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Windows 2000 Performance Guide by Odysseas Pentakalos, Mark Friedman

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Host-to-Host Connections

Layer 4 of the Internet Protocol suite provides host-to-host connection services. As the name implies, Layer 4 software runs on host computers exclusively. The Internet protocols provide two flavors of Layer 4 support: the lightweight User Datagram Protocol (UDP) and the more robust Transmission Control Protocol (TCP). TCP is the workhorse of the Internet, providing session management, error detection and recovery, and flow control. We review the facilities of UDP only briefly, concentrating instead on some of the key mechanisms in TCP that impact network performance. We will see that the way TCP works has a major impact on the response time and throughput of networked applications.

UDP

User Datagram Protocol (UDP) is a simple implementation of the Layer 4 host-to-host connection layer that provides an unreliable, connectionless service. UDP is a thin layer above IP that adds almost nothing to the services available in the underlying IP layer. For example, it performs no error recovery to speak of, nor does it introduce any additional performance considerations beyond those we have already discussed related to IP. Consequently, it is not necessary to devote much time and space to discussing UDP here.

UDP is used most appropriately by applications that communicate using simple messages that do not require reliable delivery. For instance, applications that perform their own error recovery may find that UDP provides a suitable set of host-to-host connection ...

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