Extending the UMIOP Specification for Reliable Multicast in CORBA ⋆ Alysson Neves Bessani 1 , Joni da Silva Fraga 1 , and Lau Cheuk Lung 2 1 DAS - Departamento de Automa¸ c˜ ao e Sistemas, UFSC - Universidade Federal de Santa Catarina, Florian´opolis - Santa Catarina - Brazil {neves, fraga}@das.ufsc.br 2 Graduate Program in Applied Computer Science, Pontifical Catholic University of Paran´a, Curitiba - Paran´a - Brazil lau@ppgia.pucpr.br Abstract. OMG has published an unreliable multicast specification for distributed applications developed in CORBA (UMIOP). This mecha- nism can be implemented based on IP Multicast, a best-effort proto- col, which provides no guarantees about the message delivery. However, many fault-tolerant or groupware applications demand more restrictive agreement and ordering guarantees (for instance, reliable multicast with FIFO, causal or total ordering) from the available support for group communication. OMG has not yet provided any specification for sup- porting those requirements. This paper presents an important contribu- tion towards this direction. We proposed the ReMIOP, an extension to the UMIOP/OMG protocol, for the conception of a reliable multicast mechanism in CORBA middleware. Performance measures comparing ReMIOP, UMIOP and UDP sockets for IP multicast communication are presented in order to evidence the costs for adding reliable and unreliable multicast in middleware level. 1 Introduction When CORBA architecture (Common Object Request Broker ) [20] was intro- duced by OMG (Object Management Group ), only point-to-point communica- tions (using static or dynamic invocation) was available through the ORB (Ob- ject Request Broker ). The messages that pass through this channel obey a proper transference syntax defined by the GIOP (General Inter-ORB Protocol ). This syntax makes the messages involved in the communications independent from ORBs implementations and the consequences of an heterogeneous environment. The mapping of GIOP over TCP/IP transport layer is made by IIOP (Internet Inter-ORB Protocol ) protocol. The IIOP and TCP/IP combination is a good so- lution for distributed objects communications in the client/server model, since it considers aspects like error control, FIFO ordering, etc. ⋆ This work is supported by CNPq (Brazilian National Research Council) through processes 401802/2003-5 and 481523/2004-9. R. Meersman and Z. Tari (Eds.): CoopIS/DOA/ODBASE 2005, LNCS 3760, pp. 662–679, 2005. c  Springer-Verlag Berlin Heidelberg 2005