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Versions: (draft-xie-rserpool-enrp) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 RFC 5353

Network Working Group                                             Q. Xie
Internet-Draft                                                  Motorola
Expires: November 13, 2003                                    R. Stewart
                                                                   Cisco
                                                             M. Stillman
                                                                   Nokia
                                                            May 15, 2003


                Endpoint Name Resolution Protocol (ENRP)
                    draft-ietf-rserpool-enrp-06.txt

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.

   This Internet-Draft will expire on November 13, 2003.

Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.

Abstract

   Endpoint Name Resolution Protocol (ENRP) is designed to work in
   conjunction with the Aggregate Server Access Protocol (ASAP) to
   accomplish the functionality of the Reliable Server Pooling
   (Rserpool) requirements and architecture. Within the operational
   scope of Rserpool, ENRP defines the procedures and message formats of
   a distributed, fault-tolerant registry service for storing,
   bookkeeping, retrieving, and distributing pool operation and
   membership information.




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Table of Contents

   1.     Introduction . . . . . . . . . . . . . . . . . . . . . . .   4
   1.1    Definitions  . . . . . . . . . . . . . . . . . . . . . . .   4
   2.     Conventions  . . . . . . . . . . . . . . . . . . . . . . .   6
   3.     ENRP Message Definitions . . . . . . . . . . . . . . . . .   7
   3.1    PEER_PRESENCE message  . . . . . . . . . . . . . . . . . .   7
   3.2    PEER_NAME_TABLE_REQUEST message  . . . . . . . . . . . . .   8
   3.3    PEER_NAME_TABLE_RESPONSE message . . . . . . . . . . . . .   9
   3.4    PEER_NAME_UPDATE message . . . . . . . . . . . . . . . . .  11
   3.5    PEER_LIST_REQUEST message  . . . . . . . . . . . . . . . .  12
   3.6    PEER_LIST_RESPONSE message . . . . . . . . . . . . . . . .  13
   3.7    PEER_INIT_TAKEOVER message . . . . . . . . . . . . . . . .  14
   3.8    PEER_INIT_TAKEOVER_ACK message . . . . . . . . . . . . . .  15
   3.9    PEER_TAKEOVER_SERVER message . . . . . . . . . . . . . . .  15
   3.10   PEER_OWNERSHIP_CHANGE message  . . . . . . . . . . . . . .  16
   3.11   PEER_ERROR message . . . . . . . . . . . . . . . . . . . .  18
   4.     ENRP Operation Procedures  . . . . . . . . . . . . . . . .  19
   4.1    Methods for Communicating amongst ENRP Servers . . . . . .  19
   4.2    ENRP Server Initialization . . . . . . . . . . . . . . . .  20
   4.2.1  Generate a Server Identifier . . . . . . . . . . . . . . .  21
   4.2.2  Acquire Peer Server List . . . . . . . . . . . . . . . . .  21
   4.2.3  Download ENRP Namespace Data from Mentor Peer  . . . . . .  23
   4.3    Handle PE Registration . . . . . . . . . . . . . . . . . .  25
   4.3.1  Rules on PE Re-registration  . . . . . . . . . . . . . . .  27
   4.4    Handle PE De-registration  . . . . . . . . . . . . . . . .  27
   4.5    Pool Handle Translation  . . . . . . . . . . . . . . . . .  28
   4.6    Server Namespace Update  . . . . . . . . . . . . . . . . .  29
   4.6.1  Announcing Addition or Update of PE  . . . . . . . . . . .  29
   4.6.2  Announcing Removal of PE . . . . . . . . . . . . . . . . .  30
   4.7    Detecting and Removing Unreachable PE  . . . . . . . . . .  31
   4.8    Helping PE and PU to Discover Home ENRP Server . . . . . .  31
   4.9    Maintaining Peer List and Monitoring Peer Status . . . . .  32
   4.9.1  Discovering New Peer . . . . . . . . . . . . . . . . . . .  32
   4.9.2  Server Sending Heartbeat . . . . . . . . . . . . . . . . .  32
   4.9.3  Detecting Peer Server Failure  . . . . . . . . . . . . . .  32
   4.10   Taking-over a Failed Peer Server . . . . . . . . . . . . .  33
   4.10.1 Initiate Server Take-over Arbitration  . . . . . . . . . .  33
   4.10.2 Take-over Target Peer Server . . . . . . . . . . . . . . .  34
   4.11   Namespace Data Auditing and Re-synchronization . . . . . .  35
   4.11.1 Auditing Prodecures  . . . . . . . . . . . . . . . . . . .  35
   4.11.2 Re-synchronization Prodecures  . . . . . . . . . . . . . .  35
   4.12   Handling Unrecognized Message or Unrecognized Parameter  .  36
   5.     Variables and Time Constants . . . . . . . . . . . . . . .  37
   5.1    Variables  . . . . . . . . . . . . . . . . . . . . . . . .  37
   5.2    Timer Constants  . . . . . . . . . . . . . . . . . . . . .  37
   6.     Security Considerations  . . . . . . . . . . . . . . . . .  38
   7.     Acknowledgements . . . . . . . . . . . . . . . . . . . . .  39



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          Normative References . . . . . . . . . . . . . . . . . . .  40
          Informative References . . . . . . . . . . . . . . . . . .  41
          Authors' Addresses . . . . . . . . . . . . . . . . . . . .  41
          Intellectual Property and Copyright Statements . . . . . .  42















































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1. Introduction

   ENRP is designed to work in conjunction with ASAP [1] to accomplish
   the functionality of Rserpool as defined by its requirements [2] and
   architecture [3].

   Within the operation scope of Rserpool, ENRP defines the procedures
   and message formats of a distributed fault-tolerant registry service
   for storing, bookkeeping, retrieving, and distributing pool operation
   and membership information.

   Whenever appropriate, in the rest of this document we will refer to
   this Rserpool registry service as ENRP namespace, or simply
   namespace.

1.1 Definitions

   This document uses the following terms:

   Operation scope: See [3];

   Pool (or server pool): See [3];

   Pool handle (or pool name): See [3];

   Pool element (PE): See [3];

   Pool user (PU): See [3];

   Pool element handle: See [3];

   ENRP namespace (or namespace): See [3];

   ENRP namespace server (or ENRP server): See [3];

   ENRP client channel: The communication channel through which a PE
      requests for ENRP namespace service. The ENRP client channel is
      usually defined by the transport address of the home ENRP server
      and a well known port number;

   ENRP server channel: Defined by a well known multicast IP address and
      a well known port number. All ENRP servers in an operation scope
      can send multicast messages to other servers through this channel.
      PEs are also allowed to multicast on this channel occasionally;

   Home ENRP server: The ENRP server to which a PE or PU currently
      belongs. A PE MUST only have one home ENRP server at any given
      time and both the PE and its home ENRP server MUST keep track of



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      this master/slave relationship between them. A PU SHOULD select
      one of the available ENRP servers as its home ENRP server, but the
      ENRP server does not need to know, nor does it need to keep track
      of this relationship.















































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2. Conventions

   The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
   SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when
   they appear in this document, are to be interpreted as described in
   [5].













































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3. ENRP Message Definitions

   In this section, we defines the format of all ENRP messages. These
   are messages sent and received amongst ENRP servers in an operation
   scope. Messages sent and received between a PE/PU and an ENRP server
   are part of ASAP and are defined in [1]. A common format, defined in
   [10], is used for all ENRP and ASAP messages.

   Most ENRP messages contains a combination of fixed fields and TLV
   parameters. The TLV parameters are also defined in [10].

   All messages, as well as their fields/parameters described below,
   MUST be transmitted in network byte order (a.k.a. Big Endian, i.e.,
   the most significant byte first).

   For ENRP, the following message types are defined:

         Type       Message Name
         -----      -------------------------
         0x0       - (reserved by IETF)
         0x1       - PEER_PRESENCE
         0x2       - PEER_NAME_TABLE_REQUEST
         0x3       - PEER_NAME_TABLE_RESPONSE
         0x4       - PEER_NAME_UPDATE
         0x5       - PEER_LIST_REQUEST
         0x6       - PEER_LIST_RESPONSE
         0x7       - PEER_INIT_TAKEOVER
         0x8       - PEER_INIT_TAKEOVER_ACK
         0x9       - PEER_TAKEOVER_SERVER
         0xa       - PEER_OWNERSHIP_CHANGE
         0xb       - PEER_ERROR
         0xc-0xFF  - (reserved by IETF)


3.1 PEER_PRESENCE message

   This ENRP message is used to announce (periodically) the presence of
   an ENRP server, or to probe the status of a peer ENRP sever.













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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Type = 0x1  |0|0|0|0|0|0|0|R|     Message Length = 0xC      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Sender Server's ID                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Receiver Server's ID                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :               Server Information Param (optional)             :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



      R (reply_required) flag: 1 bit

         Set to '1' if the sender requires a response to this message,
         otherwise set to '0'.

      Sender Server's ID: 32 bit (unsiged integer)

         This is the ID of the ENRP server which sends the message.

      Receiver Server's ID: 32 bit (unsiged integer)

         This is the ID of the ENRP server to which the message is
         intended. If the message is not intended to an individual
         server (e.g., the message is multicasted to a group of
         servers), this field MUST be set with all 0's.

      Server Information Parameter:

         If present, contains the server information of the sender of
         this message (Server Information Parameter is defined in [10]).
         This parameter is optional. However, if this message is sent in
         response to a received "reply required" PEER_PRESENCE from a
         peer, the sender then MUST include its server information.

   Note, at startup an ENRP server MUST pick a randomly generated,
   non-zero 32-bit unsigned integer as its ID and MUST use this same ID
   for its entire life.

3.2 PEER_NAME_TABLE_REQUEST message

   An ENRP server sends this message to one of its peers to request a
   copy of the namespace data. This message is normally used during
   server initialization or namespace re-synchronization.




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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Type = 0x2  |0|0|0|0|0|0|0|W|    Message Length = 0xC       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Sender Server's ID                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Receiver Server's ID                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



      W (oWn-children-only) flag: 1 bit

         Set to '1' if the sender of this message is only requesting
         information about the PEs owned by the message receiver.
         Otherwise, set to '0'.

      Sender Server's ID:

         See Section 3.1.

      Receiver Server's ID:

         See Section 3.1.


3.3 PEER_NAME_TABLE_RESPONSE message























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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Type = 0x3  |0|0|0|0|0|0|R|M|        Message Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Sender Server's ID                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Receiver Server's ID                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                                                               :
      :                     Pool entry #1 (see below)                 :
      :                                                               :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                                                               :
      :                              ...                              :
      :                                                               :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                                                               :
      :                     Pool entry #n (see below)                 :
      :                                                               :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



      R (Reject) flag: 1 bit

         MUST be set to '1' if the sender of this message is rejecting a
         namespace request. In such a case, this message MUST be sent
         with no pool entries included.

      M (More_to_send) flag: 1 bit

         Set to '1' if the sender has more pool entries to sent in
         subsequent PEER_NAME_TABLE_RESPONSE messages, otherwise, set to
         '0'.

      Message Length: 16 bits (unsigned integer)

         Indicates the entire length of the message in number of octets.

         Note, the value in Message Length field will NOT cover any
         padding at the end of this message.

      Sender Server's ID:

         See Section 3.1.





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      Receiver Server's ID:

         See Section 3.1.

      Pool entry #1-#n:

         If R flag is '0', at least one pool entry SHOULD be present in
         the message. Each pool entry MUST start with a pool handle
         parameter as defined in section 3.1.7, followed by one or more
         pool element parameters, i.e.:

                   +---------------------------+
                   :      Pool handle          :
                   +---------------------------+
                   :         PE #1             :
                   +---------------------------+
                   :         PE #2             :
                   +---------------------------+
                   :          ...              :
                   +---------------------------+
                   :         PE #n             :
                   +---------------------------+


3.4 PEER_NAME_UPDATE message


       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Type = 0x4  |0|0|0|0|0|0|0|0|        Message Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        Update Action          |        (reserved)             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Sender Server's ID                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Receiver Server's ID                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                        Pool handle                            :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                        Pool Element                           :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



      Message Length: 16 bits (unsigned integer)

         Indicates the entire length of the message in number of octets.



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         Note, the value in Message Length field will NOT cover any
         padding at the end of this message.

      Update Action: 16 bits (unsigned integer)

         This field indicates what act is requested to the specified PE.
         It MUST take one of the following values:

         0x0 - ADD_PE: add or update the specified PE in the ENRP
            namespace

         0x1 - DEL_PE: delete the specified PE from the ENRP namespace.

         Other values are reserved by IETF and MUST not be used.

      Reserved: 16 bits

         MUST be set to 0's by sender and ignored by the receiver.

      Sender Server's ID:

         See Section 3.1.

      Receiver Server's ID:

         See Section 3.1.

      Pool handle:

         Specifies to which the PE belongs.

      Pool Element:

         Specifies the PE.


3.5 PEER_LIST_REQUEST message

   This ENRP message is used to request a copy of the current known ENRP
   peer server list. This message is normally sent from a newly started
   ENRP server to an existing ENRP server as part of the initialization
   process of the new server.











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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Type = 0x5  |0|0|0|0|0|0|0|0|    Message Length = 0xC       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Sender Server's ID                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Receiver Server's ID                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



      Sender Server's ID:

         See Section 3.1.

      Receiver Server's ID:

         See Section 3.1.


3.6 PEER_LIST_RESPONSE message

   This message is used to respond a PEER_LIST_REQUEST.


       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Type = 0x6  |0|0|0|0|0|0|0|R|        Message Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Sender Server's ID                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Receiver Server's ID                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                   Server Info Param of Peer #1                :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                           ...                                 :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                   Server Info Param of Peer #n                :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



      R (Reject) flag: 1 bit

         MUST be set to '1' if the sender of this message is rejecting a
         peer list request. In such a case, this message MUST be sent



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         with no peer server ID included.

      Message Length: 16 bits (unsigned integer)

         Indicates the entire length of the message in number of octets.

         Note, the value in Message Length field will NOT cover any
         padding at the end of this message.

      Sender Server's ID:

         See Section 3.1.

      Receiver Server's ID:

         See Section 3.1.

      Server Information Parameter of Peer #1-#n:

         Each contains a Server Information Parameter of a peer known to
         the sender. The Server Information Parameter is defined in
         [10].


3.7 PEER_INIT_TAKEOVER message

   This message is used by an ENRP server (the takeover initiator) to
   declare its intention of taking over a specific peer ENRP server.


       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Type = 0x7  |0|0|0|0|0|0|0|0|        Message Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Sender Server's ID                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Receiver Server's ID                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Target Server's ID                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



      Sender Server's ID:

         See Section 3.1.




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      Receiver Server's ID:

         See Section 3.1.

      Target Server's ID:

         Contains the 32-bit server ID of the peer ENRP that is the
         target of this takeover attempt.


3.8 PEER_INIT_TAKEOVER_ACK message

   This message is used to acknowledge the takeover initiator that the
   sender of this message received the PEER_INIT_TAKEOVER message and
   that it does not object to the takeover.


       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Type = 0x8  |0|0|0|0|0|0|0|0|        Message Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Sender Server's ID                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Receiver Server's ID                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Target Server's ID                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



      Sender Server's ID:

         See Section 3.1.

      Receiver Server's ID:

         See Section 3.1.

      Target Server's ID:

         Contains the 32-bit server ID of the peer ENRP that is the
         target of this takeover attempt.


3.9 PEER_TAKEOVER_SERVER message

   This message is used by the takeover initiator to declare that a



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   takeover is underway.


       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Type = 0x9  |0|0|0|0|0|0|0|0|        Message Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Sender Server's ID                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Receiver Server's ID                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Target Server's ID                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



      Sender Server's ID:

         See Section 3.1.

      Receiver Server's ID:

         See Section 3.1.

      Target Server's ID:

         Contains the 32-bit server ID of the peer ENRP that is the
         target of this takeover operation.


3.10 PEER_OWNERSHIP_CHANGE message

   This message is used by the ENRP server, normally after a successful
   takeover, to declare that it is now the new home ENRP server of the
   listed PEs in the listed pools.















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       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Type = 0xa  |0|0|0|0|0|0|0|0|        Message Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Sender Server's ID                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Receiver Server's ID                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                       Pool handle #1                          :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :              PE Identifier Param #1 of pool #1                :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                              ...                              :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :              PE Identifier Param #k of pool #1                :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                                                               :
      :                              ...                              :
      :                                                               :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                       Pool handle #M                          :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :              PE Identifier Param #1 of pool #M                :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                              ...                              :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :              PE Identifier Param #n of pool #M                :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



      Sender Server's ID:

         See Section 3.1.

      Receiver Server's ID:

         See Section 3.1.

      Pool handles and PE Identifier parameters:

         Each listed pool handle is followed by a list of PE Identifier
         parameters, indicating that the sender of this message is
         taking ownership of the listed PEs in the pool.






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3.11 PEER_ERROR message

   This message is used by an ENRP server to report an operation error
   to one of its peers.


       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Type = 0xb  |0|0|0|0|0|0|0|0|        Message Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      Sender Server's ID                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     Receiver Server's ID                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                   Operation Error Parameter                   :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



      Sender Server's ID:

         See Section 3.1.

      Receiver Server's ID:

         See Section 3.1.

      Operation Error Parameter:

         This parameter, defined in [10], indicates the type of error(s)
         being reported.



















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4. ENRP Operation Procedures

   In this section, we discuss the operation procedures defined by ENRP.
   An ENRP server MUST following these procedures when sending,
   receiving, or processing ENRP messages.

   Many of the Rserpool events call for both server-to-server and PU/
   PE-to-server message exchanges. Only the message exchanges and
   activities between an ENRP server and its peer(s) are considered
   within the ENRP scope and are defined in this document.

   Procedures for exchanging messages between a PE/PU and ENRP servers
   are defined in [1].

4.1 Methods for Communicating amongst ENRP Servers

   Within an Rserpool operation scope, ENRP servers need to communicate
   with each other in order to exchange information such as the pool
   membership changes, namespace data synchronization, etc.

   Two types of communications are used amongst ENRP servers:

   o  point-to-point message exchange from one ENPR server to a specific
      peer server, and

   o  announcements from one server to all its peer servers in the
      operation scope.

   Point-to-point communication is always carried out over an SCTP
   associaiton between the sending server and the receiving server.

   Announcements are communicated out with one of the following two
   approaches:

   1.  The sending server sends the announcement message to a well-known
       RSERPOOL IP multicast channel that its peer servers subscribe to.

       Note: Because IP multicast is not reliable, this approach does
       not gaurrantee that all the peers will receive the announcement
       message. Moreover, since IP multicast is not secure, this
       approach cannot provide any security to the communication.

   2.  The sending server sends multiple copies of the announcement, one
       to each of its peer servers, over a set of point-to-point SCTP
       associations between the sending server and the peers.

       This approach gaurrantees the reliabe receiption of the message.
       When needed, data security can be achieved by using IP security



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       mechanisms such as IPsec [9] or TLS [8].

   In order to maximize inter-operability of ENRP servers, the following
   rules MUST be followed:

   1.  At the startup time, a new ENRP server SHOULD make a decision on
       whether it will enable IP multicast for ENRP announcements. This
       decision should be based on factors such as the availability of
       IP multicast and the security requirements from the user of
       Rserpool.

   2.  If an ENRP server disables multicast, it then:

       A.  MUST NOT subscribe to the well-known server multicast
           channel, i.e., it only receives peer announcements over SCTP
           associations, and

       B.  MUST transmit all its out-going announcements over
           point-to-point SCTP associations with its peers.

   3.  If an ENRP server enables itself to use multicast, it then:

       A.  MUST subcribe to the well-known server multicast channel to
           ready itself for receiving peers' multicast announcements,

       B.  MUST also be prepared to receive peer announcements over
           point-to-point SCTP associations from peers.

       C.  MUST track internally which peers are multicast-enabled and
           which are not. Note: A peer is always assumed to be
           multicast-disabled until/unless an ENRP message of any type
           is received from that peer over the well-known server
           multicast channel.

       D.  when sending out an announcement, MUST send a copy to the
           well-known server multicast channel AND a copy to each of the
           peers that are marked as multicast-disabled over a
           point-to-point SCTP association.


4.2 ENRP Server Initialization

   This section describes the steps a new ENRP server needs to take in
   order to join the other existing ENRP servers, or to initiate the
   namespace service if it is the first ENRP server started in the
   operation scope.





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4.2.1 Generate a Server Identifier

   A new ENRP server MUST generate a non-zero, 32-bit server Id that is
   as unique as possible in the operation scope and this server Id MUST
   remain unchanged for the lifetime of the server. Normally, a good
   32-bit random number will be good enough as the server Id ([11]
   provides some information on randomness guidelines).

4.2.2 Acquire Peer Server List

   At startup, the ENRP server (initiating server) will first attempt to
   learn all existing peer ENRP servers in the same operation scope, or
   to determine that it is along in the scope.

   The initiating server uses an existing peer server to bootstrap
   itself into service. We call this peer server the mentor server.

4.2.2.1 Find the mentor server

   If the initiating server is told about an existing peer server
   through some administrative means (such as DNS query, configuration
   database, startup scripts, etc), the initiating server SHOULD then
   use this peer server as its mentor server and SHOULD skip the
   remaining steps in this subsection.

   If multiple existing peer servers are specified, the initiating
   server SHOULD pick one of them as its mentor peer server, keep the
   others as its backup menter peers, and skip the remaining steps in
   this subsection.

   If no existing peer server is specified to the initiating server AND
   if multicast is available in the operation scope, the following
   mentor peer discovery procedures SHOULD be followed:

   1.  The initiating server SHOULD first join the well-known ENRP
       server multicast channel.

   2.  Then the initiating server SHOULD send a PEER_PRESENCE message,
       with the 'Reply_required' flag set, over the multicast channel.
       Upon the reception of this PEER_PRESENCE message, a peer server
       MUST send a PEER_PRESENCE, without the 'Reply_required' flag,
       back to the initiating server.

   3.  When the first response to its original PEER_PRESENCE arrives,
       the initiating server SHOULD take the sender of this received
       response as its mentor peer server. This completes the discovery
       of the mentor peer server.




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       If responses are also received from other peers (a likely event
       when multiple peers exist in the operation scope at the time the
       new server started), the initiating server SHOULD keep a list of
       those responded as its backup mentor peers (see below).

   4.  If no response to its PEER_PRESENCE message are received after
       TIMEOUT-SERVER-HUNT seconds, the initiating server SHOULD repeat
       steps 2) and 3) for up to MAX-TIME-SERVER-HUNT times. After that,
       if there is still no response, the initiating server MUST assume
       that it is alone in the operation scope.

   5.  If the initiating server determined that it is alone in the
       scope, it MUST skip the procedures in Section 4.2.2.2 and Section
       4.2.3 and MUST consider its initialization completed and start
       offering ENRP services.

   Note, if multicast is not available (or not allowed for reasons such
   as security concerns) in the operation scope, at least one peer
   server MUST be specified to the initiating server through
   administrative means, unless the initiation server is the first
   server to start in the operation scope.

   Note, if the administratively specified menter peer(s) fails, the
   initiating server SHOULD use the auto-discover procedure defined in
   steps 1-5 above.

4.2.2.2 Request complete server list from mentor peer

   Once the initiating server finds its mentor peer server (by either
   discovery or administrative means), the initiating server MUST send a
   PEER_LIST_REQUEST message to the mentor peer server to request a copy
   of the complete server list maintained by the mentor peer (see
   Section 4.9 for maintaining server list).

   Upon the reception of this request, the mentor peer server SHOULD
   reply with a PEER_LIST_RESPONSE message and include in the message
   body all existing ENRP servers known by the mentor peer.

   Upon the reception of the PEER_LIST_RESPONSE message from the mentor
   peer, the initiating server MUST use the server information carried
   in the message to initialize its own peer list.

   However, if the mentor itself is in the process of startup and not
   ready to provide a peer server list (for example, the mentor peer is
   waiting for a response to its own PEER_LIST_REQUEST to another
   server), it MUST rejest the request by the initiating server and
   respond with a PEER_LIST_RESPONSE message with the R flag set to '1',
   and with no server information included in the response.



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   In the case where its PEER_LIST_REQUEST is rejected by the mentor
   peer, the initiating server SHOULD either wait for a few seconds and
   re-send the PEER_LIST_REQUEST to the mentor server, or if there is a
   backup mentor peer available, select another mentor peer server and
   send the PEER_LIST_REQUEST to the new mentor server.

4.2.3 Download ENRP Namespace Data from Mentor Peer

   After a peer list download is completed, the initiating server MUST
   request a copy of the current namespace data from its mentor peer
   server, by taking the following steps:

   1.  The initiating server MUST first send a PEER_NAME_TABLE_REQUEST
       message to the mentor peer, with W flag set to '0', indicating
       that the entire namespace is requested.

   2.  Upon the reception of this message, the mentor peer MUST start a
       download session in which a copy of the current namespace data
       maintained by the mentor peer is sent to the initiating server in
       one or more PEER_NAME_TABLE_RESPONSE messages (Note, the mentor
       server may find it particularly desirable to use multiple
       PEER_NAME_TABLE_RESPONSE messages to send the namespace when the
       namespace is large, especially when forming and sending out a
       single response containing a large namespace may interrupt its
       other services).

       If more than one PEER_NAME_TABLE_RESPONSE message are used during
       the download, the mentor peer MUST use the M flag in each
       PEER_NAME_TABLE_RESPONSE message to indicate whether this message
       is the last one for the download session. In particular, the
       mentor peer MUST set the M flag to '1' in the outbound
       PEER_NAME_TABLE_RESPONSE if there is more data to be transferred
       and MUST keep track of the progress of the current download
       session. The mentor peer MUST set the M flag to '0' in the last
       PEER_NAME_TABLE_RESPONSE for the download session and close the
       download session (i.e., removing any internal record of the
       session) after sending out the last message.

   3.  During the downloading, every time the initiating server receives
       a PEER_NAME_TABLE_RESPONSE message, it MUST transfer the data
       entries carried in the message into its local namespace database,
       and then check whether or not this message is the last one for
       the download session.

       If the M flag is set to '1' in the just processed
       PEER_NAME_TABLE_RESPONSE message, the initiating server MUST send
       another PEER_NAME_TABLE_REQUEST message to the mentor peer to
       request for the next PEER_NAME_TABLE_RESPONSE message.



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   4.  When unpacking the data entries from a PEER_NAME_TABLE_RESPONSE
       message into its local namespace database, the initiating server
       MUST handle each pool entry carried in the message using the
       following rules:

       A.  If the pool does not exist in the local namespace, the
           initiating server MUST creates the pool in the local
           namespace and add the PE(s) in the pool entry to the pool.

           When creating the pool, the initiation server MUST set the
           overall member selection policy type of the pool to the
           policy type indicated in the first PE.

       B.  If the pool already exists in the local namespace, but the
           PE(s) in the pool entry is not currently a member of the
           pool, the initiating server MUST add the PE(s) to the pool.

       C.  If the pool already exists in the local namespace AND the
           PE(s) in the Pool entry is already a member of the pool, the
           initiating server server SHOULD replace the attributes of the
           existing PE(s) with the new information.

   5.  When the last PEER_NAME_TABLE_RESPONSE message is received from
       the mentor peer and unpacked into the local namespace, the
       initialization process is completed and the initiating server
       SHOULD start to provide ENRP services.

   Under certain circumstances, the mentor peer itself may not be able
   to provide a namespace download to the initiating server. For
   example, the mentor peer is in the middle of initializing its own
   namespace database, or it has currently too many download sessions
   open to other servers.

   In such a case, the mentor peer MUST rejest the request by the
   initiating server and respond with a PEER_NAME_TABLE_RESPONSE message
   with the R flag set to '1', and with no pool entries included in the
   response.

   In the case where its PEER_NAME_TABLE_REQUEST is rejected by the
   mentor peer, the initiating server SHOULD either wait for a few
   seconds and re-send the PEER_NAME_TABLE_REQUEST to the mentor server,
   or if there is a backup mentor peer available, select another mentor
   peer server and send the PEER_NAME_TABLE_REQUEST to the new mentor
   server.

   A started namespace download session may get interrupted for some
   reason. To cope with this, the initiating server SHOULD start a timer
   everytime it finishes sending a PEER_NAME_TABLE_REQUEST to its mentor



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   peer. If this timer expires without receiving a response from the
   mentor peer, the initiating server SHOULD abort the current download
   session and re-start a new namespace download with a backup mentor
   peer, if one is available.

   Similarly, after sending out a PEER_NAME_TABLE_RESPONSE, if the
   mentor peer has still more data to send, it SHOULD start a session
   timer. If this timer expires without receiving another request from
   the initiating server, the mentor peer SHOULD abort the session,
   cleaning out any resource and record of the session.

4.3 Handle PE Registration

   To register itself with the namespace, a PE sends a REGISTRATION
   message to its home ENRP server. The format of REGISTRATION message
   and rules of sending it are defined in [1].

   In the REGISTRATION message, the PE indicates the name of the pool it
   wishes to join in a pool handle parameter, and its complete transport
   information and any load control information in a PE parameter.

   The ENRP server handles the REGISTRATION message according to the
   following rules:

   1.  If the named pool does not exist in the namespace, the ENRP
       server MUST creates a new pool with that name in the namespace
       and add the PE to the pool as its first PE;

       When a new pool is created, the overall member selection policy
       of the pool MUST be set to the policy type indicated by the first
       PE, the overall pool transport type MUST be set to the transport
       type indicated by the PE, and the overall pool data/control
       channel configuration MUST be set to what is indicated in the
       Transport Use field of the User Transport parameter by the
       registering PE.

   2.  If the named pool already exists in the namespace, but the
       requesting PE is not currently a member of the pool, the ENRP
       server will add the PE as a new member to the pool;

       However, before adding the PE to the pool, the server MUST check
       if the policy type, transport type, and transport usage indicated
       by the registering PE is consistent with those of the pool. If
       different, the ENRP server MUST either attempt to override the
       PE's value(s) or to reject the registration if overriding is not
       possible.

       A.  Inconsistent policy - If no additional policy-related



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           information are required to perform an override of pool
           policy (e.g., overriding Least-used with Round-robin does not
           require additional policy-related information), the ENRP
           server MUST replace the PE's policy type with the overall
           policy type of the pool. However, if additional policy
           information is required for the overriding (e.g., overriding
           Round-robin with Least-load will require the knowledge of the
           load factor of the PE), the ENRP server MUST reject the
           registration.

       B.  Inconsistent transport type - The ENRP server MUST reject the
           registration.

       C.  Inconsistent data/control configuration - If the overall pool
           configuration is "DATA ONLY", and the registering PE
           indicates "CONTORL plus DATA", the ENRP server SHOULD accept
           the registration but warn the PE that control channel cannot
           be used. If the pool configuration is "CONTROL plus DATA" and
           the PE indicates "DATA ONLY", the ENRP server MUST reject the
           registration.

   3.  If the named pool already exists in the namespace AND the
       requesting PE is already a member of the pool, the ENRP server
       SHOULD consider this as a re-registration case. The ENRP server
       MUST perform the same tests on policy, transport type, transport
       use, as described above. If the re-registration is accepted after
       the test, the ENRP Server SHOULD replace the attributes of the
       existing PE with the information carried in the received
       REGISTRATION message.

   4.  After accepting the registration, the ENRP server MUST assgin
       itself the owner of this PE. If this is a re-registration, the
       ENRP server MUST take over ownership of this PE regardless of
       whether the PE was previously owned by this server or by another
       server.

   5.  The ENRP server may reject the registration due to reasons such
       as invalid values, lack of resource, authentication failure, etc.

   In all above cases, the ENRP server MUST reply to the requesting PE
   with a REGISTRATION_RESPONSE message. If the registration is
   accepted, the ENRP server MUST set the 'R' flag in the
   REGISTRATION_RESPONSE to '0'. If the registration is rejected, the
   ENRP server MUST indicate the rejection by setting the 'R' flag in
   the REGISTRATION_RESPONSE to '1'.

   If the registration is rejected, the ENRP server SHOULD include the
   proper error cause(s) in the REGISTRATION_RESPONSE message.



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   If the registration is granted but with an override of some PE's
   original values, in the REGISTRATION_RESPONSE message the ENRP server
   SHOULD include the proper error cause(s) so that the PE can be warned
   about the overriding and be informed about the new value(s).

   If the registration is granted (either a new registration or a
   re-registration case), the ENRP server MUST assign itself to be the
   home ENRP server of the PE, i.e., to "own" the PE.

      Implementation note: for better performance, the ENRP server may
      find it both efficient and convenient to internally maintain two
      separate PE lists or tables - one is for the PEs that are "owned"
      by the ENRP server and the other for all the PEs owned by its
      peer(s).

   Moreover, if the registration is granted, the ENRP server MUST take
   the namespace update action as described in Section 4.6 to inform its
   peers about the change just made. If the registration is denied, no
   message will be sent to its peers.

4.3.1 Rules on PE Re-registration

   A PE may re-register itself to the namespace with a new set of
   attributtes in order to, for example, extend its registration life,
   change its load factor value, etc.

   A PE may modify its load factor value at any time via
   re-registration. Based on the number of PEs in the pool and the
   pool's overall policy type, this operation allows the PE to
   dynamically control its share of inbound messages received by the
   pool (also see Section ???? in [1] for more on load control).

   Moreover, when re-registering, the PE MUST NOT change its policy
   type. The server MUST reject the re-registration if the PE attempt to
   change its policy type. In the rejection, the server SHOULD attach an
   error code "Pooling Policy Inconsistent".

   Regardless whether it is the current owner of the PE, if the
   re-registration is granted to the PE, the ENRP server MUST assign
   itself to be the new home ENRP server of the PE.

   Moreover, if the re-registration is granted, the ENRP server MUST
   take the namespace update action as described in Section 4.6 to
   inform its peers about the change just made. If the re-registration
   is denied, no message will be sent to its peers.

4.4 Handle PE De-registration




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   To remove itself from a pool, a PE sends a DEREGISTRATION message to
   its home ENRP server. The complete format of DEREGISTRATION message
   and rules of sending it are defined in [1].

   In the DEREGISTRATION message the PE indicates the name of the pool
   it belongs to in a pool handle parameter and provides its PE
   identifer.

   Upon receiving the message, the ENRP server SHALL remove the PE from
   its namespace. Moreover, if the PE is the last one of the named pool,
   the ENRP server will remove the pool from the namespace as well.

   If the ENRP server fails to find any record of the PE in its
   namespace, it SHOULD consider the de-registration granted and
   completed.

   The ENRP server may reject the de-registration request for various
   reasons, such as invalid parameters, authentication failure, etc.

   In response, the ENRP server MUST send a DEREGISTRATION_RESPONSE
   message to the PE. If the de-registration is rejected, the ENRP
   server MUST indicate the rejection by including the proper Operation
   Error parameter.

   It should be noted that de-registration does not stop the PE from
   sending or receiving application messages.

   Once the de-registration request is granted AND the PE removed from
   its local copy of the namespace, the ENRP server MUST take the
   namespace update action described in Section 4.6 to inform its peers
   about the change just made. Otherwise, NO message SHALL be send to
   its peers.

4.5 Pool Handle Translation

   A PU uses the pool handle translation service of an ENRP server to
   resolve a pool handle to a list of accessible transport addresses of
   the member PEs of the pool.

   This requires the PU to send a NAME_RESOLUTION message to its home
   ENRP server and in the NAME_RESOLUTION message specify the pool
   handle to be translated in a Pool Handle parameter. Complete
   defintion of the NAME_RESOLUTION message and the rules of sending it
   are defined in [1].

   An ENRP server SHOULD be prepared to receive NAME_RESOLUTION requests
   from PUs either over an SCTP associaiton on the well-know SCTP port,
   or over a TCP connection on the well-know TCP port.



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   Upon reception of the NAME_RESOLUTION message, the ENRP server MUST
   first look up the pool handle in its namespace. If the pool exits,
   the home ENRP server MUST compose and send back a
   NAME_RESOLUTION_RESPONSE message to the requesting PU.

   In the response message, the ENRP server MUST list all the PEs
   currently registered in this pool, in a list of PE parameters. The
   ENRP server MUST also include a pool member selection policy
   parameter to indicate the overall member selection policy for the
   pool, if the current pool member selection policy is not round-robin
   (if the overall policy is round-Robin, this parameter MAY be
   omitted?).

   If the named pool does not exist in the namespace, the ENRP server
   MUST respond with a NAME_UNKNOWN message.

   The complete format of NAME_RESOLUTION_RESPONSE and NAME_UNKNOWN
   messages and the rules of receiving them are defined in [1].

4.6 Server Namespace Update

   This includes a set of update operations used by an ENRP server to
   inform its peers when its local namespace is modified, e.g., addition
   of a new PE, removal of an existing PE, change of pool or PE
   properties.

4.6.1 Announcing Addition or Update of PE

   When a new PE is granted registration to the namespace or an existing
   PE is granted a re-registration, the home ENRP server uses this
   procedure to inform all its peers.

   This is an ENRP announcement and is sent to all the peer of the home
   ENRP server. See Section 4.1 on how annoucements are sent.

   An ENRP server MUST announce this update to all its peers in a
   PEER_NAME_UPDATE message with the Update Action field set to ADD_PE,
   indicating the addition of a new PE or the modification of an
   existing PE. The complete new information of the PE and the pool its
   belongs to MUST be indicated in the message with a PE parameter and a
   Pool Handle parameter, respectively.

   The home ENRP server SHOULD fill in its server Id in the Sender
   Server's ID field and leave the Receiver Server's ID blank (i.e., all
   0's).

   When a peer receives this PEER_NAME_UPDATE message, it MUST take the
   following actions:



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   1.  If the named pool indicated by the pool handle does not exist in
       its local copy of the namespace, the peer MUST create the named
       pool in its local namespace and add the PE to the pool as the
       first PE. It MUST then copy in all other attributes of the PE
       carried in the message.

       When the new pool is created, the overall member selection policy
       of the pool MUST be set to the policy type indicated by the PE.

   2.  If the named pool already exists in the peer's local copy of the
       namespace AND the PE does not exist, the peer MUST add the PE to
       the pool as a new PE and copy in all attributes of the PE carried
       in the message.

   3.  If the named pool exists AND the PE is already a member of the
       pool, the peer MUST replace the attributes of the PE with the new
       information carried in the message.


4.6.2 Announcing Removal of PE

   When an existing PE is granted de-registration or is removed from its
   namespace for some other reasons (e.g., purging an unreachable PE,
   see Section 4.7), the ENRP server MUST uses this procedure to inform
   all its peers about the change just made.

   This is an ENRP announcement and is sent to all the peer of the home
   ENRP server. See Section 4.1 on how annoucements are sent.

   An ENRP server MUST announce the PE removal to all its peers in a
   PEER_NAME_UPDATE message with the Update Action field set to DEL_PE,
   indicating the removal of an existing PE. The complete information of
   the PE and the pool its belongs to MUST be indicated in the message
   with a PE parameter and a Pool Handle parameter, respectively.

   [editor's note: only the pool handle and the PE's id are needed, it
   should reduce the size of the message]

   The sending server MUST fill in its server ID in the Sender Server's
   ID field and leave the Receiver Server's ID blank (i.e., set to all
   0's).

   When a peer receives this PEER_NAME_UPDATE message, it MUST first
   find pool and the PE in its own namespace, and then remove the PE
   from its local namespace. If the removed PE is the last one in the
   pool, the peer MUST also delete the pool from its local namespace.

   If the peer fails to find the PE or the pool in its namespace, it



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   SHOULD take no further actions.

4.7 Detecting and Removing Unreachable PE

   Whenever a PU finds a PE unreachable (e.g., via an SCTP SEND.FAILURE
   Notification, see section 10.2 of [7]), the PU SHOULD send an
   ENDPOINT_UNREACHABLE message to its home ENRP server. The message
   SHOULD contain the pool handle and the PE Id of the unreachable PE.

   Upon the reception of an ENDPOINT_UNREACHABLE message, a server MUST
   immediately send a point-to-point ENDPOINT_KEEP_ALIVE message to the
   PE in question. If this ENDPOINT_KEEP_ALIVE fails (e.g., it results
   in an SCTP SEND.FAILURE notification), the ENRP server MUST consider
   the PE as truly unreachable and MUST remove the PE from its namespace
   and take actions described in Section 4.6.2.

   If the ENDPOINT_UNREACHABLE message is transmitted successfully to
   the PE, the ENRP server MUST retain the PE in its namespace.
   Moreover, the server SHOULD keep a counter to record how many
   ENDPOINT_UNREACHABLE messages it has received reporting reachability
   problem relating to this PE. If the counter exceeds the protocol
   threshold MAX-BAD-PE-REPORT, the ENRP server SHOULD remove the PE
   from its namespace and take actions described in Section 4.6.2.

   Optionally, an ENRP server may also periodically send point-to-point
   ENDPOINT_KEEP_ALIVE messages to each of the PEs owned by the ENRP
   server in order to check their reachability status. If the send of
   ENDPOINT_KEEP_ALIVE to a PE fails, the ENRP server MUST consider the
   PE as unreachable and MUST remove the PE from its namespace and take
   actions described in Section 4.6.2. Note, if an ENRP server owns a
   large number of PEs, the implementation should pay attention not to
   flood the network with bursts of ENDPOINT_KEEP_ALIVE messages.
   Instead, the implementation should try to smooth out the
   ENDPOINT_KEEP_ALIVE message traffic over time.

   The complete definition and rules of sending ENDPOINT_UNREACHABLE and
   receiving ENDPOINT_KEEP_ALIVE messages are described in [1].

4.8 Helping PE and PU to Discover Home ENRP Server

   At its startup time, or whenever its current home ENRP server is not
   providing services, a PE or PU will attempt to find a new home
   server. For this reason, the PE or PU will need to maintain a list of
   currently available ENRP servers in its scope.

   To help the PE or PU maintaining this list, an ENRP server, if it is
   enabled for multicast, SHOULD periodically send out a SERVER_ANNOUNE
   message every SERVER-ANNOUNCE-CYCLE seconds to the well-known ASAP



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   multicast channel. And in the SERVER_ANNOUNE message the ENRP server
   SHOULD include all the transport addresses available for ASAP
   communications. If the ENRP server only supports SCTP for ASAP
   communications, the transport information MAY be omitted in the
   SERVER_ANNOUNCE message.

   For the complete procedure of this, see Section 3.6?? in [1].

4.9 Maintaining Peer List and Monitoring Peer Status

   An ENRP server MUST keep an internal record on the status of each of
   its known peers. This record is referred to as the server's "peer
   list"

4.9.1 Discovering New Peer

   If a message of any type is received from a previously unknown peer,
   the ENRP server MUST consider this peer a new peer in the operation
   scope and add it to the peer list.

   The ENRP server MUST send a PEER_PRESENCE message with the
   Reply-required flag set to '1' to the source address found in the
   arrived message. This will force the new peer to reply with its own
   PEER_PRESENCE containing its full server information (see Section
   3.1).

   [editor's note: should we ask for a peer list from the new peer?
   this may help mending two splitted networks.]

4.9.2 Server Sending Heartbeat

   Every PEER-HEARTBEAT-CYCLE seconds, an ENRP server MUST announce its
   continued presence to all its peer with a PEER_PRESENCE message. In
   the PEER_PRESENCE message, the ENRP server MUST set the
   'Replay_required' flag to '0', indicating that no response is
   required.

   The arrival of this periodic PEER_PRESENCE message will cause all its
   peers to update their internal variable "Peer-last-heared" for the
   sending server (see Section 4.9.3 for more details).

4.9.3 Detecting Peer Server Failure

   An ENRP server MUST keep an interanl variable "Peer-last-heared" for
   each of its known peers and the value of this variable MUST be
   updated to the current local time everytime a message of any type
   (point-to-point or announcement) is received from the cooresponding
   peer.



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   If a peer has not been heard for more than MAX-TIME-LAST-HEARD
   seconds, the ENRP server MUST immediately send a point-to-point
   PEER_PRESENCE with 'Reply_request' flag set to '1' to that peer.

   If the send fails or the peer does not reply after
   MAX-TIME-NO-RESPONSE seconds, the ENRP server MUST consider the peer
   server dead and SHOULD initiate the takeover procedure defined in
   Section 4.10.

4.10 Taking-over a Failed Peer Server

   In the following descriptions, We call the ENRP server that detects
   the failed peer server and initiates the take-over the "initiating
   server" and the failed peer server the "target server."

4.10.1 Initiate Server Take-over Arbitration

   The initiating server SHOULD fisrt start a take-over arbitration
   process by announcing a PEER_INIT_TAKEOVER message to all its peer
   servers. See Section 4.1 on how annoucements are sent. In the
   message, the initiating server MUST fill in the Sender Server's ID
   and Target Server's ID.

   After announcing the PEER_INIT_TAKEOVER message, the initiating
   server SHOULD wait for a PEER_INIT_TAKEOVER_ACK message from _each_
   of its known peers, except of the target server. [editor's note: how
   long should it wait?]

   Each of the peer servers that receives the PEER_INIT_TAKEOVER message
   from the initiating server SHOULD take the following actions:

   1.  If the peer server finds that itself is the target server
       indicated in the PEER_INIT_TAKEOVER message, it MUST immediately
       announce a PEER_PRESENCE message to all its peer ENRP servers in
       an attempt to stop this take-over process. This indicates a false
       failure detection case by the initiating server.

   2.  If the peer server finds that itself has already started its own
       take-over arbitration process on the same target server, it MUST
       perform the following arbitration:

       A.  if the peer's server ID is smaller in value than the Sender
           Server's ID in the arrived PEER_INIT_TAKEOVER message, the
           peer server SHOULD immediately abort its own take-over
           attempt. Moreover, the peer SHOULD mark the target server as
           "not active" on its internal peer list so that its status
           will no longer be monitored by the peer, and reply the
           initiating server with a PEER_INIT_TAKEOVER_ACK message.



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       B.  Otherwise, the peer MUST ignore the PEER_INIT_TAKEOVER
           message and take no action.

   3.  If the peer finds that it is neither the target server nor is in
       its own take-over process, the peer SHOULD: a) mark the target
       server as "not active" on its internal peer list so that its
       status will no longer be monitored by this peer, and b) reply to
       the initiating server with a PEER_INIT_TAKEOVER_ACK message.

   Once the initiating server has received PEER_INIT_TAKEOVER_ACK
   message from _all_ of its currently known peers (except for the
   target server), it SHOULD consider that it has won the arbitration
   and SHOULD proceed to complete the take-over, following the steps
   described in Section 4.10.2.

   However, if it receives a PEER_PRESENCE from the target server at any
   point in the arbitration process, the initiating server SHOULD
   immediately abort the take-over process and mark the status of the
   target server as "active".

4.10.2 Take-over Target Peer Server

   The initiating ENRP server SHOULD first send, via an announcement, a
   PEER_TAKEOVER_SERVER message to inform all its active peers that the
   take-over is enforced. The target server's ID MUST be filled in the
   message. The initiating server SHOULD then remove the target server
   from its internal peer list.

   [editor's note: peers should remove the target server from their list
   upon receiving this message. Do we really need this message? we can
   consolidate this with the ownership_change msg.]

   Then it SHOULD examine its local copy of the namespace and claim
   ownership of each of the PEs originally owned by the target server,
   by following these steps:

   1.  mark itself as the home ENRP server of each of the PEs originally
       owned by the target server;

   2.  send a point-to-point ENDPOINT_KEEP_ALIVE message to each of the
       PEs. This will trigger the PE to adopt the initiating sever as
       its new home ENRP server;

   3.  after claiming the ownership of all the PEs originally owned by
       the target server, announce the ownership changes of all the
       affected PEs in a PEER_OWNERSHIP_CHANGE message to all the
       currently known peers. Note, if the list of affected PEs is long,
       the sender MAY announce the ownership changes in multiple



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       PEER_OWNERSHIP_CHANGE messages.

   When a peer receives the PEER_OWNERSHIP_CHANGE message from the
   initiating server, it SHOULD find each of the reported PEs in its
   local copy of the namespace and update the PE's home ENRP server to
   be the sender of the message (i.e., the initiating server).

4.11 Namespace Data Auditing and Re-synchronization

   Message losses or certain temporary breaks in network connectivity
   may result in data inconsistency in the local namespace copy of some
   of the ENRP servers in an operation scope. Therefore, each ENRP
   server in the operation scope SHOULD periodically verify that its
   local copy of namespace data is still in sync with that of its peers.

   This section defines the auditing and re-synchronization procedures
   for an ENRP server to maintain its namespace data consistency.

4.11.1 Auditing Prodecures

   [TBD]

4.11.2 Re-synchronization Prodecures

   Once an ENRP server determines that there is inconsistancy between
   its local namespace data and a peer's namespace data with regarding
   to the PEs owned by that peer, it SHOULD perform the following steps
   to re-synchronize the data:

   1.  The ENRP server SHOULD first "mark" every PE it knows about that
       is owned by the peer in its local namespace database;

   2.  The ENRP server SHOULD then send a PEER_NAME_TABLE_REQUEST
       message with W flag set to '1' to the peer to request a complete
       list of PEs owned by the peer;

   3.  Upon reception of the PEER_NAME_TABLE_REQUEST message with W flag
       set to '1', the peer server SHOULD immediately respond with a
       PEER_NAME_TABLE_RESPONSE message listing all PEs currently owned
       by the peer.

   4.  Upon reception of the PEER_NAME_TABLE_RESPONSE message, the ENRP
       server SHOULD transfer the PE entries carried in the message into
       its local namespace database. If an PE entry being transferred
       already exists in its local database, the ENRP server MUST
       replace the entry with the copy found in the message and remove
       the "mark" from the entry.




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   5.  After transferring all the PE entries from the received
       PEER_NAME_TABLE_RESPONSE message into its local database, the
       ENRP server SHOULD check whether there are still PE entries that
       remain "marked" in its local namespace. If so, the ENRP server
       SHOULD silently remove those "marked" entries.

   Note, similar to what is described in Section 4.2.3, the peer may
   reject the PEER_NAME_TABLE_REQUEST or use more than one
   PEER_NAME_TABLE_RESPONSE message to respond.

4.12 Handling Unrecognized Message or Unrecognized Parameter

   When an ENRP server receives an ENRP message with an unknown message
   type or a message of known type that contains an unknow parameter, it
   SHOULD handle the unknow message or the unknown parameter according
   to the unrecognized message and parameter handling rules defined in
   Sections 3 and 4 in [10].

   According to the rules, if an error report to the message sender is
   needed, the ENRP server that discovered the error SHOULD send back an
   ENRP_ERROR message with proper error cause code.






























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5. Variables and Time Constants

5.1 Variables

   Peer-last-heared - the local time that a peer server was last heard
      (via receiving either a multicast or point-to-point message from
      the peer).


5.2 Timer Constants

   MAX-TIME-SERVER-HUNT - the maximal number of attempts a sender will
      make to contact an ENRP server (Default=3 times).

   TIMEOUT-SERVER-HUNT - pre-set threshold for how long a sender will
      wait for a response from an ENRP server (Default=5 secends).

   PEER-HEARTBEAT-CYCLE - the period for an ENRP server to announce a
      heartheat message to all its known peers. (Default=30 secs.)

   SERVER-ANNOUNCE-CYCLE - the period for an ENRP server to announce a
      SERVER_ANNOUNCE message to all PEs and PUs. (Default=5 secs.)

   MAX-TIME-LAST-HEARD - pre-set threshold for how long an ENRP server
      will wait before considering a silent peer server potentially
      dead.  (Default=61 secs.)

   MAX-TIME-NO-RESPONSE - pre-set threshold for how long a message
      sender will wait for a response after sending out a message.
      (Default=5 secs.)

   MAX-BAD-PE-REPORT - the maximal number of unreachability reports on a
      PE that an ENRP server will allow before purging this PE from the
      namespace.  (Default=3)

















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6. Security Considerations

   Due to varying requirements and multiple use cases of Rserpool, we
   point out two basic security protocols, IPsec and TLS. We
   specifically do not discuss whether one security protocol would be
   preferred over the other.  This choice will be made by designers and
   network architects based on system requirements.

   For networks that demand IPsec security, implementations MUST support
   [9] which describes IPsec-SCTP. IPsec is two layers below RSerPool.
   Therefore, if IPsec is used for securing Rserpool, no changes or
   special considerations need to be made to Rserpool to secure the
   protocol.

   For networks that cannot or do not wish to use IPsec and prefer
   instead TLS, implementations MUST support TLS with SCTP as described
   in [8] or TLS over TCP as described in [6].  When using TLS/SCTP we
   must ensure that RSerPool does not use any features of SCTP that are
   not available to an TLS/SCTP user.  This is not a difficult technical
   problem, but simply a requirement. When describing an API of the
   RSerPool lower layer we have also to take into account the
   differences between TLS and SCTP. This is also not difficult, but it
   is in contrast to the IPsec solution which is transparently layered
   below Rserpool.

   Support for security is required for the ENRP server and the PEs.
   Security support for the Rserpool end user is optional.  Note that
   the end user implementation contains a piece of the Rserpool protocol
   -- namely ASAP -- whereby the pool handle is passed for name
   resolution to the ENRP server and IP address(es) are returned.

   The argument for optional end user security is as follows: If the
   user doesn't require security protection for example, against
   eavesdropping for the request for pool handle resolution and
   response, then they are free to make that choice.  However, if the
   end user does require security, they are guaranteed to get it due to
   the requirement for security support for the ENRP server. It is also
   possible for the ENRP server to reject an unsecured request from the
   user due to its security policy in the case that it requires
   enforcement of strong security.  But this will be determined by the
   security requirements of the individual network design.










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7. Acknowledgements

   The authors wish to thank John Loughney, Lyndon Ong, and many others
   for their invaluable comments.















































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Normative References

   [1]   Stewart, R., Xie, Q., Stillman, M. and M. Tuexen, "Aggregate
         Server Access Protocol (ASAP)", draft-ietf-rserpool-asap-05
         (work in progress), October 2002.

   [2]   Tuexen, M., Xie, Q., Stewart, R., Shore, M., Ong, L., Loughney,
         J. and M. Stillman, "Requirements for Reliable Server Pooling",
         RFC 3237, January 2002.

   [3]   Tuexen, M., Xie, Q., Stewart, R., Shore, M., Ong, L., Loughney,
         J. and M. Stillman, "Architecture for Reliable Server Pooling",
         draft-ietf-rserpool-arch-03 (work in progress), July 2002.

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

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

   [6]   Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC
         2246, January 1999.

   [7]   Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer,
         H., Taylor, T., Rytina, I., Kalla, M., Zhang, L. and V. Paxson,
         "Stream Control Transmission Protocol", RFC 2960, October 2000.

   [8]   Jungmaier, A., Rescorla, E. and M. Tuexen, "TLS over SCTP",
         draft-ietf-tsvwg-tls-over-sctp-00 (work in progress), November
         2001.

   [9]   Bellovin, S., Ioannidis, J., Keromytis, A. and R. Stewart, "On
         the Use of SCTP with IPsec", draft-ietf-ipsec-sctp-03 (work in
         progress), February 2002.

   [10]  Stewart, R. and Q. Xie, "Aggregate Server Access Protocol
         (ASAP) and Endpoint Name Resolution (ENRP) common parameters
         document", draft-ietf-rserpool-common-param-00 (work in
         progress), July 2002.












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Informative References

   [11]  Eastlake, D., Crocker, S. and J. Schiller, "Randomness
         Recommendations for Security", RFC 1750, December 1994.


Authors' Addresses

   Qiaobing Xie
   Motorola, Inc.
   1501 W. Shure Drive, 2-F9
   Arlington Heights, IL  60004
   US

   Phone: +1-847-632-3028
   EMail: qxie1@email.mot.com


   Randall R. Stewart
   Cisco
   24 Burning Bush Trail
   Crystal Lake, IL  60012
   US

   Phone: +1-815-477-2127
   EMail: rrs@cisco.com


   Maureen Stillman
   Nokia
   127 W. State Street
   Ithaca, NY  14850
   US

   Phone: +1 607 273 0724 62
   EMail: maureen.stillman@nokia.com















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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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Acknowledgement

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