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


expires in six months                                    November 15,2000


                 Enpoint Name Resolution Protocol (enrp)
                  <draft-xie-rserpool-enrp-01.txt>

Status of This Memo

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC 2026. 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


Endpoint Name Resolution Protocol (ENRP) is designed to work in
conjunction with Aggregate Server Access Protocol (ASAP) [ASAP]. ENRP when
combined with ASAP provdes a high availablitity 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.

The high availablitity server pooling is gained by combining the two parts,
namely ASAP and the Endpoint Name Resolution Part (ENRP).  ASAP
provides the user interface for name to address translation, load
sharing management, and fault management.  ENRP defines the fault
tolerant name translation service.


Table Of Contents

<TBD>


1. Introduction

ENRP is designed to provide a fully distributed fault-tolerant
real-time translation service that maps a name to a set of transport
addresses pointing to a specific group of networked communication
endpoints registered under that name.  ENRP employs a client-server
model with which an ENRP server will respond to the name translation
service requests from endpoint clients on both the local host and
remote hosts.

This document defines  ENRP client-server interface and the
ENRP server functionalities, including the establishment and
management of a fully distributed fault-tolerant endpoint name space.

1.1 Motivation

In this section, we will discuss the motivation for developing
ASAP. Our discussion will be focused on the analysis of the
inadequateness of two existing technologies, namely CORBA and DNS,
in providing solutions to fault-tolerance design of IP distributed
applications.

1.1.1 CORBA and Its Limitations

Often referred to as a Distributed Processing Environment (DPE),
CORBA was mainly desinged to provide location transparency for
distributed applications. However, the following limitations may exist
when applying CORBA to the design of real time fault-tolerant system:

 1) CORBA is traditionally weak in fault tolerance. The recent
    development of a high availablitity version of CORBA by OMG is perhaps
    a step in the right direction towards fixing this
    weakness. Nevertheless, the maturity, implementablity, and
    real-time performance of the design is yet to be proven.

    [Editor's Note: the fault tolerance mechanism being developed by
     OMG for CORBA bears quite some similarities to ASAP.]

 2) CORBA's distribution model encourages an object-based view,
    i.e., each communication endpoint is normally an object. We
    consider this kind of granularity too fine to be efficient and
    effective for designing real-time fault-tolerant applications.

 3) CORBA in general has a large signature that makes the use of it a
    challenge in real-time environments. Small devices with limited
    memory and CPU resource (e.g., H323 or SIP terminals) will find
    CORBA hard to fit in.

 4) CORBA uses TCP as its transport (Note, some effort is currently
    underway to separate CORBA from its transport). This makes CORBA
    suffer from the same limitations of TCP in terms of real-time and
    fault-tolerance performance.

 5) CORBA has long lacked easily usable support for the asynchronous
    communication model, and this may be an issue in many
    applications. An apparently improved API for asynchronous
    communication has been added to the CORBA standards only recently,
    and many, if not most, CORBA implementations still do not support
    it. There is as yet insufficient user experience with it to make
    conclusions regarding this new feature's usability.


1.1.2 DNS and Its Limitations


Undoubtedly DNS is the best-known and proven IP namespace mechanism.
However, namespace function alone does NOT provide real time
fault-tolerance solution. Other mechanisms and procedures, such as
server process failure detection, back-up server control and
selection, fast fail-over/switch-over, load balancing, etc., also play
crucial roles. These functions are supported by ASAP but not by DNS
DNS provides a loose binding where as ASAP and ENRP are designed to
provide a tight binding.

As will be further elaborated later in this document, the fault
tolerant design for server pools is made up in two parts, namely ASAP
and ENRP, where ENRP defines a light-weight yet highly efficient
namespace mechanism optimized for building real time fault-tolerant
applications. Nevertheless, ASAP does not restrict itself to ENRP for
namespace services. In fact, it is not only feasible but also
desirable in the future to generalize ASAP design so that the ENRP can
provide a generic interface that is capable of inter-working with
different namespace, including DNS, at the ASAP implementor's choice.

In the following, we list some limitations of the current DNS
namespace capability when compared to that of ENRP:

 1) DNS name registration and translation services have been primarily
    optimized for host names. But we consider namespace services
    optimized for process names or endpoint names more appropriate and
    efficient for supporting real time server-level fault-tolerance
    applications.

 2) DNS is primarily passive. It provides a query/response database
    that allows one to find information, but does NOT provide
    monitoring of hosts or processes to assure consistency within
    its database.

 3) DNS has dynamic extensions but is not designed around the
    dynamic fast changing process address space that is typical to
    real time distributed applications.

It has also been suggested that ASAP be extended to work with DNS to
bridge multiple ASAP planes and provide an "inter-ASAP-Domain" bridging
function.


1.2 Definitions

This document uses the following terms:

Operation scope --- the part of the network visible by ENRP.

ASAP Endpoint --- a logical entity in the operation scope which
implements the ASAP stack and is capable of sending and receiving
messages.

ASAP Node --- a host machine in the network which contains one or
more ASAP endpoints.

ASAP Plane or ASAP operational domain --- A relam of tight binding
controlled by a set of one or more ENRP deamons. A process or application
entitiy registers its name within this "plane" and is peroidically
checked for sanity. Note that a plane does not imply geographical locality.


Endpoint name --- the registered tag of a ASAP endpoint, consisting of
a NULL terminated ASCII string of fixed length.

Named group --- a group of ASAP endpoints sharing the same endpoint
name in the name space.

Endpoint handle --- a logical pointer, consisting of a name and the
primary destination transport address to a particular endpoint in a
named group.

ENRP client --- a ASAP endpoint using ENRP to obtain name translation
and other related services. In this document, the term "ASAP endpoint" is
exchangeable with "ENRP client", unless otherwise stated.

ENRP maintenance client --- a ASAP endpoint that has the additional
capability of exchanging ENRP maintenance messages with an ENRP
server in order to perform certain maintenance functions.

ENRP server --- a server program running on a node that manages the
name space collectively with its peer ENRP servers and replies to the
service requests from any ENRP client.

Home ENRP server --- the ENRP server to which an endpoint currently
belongs. Endpoints normally choose the ENRP server on their local
host as the home ENRP server, if one exists.  An endpoint shall only
have one home ENRP server at any given time, and both the endpoint 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 ENRP endpoints on a node and becomes their home
server.

Caretaker ENRP server --- The ENRP server on a remote node which takes
ownership of all endpoints on the local node because of the absence of
an active local server.

ENRP client channel --- the communication channel through which a ASAP
endpoint requests for ENRP service. The ENRP 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. All ENRP servers in an operation scope
can communicate with one another through this channel. Endpoints are
also allowed to communicate on this channel occasionally.

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.


1.3 Protocol overview

At startup, each endpoint in a ASAP operational domain registers its
name to in name space. Here a name is defined as a NULL terminated
ASCII string of fixed length.

When sending a message, the sender addresses the receiver endpoint by
its name and passes the message to its ASAP layer. The ASAP layer, with
the help from the ENRP name space daemon server(s), translates the
name to a valid transport address (or a list of transport addresses if
the receiver is multi-homed) and sends the message to the receiving
endpoint.

The following diagram illustrates the components of ASAP and their
relationships.

                           Figure 1.


                          Data Sender          Data Receiver
              ENRP        (ASAP-user)            (ASAP-user)
             Server       +---------+           +---------+
                          |   ASAP  |<---//---->|   ASAP  |
            +------+      |------+  |           |------+  |
     <----->| ENRP |<---->| ENRP |  |           | ENRP |  |
 To peer    +------+      +---------+           +---------+
 ENRP server| SCTP |      |   SCTP  |           |   SCTP  |
            +------+      +---------+           +---------+
            |  IP  |      |    IP   |           |    IP   |
            +------+      +---------+           +---------+
               |_______________|_____________________|


Multiple endpoints can register themselves under the same name. In
that case they will be treated as a receiver pool, and ASAP, when
sending a message addressed to that name, will use a predefined
load-sharing policy to determine which endpoint(s) in the pool to
send (or address) the message.

ASAP design has a high emphasis on seamless support of "server
pooling", high availability, dynamic scalability, and
close-to-real-time name translation.

In particular, ASAP can be characterized by:

A) Seamless support of "server pooling" --- ASAP allows multiple
   servers to register under the same name. It also allows servers to
   be dynamically add to or removed from a server pool without any
   reconfiguration.

B) Support automatic receiver "fail-over" --- when the chosen message
   receiver fails, ASAP, with pre-stated permission from its upper
   layer, can automatically re-direct the message to an alternative
   server under the same name if one exists.

C) Transaction management by nickname or "association handle" --- this
   is to allow a continuous transaction or session consisting of
   multiple interactions be held between a client endpoint and and one
   particular server in a server pool.

   Note: For details on ASAP please see [ASAP].

D) Fully distributed name space --- For achieving a high degree of
   fault tolerance and operation efficiency, the ENRP daemons which
   provide name translation service and the name space data are
   distributed across the operational scope of the network.

   ENRP daemon servers can be added to or removed from the operation
   scope dynamically, without interrupting the current name translation
   service.

   For example, a node may be originally configured to operate without a
   local ENRP server. When the load condition changes, one can start a
   new ENRP server on that node to increase the operation capacity. The
   new ENRP server will automatically integrate itself with the existing
   ENRP server(s) in the scope.

   Similarly, when an ENRP server becomes unavailable for service (e.g.,
   being intentionally shutdown, or suffered failure), its ASAP clients
   will be automatically taken-over by a remote ENRP server and
   continuously have ENRP services provided.

E) Network failure detection and automatic recovery  --- In the case
   when a major network failure breaks the operation scope into
   isolated communication islands, the name translation service will
   survive and continue inside each island so long as there is one or
   more ENRP servers present in that island. Endpoints inside each
   island will still continue to be able to communicate with each other.
   Moreover, when the network recovers, the isolated ENRP servers will
   re-discover each other and re-integrate the name space back into
   its original form.

Figure 2. shows an example of distributed applications operating in a
scope that is connected by a pair of redundant networks.


                        Figure 2.

        Node 1                      Node 2
       +--------------+   ||       +--------------+
       |              |   ||   ||  |              |
       |  Apps1       |   |+===||==|              |
       |              |   ||   ||  |   Apps2      |
       |              |===+|   ||  |              |
       |        Apps2 |   ||   |+==|        Apps3 |
       |              |   ||   ||  |              |
       |              |========+|  |              |
       | (ENRP Svr)   |   ||   ||  | (ENRP Svr)   |
       +--------------+   ||   ||  +--------------+
                          ||   ||
        Node 3            ||   ||   Node 4
       +--------------+   ||   ||  +--------------+
       |              |   ||   ||  |              |
       |  Apps2       |   ||   ||  |              |
       |              |========+|  |    Apps3     |
       |              |   ||   ||  |              |
       |        Apps4 |   ||   ||  |              |
       |              |===+|   |+==| Apps1        |
       |              |   ||   ||  |              |
       | (ENRP Svr)   |   |+===||==|              |
       +--------------+   ||   ||  +--------------+
                          ||   ||
                    network1  network2


In this example, there are four nodes in the scope, as shown in Figure
2. On Node 1, Node 2, and Node 3, there is an ENRP server running. On
each of the nodes, there are also some applications running. Each
application has a registered name in the name space collectively
managed by the three ENRP servers. In the example, the registered
names are "Apps1", "Apps2", "Apps3", and "Apps4". Some of the
applications (Apps1, Apps2, and Apps3) are distributed as server
pools.

When sending messages to each other, the sender application simply
addresses the recipient by its registered name. The ASAP layer inside
the sender application will query its home ENRP server to obtain the
transport address(es) and load control information of the recipient
before sending the message out.

Also note in the example, there is no ENRP server on Node 4. But the
applications on Node 4 will be served by one of the ENRP servers on
other nodes.


1.4 Organization of this document

Chapter 2 we give the details of the ENRP interface. ENRP defines the
messaging structure and relevant rules for communications between an
ASAP endpoint and an ENRP server. This chapter discusses how ENRP
maintains the name space in a high availablitity manner. Chapter 3
defines the message format and structures used by ENRP (in conjunction
with those used by ASAP). Chapter 4 provides settable protocol values.


1.5 Scope of ENRP

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 and 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.


2. The ENRP interface

This section discusses the messages and procedures for communicating
between the ASAP layer of a ASAP endpoint and an ENRP name space server,
as well as that between peer ENRP servers.


2.1 Functional Summary

In this section, we discuss the functions defined by ENRP. The
functions are divided into three groups, namely the basic ENRP
operations, fault management, and control and maintenance functions.

Most of the ENRP operations involve message exchanges between an ENRP
server and a ASAP endpoint, as well as message exchanges between the
ENRP server and its peers. Some of the ENRP message formats are
also found in [ASAP]


2.1.1 Basic ENRP Operations

2.1.1.1 Endpoint Registration

ENRP server <-> endpoint:

A ASAP endpoint shall send a REGISTRATION message, over the ENRP client
channel, to its home ENRP server, in order to register itself with the
name space.

In the REGISTRATION message, the endpoint shall indicate its name in
the form of a character string, network access information (e.g., a
list of valid transport addresses with which the endpoint
can be reached), and load control information.

The ENRP server shall handle the REGISTRATION message following the
rules listed below:

o If the name does not exist in the name space, the ENRP server shall
  create the name and add the new endpoint under that name.

o If the name already exists in the name space, the requesting
  endpoint shall be added under the same name and be made a member of
  the named group.

o If both the name and the requesting endpoint already exist in the
  name space, i.e., a case of duplicated registration, the ENRP
  server shall grant the request without taking any further actions.

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

In all the above cases, if the REGISTRATION request is granted, the
ENRP server shall assume the ownership of the requesting endpoint.

In response, the home ENRP server shall reply to the requesting
endpoint with a REGISTRATION_RESPONSE message, and shall indicate in
the message body whether the registration is granted or rejected.

ENRP server <-> peers:

If the registration request is not a duplicate and is granted, the
home ENRP server shall take the name space modification action
described in section 3.1.1.8??. Otherwise, no message shall be
exchanged with its peers.


2.1.1.2 Endpoint De-registration

ENRP server <-> endpoint:

A ASAP endpoint shall send a DEREGISTRATION message, over the ENRP
client channel, to its home ENRP server in order to remove itself from
the name space.

If the endpoint is the last one under that name in the name space the
home ENRP server shall remove the name from its space as well.

The ENRP server may reject the de-registration request due to reasons
such as invalid parameters, etc.

In response, the home ENRP server shall send a REGISTRATION_RESPONSE
message to the endpoint, and shall indicate in the message body
whether the request is granted or rejected.

It should be noted that de-registration does not stop the ASAP endpoint
from sending or receiving messages. It only means that other ASAP
endpoints will no longer be able to send message to that endpoint by
name.

ENRP server <-> peers:

Once the de-registration request is granted and the endpoint removed
from its local copy of the name space, the home ENRP server shall take
the name space modification action described in section 2.1.1.9.


2.1.1.3 Name Translation

ENRP server <-> endpoint:

An endpoint shall send a NAME_REQUEST messages to its home ENRP server
to get a name translation service. In the NAME_REQUEST message, the
endpoint shall include the name it wants to be translated.

If the name exits in the name space, the ENRP server shall send back a
NAME_INFORMATION message that shall carry all information of the ASAP
endpoint(s) currently registered under that name, including current
load control policy of the group, policy value of each endpoint in
the group, and a list of transport addresses for each endpoint in the
group with which the endpoint can be reached, etc.

If the name does not exist in the name space, the ENRP server shall
respond with a NAME_UNKNOWN message.

ENRP server <-> peers:

None.


2.1.1.4 Server Name Space Update

This includes a set of update operations used by an ENRP server to
inform its peer(s) the addition a new ASAP endpoint, removal of an
existing ASAP endpoint, change property of a named group, etc.


2.1.1.4.1 Addition of a New ASAP Endpoint

When a new ASAP endpoint is granted registration to the name space, the
home ENRP server uses this procedure to inform all its peers.

ENRP server <-> endpoint:

None:

ENRP server <-> peers:

An ENRP server shall multicast over the ENRP server channel a
PEER_NAME_UPDATE message with the appropriate flag set to indicate to its
peers about the addition of the new endpoint to the name space.

Upon the reception of this PEER_NAME_UPDATE message, each of the peer ENRP
servers shall take the following actions:

o If the name does not exist in its local copy of the name space, the
  peer ENRP server shall create the name and add the new endpoint
  under that name in its local name space copy, along with other
  attributes about the endpoint carried in the message.

o If the name already exists in the peer server's local copy of the
  name space, the new endpoint endpoint shall be added as a new member
  of the named group.

o If both the same ASAP endpoint already exists in the named group in
  the local copy of the name space of the peer, the peer ENRP server
  shall take no actions.

After adding the endpoint into its local copy of name space, the peer
ENRP server shall check if this endpoint is located on the same host
as the peer ENRP server itself does. If so, the peer ENRP server shall
assume the ownership of the endpoint, and take the ?? actions
described in section 2.1.1.12??.


2.1.1.4.2 Removal of a ASAP Endpoint

This procedure is used by an ENRP server to inform its peer(s) to
remove an existing ASAP endpoint, regardless of the ownership of the
endpoint.

ENRP server <-> endpoint:

None:

ENRP server <-> peers:

The ENRP server shall multicast over the ENRP server channel a
PEER_NAME_UPDATE message with the appropriate flag set to instruct its
peers to remove of the endpoint from their local copy of the name
space.

On the reception of this PEER_NAME_UPDATE message, each peer ENRP
server shall find and remove the ASAP endpoint from its local copy of
the name space regardless whether or not it has ownership on the
endpoint.


2.1.1.4.3 Removal of a ASAP Endpoint with no Ownership

This operation is used by an ENRP server to instruct its peers to
remove an existing ASAP endpoint which the peer does not have an
ownership on.

ENRP server <-> endpoint:

None:

ENRP server <-> peers:

An ENRP server shall multicast over the ENRP server channel a
PEER_NAME_UPDATE message with the appropriate flag set to instruct its
peers to remove the specified endpoint from its local copy of the name
space IF the peer does not have ownership on the endpoint.

On the reception of this PEER_NAME_UPDATE message, a peer ENRP server
shall find and remove the endpoint from its local copy of the name
space only if the peer server does not own this endpoint.


2.1.1.4.4 Update Endpoint Attributes

This operation is used by an ENRP server to inform its peers to update
the attributes of an existing ASAP endpoint.

ENRP server <-> endpoint:

None:

ENRP server <-> peers:

An ENRP server shall multicast over the ENRP server channel a
PEER_NAME_UPDATE message with the appropriate flag set to instruct
its peers to replace the attributes of an existing ASAP endpoint in its
local copy of the name space.

On the reception of this PEER_NAME_UPDATE message, a peer ENRP server
shall replace the attributes of the existing endpoint with the new
information carried in the message if the endpoint exists in its local
copy of the name space. If the specified endpoint is not found in its
local name space copy, the peer server shall add the endpoint
following the steps in Section 2.1.1.4.1??.


2.1.1.4.5 Claim Endpoint Ownership

This operation is used by an ENRP server to claim the ownership on a
specific endpoint and to inform its peers about its claim.

ENRP server <-> endpoint:

An ENRP server shall send an ENDPOINT_KEEP_ALIVE message to the
endpoint. This message will cause the endpoint to adopt this ENRP
server as its new home ENRP server (see Section 2.5.3).

ENRP server <-> peers:

An ENRP server shall multicast over the ENRP server channel a
PEER_NAME_UPDATE message with the appropriate flag set to inform its
peers that it has taken the ownership of the specified endpoint.

Upon the reception of this PEER_NAME_UPDATE message, a peer server
shall check whether it is the current owner of the endpoint. If so,
this peer server shall relinquish its ownership on that
endpoint. Otherwise, no action is needed.


2.1.1.4.6 Report Endpoint Failure

This operation is used by an ENRP server to warn its peers that it has
noticed a potentially unreachable endpoint that the server does not
have ownership on.

ENRP server <-> endpoint:

None:

ENRP server <-> peers:

An ENRP server shall multicast over the ENRP server channel a
PEER_NAME_UPDATE message with the appropriate flag set to indicate
that the specified ASAP endpoint is potentially unreachable.

On the reception of this message, each peer ENRP server shall check
whether it owns the specified endpoint. If it does, the peer server
shall increase the <endpoint-report-failures> counter of the specified
endpoint by 1. If the value of the <endpoint-report-failures> counter
has exceeded the protocol parameter Max-Endpoint-Report-Failures, the
peer server shall remove the endpoint from its local name space and
take actions described in Section 2.1.1.4.3. If the peer server does
not own the specified endpoint, it shall take no action.


2.1.1.5 Endpoint Change Policy Value

A ASAP endpoint can modify its policy value at any time. Depending on
the current number of members in the named group and the server pooling
policy, this operation allows the ASAP endpoint to control its share of
inbound messages received within the named group dynamically (also see
Section 2.1.5.1 for more on load control).

ENRP server <-> endpoint:

A ASAP endpoint shall send an UPDATE_POLICY_VALUE message over the
ENRP client channel to its home ENRP server in order to modify its
policy value. The new policy value shall be indicated in the
message.

Upon the reception of this UPDATE_POLICY_VALUE message, the home ENRP
server shall replace the policy value of that endpoint in its local
copy of the name space with the new value indicated in the message.

ENRP server <-> peers:

If the update on its local copy of the name space is successful, the
home ENRP server shall take the Server Name Space Update actions as
described in Section 2.1.1.4.4.


2.1.1.6 Server Down Load Name Space from a Peer

This operation allows an ENRP server to request and receive a copy of
a specific portion of the name space from one of its peer ENRP servers.
This is useful for a newly started ENRP server to initiate its local
copy of the name space, or for correcting name space inconsistency.

ENRP server <-> endpoint:

None.

ENRP server <-> peers:

An ENRP server shall first send a PEER_NAME_TABLE_REQUEST message
directly to one of its peers. In the message, it shall indicate which
portion of the name space is requested.

Upon the reception of this message, the peer server shall initiate a
download session in which the requested portion of the name space
shall be sent to the requesting ENRP server in one or more
PEER_NAME_TABLE_RESPONSE messages.

If the sending ENRP server determines that multiple
PEER_NAME_TABLE_RESPONSE messages are needed for the session, it shall
set the appropriate flag in each PEER_NAME_TABLE_RESPONSE message to
inform the receiving ENRP server whether or not the data in this
message is the last piece of the transfer.

Every time the requesting ENRP server receives a
PEER_NAME_TABLE_RESPONSE message, it shall transfer the data entries
carried in the message into its local name space database, and then
check whether or not the data in this message is the last piece to be
transfered. If more data transfer is indicated, the requesting ENRP
server shall send another PEER_NAME_TABLE_REQUEST message to the same
peer to prompt for the next piece.

When transferring the data entries from the PEER_NAME_TABLE_RESPONSE
message into its local name space database, the requesting ENRP server
shall follow the same procedures as described in section 2.1.1.4.1
when parsing through the endpoints carrying in the message one by one.


2.1.1.7 Server Monitor Peer Status

ENRP server <-> endpoint:

None:

ENRP server <-> peers:

An ENRP server shall keep a record on the status of each of its peers.

If a message of any type is received from a peer, the server shall
update that peers status as <active>.  If a message of any type is
received from a peer previously unknown to this server, i.e., a new
peer, the server shall create a record for the new peer and mark the
new peer as <active>.


2.1.1.8 Server Down Load Peer List

This operation allows an ENRP server to request from a peer server a
copy of its internal peer list. This is useful for a new ENRP server
to initiate its own peer list at startup.

ENRP server <-> endpoint:

None.

ENRP server <-> peers:

An ENRP server shall send a PEER_LIST_REQUEST message to a peer to
request a copy of its peer list.

Upon the reception of this message, the peer server shall reply with a
PEER_LIST_RESPONSE message and include in the message body a copy of its
internal peer list, if the peer itself is in operational state.

If the peer itself is in the process of startup, it shall response
with a PEER_LIST_RESPONSE message but set the appropriate flag to
indicate that it can not grant the PEER_LIST_REQUEST. In such a case,
the requesting ENRP server shall select another peer and repeat the
peer list request with the new peer at a later time.


2.1.1.9 Endpoint Initialization

At startup, a ASAP endpoint shall always assume the existence of a local
ENRP server on the local host and mark it as its home ENRP server, and
initiate the registration procedure described in 2.1.1.1??.


2.1.1.10 Server Initialization

At startup, before getting into service, an ENRP server (initiating
server) shall multicast a PEER_PRESENCE message with reply required
flag set over the ENRP server channel, in order to inform any other
active peers in the operation scope about its presence.

Upon the reception of this message, a peer shall send a PEER_PRESENCE
without reply required flag back to the initiating server, in order to
help the initiating server to build its peer list.

If no response to its PEER_PRESENCE message are received, the
initiating server shall assume that it is alone in the operation scope
and shall mark the initialization process as completed.

If there are responses to its PEER_PRESENCE message, the initiating
server shall then take the actions described in 2.1.1.8 to request a
peer list from one of the peers that have responded.

Upon the reception of the PEER_LIST_RESPONSE message from that peer,
the initiating server shall use the information carried in the message
to build a complete peer list, including both active and inactive
peers in the operation scope.

Then, the initiating server shall perform a name database download, as
described in 2.1.1.6, with each of the active peers on the peer list,
indicating that the portion of the name database to download shall
only include the endpoints owned by that peer.

Moreover, the initiating server shall also pick one of the active peer
and request to that peer for a download of the table of remote
endpoints.


2.1.2 Fault Management Operations

The following operations are used to detect and recover from various
system faults.


2.1.2.1 Detect and Report Unreachable Endpoint

Two mechanisms exist to detect and report an unreachable ASAP endpoint:

1) Home ENRP server periodic sanity check

An ENRP server shall send, in every <Endpoint-sanity-cycle> seconds,
an ENDPOINT_KEEP_ALIVE message to each of the endpoints it owns, and
shall keep the number of consecutive failed send attempts in the
counter <Endpoint-sanity-failures> of that endpoint.

If the value of <Endpoint-sanity-failures> of an endpoint exceeds the
pre-set threshold Max-endpoint-sanity-failures, the home ENRP server
shall remove the endpoint from its copy of the name database and take
the actions described in section 2.1.1.4.3 to inform its peers.

The handling of the ENDPOINT_KEEP_ALIVE message by the endpoint is
described in Section 2.5.3??.


2) Detection by peer endpoints

Whenever a ASAP endpoint finds a peer unreachable (e.g., via an SCTP
SEND.FAILURE Notification, see Section 2.2.5??), the endpoint shall
send an ENDPOINT_UNREACHABLE message over the ENRP client channel to
its home ENRP server.  The message shall contain one of the transport
addresses of the unreachable peer and have the severity flag set to
NORMAL_REPORT.

Upon the reception of this message, the home ENRP server shall first
check whether it owns the unreachable endpoint. If not, the server
shall take the actions described in section 2.1.1.4.6??.

Otherwise, the server shall increase the <Endpoint-report-failures>
counter of the unreachable endpoint by 1. If the value of the
<Endpoint-report-failures> counter has exceeded
Max-endpoint-report-failures, the server shall remove the endpoint
from its name database and take actions described in 2.1.1.4.3??.


2.1.2.2 ENRP Server Heartbeat

An ENRP server shall multicast, in every <Peer-heartbeat-cycle>
seconds, a PEER_PRESENCE message over the ENRP server channel to
inform its peers that it is still operational. In the PEER_PRESENCE
message, the sending ENRP server shall set the appropriate flag to
indicate that no reply is required.

>From time to time, an ENRP server may also send a point-to-point
PEER_PRESENCE message to a specific peer server, with the flag setting
in the message indicates that a reply is required. In such a case, the
peer server shall immediately respond to the sender with its own
point-to-point PEER_PRESENCE message, and shall indicate in the
message that no reply is required.


2.1.2.3 ENRP Server Hunt

An endpoint shall initiate the following home server hunt procedure if
it fails to send to, or times out on a service request with its
current home server.

In the home server hunt procedure, the endpoint 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. Each
time the 'Timeout-server-hunt' timer expires the criticality should
be raised (initially criticality should be set to LOW_CRITICALITY).

Then the endpoint shall pick one of the servers that have responded as
its new home server, and continue the service request with that
server.

Upon the reception of the SERVER_HUNT message, a server shall reply to
the endpoint with a SERVER_HUNT_RESPONSE message, unless:

1) its peer status information indicates that there is a caretaker
   server other than itself for the node where the endpoint is from,
   AND

2) the criticality flag in the SERVER_HUNT message is not
   HIGH_CRITICALITY.


2.1.2.4 ENRP Server Detect and Take-over Inactive Peer

An ENRP server shall keep track the time when the last message
(multicast or point-to-point) was received from each known peer.

If a peer has not been heard for more than Max-time-last-heard, the
ENRP server shall send a point-to-point PEER_PRESENCE with reply
request to that peer.

If the send fails or the peer does not reply after
Max-time-no-response seconds, the ENRP server shall initiate the
following server take-over procedures:

1) Initiate Server Take-over Arbitration

The ENRP server (the initiating server) shall initiate a take-over
arbitration on the inactive peer (the target server) by multicasting a
TAKEOVER_INITIATE message over the ENRP server channel. In the
message, the initiating server shall specify the identification of the
target server.

After multicasting the TAKEOVER_INITIATE message, the initiating
server shall wait for a TAKEOVER_INITIATE_RESPONSE message from each
of its active peers.

Upon the reception of this message, other peer servers shall take the
following actions accordingly:

o If the peer server finds that itself is the target server indicated
  in the TAKEOVER_INITIATE message, it shall immediately multicast a
  PEER_PRESENCE message over the ENRP server channel in an attempt of
  stopping the take-over process.

o If the peer server finds that itself has also initiated a take-over
  process on the same target server and its IP address is smaller in
  value than that of the sender of the TAKEOVER_INITIATE message, it
  shall abort its own take-over process.

o Peers other than the target peer and the peer that is taking-over
  shall mark the target server as <inactive> and mark the initiating
  server as the caretaker of the target server and reply to the
  initiating server with a TAKEOVER_INITIATE_RESPONSE message.

Once it has received TAKEOVER_INITIATE_RESPONSE message from all of
its active peers, the initiating server shall consider it won
the arbitration and shall then take the actions in 2) in order to
complete the take-over.

However, if it receives a PEER_PRESENCE from the target server at any
point of the take-over, the initiating server shall immediately abort
the take-over process and re-mark the target server as <active>.

2) Take-over the target peer server

An ENRP server shall multicast a TAKEOVER_PEER_SERVER message over the
ENRP server channel in order to inform all its peers about the
take-over. In the message, identification of the inactive peer server
targeted for the take-over shall be included.

The server shall mark the target server as <inactive> and mark itself
as the caretaker of the target server.

Then it shall assume ownership on each of the endpoints originally
owned by the target server.

The server shall also check whether there are any other inactive peers
which has designated the target server as their caretaker. The server
shall perform the above take-over procedure on each one of those
inactive peers as well.


2.1.2.5 Register Homeless Endpoints

When an ENRP server receives a REGISTRATION message from an endpoint
located on a remote node, it shall always accept and grant the
registration, unless its peer status information indicates that the
peer on that node is inactive and a caretaker other than itself exists
for that node. In that case, the server shall reject the registration
and take no further actions.

If the server has no record about the peer on that node, the
server shall grant the registration and then create a record about
that peer, mark it as inactive, and initiate a take-over procedure on
it, as described in 2.1.2.4??.


2.1.3 Maintenance Operations

The following operations are used by an ENRP maintenance client to
monitor the name space data and perform maintenances on ENRP servers
in an operation scope.


2.1.3.1 Forceful Removal of Endpoint

A maintenance endpoint shall send a ENDPOINT_UNREACHABLE message to an
ENRP server, in order to force the removal of another endpoint from
the name space.  The message shall contain one of the transport
addresses of the target endpoint and have the severity flag set to
FINAL_REPORT.

Upon the reception of this message, the ENRP server shall immediately
remove the target endpoint from its copy of the name database and take
actions described in Section 2.1.1.4.2.


2.1.3.2 Dump Home Endpoint List

A maintenance endpoint shall send a SERVER_DUMP message with type flag
set to HOME_LIST to a server, in order to require a copy of the
information on all the endpoints owned by that server.

Upon receiving this message, the server shall response with a
SERVER_DUMP_RESPONSE message with the type flag set to HOME_LIST to
the maintenance endpoint. In the message body, the server shall
include information on all the endpoints the server currently owns.


2.1.3.3 Dump Remote Endpoint List

A maintenance endpoint shall send a SERVER_DUMP message with type flag
set to REMOTE_LIST to a server, in order to require a copy of the
information on all the endpoints NOT owned by that server.

Upon receiving this message, the server shall response with a
SERVER_DUMP_RESPONSE message with the type flag set to REMOTE_LIST to
the maintenance endpoint. In the message body, the server shall
include information on all the endpoints the server currently does NOT
owns.


2.1.3.4 Dump Peer Server List

A maintenance endpoint shall send a SERVER_DUMP message with the type
flag set to PEER_SERVER_LIST to a server, in order to require a copy
of the peer list known to that server.

Upon receiving this message, the server shall response with a
SERVER_DUMP_RESPONSE message with the type flag set to
PEER_SERVER_LIST to the maintenance endpoint. In the message body, the
server shall include information on all the peers that server
currently knows.


3 Message Summary

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.


3.1 Endpoint Entry

This field is used to represent a ASAP endpoint and the associated
information, such as its transport address(es), load control, and
other operational status information.

The field is defined to support endpoint with up to 8 different
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               |
   +-------------------------------+-------------------------------+
   |  Server Pooling Policy        |       Policy Value            |
   +---------------+---------------+---------------+---------------+

The size of the endpoint entry is 40 octets.


3.2 PEER_NAME_TABLE_REQUEST 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 server message identifier #1 = 0x27047729         |
   +-------------------------------+-------------------------------+
   |        ENRP server message identifier #2 = 0x53829149         |
   +-------------------------------+-------------------------------+
   |                       Type = 0x102                            |
   +-------------------------------+-------------------------------+
   |                 sending server's IP address                   |
   +-------------------------------+-------------------------------+
   |       sender's SCTP port      |         padding               |
   +-------------------------------+-------------------------------+
   |                receiving server's IP address                  |
   +-------------------------------+-------------------------------+
   |      receiver's SCTP port     |         padding               |
   +-------------------------------+-------------------------------+
   |                      Table type = (see below)                 |
   +-------------------------------+-------------------------------+

Note, the receiver's IP address and port do not need to be filled in
if the message is being multicasted.

The requested table type shall take one of the following values:
 0x1 --- HOME_LIST: endpoints owned by the server.
 0x2 --- REMOTE_LIST: endpoint NOT owned by the server.


3.3 PEER_NAME_TABLE_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 server message identifier #1 = 0x27047729         |
   +-------------------------------+-------------------------------+
   |        ENRP server message identifier #2 = 0x53829149         |
   +-------------------------------+-------------------------------+
   |                       Type = 0x103                            |
   +-------------------------------+-------------------------------+
   |                     sender's IP address                       |
   +-------------------------------+-------------------------------+
   |      sender's SCTP port       |         padding               |
   +-------------------------------+-------------------------------+
   |                     receiver's IP address                     |
   +-------------------------------+-------------------------------+
   |      receiver's SCTP port     |         padding               |
   +-------------------------------+-------------------------------+
   |                    Table type = (see below)                   |
   +-------------------------------+-------------------------------+
   |                  More to send = (see below)                   |
   +-------------------------------+-------------------------------+
   |                     number of names = n                       |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                   Name entry 1 (see below)                    |
   |                                                               |
   +-------------------------------+-------------------------------+
   /                                                               /
   \                                                               \
   /                                                               /
   +-------------------------------+-------------------------------+
   |                                                               |
   |                   Name entry n (see below)                    |
   |                                                               |
   +-------------------------------+-------------------------------+


'Table type' shall take one of the following values:
 0x1 --- HOME_LIST: endpoints owned by the server.
 0x2 --- REMOTE_LIST: endpoint NOT owned by the server.

'More to send' flag shall be set to 0x1 if there are more name entries
to be sent for the requested table type. Otherwise, it shall be set to
0x0.

Each 'Name entry' represents an endpoint and shall consist of the
following:

   +-------------------------------+-------------------------------+
   |                                                               |
   |                    Endpoint name (32)                         |
   |                                                               |
   +-------------------------------+-------------------------------+
   |                   number of endpoints  = m                    |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                 endpoint entry 1 (40)                         |
   |                                                               |
   +-------------------------------+-------------------------------+
   /                                                               /
   \                                                               \
   /                                                               /
   +-------------------------------+-------------------------------+
   |                                                               |
   |                 endpoint entry m (40)                         |
   |                                                               |
   +-------------------------------+-------------------------------+


3.4 PEER_LIST_REQUEST 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 server message identifier #1 = 0x27047729         |
   +-------------------------------+-------------------------------+
   |        ENRP server message identifier #2 = 0x53829149         |
   +-------------------------------+-------------------------------+
   |                       Type = 0x10b                            |
   +-------------------------------+-------------------------------+
   |                      sender's IP address                      |
   +-------------------------------+-------------------------------+
   |      sender's SCTP port       |         padding               |
   +-------------------------------+-------------------------------+
   |                     receiver's IP address                     |
   +-------------------------------+-------------------------------+
   |      receiver's SCTP port     |         padding               |
   +-------------------------------+-------------------------------+

The receiver's IP address and port do not need to be filled in if
the message is being multicasted.


3.5 PEER_LIST_RESPONSE message

This message shall contain all the peer information of the sending server.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        ENRP server message identifier #1 = 0x27047729         |
   +-------------------------------+-------------------------------+
   |        ENRP server message identifier #2 = 0x53829149         |
   +-------------------------------+-------------------------------+
   |                       Type = 0x10c                            |
   +-------------------------------+-------------------------------+
   |                     sender's IP address                       |
   +-------------------------------+-------------------------------+
   |      senders SCTP port        |         padding               |
   +-------------------------------+-------------------------------+
   |                    receiver's IP address                      |
   +-------------------------------+-------------------------------+
   |      receiver's SCTP port     |         padding               |
   +-------------------------------+-------------------------------+
   |                  responseIndication (see below)               |
   +-------------------------------+-------------------------------+
   |                     number of peers = n                       |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                   Peer entry 1 (see below)                    |
   |                                                               |
   +-------------------------------+-------------------------------+
   /                                                               /
   \                                                               \
   /                                                               /
   +-------------------------------+-------------------------------+
   |                                                               |
   |                   Peer entry n (see below)                    |
   |                                                               |
   +-------------------------------+-------------------------------+

The 'responseIndication' flag shall be set to 0x2 to indicate a
rejection to the request, and no 'Peer entry' shall be attached if the
request is rejected.

Otherwise, the 'responseIndication' flag shall be set to 0x1 and n
'Peer entries' attached.

Each 'Peer entry' shall consist of the following fields:

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Peer's IP address                       |
   +-------------------------------+-------------------------------+
   |       Peer's SCTP port        |         padding               |
   +-------------------------------+-------------------------------+
   |                     Caretaker's IP address                    |
   +-------------------------------+-------------------------------+
   |     caretaker's SCTP port     |         padding               |
   +-------------------------------+-------------------------------+

The peer's IP address and port number serve as the identification of
that peer. If the peer is inactive, its caretaker's IP address and port
number shall be filled in. Otherwise, the caretaker IP and port fields
shall be set to zeros.


3.6 PEER_NAME_UPDATE message

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        ENRP server message identifier #1 = 0x27047729         |
   +-------------------------------+-------------------------------+
   |        ENRP server message identifier #2 = 0x53829149         |
   +-------------------------------+-------------------------------+
   |                       Type = 0x104                            |
   +-------------------------------+-------------------------------+
   |                     sender's IP address                       |
   +-------------------------------+-------------------------------+
   |      sender's SCTP port       |         padding               |
   +-------------------------------+-------------------------------+
   |                    receiver's IP address                      |
   +-------------------------------+-------------------------------+
   |      receiver's SCTP port     |         padding               |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                     Endpoint name (32)                        |
   |                                                               |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                     endpoint entry (40)                        |
   |                                                               |
   +-------------------------------+-------------------------------+
   |                 Update action (see below)                     |
   +-------------------------------+-------------------------------+

The receiver's IP address and port do not need to be filled in if
the message is being multicasted.

'Update action' shall take one of the following values:
  0x0 --- ADD_ENDPOINT: add a new endpoint, as specified by 'Endpoint
          name' and 'endpoint entry' fields, to the name space.
  0x1 --- DELETE_ENDPOINT: delete the named endpoint from the name
          database, if the receiving server owns the endpoint.
  0x2 --- REMOVE_ENDPOINT: remove the named endpoint from the name
          database, regardless who owns the endpoint.
  0x3 --- UPDATE_ENDPOINT: replace the endpoint's attributes with the
          new information carried in this message.
  0x4 --- ENDPOINT_FAILURE: warn the receiver that the named endpoint
          is potentially unreachable.
  0x5 --- CLAIM_ENDPOINT: inform the receiver that the sender has
          taken the ownership of the specified endpoint.


3.7 PEER_PRESENCE 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 server message identifier #1 = 0x27047729         |
   +-------------------------------+-------------------------------+
   |        ENRP server message identifier #2 = 0x53829149         |
   +-------------------------------+-------------------------------+
   |                       Type = 0x100                            |
   +-------------------------------+-------------------------------+
   |                      sender's IP address                      |
   +-------------------------------+-------------------------------+
   |      sender's SCTP port       |         padding               |
   +-------------------------------+-------------------------------+
   |                    receiver's IP address                      |
   +-------------------------------+-------------------------------+
   |      receiver's SCTP port     |         padding               |
   +-------------------------------+-------------------------------+
   |                       Reply required                          |
   +-------------------------------+-------------------------------+

The receiving server's IP address and port do not need to be filled in
if the message is being multicasted.

'Reply required' shall be set to 0x1 if response to this message is
required, otherwise set to 0x0.


3.8 TAKEOVER_INITIATE 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 server message identifier #1 = 0x27047729         |
   +-------------------------------+-------------------------------+
   |        ENRP server message identifier #2 = 0x53829149         |
   +-------------------------------+-------------------------------+
   |                       Type = 0x106                            |
   +-------------------------------+-------------------------------+
   |                 sending server's IP address                   |
   +-------------------------------+-------------------------------+
   |      sender's SCTP port       |         padding               |
   +-------------------------------+-------------------------------+
   |                receiving server's IP address                  |
   +-------------------------------+-------------------------------+
   |      receiver's SCTP port     |         padding               |
   +-------------------------------+-------------------------------+
   |                   Target server's IP address                  |
   +-------------------------------+-------------------------------+
   |    Target server's SCTP port  |         padding               |
   +-------------------------------+-------------------------------+

The receiving server's address and port do not need to be filled in if
the message is being multicasted.

'Target server's IP address and port number must be supplied.


3.9 TAKEOVER_INITIATE_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 server message identifier #1 = 0x27047729         |
   +-------------------------------+-------------------------------+
   |        ENRP server message identifier #2 = 0x53829149         |
   +-------------------------------+-------------------------------+
   |                       Type = 0x107                            |
   +-------------------------------+-------------------------------+
   |                 sending server's IP address                   |
   +-------------------------------+-------------------------------+
   |      sender's SCTP port       |         padding               |
   +-------------------------------+-------------------------------+
   |                receiving server's IP address                  |
   +-------------------------------+-------------------------------+
   |      receiver's SCTP port     |         padding               |
   +-------------------------------+-------------------------------+
   |                   Target server's IP address                  |
   +-------------------------------+-------------------------------+
   |    Target server's SCTP port  |         padding               |
   +-------------------------------+-------------------------------+

The receiving server's address and port do not need to be filled in if
the message is being multicasted.

'Target server's IP address and port number must be supplied.


3.10 TAKEOVER_PEER_SERVER 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 server message identifier #1 = 0x27047729         |
   +-------------------------------+-------------------------------+
   |        ENRP server message identifier #2 = 0x53829149         |
   +-------------------------------+-------------------------------+
   |                       Type = 0x108                            |
   +-------------------------------+-------------------------------+
   |                 sending server's IP address                   |
   +-------------------------------+-------------------------------+
   |      sender's SCTP port       |         padding               |
   +-------------------------------+-------------------------------+
   |                receiving server's IP address                  |
   +-------------------------------+-------------------------------+
   |      receiver's SCTP port     |         padding               |
   +-------------------------------+-------------------------------+
   |                   Target server's IP address                  |
   +-------------------------------+-------------------------------+
   |    Target server's SCTP port  |         padding               |
   +-------------------------------+-------------------------------+

The receiving server's address and port do not need to be filled in if
the message is being multicasted.

'Target server's IP address and port number must be supplied.


3.11 SERVER_DUMP 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 = 0x7                              |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                      Endpoint name (32)                       |
   |                                                               |
   +-------------------------------+-------------------------------+
   |                      Dump Type (see below)                    |
   +-------------------------------+-------------------------------+

The 'Dump Type' field shall take one of the following values:
  0x0 --- HOME_LIST: dump a copy of the home endpoint portion of the
          name database of the server (i.e., endpoints owned by the
          server).
  0x1 --- REMOTE_LIST: dump a copy of the remote endpoint portion of the
          name database of the server (i.e., endpoints NOT owned by the
          server).
  0x2 --- PEER_LIST: dump a copy of a list containing all the peers
          known to the server.


3.12 SERVER_DUMP_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 = 0x8                              |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                      Endpoint name (32)                       |
   |                                                               |
   +-------------------------------+-------------------------------+
   |                      Dump Type (see below)                    |
   +-------------------------------+-------------------------------+
   |                  Number of Entries = n (see below)            |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                   Dump entry 1 (see below)                    |
   |                                                               |
   +-------------------------------+-------------------------------+
   /                                                               /
   \                                                               \
   /                                                               /
   +-------------------------------+-------------------------------+
   |                                                               |
   |                   Dump entry n (see below)                    |
   |                                                               |
   +-------------------------------+-------------------------------+

The 'Dump Type' fields shall take the same values as defined in
Section 3.2.29??.

If 'Dump Type' is HOME_LIST, or REMOTE_LIST, the 'Number of Entries'
field shall be the number of endpoint entries carried in the message,
and each 'Dump entry' field shall contain an endpoint entry and shall
be defined as:

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                       Endpoint name (32)                      |
   |                                                               |
   +-------------------------------+-------------------------------+
   |                        number of endpoints = m                |
   +-------------------------------+-------------------------------+
   |                                                               |
   |                 endpoint entry 1 (40)                          |
   |                                                               |
   +-------------------------------+-------------------------------+
   /                                                               /
   \                                                               \
   /                                                               /
   +-------------------------------+-------------------------------+
   |                                                               |
   |                 endpoint entry m (40)                          |
   |                                                               |
   +-------------------------------+-------------------------------+

If 'Dump Type' is PEER_LIST, the 'Number of Entries' field shall be
the number of peer entries carried in the message, and each 'Dump
entry' field shall contain a peer entry and shall be defined as:

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Peer's IP address                       |
   +-------------------------------+-------------------------------+
   |       Peer's SCTP port        |         padding               |
   +-------------------------------+-------------------------------+
   |                     Caretaker's IP address                    |
   +-------------------------------+-------------------------------+
   |     caretaker's SCTP port      |         padding               |
   +-------------------------------+-------------------------------+

In a peer entry, the peer's IP address and port number serve as the
identification of that peer. If the peer is inactive, its caretaker's
IP address and port number shall be filled in. Otherwise, the
caretaker IP and port fields shall be zeroed out.


4.  Variables, Time Values, and Thresholds

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


4.1 Variables

Endpoint-report-failures --- per endpoint; keeps the number of
endpoint-unreachable reports concerning this endpoint.

Endpoint-sanity-failures --- per endpoint; keeps the number of failed
sanity message send attempts concerning this endpoint.

Peer-server-last-heard --- per peer server; a time stamp on when the
last message was received from this peer server.


4.2 Time values

Endpoint-sanity-cycle --- the period for a home ENRP server to start a
new round of endpoint sanity check.

Peer-heartbeat-cycle ---the period for an ENRP server to send out a
heart heat message.

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.


4.3 Thresholds

Max-endpoint-sanity-failures --- pre-set threshold for
Endpoint-sanity-failures.

Max-endpoint-report-failures --- pre-set threshold for
Endpoint-report-failures.

Max-time-last-heard --- pre-set threshold for Peer-last-heard.

Max-time-no-response --- pre-set threshold for a peer server to answer
a PEER_PRESENCE message with reply required.

Timeout-registration --- pre-set threshold; how long an endpoint 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.


5. References

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


[ASAP] Q. Xie, R. R. Stewart "Aggregate Server Access Protocol",
draft-stewart-rserpool-asap-00.txt, work in progress.


6. Acknowledgements

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

7.  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


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