TRANSMISSION CONTROL PROTOCOL (TCP)

TCP provides a connection-oriented transport layer service. TCP does the following 

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(a) The sending TCP accepts a stream of characters from the sending application program.

(b) It creates packets, called segments, of appropriate size extracted from the stream.

(c) It sends them across the network.

(d) The receiving TCP receives segments and extracts data from them.

(e) It orders segments if they have arrived out of order.

(f) It delivers them as a stream of characters to the receiving application program.

    For delivery of segments, the sending and receiving TCPs make use of buffer memory. The sending TCP uses a sending buffer to store the data coming from the sending application program. The sending application program writes data to the buffer of the sending TCP. But, the sending TCP does not create a segment of data for each write operation issued from the sending application program. TCP can combine the result of several write operations into one segment to make transmission more speedy.


   The receiving TCP receives the segments and stores them in a receiving buffer. The receiving application program uses the read operation to read the data from the receiving buffer. It may not read all of the data contained in one segment in one operation. Since the rate of reading can be slower than the rate of receiving, the data is kept in the buffer until the receiving application will complete reading.


    TCP gives full-duplex service which means that data can flow in both directions at the same time. One TCP connection can carry data from application X to Y. At the same time, data from Y to X. It supports piggy backing as acknowledgments can be sent along with data.
  


Note -- TCP is a reliable transport protocol. It uses the acknowledgment mechanism to check the safe and sound arrival of data segments and places them in order before giving them to application layer.