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Versions: (draft-xie-rserpool-asap) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 RFC 5352

Network Working Group                                       R. R. Stewart
INTERNET-DRAFT                                         Cisco Systems Inc.
                                                                   Q. Xie
                                                                 Motorola


expires in six months                                    November 19,2001


                Aggregate Server Access Protocol (ASAP)
                  <draft-ietf-rserpool-asap-01.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.

    The list of current Internet-Drafts can be accessed at
    http://www.ietf.org/ietf/1id-abstracts.txt

    The list of Internet-Draft Shadow Directories can be accessed at
    http://www.ietf.org/shadow.html.

Abstract

    Aggregate Server Access Protocol (ASAP) in conjunction with the
    Endpoint Name Resolution Protocol (ENRP) [ENRP] provides a high
    availability data transfer mechanism over IP networks. ASAP uses a
    name-based addressing model which isolates a logical communication
    endpoint from its IP address(es), thus effectively eliminating the
    binding between the communication endpoint and its physical IP
    address(es) which normally constitutes a single point of failure.

    In addition, ASAP defines each logical communication destination
    as a pool, providing full transparent support for server-pooling
    and load sharing. It also allows dynamic system scalability -
    members of a server pool can be added or removed at any time
    without interrupting the service.

    ASAP is designed to take full advantage of the network level
    redundancy provided by the Stream Transmission Control Protocol
    (SCTP) [SCTP].

    The high availability server pooling is gained by combining two
    protocols, namely ASAP and ENRP, in which ASAP provides the user
    interface for name to address translation, load sharing
    management, and fault management while ENRP defines the high
    availability name translation service.



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Table Of Contents

    1. Introduction...............................................3
       1.1 Definitions............................................3
       1.2 Organization of this document..........................5
       1.3 Scope of ASAP..........................................5
           1.3.1 Extent of the Namespace..........................5
    2. Conventions................................................5
    3. Message Definitions........................................5
       3.1 ASAP Parameter Formats.................................6
           3.1.1 IPv4 Address Parameter...........................7
           3.1.2 IPv6 Address Parameter ..........................7
           3.1.3 Pool Element Parameter...........................7
           3.1.4 Pool Handle Parameter............................8
           3.1.5 Authorization Parameter..........................8
       3.2 ASAP Message Formats...................................9
           3.2.1 REGISTRATION message.............................10
           3.2.2 DEREGISTRATION message...........................10
           3.2.3 REGISTRATION_RESPONSE message....................11
           3.2.4 NAME_RESOLUTION message..........................11
           3.2.5 NAME_RESOLUTION_RESPONSE message.................12
           3.2.6 NAME_UNKNOWN message.............................12
           3.2.7 ENDPOINT_KEEP_ALIVE message......................12
           3.2.8 ENDPOINT_UNREACHABLE message ....................12
           3.2.9 SERVER_HUNT message .............................13
           3.2.10 SERVER_HUNT_RESPONSE message....................13
    4. The ASAP Interfaces........................................13
       4.1 Registration.Request Primitive.........................13
       4.2 Deregistration.Request Primitive.......................14
       4.3 Cache.Populate.Request Primitive.......................14
       4.4 Cache.Purge.Request Primitive..........................14
       4.5 Data.Send.Request Primitive............................14
           4.5.1 Sending to a Pool Handle.........................15
           4.5.2 Pool Element Selection...........................16
                 4.5.2.1 Round Robin Policy.......................16
                 4.5.2.2 Least Used Policy........................17
                 4.5.2.3 Least Used with Degradation Policy.......17
                 4.5.2.4 Weighted Round Robin Policy..............17
           4.5.3 Sending to a Pool Element Handle.................17
           4.5.4 Send by Transport Address........................18
           4.5.5  Message Delivery Options........................18
       4.6 Data.Received Notification.............................19
       4.7 Error.Report Notification..............................20
       4.8 Examples...............................................20
           4.8.1 Send to a New Pool Handle........................20
           4.8.2 Send to a Cached Pool Handle.....................21
       4.9 Handle ASAP to ENRP Communication Failures.............22
           4.9.1 SCTP Send Failure................................22
           4.9.2 T1-ENRPrequest Timer Expiration..................22
           4.9.3 Handle ENDPOINT_KEEP_ALIVE Messages..............22
           4.9.4 Home ENRP Server Hunt............................23
    5. Variables, Timers, and Constants...........................23
       5.1 Timers.................................................23
       5.2 Thresholds.............................................23
    6. Security Considerations....................................24
    7. References.................................................24

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    8. Acknowledgements...........................................24
    9. Authors' Addresses.........................................24


1. Introduction

    Aggregate Server Access Protocol (ASAP) in conjunction with ENRP
    [ENRP] provides a high availability data transfer mechanism over IP
    networks. ASAP uses a name-based addressing model which isolates a
    logical communication endpoint from its IP address(es), thus
    effectively eliminating the binding between the communication
    endpoint and its physical IP address(es) which normally constitutes
    a single point of failure.

    When multiple receiver instances exist under the same name, a.k.a, a
    server pool, ASAP will select one Pool Element (PE), based on the
    current load sharing policy indicated by the server pool, and
    deliver the message to the selected PE.

    While delivering the message, ASAP monitors the reachability of the
    selected PE. If it is found unreachable, before notifying the sender
    of the failure, ASAP can automatically select another PE (if one
    exists) under that pool and attempt to deliver the message to that
    PE. In other words, ASAP is capable of transparent fail-over amongst
    instances of a server pool.

    ASAP uses the Endpoint Name Resolution Protocol (ENRP) to provide a high
    availability name space.  ASAP is responsible for the abstraction of
    the underlying transport technologies, load distribution management,
    fault management, as well as the presentation to the upper layer
    (i.e., the ASAP user) a unified primitive interface.

    When SCTP [RFC2960] is used as the transport layer protocol, ASAP can
    seamlessly incorporate the link-layer redundancy provided by the
    SCTP.

    This document defines the ASAP portion of the high availability server
    pool. ASAP depends on the services of a high availiablity name space
    a.k.a. ENRP.

1.1 Definitions

    This document uses the following terms:

    ASAP User:
         Either a PE or PU that uses ASAP.

    Operation scope:
         The part of the network visible to Pool Users by a specific
         instance of the reliable server pooling protocols.

    Server pool (or Pool):
         A collection of servers providing the same application
         functionality.

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    Pool handle (or pool name):
         A logical pointer to a pool. Each server pool will be
         identifiable in the operation scope of the system by a unique
         pool handle or "name".

    Pool Element (PE):
         A server entity having registered to a pool.

    Pool User (PU):
         A server Pool User.

    Pool Element handle (PE handle):
         A logical pointer to a particular Pool Element in a pool,

    ENRP server:
         A server program running on a host that manages the
         name space collectively with its peer ENRP servers and
         replies to the service requests from any Pool User or
         Pool Element.

    Home ENRP server:
        The ENRP server to which a Pool Element currently uses. A PU
        or PE normally chooses the ENRP server on their local host as
        the home ENRP server (if one exists). A PU or PE should only
        have one home ENRP server at any given time.

    ENRP client channel:
        The communication channel through which an ASAP User (either a
        PE or PU) requests ENRP namespace service. The client channel
        is usually defined by the transport address of the
        home server and a well known port number.

    ENRP server channel:
        Defined by a well known multicast IP address and a well
        known port number, or a well known list of transport
        addresses for a group of ENRP servers spanning an
        operational scope. All ENRP servers in an operation scope
        can communicate with one another through this channel.

    ENRP name domain:
        Defined by the combination of the ENRP client channel and the
        ENRP server channel in the operation scope.

    Network Byte Order:
        Most significant byte first, a.k.a Big Endian.

    Transport address:
        A Transport Address is traditionally defined by Network Layer
        address, Transport Layer protocol and Transport Layer port
        number.  In the case of SCTP running over IP, a transport
        address is defined by the combination of an IP address and an
        SCTP port number (where SCTP is the Transport protocol).


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1.2 Organization of this document

    Chapter 3 details ASAP message formats. In Chapter 4 we give the
    details of the ASAP interface, focusing on the communication
    primitives between the applications above ASAP and ASAP itself, and
    the communications primitives between ASAP and SCTP (or other
    transport layer). Also included in this discussion is relevant
    timers and configurable parameters as appropriate.  Chapter 5
    provides settable protocol values.


1.3 Scope of ASAP

    The requirements for high availability and scalability do not imply
    requirements on shared state and data. ASAP does not provide
    transaction failover.  If a host or application fails during
    processing of a transaction this transaction may be lost. Some
    services may provide a way to handle the failure, but this is not
    guaranteed. ASAP MAY provide hooks to assist an application in
    building a mechanism to share state but ASAP in itself will NOT
    share any state.


1.3.1 Extent of the Namespace

    The scope of the ASAP/ENRP is NOT Internet wide.  The namespace is
    neither hierarchical nor arbitrarily large like DNS.  We propose a
    flat peer-to-peer model.  Pools of servers will exist in different
    administrative domains. For example, suppose we want to use
    ASAP/ENRP.  First, the PU may use DNS to contact an ENRP server.
    Suppose a PU in North America wishes to contact the server pool in
    Japan instead of North America. The PU would use DNS to get the IP
    address of the Japanese server pool domain, that is, the address of
    an ENRP server(s) in Japan. From there the PU would query the
    ENRP server and then directly contact the PE(s) of interest.


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
   [RFC2119].


3. Message Definitions

   All messages as well as their fields described below shall be in
   Network Byte Order during transmission. For fields with a length
   bigger than 4 octets, a number in a pair of parentheses may follow
   the filed name to indicate the length of the field in number of
   octets.


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3.1 ASAP Parameter Formats

   ASAP parameters are defined in a Type-length-value (TLV) format as
   shown below.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Parameter Type       |       Parameter Length        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                                                               :
      :                       Parameter Value                         :
      :                                                               :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameter Type:  16 bits (unsigned integer)

      The Type field is a 16 bit identifier of the type of parameter.
      It takes a value of 0 to 65534.

      The value of 65535 is reserved for IETF-defined extensions. Values
      other than those defined in specific SCTP chunk description are
      reserved for use by IETF.

   Parameter Length:  16 bits (unsigned integer)

      The Parameter Length field contains the size of the parameter in
      bytes, including the Parameter Type, Parameter Length, and
      Parameter Value fields.  Thus, a parameter with a zero-length
      Parameter Value field would have a Length field of 4.  The
      Parameter Length does not include any padding bytes.

   Parameter Value: variable-length.

      The Parameter Value field contains the actual information to be
      transferred in the parameter.

   The total length of a parameter (including Type, Parameter Length and
   Value fields) MUST be a multiple of 4 bytes.  If the length of the
   parameter is not a multiple of 4 bytes, the sender pads the Parameter
   at the end (i.e., after the Parameter Value field) with all zero
   bytes.  The length of the padding is not included in the parameter
   length field.  A sender SHOULD NOT pad with more than 3 bytes.  The
   receiver MUST ignore the padding bytes.

   The Parameter Types are encoded such that the highest-order two bits
   specify the action that must be taken if the processing endpoint does
   not recognize the Parameter Type.

   00 - Stop processing this ASAP message and discard it, do not process
        any further parameters within it.

   01 - Stop processing this ASAP message and discard it, do not process

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        any further parameters within it, and report the unrecognized
        parameter in an 'Unrecognized Parameter Type' error.

   10 - Skip this parameter and continue processing.

   11 - Skip this parameter and continue processing but report the
        unrecognized parameter in an 'Unrecognized Parameter Type'
        error.

   In the following sections, we define the common parameter formats
   used in ASAP.


3.1.1 IPv4 Address Parameter

       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             |      Length = 8               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        IPv4 Address                           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   IPv4 Address: 32 bits (unsigned integer)

      Contains an IPv4 address of the sending endpoint.  It is binary
      encoded.


3.1.2 IPv6 Address Parameter

       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         |          Length = 20          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                         IPv6 Address                          |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   IPv6 Address: 128 bit (unsigned integer)

      Contains an IPv6 address of the sending endpoint.  It is binary
      encoded.


3.1.3 Pool Element Parameter

    This parameter is used in multiple ASAP message to represent an ASAP
    endpoint (i.e., a PE in a pool) and the associated information, such
    as its transport address(es), load control, and other operational

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    status information of the PE.

     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            |       Length=variable         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          SCTP Port            |    Number of IP addrs=k       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    :                        IP addr param #0                       :
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    :                        IP addr param #1                       :
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    :                                                               :
    :                             .....                             :
    :                                                               :
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    :                        IP addr param #k                       :
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |       Load Policy Type        |        Policy Value           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    Registration Life                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Each of the IP address parameters in a PE parameter can be either
    an IPv4 or IPv6 address parameter.


3.1.4 Pool Handle Parameter

     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            |       Length=variable         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    :                                                               :
    :                         Pool Handle                           :
    :                                                               :
    :                                                               :
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    This parameter holds a pool handle that is a NULL terminated ASCII
    string.


3.1.5 Authorization Parameter

     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            |       Length=variable         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    :                                                               :
    :                   Authorization Signature                     :

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    :                                                               :
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


    This parameter is used to hold an authorization signature. The
    signature is signed over the entire ASAP message and uses a
    preconfigured public/private key pair. The receiver of a message
    which includes this parameter can validate the message is
    from the sender by comparing the signature to one generated
    using the peers public key.


3.2 ASAP Message Formats

   The figure below illustrates the common format for all ASAP
   messages. Each message is formatted with a Message
   Type field, a message-specific Flag field, a Message Length field,
   and a Value field.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Message Type  |   Msg Flags   |        Message Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                                                               :
      :                        Message Value                          :
      :                                                               :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Message Type: 8 bits (unsigned integer)

      This field identifies the type of information contained in the
      Message Value field. It takes a value from 0 to 254.  The value
      of 255 is reserved for future use as an extension field.

      Message Types are encoded such that the highest-order two bits
      specify the action that must be taken if the message receiver
      does not recognize the Message Type.

      00 - Stop processing this message and discard it.

      01 - Stop processing this message and discard it, and report the
           unrecognized message in an 'Unrecognized Parameter Type'
           error.

      10 - reserved.

      11 - reserved.

   Message Flags: 8 bits

      The usage of these bits depends on the message type as given by
      the Message Type. Unless otherwise specified, they are set to
      zero on transmit and are ignored on receipt.

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   Message Length: 16 bits (unsigned integer)

      This value represents the size of the message in bytes including
      the Message Type, Message Flags, Message Length, and Message
      Value fields. Therefore, if the Message Value field is
      zero-length, the Length field will be set to 4.  The Message
      Length field does not count any padding.

   Message Value: variable length

      The Message Value field contains the actual information to be
      transferred in the message.  The usage and format of this field
      is dependent on the Message Type.

   The total length of a message (including Type, Length and Value
   fields) MUST be a multiple of 4 bytes.  If the length of the
   message is not a multiple of 4 bytes, the sender MUST pad the
   message with all zero bytes and this padding is not included in the
   message length field. The sender should never pad with more than 3
   bytes.  The receiver MUST ignore the padding bytes.


3.2.1 REGISTRATION 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 = 0x1  |0|0|0|0|0|0|0|0|        Message Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                          Pool Handle                          :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                     Pool Element Parameter                    :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                    Authorization Parameter (optional)         :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    The pool handle parameter field specifies the name to be registered.
    The PE Parameter field shall be filled in by the registrant
    endpoint to declare its transport addresses, server pooling
    policy and value, and other operation preferences.


3.2.2 DEREGISTRATION 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 = 0x2  |0|0|0|0|0|0|0|0|        Message Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                     Pool Handle Parameter                     :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                     Pool Element Parameter                    :

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      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                    Authorization Parameter  (optional)        :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      The PE sending the DEREGISTRATION shall fill in the pool handle
      and the PE Parameter in order to allow the ENRP server to verify
      the identity of the endpoint.


3.2.3 REGISTRATION_RESPONSE message

       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|0|0|        Message Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                     Pool Handle Parameter                     :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                     Pool Element Parameter                    :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Action code   |  Result code  |        (reserved)             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                    Authorization Parameter  (optional)        :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Action: (8 bits)

       The message that this results code is in response to:

       0x0 -- registration
       0x1 -- de-registration

    Result code: (8 bits)

       0x0 -- request granted
       0x1 -- request denied, unspecifed
       0x2 -- request denied, authorization failure
       0x3 -- request denied, invalid values

    Reserved: (16 bits)

       Ignored by the receiver and set to 0 by the sender.


3.2.4 NAME_RESOLUTION message

       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         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                     Pool Handle Parameter                     :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                    Authorization Parameter  (optional)        :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


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3.2.5 NAME_RESOLUTION_RESPONSE message

       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         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                     Pool Handle Parameter                     :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                    Pool Element Parameter 1                   :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                              ...                              :
      :                                                               :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                    Pool Element Parameter N                   :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                    Authorization Parameter  (optional)        :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


3.2.6 NAME_UNKNOWN message

       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|0|        Message Length         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                     Pool Handle Parameter                     :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                    Authorization Parameter  (optional)        :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


3.2.7 ENDPOINT_KEEP_ALIVE message


       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         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                     Pool Handle Parameter                     :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                    Authorization Parameter  (optional)        :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


3.2.8 ENDPOINT_UNREACHABLE message

       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         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                     Pool Handle Parameter                     :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                     Pool Element Parameter                    :

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      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                    Authorization Parameter (optional)         :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


3.2.9 SERVER_HUNT message

       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         :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                 Authorization Parameter (optional)            :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


3.2.10 SERVER_HUNT_RESPONSE message

       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         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                 Authorization Parameter (optional)            :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


4. The ASAP Interfaces

    This chapter will focus primarily on the primitives and
    notifications that form the interface between the ASAP-user and the
    ASAP and that between ASAP and its lower layer transport protocol
    (e.g., SCTP).

    Appropriate timers and recovery actions for failure detection and
    management are also discussed.

    An ASAP User passes primitives to the ASAP sub-layer to
    request certain actions. Upon the completion of those actions or
    upon the detection of certain events, the ASAP will notify the
    ASAP user.


4.1 Registration.Request Primitive

    Format: registration.request(poolHandle)

    where the poolHandle parameter contains a NULL terminated ASCII
    string of fixed length.

    The ASAP user invokes this primitive to add itself to the
    namespace, thus becoming a Pool Element of a pool. The ASAP user
    must register itself with the ENRP server by using this primitive
    before other ASAP users using the namespace can send message(s) to
    this ASAP user by pool handle or by PE handle (see Sections 4.5.1
    and 4.5.2).

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    In response to the registration primitive, the ASAP layer will send
    a REGISTRATION message to the home ENRP server (See section 3.2.1),
    and start a T2-registration timer.

    If the T2-registration timer expires before receiving a
    REGISTRATION_RESPONSE message, or a SEND.FAILURE notification is
    received from the SCTP layer, the ASAP layer shall start the Server
    Hunt procedure (see Section 4.9.4) in an attempt to get service
    from a different ENRP server.


4.2 Deregistration.Request Primitive

    Format: deregistration.request(poolHandle)

    The ASAP PE invokes this primitive to remove itself from the
    Server Pool.  This should be used as a part of the graceful shutdown
    process by the application.

    A DEREGISTRATION message will be sent by ASAP layer to the home ENRP
    server (see Section 3.2.2).


4.3 Cache.Populate.Request Primitive

    Format: cache.populate.request(destinationAddress, typeOfAddress)

    If the address type is a Pool handle and a local name
    translation cache exists, the ASAP layer should initiate a mapping
    information query by sending a NAME.RESOLUTION message on the Pool
    handle and update it local cache when the response comes back from
    the ENRP server.

    The destinationAddress field contains the address for which the
    cache needs to be populated. The typeOfAddress indicates the address
    type. Allowable types are Pool handle and Pool Element handle.  In
    the case of a Pool Element handle, the Pool handle is extracted from
    the Pool Element handle and used to form a NAME.RESOLUTION
    message (see Section 3.5).


4.4 Cache.Purge.Request Primitive

    Format: cache.purge.request(destinationAddress, typeOfAddress)

    If the address type is a Pool handle and local name
    translation cache exists, the ASAP layer should remove the mapping
    information on the Pool handle from its local cache.


4.5 Data.Send.Request Primitive

    Format: data.send.request(destinationAddress, typeOfAddress,

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                              message, sizeOfMessage, Options);

    This primitive requests ASAP to send a message to some specified
    Pool or Pool Element within the current Operational scope.

    Depending on the address type used for the send request, the
    sender's ASAP layer may perform address translation and Pool Element
    selection before sending the message out.

    The data.send.request primitive can take different forms of
    address types as described in the following sections.


4.5.1 Sending to a Pool Handle

    In this case the destinationAddress and typeOfAddress together
    indicates a pool handle.

    This is the simplest form of send.data.request primitive. By
    default, this directs ASAP to send the message to one of the Pool
    Elements in the specified pool.

    Before sending the message out to the pool, the sender's ASAP layer
    MUST first perform a pool handle to address translation. It may
    also need to perform Pool Element selection if multiple Pool
    Elements exist in the pool.

    If the sender's ASAP implementation does not support a local cache
    of the mapping information or if it does not have the mapping
    information on the pool in its local cache, it will transmit a
    NAME.RESOLUTION message to the current home ENRP server, and
    MUST hold the outbound message in queue while awaiting the response
    from the ENRP server (any further send request to this pool before
    the ENRP server responds SHOULD also be queued).

    Once the necessary mapping information arrives from the ENRP server,
    the sender's ASAP will:

    A) map the pool handle into a list of transport addresses of the
       destination PE(s),

    B) if multiple PEs exist in the pool, ASAP will choose
       one of them and transmit the message to it. In that case, the
       choice of the PE is made by ASAP layer of the sender based on
       the server pooling policy as discussed in section 4.5.2.

    C) if no transport association exists towards the destination PE,
       ASAP will establish a new transport association,

    NOTE: if the underlying SCTP implementation supports implicit
    association setup, this step is not needed (see [SCTP-API]).

    D) send out the queued message(s) to the SCTP association using the
       SEND primitive (see [RFC2960]), and,

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    E) if the local cache is implemented, append/update the local cache
       with the mapping information received in the ENRP server's
       response. Also, record the local SCTP association id, if a new
       association was created.

    For more on the ENRP server request procedures see [ENRP].

    Optionally, the ASAP layer of the sender may return a Pool Element
    handle of the selected PE to the application after sending the
    message. This PE handle can then be used for future transmissions to
    that same PE (see Section 4.5.3).

    Section 4.5.5 defines the fail-over procedures for cases where the
    selected PE is found unreachable.


4.5.2 Pool Element Selection

    Each time an ASAP user sends a message to a pool that contains
    more than one PE, the sender's ASAP layer must select one of
    the PEs in the pool as the receiver of the current
    message. The selection is done according to the current server
    pooling policy of the pool to which the message is sent.

    Note, no selection is needed if the ASAP_SEND_TOALL option is set
    (see Section 4.5.5).

    When joining a pool, along with its registration each
    PE specifies its preferred server pooling policy for receiving
    messages sent to this pool. But only the server pooling
    policy specified by the first PE joining the pool will
    become the current server pooling policy of the group.

    Moreover, together with the server pooling policy, each PE can
    also specify a Policy Value for itself at the registration time. The
    meaning of the policy value depends on the current server pooling
    policy of the group. A PE can also change its policy value
    whenever it desires, by re-registering itself with the namespace
    with a new policy value. Re-registration shall be done by simply
    sending another REGISTRATION to its home ENRP server.

    Note, if this first PE removes itself from the pool
    (e.g., by de-registration from the name space) and the remaining
    PEs have specified conflicting server pooling policies at
    their corresponding registrations, it is implementation specific to
    determine the new current server pooling policy.

    Four basic server pooling policies are defined in ASAP, namely the
    Round Robin, Least Used, Least Used Degrading and Weighted Round
    Robin. The following sections describes each of these policies.


4.5.2.1 Round Robin Policy

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    When a ASAP endpoint sends messages by Pool Handle and Round-Robin
    is the current policy of that Pool, the ASAP layer of the sender
    will select the receiver for each outbound message by round-Robining
    through all the registered PEs in that Pool, in an attempt to
    achieve an even distribution of outbound messages. Note that in a
    large server pool, the ENRP server may NOT send back all PEs
    to the ASAP client. In this case the client or PU will be
    performing a round robin policy on a subset of the entire Pool.


4.5.2.2 Least Used Policy

    When the destination Pool is under the Least Used server pooling
    policy, the ASAP layer of the message sender will select the PE that
    has the lowest policy value in the group as the receiver of the
    current message. If more than one PE from the group share the same
    lowest policy value, the selection will be done round Robin amongst
    those PEs.

    It is important to note that this policy means that the same PE will
    be always selected as the message receiver by the sender until the
    load control information of the pool is updated and changed in the
    local cache of the sender (see section ?).


4.5.2.3 Least Used with Degradation Policy

    This policy is the same as the Least Used policy with the exception
    that, each time the PE with the lowest policy value is selected from
    the Pool as the receiver of the current message, its policy value is
    incremented, and thus it may no longer be the lowest value in the
    Pool.

    This provides a degradation of the policy towards round Robin policy
    over time. As with the Least Used policy, every local cache update
    at the sender will bring the policy back to Least Used with
    Degradation.


4.5.2.4 Weighted Round Robin Policy

    [TBD]


4.5.3 Sending to a Pool Element Handle

    In this case the destinationAddress and typeOfAddress together
    indicate an ASAP Pool Element handle.

    This requests the ASAP layer to deliver the message to the PE
    identified by the Pool Element handle.

    The Pool Element handle should contain the poolHandle and a

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    destination transport address of the destination PE or the
    poolHandle and the SCTP 'association id'.

    The ASAP layer shall use the transport address to identify the
    SCTP association (or to setup a new one if necessary) and then
    invoke the SCTP SEND primitive to send the message to the PE.

    In addition, if a local translation cache is supported the
    endpoint will:

    A) send out the message to the transport address (or association
       id) designated by the PE handle.

    B) determine if the pool handle is in the local cache.

       If it is NOT, the endpoint will:
       i) ask the home ENRP server for name resolution on pool handle
          by sending a NAME.RESOLUTION message, and
       ii) use the response to update the local cache.

       If the pool handle is in the cache, the endpoint will only
       update the pool handle if the cache is stale. A stale cache is
       indicated by it being older than the protocol parameter
       'stale.cache.value'.

    Section 4.5.5? defines the fail-over procedures for cases where
    the PE pointed to by the Pool Element handle is found unreachable.

    Optionally, the ASAP layer may return the actual Pool Elment handle
    to which the message was sent (this may be different from the Pool
    Element handle specified when the primitive is invoked, due to the
    possibility of automatic fail-over).


4.5.4 Send by Transport Address

    In this case the destinationAddress and typeOfAddress together
    indicate an SCTP transport address.

    This directs the sender's ASAP layer to send the message out to the
    specified transport address.

    No endpoint fail-over is support when this form of send request is
    used. This form of send request effectively by-passes the ASAP
    layer.


4.5.5 Message Delivery Options

    The Options parameter passed in the various forms of the above
    data.send.request primitive gives directions to the sender's ASAP
    layer on special handling of the message delivery.

    The value of the Options parameter is generated by bit-wise

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    "OR"ing of the following pre-defined constants:

    ASAP_USE_DEFAULT: 0x0000

    Use default setting.

    ASAP_SEND_FAILOVER: 0x0001

    Enables PE fail-over on this message. In case where the first
    selected PE or the PE pointed to by the PE handle is found
    unreachable, this option allows the sender's ASAP layer to
    re-select an alternate PE from the same pool if one exists, and
    silently re-send the message to this newly selected endpoint.

    Endpoint unreachable is normally indicated by the SCTP
    COMMUNICATION.LOST or SEND.FAILURE notification.

    ASAP_SEND_NO_FAILOVER: 0x0002

    This option prohibits the sender's ASAP layer from re-sending the
    message to any alternate PE in case that the first selected PE or
    the PE pointed to by the PE handle is found unreachable. Instead,
    the sender's ASAP layer shall notify its upper layer about the
    unreachability with an Error.Report and return any unsent data.

    ASAP_SEND_TO_LAST: 0x0004

    This option requests the sender's ASAP layer to send the message to
    the same PE in the pool that the previous message destined to this
    pool was sent to.

    ASAP_SEND_TO_ALL: 0x0008

    When sending by Pool Handle, this option directs the sender's ASAP
    layer to send a copy of the message to all the PEs, except for the
    sender itself if the sender is a PE, in that pool.

    ASAP_SEND_TO_SELF: 0x0010.

    This option only applies in combination with ASAP_SEND_TO_ALL option.
    It permits the sender's ASAP layer also deliver a copy of the
    message to itself if the sender is a PE of the pool (i.e., loopback).

    ASAP_SCTP_UNORDER: 0x1000

    This option instructs the SCTP transport layer to send the current
    message using un-ordered delivery.


4.6 Data.Received Notification

    Format: data.received(messageReceived, sizeOfMessage, senderAddress,
                          typeOfAddress)


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    When a new user message is received, the ASAP layer of the receiver
    uses this notification to pass the message to its upper layer.

    Along with the message being passed, the ASAP layer of the receiver
    should also indicate to its upper layer the message sender's
    address. The sender's address can be in the form of either an SCTP
    association id, or a ASAP Pool Element handle.

    A) If the name translation local cache is implemented at the
    receiver's ASAP layer, a reverse mapping from the sender's IP
    address to the pool handle should be performed and if the mapping is
    successful, the sender's ASAP Pool Element handle should be
    constructed and passed in the senderAddress field.

    B) If there is no local cache or the reverse mapping is not
    successful, the SCTP association id should be passed in the
    senderAddress field.


4.7 Error.Report Notification

    Format: error.report(destinationAddress, typeOfAddress,
                         failedMessage, sizeOfMessage)

    An error.report should be generated to notify the ASAP user about
    failed message delivery as well as other abnormalities (see Section
    ? for details).

    The destinationAddress and typeOfAddress together indicates to whom
    the message was originally sent. The address type can be either a
    ASAP Pool Element handle, association id, or a transport address.

    The original message (or the first portion of it if the message is
    too big) and its size should be passed in the failedMessage and
    sizeOfMessage fields, respectively.


4.8 Examples


4.8.1 Send to a New Pool

    This example shows the event sequence when a Pool User sends the
    message "hello" to a pool which is not in the local
    translation cache (assuming local caching is supported).


    ENRP Server                       PU         new-name:PEx

      |                                |                 |
      |                              +---+               |
      |                              | 1 |               |
      |  2. NAME_RESOLUTION          +---+               |
      |<-------------------------------|                 |

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      |                              +---+               |
      |                              | 3 |               |
      |  4. NAME_RESOLUTION_REPONSE  +---+               |
      |------------------------------->|                 |
      |                              +---+               |
      |                              | 5 |               |
      |                              +---+  6. "hello1"   |
      |                                |---------------->|
      |                                |                 |


    1) The user at PU invokes:

       data.send.request("new-name", name-type, "hello1", 6, 0);

       The ASAP layer, in response, looks up the pool "new-name" in its
       local cache but fails to find it.

    2) The ASAP layer of PU queues the message, and sends a
       NAME_RESOLUTION request to the ENRP server asking for all
       information about pool "new-name".

    3) A T1-ENRPrequest timer is started while the ASAP layer is waiting
       for the response from the ENRP server.

    4) The ENRP Server responds to the query with a
       NAME_RESOLUTION_REPONSE message that contains all the information
       about pool "new-name".

    5) ASAP at PU cancels the T1-ENRPrequest timer and populate its
       local cache with information on pool "new-name".

    6) Based on the server pooling policy of pool "new-name", ASAP at
       PU selects the destination PE (PEx), sets up, if necessary, an
       SCTP association towards PEx (explicitly or implicitly), and
       send out the queued "hello1" user message.


4.8.2 Send to a Cached Pool Handle

    This shows the event sequence when the ASAP user PU sends
    another message to the pool "new-name" after what happened in
    Section 4.8.1.

    ENRP Server                       PU         new-name:PEx

      |                                |                 |
      |                              +---+               |
      |                              | 1 |               |
      |                              +---+  2. "hello2"   |
      |                                |---------------->|
      |                                |                 |

    1) The user at PU invokes:

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       data.send.request("new-name", name-type, "hello2", 6, 0);

       The ASAP layer, in response, looks up the pool "new-name" in its
       local cache and find the mapping information.

    2) Based on the server pooling policy of "new-name", ASAP at PU
       selects the PE (assume EPx is selected again), and sends out
       "hello2" message (assume the SCTP association is already set
       up).


4.9 Handle ASAP to ENRP Communication Failures

    Three types of failure may occur when the ASAP layer at an endpoint
    tries to communicate with the ENRP server:

    A) SCTP send failure
    B) T1-ENRPrequest timer expiration
    C) Registration failure

    Registration failure is discussed in section ?.


4.9.1 SCTP Send Failure

    This indicates that the SCTP layer failed to deliver a message sent
    to the ENRP server. In other words, the ENRP server is currently
    unreachable.

    In such a case, the ASAP layer should not re-send the failed
    message. Instead, it should discard the failed message and start the
    ENRP server hunt procedure as described in Section ?.


4.9.2 T1-ENRPrequest Timer Expiration

    When a T1-ENRPrequest timer expires, the ASAP should re-send the
    original request to the ENRP server and re-start the T1-ENRPrequest
    timer. In parallel, a SERVER_HUNT message should be issued per
    Section ?.

    This should be repeated up to 'max-request-retransmit' times. After
    that, an Error.Report notification should be generated to inform the
    ASAP user and the ENRP request message associated with the timer
    should be discarded.


4.9.3 Handle ENDPOINT_KEEP_ALIVE Messages

    At times, an ASAP endpoint may receive ENDPOINT_KEEP_ALIVE messages
    (see Section 3.2.7?) from the ENRP server. This message requires
    no response and should be silently discarded by the ASAP layer.


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4.9.4 Home ENRP Server Hunt

    At its startup, or when it fails to send to (i.e., timed-out on a
    service request) with its current home ENRP server, a PE or PU shall
    initiate the following home ENRP server hunt procedure to find a
    new home server.

    The PE or PU shall multicast a SERVER_HUNT message over the ENRP
    client channel, and shall repeat sending this message every
    <TIMEOUT-SERVER-HUNT> seconds until a SERVER_HUNT_RESPONSE message
    is received from an ENRP server.

    Then the PE or PU shall pick one of the ENRP servers that have
    responded as its new home ENRP server, and send all its subsequent
    the namespace service requests to this new home ENRP server.

    Upon the reception of the SERVER_HUNT message, an ENRP server shall
    always reply to the PE with a SERVER_HUNT_RESPONSE message.


5. Variables, Timers, and Constants

    The following is a summary of the variables, timers, and pre-set
    protocol constants used in ASAP.


5.1 Timers

    T1-ENRPrequest - A timer started when a request is sent by ASAP to
    the ENRP server (providing application information is
    queued). Normally set to 15 seconds.

    T2-registration - A timer started when sending a registration
    request to the home ENRP server, normally set to 30 seconds.

    T3-registration-reattempt - If the registration cycle does not
    complete, this timer is begun to restart the registration
    process. Normal value for this timer is 10 minutes.

    T4-reregistration - This timer is started after successful
    registration into the ASAP name space and is used to cause a
    re-registration at a periodic interval. This timer is normally set
    to 10 minutes.


5.2 Thresholds

    Timeout-registration - pre-set threshold; how long an PE
    will wait for the REGISTRATION_RESPONSE from its home ENRP server.

    Timeout-server-hunt - pre-set threshold; how long a PE will
    wait for the REGISTRATION_RESPONSE from its home ENRP server.


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    num-of-serverhunts - The current count of server hunt messages that
    have been transmitted.

    registration-count - The current count of attempted registrations.

    max-reg-attempt - The maximum number of registration attempts to be
    made before a server hunt is issued.

    max-request-retransmit - The maximum number of attempts to be made
    when requesting information from the local ENRP server before a
    server hunt is issued.


6. Security Considerations

   To be determined.


7. References

     [RFC2026]  Bradner, S., "The Internet Standards Process -- Revision
                3", BCP 9, RFC 2026, October 1996.

     [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
                Requirement Levels", BCP 14, RFC 2119, March 1997.

     [RFC2960]  R. Stewart, Q. Xie, K. Morneault, C. Sharp, H. Schwarzbauer,
                T. Taylor, I. Rytina, M. Kalla, L. Zhang, and, V. Paxson,
                "Stream Control Transmission Protocol," <RFC 2960>,
                October 2000.

     [ENRP] Q. Xie, R. R. Stewart "Endpoint Name Resolution Protocol",
            draft-ietf-rserpool-enrp-01.txt, work in progress.

     [SCTP-API] R. R. Stewart, Q. Xie, L Yarroll, J. Wood, K. Poon,
                K. Fujita "Sockets API Extensions for SCTP",
                draft-ietf-tsvwg-sctpsocket-01.txt, work in progress.


8. Acknowledgements

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


9.  Authors' Addresses

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

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

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   Qiaobing Xie
   Motorola, Inc.
   1501 W. Shure Drive, #2309
   Arlington Heights, IL 60004
   USA

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













































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