S-72.1120 Data Communications and Protocols – spring 2008
Case 1 : Transmission Errors
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Source port |
Destination port |
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Sequence number |
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Acknowledgement number |
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Header length |
Reserved |
U |
A |
P |
R |
S |
F |
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Window size |
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Checksum |
Urgent pointer |
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Options |
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Data
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Many kinds of errors may occur when data is transferred from one computer to another over some kind of a telecommunications network, e.g. the telephone network or some packet switched network. Besides, in a computer there may be several programs that use telecommunications services and they must not interfere with each others. A transport level communications protocol – say TCP – creates a transmission path between two communicating programs over the network level connection between the respective computers. The programs usually function on two separate computers but may be on the same computer, as well. The TCP (unlike UDP) creates a reliable connection between the programs, hiding mistakes due to unreliability of the transmission medium etc.
What kind of errors may occur? How does the TCP handle various kind of errors? Are there situations where the TCP does not help? How is the reliable transmission service used by an applications’ programmer in practice?