Transport protocol for a high availability manager
The high availability manager network components can be built on either a channel framework, unicast or multicast transport protocol. Channel framework is the default protocol, but there are options and features available with multicast that might be a better match for your application server environment. Multicast emulation can be used with any of these protocols.
The following network protocol configurations can be used with WebSphere Application Server:
Channel framework
Channel framework is the default network protocol configuration for the high availability manager. It provides a common model for connection management, thread usage, channel management, and message access within WebSphere Application Server. It extends the concept of a networking protocol stack, or transport chain, to the WebSphere run time. Each transport chain consists of one or more types of channels, and each channel supports a different type of I/O protocol, such as TCP, DCS or HTTP. Network ports can be shared among all of the channels within a chain. The channel framework function automatically distributes a request arriving on that port to the correct I/O protocol channel for processing.
The transport chain configuration settings determine which I/O protocols are supported for that chain. Custom channels that support requirements unique to a particular customer or environment can also be added to a transport chain.
Unicast protocol
Unicast protocol is a direct method of sending and receiving messages. JVMs are discovered when a new application server attempts to open connections to application servers in the same core group that are already running. The use of TCP/IP makes this suitable for high speed WANs and LANs. This protocol uses less CPU and memory per connection than multicast protocol, and might be more appropriate for larger core groups.
Multicast protocol
Multicast protocol requires a tuned environment. Heartbeats must be used as the failure detection method with this protocol. In this environment the JVMs cannot be swapped or kept from running. A non responsive JVM is viewed as a failed unit and all work items are taken away from that application server and dispersed among other core group members. The network used by all of the members of the core group must be able to use multicast protocol.
Performance in terms of data rate is about the same for all three protocols. WAS usually performs the best if a channel framework model is used, because this model supports using multiple protocols at the same time. However if you are choosing between a unicast and a multicast protocol, the unicast protocol is usually better because the most common WAS scenario is low fan out or point-to-point messaging. Using the multicast protocol in a low fan out environment forces all the recipients to process the message, even though only a low number of application servers use the message.
See Also
Transport chains
High availability network components