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Packet Guide to Core Network Protocols by Bruce Hartpence

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Chapter 10. User Datagram Protocol

The User Datagram Protocol (UDP) is the “other” Transport Layer protocol. In other words, if a connection is not using the Transmission Control Protocol (TCP) at Layer 4, it is using UDP. Layer 4 transmissions are often described as being either connection-oriented or connectionless. TCP, described in Chapter 9, is connection-oriented. As we know, TCP keeps track of every single byte of information sent and has several mechanisms for dealing with varying network conditions. UDP is connectionless.

What does it mean to be connectionless? As we will see later in this chapter, UDP is a relatively simple protocol, especially when compared to TCP. The header is small with little variation between packets, which also means that not much can be done to control or manage the data stream. But UDP does have a particular place in the universe: it provides encapsulation for real-time and unmonitored data.

While TCP connections are tightly controlled with rules for responses and sequence numbers that are tracked, UDP connections are not. Thus, anytime a series of messages or datagrams are required to flow between endpoints but strict control is not wanted or needed, UDP is the protocol of choice. Some very good examples of this include Voice over IP (encapsulated in the Real-time Transport Protocol), gaming, and network monitoring vehicles such as the Simple Network Management Protocol (SNMP). For protocols such as SNMP, UDP-based encapsulation makes sense because ...

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