Extending CORBA with specialised protocols for QoS provisioning

The CORBA layer in a distributed system hides the heterogeneity of the underlying computer network. The interactions of objects located at different computing systems are described in terms of IDL specifications and the ORB takes care of the actual transfer of messages along the wire. In fact, an object interaction is translated into the transfer of GIOP messages over TCP/IP networks (IIOP). The advantages in terms of interoperability and portability are obvious. Currently, OMG is in the process of standardising the Open Communication Interface (OCI). Through OCI, a protocol module can be plugged into any ORB and hence, the distributed application including the ORB can be put on top of any network without changing the application's code, thus implementing network transparency. Obviously, the QoS of distributed applications depends on the QoS of the underlying network protocols e.g., best effort versus guaranteed bandwidth. Through OCI we are able to use the network protocol that is needed to satisfy the QoS requirements of a specific distributed application. We propose to extend CORBA with specialised protocols for QoS provisioning using OCI. We have prototyped protocol plug-ins, including a plug-in that exploits IP Multicast. The IP Multicast plug-in can be used in situations where one client communicates with a group of replicated servers. We have used this mechanism to implement replication transparency in CORBA and have shown that the OCI interface can be used for QoS provisioning in CORBA. Based on our hands-on experience, we have also identified some shortcomings in the proposed OCI specification.