIP-Proxy supplies the UA an Authorization-Token which
   is to be used for bandwidth requests. The extension defined allows
   network resources to be authorized by the SIP-Proxy.

   The following syntax specification uses the augmented Backus-Naur Form
   (BNF) as described in RFC-2234 [3].




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5.1 SIP Header Extension

   The Media-Auth-Token general header conveys an identifier of the local
   Gate to a UA.  This information is used for authorizing the Media Stream.

        Media-Auth       = "Media- Authorization" ":"
                                Media-Authorization-Token

        Media-Authorization-Token       = 1*hex

5.2 SIP Procedures

   This section defines a SIP [4] profile for usage in Media Authorization
   compatible systems from the point of view of Authorizing Calls.

   The initial SIP INVITE message, as well as mid-call resource change
   messages and mid-call changes in call destination should be authorized.
   These SIP messages are sent through the proxies to receive this
   authorization.

5.2.1. User Agent Client (UAC)

   The Media-Auth-Token, contained in the Media-Authorization header, is
   included in the first response message sent by the SIP-Proxy to the UAC.

   The UAC SHOULD use the Media-Auth-Token when requesting bandwidth for
   Media data stream during initiation and retaining of the bandwidth.

5.2.2. User Agent Server (UAS)

   The User Agent Server receives the Media-Auth-Token in the INVITE message
   from SIP-Proxy.

   The UAS SHOULD use the Media-Auth-Token when requesting bandwidth for
   media data stream during initiation and retaining of the bandwidth.

5.2.3. Originating Proxy (OP)

   The Originating Proxy (OP) authenticates the caller, and verifies the
   caller is authorized to receive the requested level of QoS.  In
   cooperation with originating Policy Decision Point (PDP-o), the OP
   obtains a Media-Auth-Token that contains sufficient information for the
   UAC to get the authorized bandwidth for the media streams.











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   The Originating Proxy MUST insert the Media-Authorization header in the
   response message that it sends to the UAC.

5.2.4. Destination Proxy (DP)

   The Destination Proxy (DP) authenticates the called party, and verifies
   the called party is authorized to receive the requested level of QoS.  In
   cooperation with termination Policy Decision Point (PDP-t), the DP
   obtains a Media-Auth-Token that contains sufficient information for the
   destination UAS to get the authorized bandwidth for the media streams.

   The Destination Proxy MUST insert the Media-Authorization header in the
   INVITE message that it sends to -the UAS.

6. Examples

6.1. Requesting Bandwidth via RSVP messaging

   Resource Reservation Protocol (RSVP) is the end-to-end Layer 3
   reservation protocol that is widely used [7].

6.1.1. User Agent Client Side

   Figure 1 presents a high-level overview of a basic call flow with Media
   Authorization from the viewpoint of the UAC. It is assumed that the SIP-
   Proxy has a previously established a authentication relationship with the
   client.

   When a user goes off-hook and dials a telephone number, the UAC collects
   the dialed digits and sends the initial INVITE message to the Originating
   SIP-Proxy.

   The Originating SIP-Proxy (OP) authenticates UAC                                                                                                      and forwards the INVITE
   message to the proper SIP-proxy.

   Assuming that the call is not forwarded, the other end-point sends a 183
   response to the initial INVITE, forwarded back to OP. Included in this
   response is the negotiated bandwidth requirement for the connection.

   When OP receives the 183, it has sufficient information regarding the
   end-points, bandwidth and characteristics of the media exchange. It
   initiates a Policy-Setup message to PDP-o.











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   UAC         ER-o            PDP-o           OP
   |  Invite    |               |               | Client Authentication
   |------------------------------------------->| and Call Authorization
   |            |               |               | Invite
   |            |               |               |-------------->
   |            |               |               | 180/3
   |            |               | Auth. Profile |<--------------
   |            |               |<--------------|
   |            |               |  Auth. Token  |
   |            |               |-------------->| Auth. Token put into
   |            |               |   180/3       | Media-Authorization header
   |<-------------------------------------------| extension.
   |Copies the RSVP policy object               |
   |from the Media-Authorization                |
   | RSVP-PATHo |               |               |
   |----------->| REQ           |               |
   |            |-------------->| Using the Auth-Token and Authorized
   |            |       DEC     | Profile that is set by the SIP Proxy
   |            |<--------------| the PDP makes the decision
   |            |               |               |   RSVP-PATHo
   |            |------------------------------------------------>
   |            |               |               |   RSVP-PATHt
   |<--------------------------------------------------------------
   |Copies the RSVP policy object               |
   |from the Media-Authorization                |
   | RSVP-RESVt |               |               |
   |----------->|      REQ      |               |
   |            |-------------->| Using the Auth-Token and Authorized
   |            |       DEC     | Profile that is set by the SIP Proxy
   |            |<--------------| the PDP makes the decision
   |            |               |               |   RSVP-RESVt
   |            |--------------------------------------------------->
   |            |               |               |   RSVP-RESVo
   |<----------------------------------------------------------------
   |            |               |               |   RSVP-RESVCONFo
   |---------------------------------------------------------------->
   |            |               |               |   RSVP-RESVCONFt
   |<----------------------------------------------------------------
   |            |               |               |   200 OK
   |<-------------------------------------------|<------------------
   |            |               |               |   MEDIA
   |<===============================================================>
   |            |               |               |   ACK
   |---------------------------------------------------------------->

                                  Figure 1






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   The PDP-o stores the authorized Media description in its local store
   generates an Authorization-Token that points to this description and
   returns the Authorization-Token to OP.

   The OP includes the Authorization-Token in the Media-Auth-Token header
   extension of the 183 message.

   The UAC upon reception, stores the Media-Authorization-Token inside the
   Media-Auth-Token header extension.

   Before sending the Media stream, the UAC requests bandwidth using RSVP-
   PATH message which includes the Session info that describes the Media
   data-stream and TSpec that describes the bandwidth requested along with
   Authorization information that was stored in Media-Authorization-Token.

   ER-o, upon reception of the RSVP-PATHo message checks the authorization
   through a PDP-o COPS message exchange. The PDP-o checks the authorization
   using the stored authorized Media description that was linked to the
   Authorization-Token that it returned to OP. If authorization is
   successful PDP-o returns an "install" Decision.

   ER-o checks the admissibility for the call and if admission succeeds, it
   forwards the RSVP-PATHo message.

   Once the UAC receives the RSVP-PATHt message it sends RSVP-RESVt message
   to reserve the bandwidth.

   ER-o, upon reception of the RSVP-RESVt message checks the authorization
   through PDP-o COPS message exchange. The PDP-o checks the authorization
   using the stored authorized Media description that was linked to
   Authorization-Token that it returned to OP. If authorization is
   successful PDP-o returns "install" Decision.

   ER-o checks the admissibility for the call and if admission succeeds, it
   forwards the RSVP-RESVt message.

   Upon reception of RSVP-RESVo message the UAC sends RSVP-RESVCONFo message
   to indicate that the reservation completed for one direction.

   Upon reception of both RSVP-RESVCONFt and 200OK the UAC returns ACK
   message.

6.1.2. User Agent Server Side

   Figure 2 presents a high-level overview of a call flow with Media
   Authorization from the viewpoint of the UAS. It is assumed that the SIP-
   Proxy has a previously established authentication relationship with the -
   UAS.






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   UAS         ER-t            PDP-t          DP
    |           |               |               | Invite
    |           |               |               |<--------------
    |           |               |               | Proxy Authentication
    |           |               | Auth. Profile | and Call Authorization
    |           |               |<--------------|
    |           |               |  Auth. Token  |
    |           |               |-------------->| Auth. Token put into
    |           |               |       Invite  | Media-Authorization header
    |<------------------------------------------| extension
    |   180/3   |               |               |
    |------------------------------------------>| 180/3
    |Copies the RSVP policy object              |-------------->
    |from the Media-Authorization               |
    | RSVP-PATHt|               |               |
    |---------->| REQ           |               |
    |           |-------------->| Using the Auth-Token and Authorized
    |           |          DEC  | Profile that is set by the SIP Proxy
    |           |<--------------| the PDP makes the decision
    |           |               |               |   RSVP-PATHt
    |           |-------------------------------------------------->
    |           |               |               |   RSVP-PATHo
    |<--------------------------------------------------------------
    |Copies the RSVP policy object              |
    |from the Media-Authorization               |
    | RSVP-RESVo|               |               |
    |---------->|               |               |
    |           | REQ           |               |
    |           |-------------->| Using the Auth-Token and Authorized
    |           |         DEC   | Profile that is set by the SIP Proxy
    |           |<--------------| the PDP makes the decision
    |           |               |               |   RSVP-RESVo
    |           |--------------------------------------------------->
    |           |               |               |   RSVP-RESVt
    |<---------------------------------------------------------------
    |           |               |               |   RSVP-RESVCONFt
    |--------------------------------------------------------------->
    |           |               |               |   RSVP-RESVCONFo
    |<---------------------------------------------------------------
    |           |               |               |   200 OK
    |-----------------------------------------> |------------------->
    |           |               |               |   ACK
    |<----------------------------------------------------------------
                                        Figure 2







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   Since Destination SIP-Proxy (DP)has sufficient information regarding the
   end-points, bandwidth and characteristics of the media exchange. It
   initiates a Policy-Setup message to the termination Policy Decision Point
   (PDP-t).

   The PDP-t stores the authorized Media description in its local store
   generates an Authorization-Token that points to this description and
   returns the Authorization-Token to DP.

   Assuming that the call is not forwarded, the UAS sends a 183 response to
   the initial INVITE message, which is forwarded back to UAC. At the same
   time UAS sends RSVP-PATHt message for Media data-stream that includes the
   Session info that describes the Media data-stream and TSpec that
   describes the bandwidth requested along with Authorization information
   that was stored in Media-Authorization-Token.

   ER-t upon reception of the RSVP-PATHt message checks the authorization
   through a PDP-t COPS message exchange. The PDP-t checks the authorization
   using the stored authorized Media description that was linked to
   Authorization-Token that it returned to DP. If authorization is
   successful PDP-t returns "install" Decision.

   ER-t checks the admissibility for the call and if admission succeeds, it
   forwards the RSVP-PATHt message.

   Once UAS receives the RSVP-PATHo message it sends RSVP-RESVo message to
   reserve the bandwidth.

   ER-t upon reception of the RSVP-RESVo message checks the authorization
   through a PDP-t COPS message exchange. The PDP-t checks the authorization
   using the stored authorized Media description that was linked to
   Authorization-Token that it returned to DP. If authorization is
   successful PDP-t returns "install" Decision.

   ER-t checks the admissibility for the call and if admission succeeds, it
   forwards the RSVP- RESVo message.

   Upon reception of RSVP-RESVd message the UAS sends RSVP-RESVCONFt message
   to indicate that the reservation completed for one direction.

   Upon reception of both RSVP-RESVCONFo and 200OK the UAS returns ACK
   message.

6.2. Requesting Bandwidth via DOCSIS MAC messaging

   The DOCSIS MAC layer [5] QoS Set-Up the call flows are different in the
   sense that the Authorization token is a simple 32bit number [6]. And DSA-
   REQ, DSA-RSP, and DSA-ACK are layer 2 messages that are specific to and
   optimized for Cable environment which simplifies/reduces delays for the
   embedded client implementation [6].




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   UAC               ER/CMTSo                  OP
   |  Invite            |                       |
   |------------------------------------------->| Client Authentication
   |                    |                       |and Call Authorization
   |                    |                       |
   |                    |                       | Invite
   |                    |                       |----------->
   |                    |                       |
   |                    |                       | 180/3 OK
   |                    |                       |<------------
   |                    |                       |
   |                    |  Gate-Setup           |
   |                    |<--------------------- |
   |                    |       Gate-Setup-Ack  |
   |                    |---------------------> |
   |                    |                       | GateID put into
   |                    |                       | Media-Authorization header
   |                    |                       | extension
   |                    |       180/3 OK        |
   |<-------------------------------------------|
   |Copies the GAteID object                    |
   |from the Media-Authorization                |
   |                    |                       |
   | DSA-REQ            |                       |
   |------------------->|                       |
   |                    | Using the GateID and the Profile
   |                    | communicated during Gate-Setup
   |                    | the CMTS honors the request and creates
   | DSA-RSP            | a scheduler with appropriate settings
   |<-------------------|                       |
   |                    |                       |
   | DSA-ACK            |                       |
   |------------------->|                       |
   |                    |                       |

                                Figure 3


6.2.1. User Agent Client Side


   Figure 3 presents a high-level overview of a call flow with Media
   Authorization from the viewpoint of UAC .  It is assumed that the SIP-
   Proxy has a previously established authentication relationship with the
   client.

   When a user goes off-hook and dials a telephone number, the originating
   SIP Client (UAC) collects the dialed digits and sends the initial INVITE
   message to Originating SIP-Proxy.



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   The Originating SIP-Proxy (OP) authenticates UAC and forwards the INVITE
   message to the proper destination SIP-proxy.

   Assuming that the call is not forwarded, the other end-point sends a 183
   response to the initial INVITE, forwarded back to OP. Included in this
   response is the negotiated bandwidth requirement for the connection.
   UAS sends DSA-REQ message asking for bandwidth, which includes the 32 bit
   index value.

   ER/CMTSo, upon reception of the RSA-REQ message uses the index value to
   find the authorized media description. Checks the requested media link
   against authorized if the both authorization and admission succeeds it
   starts a layer 2 link for Media data-stream on the Cable Access link and
   returns DSA-RSP, which is acknowledged by UAC via DSA-ACK message.

   Upon reception of 200OK the UAS returns ACK message.

6.2.2. User Agent Server Side

   Figure 4 presents a high-level overview of a basic call flow with Media
   Authorization from the viewpoint of UAS (UAS). It is assumed that the
   Destination SIP-Proxy (DP) has a previously established authentication
   relationship with the UAS.

   When DP receives the INVITE message, it has sufficient information
   regarding the end-points, bandwidth and characteristics of the media
   exchange. It sends a Gate-Setup message to ER/CMTSt containing Media
   data-stream description and bandwidth characteristics. The ER/CMTSt
   returns a 32 bit index value that inside ER/CMTSt points to Media
   definition that DP send out.

   The DP includes the 32 bit index value in the Media-Auth-Token header
   extension that its including into the INVITE message.

   The UAS sends a 183 response to the initial INVITE, which is forwarded
   back to UAC. At the same time UAS sends DSA-REQ message asking for
   bandwidth which includes the 32 bit index value.

   ER/CMTSt, upon reception of the RSA-REQ message uses the index value to
   find the authorized media description. Checks the requested media link
   against authorized if the both authorization and admission succeeds it
   starts a layer 2 link for Media data-stream on the Cable Access link and
   returns DSA-RSP, which is acknowledged by UAC via DSA-ACK message. Upon
   reception of DSA-RSP the UAS returns ACK message.










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   UAS              ER/CMTSt                   DP
   |                    |                       |
   |                    |                       | Invite
   |                    |                       |<-----------
   |                    |                       | Proxy Authentication
   |                    |                       | and Call Authorization
   |                    |  Gate-Setup           |
   |                    |<----------------------|
   |                    |       Gate-Setup-Ack  |
   |                    |---------------------->|
   |                    |                       | GateID put into
   |                    |                       | Media-Authorization header
   |                    |                       | extension
   |  Invite            |                       |
   |<-------------------------------------------|
   |                    |                       |
   |                    |       180/3           |
   |------------------------------------------->|
   |                    |                       | 180/3
   |                    |                       |------------>
   |Copies the GateID object                    |
   |from the Media-Authorization                |
   |                    |                       |
   | DSA-REQ            |
   |------------------->|
   |                    | Using the GateID and the Profile
   |                    | communicated during Gate-Setup
   |                    | the CMTS honors the request and creates
   | DSA-RSP            | a scheduler with appropriate settings
   |<-------------------|
   |                    |
   | DSA-ACK            |                       |
   |------------------->|                       |
   |                    |                       |
   |                    |       200 OK          |
   |------------------------------------------->|
   |                    |                       | 200 OK
   |                    |                       |------------>

                                   Figure 4


7. Advantages of the Proposed Approach

   The use of call authorization makes it possible to control the
   utilization of network resources. This in turn makes IP Telephony more
   robust against denial of service attacks and various kinds of service
   frauds.



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   Using the authorization capability, the service provider can control the
   number of flows, the amount of bandwidth, and the end-point reached
   making the IP Telephony system dependable in the presence of scarce
   resources.

8. Security Considerations

   Media Authorization Tokens sent from a SIP-Proxy to a UAC/UAS MUST be
   protected from eavesdropping, through a mechanism such as IPSec.

9. Notice Regarding Intellectual Property Rights

   AT&T may seek patent or other intellectual property protection for some
   or all of the technologies disclosed in the document. If any standards
   arising from this disclosure are or become protected by one or more
   patents assigned to AT&T, AT&T intends to disclose those patents and
   license them on reasonable and non-discriminatory terms. Future revisions
   of this draft may contain additional information regarding specific
   intellectual property protection sought or received.

   3COM may seek patent or other intellectual property protection for some
   or all of the technologies disclosed in the document. If any standards
   arising from this disclosure are or become protected by one or more
   patents assigned to 3COM, 3COM intends to disclose those patents and
   license them on reasonable and non-discriminatory terms. Future revisions
   of this draft may contain additional information regarding specific
   intellectual property protection sought or received.

10. Reference

   1. Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9,
      RFC 2026, October 1996.

   2  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997

   3  Crocker, D. and Overell, P.(Editors), "Augmented BNF for Syntax
      Specifications: ABNF", RFC 2234, Internet Mail Consortium and Demon
      Internet Ltd., November 1997

   4  M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg, "SIP:
      session initiation protocol,"Request for Comments (Proposed
      Standard) 2543, Internet Engineering Task Force, Mar. 1999.

   5  CableLabs, "Data-Over-Cable Service Interface Specifications, Radio
      Frequency Interface Specification, SP-RFIv1.1-I04-000407", April 2000.

   6  PacketCable, Dynamic Quality of Service Specification, pkt-sp-dqos-
      i01-991201, December 1, 1999.

   7  RFC 2210, The Use of RSVP with IETF Integrated Services by J.
   Wroclawski, September 1997.


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11. Acknowledgments

   The Distributed Call Signaling work in the PacketCable project is
   the work of a large number of people, representing many different
   companies.  The authors would like to recognize and thank the
   following for their assistance: John Wheeler, Motorola; David
   Boardman, Daniel Paul, Arris Interactive; Bill Blum, Jon Fellows,
   Jay Strater, Jeff Ollis, Clive Holborow, Motorola; Doug Newlin,
   Guido Schuster, Ikhlaq Sidhu, 3Com; Jiri Matousek, Bay Networks;
   Farzi Khazai, Nortel; John Chapman, Bill Guckel, Michael Ramalho,
   Cisco; Chuck Kalmanek, Doug Nortz, John Lawser, James Cheng, Tung-
   Hai Hsiao, Partho Mishra, AT&T; Telcordia Technologies; and Lucent
   Cable Communications.

13. Author's Addresses

   Bill Marshall
   AT&T
   Florham Park, NJ  07932
   Email: wtm@research.att.com

   K. K. Ramakrishnan
   AT&T
   Florham Park, NJ  07932
   Email: kkrama@research.att.com

   Ed Miller
   CableLabs
   Louisville, CO  80027
   Email: E.Miller@Cablelabs.com

   Glenn Russell
   CableLabs
   Louisville, CO  80027
   Email: G.Russell@Cablelabs.com

   Burcak Beser
   3Com
   Mount Prospect, IL  60004
   Email: Burcak_Beser@3com.com

   Mike Mannette
   3Com
   Rolling Meadows, IL  60008
   Email: Michael_Mannette@3com.com

   Kurt Steinbrenner
   3Com
   Rolling Meadows, IL  60008
   Email: Kurt_Steinbrenner@3com.com


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   Dave Oran
   Cisco
   Acton, MA  01720
   Email: oran@cisco.com

   Flemming Andreasen
   Cisco
   Edison, NJ
   Email: fandreas@cisco.com

   John Pickens
   Com21
   San Jose, CA
   Email: jpickens@com21.com

   Poornima Lalwaney
   Nokia
   San Diego, CA  92121
   Email: poornima.lalwaney@nokia.com

   Jon Fellows
   Motorola
   San Diego, CA  92121
   Email: jfellows@gi.com

   Doc Evans
   Secure Cable Solutions
   Westminster, CO  30120
   Email: drevans@securecable.com

   Keith Kelly
   NetSpeak
   Boca Raton, FL  33587
   Email: keith@netspeak.com



















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   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."

   Expiration Date This memo is filed as <draft-dcsgroup-sip-call-auth-
   02.txt>, and expires December 31, 2000.


























    DCS Group    Category Informational _ Expiration 12/31/00       15