Multicast: An Overview
Universal Messaging's ability to provide 'ultra-low latency' messaging has been further developed with the introduction of multicast options in addition to unicast to distribute messages to client applications.
This section assumes the reader has some knowledge of IP Multicast.
Comparison of Unicast and Multicast
Universal Messaging delivers 'ultra-low latency' to a large number of connected clients by including IP Multicast functionality for the delivery of events between inter-connected realms within a Universal Messaging cluster.
With unicast, the server must physically write the message once for each destination client:
With multicast, a message is written to the network once where it is then routed to all connections in that multicast group:
Multicast has clear performance improvements in terms of scalability. Where the performance of unicast gradually degrades as the number of destinations increases, multicast performance does not as the server still only has to write a message once per destination.
Universal Messaging supports multicast for cluster communication. Universal Messaging will then transparently operate in a multicast delivery mode for clients on networks capable of supporting the multicast protocol or else continue to use unicast.
Multicast addresses packets using the User Datagram Protocol (UDP) as opposed to TCP which is used in unicast. UDP is a connectionless protocol and does therefore not guarantee delivery or packet ordering in way that TCP does. However Universal Messaging still provides these guarantees by implementing the required checks at the application layer. These checks happen completely transparently to the user and any packet retransmissions can be monitored using the nAdminAPI or the Enterprise Manager.
Universal Messaging Multicast Architecture
Each Universal Messaging interface that you configure on a Universal Messaging Realm binds to one or all of the available physical Network adapters present on the host machine. In order to successfully configure Multicast on a Universal Messaging Realm you must ensure that you know the IP addresses of each of these network adapters (including virtual addresses if running on a virtual host), and which physical network adapter and its address is capable of supporting IP Multicast. This information allows the correct network adapter to be selected and bound to by the Multicast configuration. Once this information is known, you then need to ensure that the physical network infrastructure including switches and routers can support Multicast. Once validated, the next step is to select an available Multicast address which can be used.
With this model, the client is able to seamlessly interact with the Universal Messaging server and begin consuming Multicast events with no changes to the Client application required.