Transmission Control Protocol (TCP)


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Industrial Communications Handbook

By Mick Crabtree

Chapter 5: Transmission Control Protocol (TCP)



Internet Protocol (IP) is termed an ‘unreliable’ service in that when packets are forwarded to a host, there is no automatic mechanism for acknowledgement. Once sent, we do not know whether packages have arrived or if they are in the correct sequence.

Transmission Control Protocol (TCP) on the other hand, provides a ‘reliable’ host-to-host communication service. Encapsulated within the IP, it provides a common interface to the application layer. Whereas the IP deals only with packets, TCP enables two hosts to establish a connection and exchange streams of data. TCP also guarantees delivery of data and that packets will be delivered in the order in which they were sent. In addition, whilst IP plus Media Access Control (MAC) addressing schemes deliver data to the correct host, one of the most important attributes of TCP is that it delivers directly to the application process software on the relevant machine. This is performed through the use of port numbers that are associated with particular applications.