Symptoms of Problems Occurring at the Transport Layer

When the transport layer has problems, you can observe the symptoms at the application layer. Session layer protocols and network applications rely on the correct operation and services that the transport layer provides. With transport layer problems, users notice a lack of connectivity to network resources or network applications that do not function. The main transport layer protocols of the TCP/IP suite are Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). (Real-Time Transport Protocol also has become a main player in recent years.) Familiarity with the TCP and UDP port numbers that application layer protocols use certainly facilitates problem isolation, especially when analyzing the IP access lists that are applied to router interfaces. Typical symptoms of a failure/problem at the transport layer can include one or more of the following:

■ Unreachable resources and connectivity problems are an issue, while the physical, data link, and network layers are functional.

■ The network is operating either consistently or intermittently less than the baseline level.

■ Applications generate error messages; they might report link or connectivity problems (as they perceive it).

■ Users complain that the network is slow or report of intermittent connectivity or erratic behavior.

■ Console messages report abnormal events; unexpected events are observed in system log messages.

■ Management system alarms indicate problems.

■ Partial or intermittent connectivity or erratic performance results from TCP windowing problems, long round-trip times, excess retransmissions, and so on.

Continue reading here: Symptoms of Problems Occurring at the Application Layer

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