Protocol Description

This document provides a brief description of the current prototype of the Extensible Modeling and Simulation Framework [1] Overlay Multicast (XOM). The XOM is an overlay multicast protocol designed to support many-to-many multicast for real-time distributed visual simulations. The objective is to provide multicast service over a unicast network environment using UDP. From the multicast sender and receiver’s point of view, each XOM Relay (XOMR)looks like an IP layer multicast router. XOMR performs as a multicast “relay agent ” for any application located on the same subnet as an instance of the XOMR as indicated in Figure 1. For each subnet that participates in the multicast group communication, there must be a host running a XOMR on the subnet. The XOMR listens on a set of multicast addresses to the local LAN for each multicast message generated within its local subnet and forwards this traffic to the downstream XOMRs according to its multicast tree, by using unicast. Figure 2 presents the concept and indicates the concept of group aggregation efficiency gains by using the overlay multicast. The partner XOMR will then multicast the packet to the destination local LAN, and keep on forwarding the packet to other XOMRs if necessary