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A Group Communication Protocol for CORBA

A Group Communication Protocol for CORBA

L.E.Moser,P.M.Melliar-Smith,R.Koch,K.Berket

Department of Electrical and Computer Engineering

University of California,Santa Barbara93106

Abstract

Group communication protocols are used in fault-tolerant

systems to maintain strong replica consistency.The Fault-

Tolerant Multicast Protocol(FTMP)described here is a

group communication protocol specifically designed for the

Common Object Request Broker Architecture(CORBA).

FTMP operates over IP Multicast,and consists of the

Reliable Multicast Protocol(RMP)that provides reliable

source-ordered message delivery,the Reliable Ordered

Multicast Protocol(ROMP)that provides reliable totally-

ordered message delivery,and the Processor Group Mem-

bership Protocol(PGMP)that provides processor group

membership services.

1Introduction

Fault tolerance and high availability can be provided for the

Common Object Request Broker Architecture(CORBA)

[18]by means of object replication,where the replicas of an

object form an object group.However,object replication is

of little value unless the states of the replicas of the objects

remain consistent when methods are invoked on the object

group and when faults occur.

Group communication protocols[14]can facilitate the

maintenance of strong replica consistency for CORBA

applications by multicasting request and reply messages

containing method invocations and responses,and by de-

livering the messages reliably in the same order to all of

the members of a group.Such protocols also maintain the

membership of the group.

In this paper we provide a concrete mapping of

CORBA’s Generalized Inter-ORB Protocol(GIOP)specifi-

cation onto the Fault-Tolerant Multicast Protocol(FTMP),

a multicast group communication protocol that provides

reliable totally-ordered message delivery and group mem-

bership services.