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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
                                                                   Q. Xie
                                                                 Motorola


expires in six months                                        June 01,2001


                Aggregate Server Access Protocol (ASAP)
                  <draft-ietf-rserpool-asap-00.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 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 the Endpoint Name Resolution Protocol (ENRP).
    ASAP provides the user interface for name to address translation,
    load sharing management, and fault management.  ENRP defines the
    high availability name translation service.


Table Of Contents


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    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 name space............................... 5
    2. Conventions................................................. 5
    3. Message Summary............................................. 5
     3.1 PE Parameter Definition................................... 6
     3.2 REGISTRATION message...................................... 6
     3.3 DEREGISTRATION message.................................... 7
     3.4 REGISTRATION_RESPONSE message............................. 7
     3.5 NAME_RESOLUTION message................................... 8
     3.6 NAME_RESOLUTION_RESPONSE message.......................... 8
     3.7 NAME_UNKNOWN message...................................... 9
     3.8 UPDATE_POLICY_VALUE message............................... 9
     3.9 ENDPOINT_KEEP_ALIVE message............................... 9
     3.10 ENDPOINT_UNREACHABLE message ............................10
     3.11 SERVER_HUNT message .....................................10
     3.12 SERVER_HUNT_RESPONSE message.............................11
    4. The ASAP Interfaces.........................................11
     4.1 Registration.Request Primitive............................11
     4.2 Deregistration.Request Primitive..........................12
     4.3 Cache.Populate.Request Primitive..........................12
     4.4 Cache.Purge.Request Primitive.............................12
     4.5 Data.Send.Request Primitive...............................12
     4.5.1 Sending to a Pool.......................................13
      4.5.2 Pool Element Selection.................................14
       4.5.2.1 Pool selection policy - Round Robin.................14
       4.5.2.2 Pool Selection Policy - Least Used Policy...........15
       4.5.2.3 Pool Selection Policy - Least Used with Degradation
               Policy..............................................15
       4.5.2.4 Pool Selection Policy - Weighted round robin........15
      4.5.3 Sending to a Pool Element Handle.......................15
      4.5.4 Send by Transport Address..............................16
      4.5.5 Options................................................16
     4.6 Data.Received Notification................................18
     4.7 Error.Report Notification.................................18
     4.8 SCTP primitives...........................................18
      4.8.1 SCTP SEND Primitive....................................18
      4.8.2 SCTP RECEIVE Primitive.................................19
      4.8.3 SCTP SET.PRIMARY Primitive.............................19
      4.8.4 SCTP DATA.ARRIVE Notification..........................19
      4.8.5 SCTP SEND.FAILURE Notification.........................19
      4.8.6 SCTP COMMUNICATION.LOST Notification...................20
      4.8.7 SCTP NETWORK.STATUS.CHANGE Notification................20
     4.9 Examples..................................................20
      4.9.1 Send to an Unknown Name................................20
      4.9.2 Send to a Cached Name..................................21
     4.10 Handle ASAP to ENRP Communication Failures...............22
      4.10.1 SCTP Send Failure.....................................22
      4.10.2 T1-ENRPrequest Timer Expiration.......................22
      4.10.3 Handle ENDPOINT_KEEP_ALIVE Messages...................22
    5.  Variables, Timer Values, and Thresholds....................23
     5.1 Timer values..............................................23

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     5.2 Thresholds................................................23
    6. References..................................................23
    7. Acknowledgements............................................24
    8.  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 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:

     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 (or endpoint 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
         belongs. Pool elements normally choose the ENRP server
         on their local host as the home ENRP server (if one exists).
         A Pool element shall only have one home ENRP server at
         any given time. Both the PE and the server shall
         keep track of this master/slave relationship between them.

    ENRP server takeover:
         The event that a remote ENRP server takes the ownership
         of all the Pool elements on a host and becomes their
         home server.

    Caretaker ENRP server:
        The ENRP server on a remote host which takes ownership
        of all PEs on a host because of the absence of an
        active local ENRP server.

    PU channel:
        The communication channel through which a ASAP Pool User
        requests for ENRP service. The PU 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 PU channel and the
        ENRP server channel in the operation scope.

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


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 name space

    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 I want to use
    ASAP/ENRP.  First, the PU will use DNS to contact an ENRP server.
    Suppose a PU in North America wish 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 Summary

    All messages as well as their fields described below MUST 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 PE Parameter Definition

    This parameter is used in multiple ASAP message to represent a PEP
    or endpoint and the associated information, such as its transport
    address(es), load control, and other operational status information
    of the PE.

    The parameter is defined to support PEs with up to 8 different IPv4
    transport addresses.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        IP address #0                          |
   +-------------------------------+-------------------------------+
   |                        IP address #1                          |
   +-------------------------------+-------------------------------+
   \                     \                      \                  \
   /                     /                      /                  /
   \                     \                      \                  \
   +-------------------------------+-------------------------------+
   |                        IP address #7                          |
   +-------------------------------+-------------------------------+
   |          SCTP Port            |         Padding               |
   +-------------------------------+-------------------------------+
   |  Load sharing policy type     |       Policy Value            |
   +---------------+---------------+---------------+---------------+

    The size of a PE Parameter is 40 octets.


3.2 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        ENRP endpoint message identifier #1 = 0x18038688       |
   +-------------------------------+-------------------------------+
   |        ENRP endpoint message identifier #2 = 0x77734683       |
   +-------------------------------+-------------------------------+
   |                       Type = 0x3                              |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                 pool handle (32)                              |
   |                                                               |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                 PE Parameter (40)                             |
   |                                                               |
   +-------------------------------+-------------------------------+

    The pool handle field specifies the name to be registered, that
    shall be composed of up to 32 characters. The PE Parameter field
    shall be filled in by the registrant endpoint to declare its

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    transport addresses, server pooling policy and value, and other
    operation preferences.


3.3 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        ENRP endpoint message identifier #1 = 0x18038688       |
   +-------------------------------+-------------------------------+
   |        ENRP endpoint message identifier #2 = 0x77734683       |
   +-------------------------------+-------------------------------+
   |                       Type = 0x4                              |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                 pool handle (32)                              |
   |                                                               |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                 PE Parameter (40)                             |
   |                                                               |
   +-------------------------------+-------------------------------+

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


3.4 REGISTRATION_RESPONSE 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        ENRP endpoint message identifier #1 = 0x18038688       |
   +-------------------------------+-------------------------------+
   |        ENRP endpoint message identifier #2 = 0x77734683       |
   +-------------------------------+-------------------------------+
   |                       Type = 0x5                              |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                 pool handle (32)                              |
   |                                                               |
   +-------------------------------+-------------------------------+
   |                     Result = (see below)                      |
   +-------------------------------+-------------------------------+
   |                   Requested action = (see below)              |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                 PE Parameter (40)                             |
   |                                                               |
   +-------------------------------+-------------------------------+

    In response to a REGISTRATION, the 'Requested action' field shall be

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    set to 0x0, and the 'Result' field shall take the following values:
     0x0 -- registration granted
     0x1 -- registration rejected

    In response to a DEREGISTRATION, the 'Requested action' field shall
    be set to 0x1, and the 'Result' field shall take the following
    values:

     0x2 -- de-registration granted
     0x3 -- de-registration rejected: endpoint not found
     0x4 -- de-registration rejected: other failures.

    PE Parameter shall be filled in for verification purposes.


3.5 NAME_RESOLUTION 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        ENRP endpoint message identifier #1 = 0x18038688       |
   +-------------------------------+-------------------------------+
   |        ENRP endpoint message identifier #2 = 0x77734683       |
   +-------------------------------+-------------------------------+
   |                       Type = 0x1                              |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                 requested name (32)                           |
   |                                                               |
   +-------------------------------+-------------------------------+


3.6 NAME_RESOLUTION_RESPONSE 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        ENRP endpoint message identifier #1 = 0x18038688       |
   +-------------------------------+-------------------------------+
   |        ENRP endpoint message identifier #2 = 0x77734683       |
   +-------------------------------+-------------------------------+
   |                       Type = 0x2                              |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                 pool handle (32)                              |
   |                                                               |
   +-------------------------------+-------------------------------+
   |                  number of entries = n (see below)            |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                 PE Parameter 1 (40)                           |
   |                                                               |
   +-------------------------------+-------------------------------+
   /                                                               /

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   \                                                               \
   /                                                               /
   +-------------------------------+-------------------------------+
   |                                                               |
   |                 PE Parameter n (40)                           |
   |                                                               |
   +-------------------------------+-------------------------------+


3.7 NAME_UNKNOWN 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        ENRP endpoint message identifier #1 = 0x18038688       |
   +-------------------------------+-------------------------------+
   |        ENRP endpoint message identifier #2 = 0x77734683       |
   +-------------------------------+-------------------------------+
   |                       Type = 0x0                              |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                 requested name (32)                           |
   |                                                               |
   +-------------------------------+-------------------------------+


3.8 UPDATE_POLICY_VALUE 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        ENRP endpoint message identifier #1 = 0x18038688       |
   +-------------------------------+-------------------------------+
   |        ENRP endpoint message identifier #2 = 0x77734683       |
   +-------------------------------+-------------------------------+
   |                       Type = 0x11                             |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                      pool handle (32)                         |
   |                                                               |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                      PE Parameter (40)                        |
   |                                                               |
   +-------------------------------+-------------------------------+
   |                        New policy value                       |
   +-------------------------------+-------------------------------+


3.9 ENDPOINT_KEEP_ALIVE 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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   |        ENRP endpoint message identifier #1 = 0x18038688       |
   +-------------------------------+-------------------------------+
   |        ENRP endpoint message identifier #2 = 0x77734683       |
   +-------------------------------+-------------------------------+
   |                       Type = 0x6                              |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                      pool handle (32)                         |
   |                                                               |
   +-------------------------------+-------------------------------+

3.10 ENDPOINT_UNREACHABLE 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        ENRP endpoint message identifier #1 = 0x18038688       |
   +-------------------------------+-------------------------------+
   |        ENRP endpoint message identifier #2 = 0x77734683       |
   +-------------------------------+-------------------------------+
   |                       Type = 0xa                              |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                      pool handle (32)                         |
   |                                                               |
   +-------------------------------+-------------------------------+
   |                     Endpoint IP address                       |
   +-------------------------------+-------------------------------+
   |      Endpoint's SCTP port     |         padding               |
   +-------------------------------+-------------------------------+
   |                Type of severity (see below)                   |
   +-------------------------------+-------------------------------+

    The 'pool handle' is not required to be filled in for this
    message, however the IP address and SCTP port number of the endpoint
    must be supplied in the message.

    'Type of severity' shall take one of the following values:

     0x0 --- NORMAL_REPORT: warning to the server.
     0x1 --- FINAL_REPORT: the specified endpoint must be removed by the
             server immediately.

3.11 SERVER_HUNT 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        ENRP endpoint message identifier #1 = 0x18038688       |
   +-------------------------------+-------------------------------+
   |        ENRP endpoint message identifier #2 = 0x77734683       |
   +-------------------------------+-------------------------------+
   |                       Type = 0xb                              |
   +-------------------------------+-------------------------------+

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   |                                                               |
   |                      pool handle (32)                         |
   |                                                               |
   +-------------------------------+-------------------------------+
   |                     criticality (see below)                   |
   +-------------------------------+-------------------------------+

    The 'criticality' field shall take one of the following values:

    0x1 --- LOW_CRITICALITY
    0x2 --- MED_CRITICALITY
    0x3 --- HIGH_CRITICALITY


3.12 SERVER_HUNT_RESPONSE 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        ENRP endpoint message identifier #1 = 0x18038688       |
   +-------------------------------+-------------------------------+
   |        ENRP endpoint message identifier #2 = 0x77734683       |
   +-------------------------------+-------------------------------+
   |                       Type = 0xc                              |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                      pool handle (32)                         |
   |                                                               |
   +-------------------------------+-------------------------------+


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 (PU OR PE) 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(endpointName)

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

    The ASAP user invokes this primitive to add itself to the name

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    space, thus becoming a Pool Element. The ASAP user must register its
    name with the ENRP server by using this primitive before other ASAP
    endpoints using the name space can send message(s) to this ASAP user
    by name or by Pool element handle (see Sections ? and ?).

    In response to the registration primitive, the ASAP layer will send
    a REGISTRATION message to the home ENRP server (See section ?),
    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 ?) in an attempt to get service
    from a remote ENRP server.


4.2 Deregistration.Request Primitive

    Format: deregistration.request()

    The ASAP user 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 ?).

4.3 Cache.Populate.Request Primitive

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

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

4.4 Cache.Purge.Request Primitive

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

    If the address type is a Pool handle (or name) 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(destinationAddress, typeOfAddress, 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

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    selection before sending the message out.

    The data.send primitive can take the following forms of address
    type.


4.5.1 Sending to a Pool

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

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

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

    If the sender's ASAP implementation does not support a local cache of
    the translation information or if it does not have the translation
    information on that Pool in its local cache, it will transmit
    a request for the name mapping information to the 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 name into a list of transport addresses of the
       destination PE(s),

    B) If multiple PEs exist in that 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 ?.

    C) if no association exists towards the destination, establish a new
       SCTP association,

    NOTE: if the underlying SCTP implementation supports implicit
    association setup, this step is not needed (see [RFC2960]).

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

    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].

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    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 handle can then be used for future transmissions to
    that PE (see Section ?).

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

4.5.2 Pool Element Selection

    Each time a 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 ?).

    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, see Section ? for details.

    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 Pool selection policy - Round Robin

    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 deamon 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.


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4.5.2.2 Pool Selection Policy - 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 Pool Selection Policy - 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 Pool Selection Policy - Weighted round robin

    [TBD]

4.5.3 Sending to a Pool Element Handle

    In this case the destinationAddress and typeOfAddress together
    indicates a 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 contains the name and the primary
    destination transport address of the destination PE.

    The ASAP layer shall use the 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.

    If local cache is supported and the mapping information for the Pool
    found in the pool element handle is not available in the local
    cache, the sender's ASAP layer SHOULD, after sending the message,
    also transmit a request for the Pool handle mapping information to
    the ENRP server. Once the necessary mapping information arrives from
    the ENRP server, the sender's ASAP will update its local cache with

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    the newly received mapping information for that Pool handle.

    Section ? 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
    indicates 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 mode of sending effectively by-passes the ASAP layer.


4.5.5 Options

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

    Options can be grouped as follows:

    - PE fail-over (allowed, or prohibited),
    - whether to send to one PE or to the whole Pool,
    - whether to send to the same PE last sent to within
      the Pool, and
    - options passed to the SCTP transport protocol.

    The complete list of Options is as follows:

    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 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 Communication Lost
    or Send Failure notification from SCTP.



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    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 to by the handle is found unreachable. Instead, the sender's
    ASAP layer shall notify its upper layer about the unreachability
    with an Error.Indication and 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 was
    sent to.

    ASAP_SEND_TOALL: 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_TOSELF: 0x0010.

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

    ASAP_SCTP_BUNDLE: 0x0100

    This option allows the local SCTP transport layer to bundle the
    outbound messages whenever possible into bigger datagrams before
    transmitting them onto the network.

    ASAP_SCTP_NO_BUNDLE: 0x0200

    This option disallows the local SCTP transport layer to bundle
    outbound messages.

    ASAP_SCTP_HB_ON: 0x0400

    This option instructs the local SCTP transport layer to turn on
    heartbeat on the SCTP association indicated by the
    destinationAddress parameter.

    ASAP_SCTP_HB_OFF: 0x0800

    This option instructs the local SCTP transport layer to turn off
    heartbeat on the SCTP association indicated by the
    destinationAddress parameter.

    ASAP_SCTP_UNORDER: 0x1000

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


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4.6 Data.Received Notification

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

    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 SCTP primitives

4.8.1 SCTP SEND Primitive

    Basic Format:

    SEND(association id, buffer address, byte count, options)
         -> result

    The outbound message will be held in the buffer when this primitive
    is invoked. The ASAP layer shall identify the SCTP association which
    connects to the intended destination and fill in the 'association

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    id'.

    The options field will hold the options destined to the SCTP
    transport layer (see ?).

    The returned 'result' can indicate whether there is any local error
    executing the primitive.


4.8.2 SCTP RECEIVE Primitive

    Basic Format:

    RECEIVE(association id, buffer address, buffer size) -> byte count

    This primitive reads the first user message out from the SCTP
    stack (if there is one available) and put it into the specified
    buffer. The size of the message read, in octets, will also be
    returned.


4.8.3 SCTP SET.PRIMARY Primitive

    Basic Format:

    SET.PRIMARY(association id, destination transport address) -> result

    This can be used to instructs SCTP to use the specified
    destination transport address as the new primary destination address
    for sending messages.


4.8.4 SCTP DATA.ARRIVE Notification

    SCTP layer invokes this notification when a user message is
    successfully received and ready for retrieval. This shall prompt the
    ASAP layer to invoke the RECEIVE primitive to get the data (see ?).

4.8.5 SCTP SEND.FAILURE Notification

    If a message can not be delivered to the specified association id,
    for any reason, SCTP will invoke this notification to notify ASAP.

    In response, the ASAP shall take the following steps:

    A) If the message was originally sent by Pool handle or Pool Element
       handle and with option ASAP_SEND_FAILOVER set, retransmit the
       message to an alternate PE of the same Pool if one exists in
       the Server Pool. The proper server pooling policy shall be followed
       if more than one alternates exist in the group.

    B) If no alternate exists or option ASAP_SEND_FAILOVER is not set
       when the message was originally sent, generate an Error.report to
       report the failure to the ASAP user.

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4.8.6 SCTP COMMUNICATION.LOST Notification

    When SCTP loses communication to an PE completely or detects that
    the PE has performed an abort or graceful shutdown operation, it
    invokes this notification to notify ASAP layer.

    When handling this notification ASAP shall report this event to its
    ENRP server via an ENDPOINT_UNREACHABLE message with the severity
    level set to NORMAL_REPORT (see ?).

    If local mapping cache is implemented, the ASAP layer should also
    mark the PE as unreachable in its local cache. And if all the PEs in
    that Pool are marked as unreachable, the ASAP layer should remove
    the Pool from its local cache.


4.8.7 SCTP NETWORK.STATUS.CHANGE Notification

    The SCTP sends this notification to the ASAP layer when the
    reachability status of a transport address of a specific SCTP
    association has changed.

    If the local mapping cache is supported, the ASAP layer, upon
    reception of this notification, should look up the information of
    this PE in its local cache and record the reachability change.

    If the address in question becomes unreachable and is the primary
    address of the association, the ASAP layer MAY also elect a new
    primary for this association by invoking the SET.PRIMARY primitive
    (Section ?).

    If the local cache is not support or the reverse look up does not
    succeed, ASAP takes no action.


4.9 Examples


4.9.1 Send to an Unknown Name

    This example shows the event sequence when the Pool user,
    Endpoint 1 (EP1) sends the message "hello world" to a name
    which is not in the local mapping cache (assuming local
    caching is supported).


    ENRP Server                            EP1         new-name:EP2

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

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        |<----------------------------------|                  |
        |                                 +---+                |
        |                                 | 3 |                |
        |  4. NAME_RESOLUTION_REPONSE     +---+                |
        |---------------------------------->|                  |
        |                                 +---+                |
        |                                 | 5 |                |
        |                                 +---+  6. "hello"    |
        |                                   |----------------->|
        |                                   |                  |


    1) The user at EP1 invokes:

       data.send("new-name", name-type, "hello", 5 0);

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

    2) The ASAP layer of EP1 queues the message, and sends a
       NAME_RESOLUTION request to the ENRP server asking for all
       information about "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 "new-name".

    5) ASAP at EP1 cancels the T1-ENRPrequest timer and populate its
       local cache with information on "new-name".

    6) Based on the server pooling policy of "new-name", ASAP at EP1
       selects the PE (EP2), sets up, if necessary, an SCTP
       association towards EP2 (explicitly or implicitly), and send out
       "hello" message.


4.9.2 Send to a Cached Name

    This shows the event sequence when the ASAP user at EP1 sends
    another message to the "new-name".


    ENRP Server                  EP1                    new-name:EP2
        |                         |                          |
        |                       +---+                        |
        |                       | 1 |                        |
        |                       +---+  2. "hello world 2"    |
        |                         |------------------------->|
        |                         |                          |



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    1) The user at EP1 invokes:

       data.request("new-name", name-type, "hello world 2", 13, 0);

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

    2) Based on the server pooling policy of "new-name", ASAP at EP1
       selects the PE (assume EP2 is selected again), and sends out
       "hello world 2" message (assume the SCTP association is already set
       up).


4.10 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 ?.


4.10.1 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 ?.


4.10.2 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.


4.10.3 Handle ENDPOINT_KEEP_ALIVE Messages

    At times, a ASAP endpoint may receive ENDPOINT_KEEP_ALIVE messages
    (see section 3.1.2.1?) from the ENRP server. This message requires
    no response and should be silently discarded by the ASAP

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    layer. However, each time when an ENDPOINT_KEEP_ALIVE is received,
    the receiver should update its home ENRP server to the sender of the
    latest Keep Alive message.


5.  Variables, Timer Values, and Thresholds

    The following is a summary of the variables, time values, and
    pre-set thresholds used in ASAP and ENRP protocol.


5.1 Timer values

    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 local 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 an endpoint will
    wait for the REGISTRATION_RESPONSE from its home ENRP server.

    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. References

     [RFC2026]  Bradner, S., "The Internet Standards Process -- Revision

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                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-00.txt, work in progress.


7. Acknowledgements

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

8.  Authors' Addresses

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

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


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

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

















Stewart, Xie                                                   [Page 24]


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