O'Reilly - Java Message Service

Java Message Service
that your memory requirements are growing (possibly the result of a memory leak), which
is a good start.
7.2 To Multicast or Not to Multicast
An increasing number of vendors are releasing products based on IP multicasting. To
understand the tradeoffs involved in these products, you need a basic understanding of
how the TCP/IP protocol family works, and how multicasting fits into the bigger picture. [2]
We won't discuss any particular JMS implementations, or suggest that one vendor might
be better than another; our goal is to give you the tools that you need to ask intelligent
questions, evaluate different products, and map out a deployment strategy.
[2] This is not the place for a comprehensive discussion of TCP/IP networking. If you want detailed
treatment of these protocols, see Internet Core Protocols, by Eric Hall (O'Reilly). If you're interested
in network programming in Java, see Java Network Programming, by Elliotte Rusty Harold
(O'Reilly).
7.2.1 TCP/IP
TCP/IP is the name for a family of protocols that includes TCP (Transmission Control
Protocol), UDP (User Datagram Protocol), and IP (Internet Protocol). The protocols are
layered: IP provides low-level services; both TCP and UDP sit "on top of " IP.
TCP is a reliable, connection-oriented protocol. A process wishing to establish
communication with one or more processes across a network creates a connection to each
of the other processes and sends and receives data using those connections. The network
software, rather than the application, is responsible for making sure that all the data
arrives, and that it arrives in the correct order. It takes care of acknowledging that data has
been received, automatically discards duplicate data, and performs many other services for
the application. If something happens with the connection, the process on either side of the
connection will know almost immediately that the connection has been permanently
broken. [3]
[3] If a connection is not sending or receiving any data, it could take a while before the owning
process is signaled about a problem, depending on the network settings.
Most high-level network protocols (and most JMS implementations) are built on top of
TCP, for obvious reasons: it's a lot easier to use a protocol that takes care of reliability for
you. However, reliability comes with a cost: a lot of work is involved in setting up and
tearing down connections, and additional overhead is required to acknowledge data that's
sent and received. Therefore, TCP is slower than its unreliable relative, UDP.
7.2.2 UDP
UDP (User Datagram Protocol) is an unreliable protocol: you send data to a destination,
but there's no guarantee that the data will arrive. If it doesn't arrive, you'll never find out;
furthermore, the process receiving the data will never know that you sent anything.
This sounds like a bad basis for reliable software, but it really only means that applications
using UDP have to take reliability into their own hands: they need to come up with their
own mechanism for verifying that data was received, and for retransmitting data that went
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