Specifications

University of Hertfordshire

The TCP/IP protocol suite comprises two protocols that correspond roughly to the OSI Transport

and Session Layers; these protocols are called the Transmission Control Protocol (TCP) and the

User Datagram Protocol (UDP).

4.3.1 Transmission Control Protocol (TCP)

The Transmission Control Protocol specifies the format of the data and acknowledgements that two

computers exchange to achieve a reliable transfer, as well as the procedures the computers use to

ensure that the data arrives correctly. It specifies how TCP software distinguishes among multiple

destinations on a given machine, and how communicating machines recover from errors like lost or

duplicated packets. The protocol also specifies how two computers initiate a TCP stream transfer

and how they agree when it is complete.

Because TCP depends on little about the underlying communication system, TCP can be used with a

variety of packet delivery systems. For examples, TCP can be implemented to the Internet, a high

speed fiber optic network or a Local Area Network (LAN).

TCP uses the underlying Internet Protocol (IP) to transport a message from one machine to another.

4.3.2 User Datagram Protocol (UDP)

In TCP/IP environment, application programs use UDP to send datagrams to other application

programs. UDP use protocol ports to distinguish different multiple programs executing on a single

machine. In addition, each UDP message contains both a destination port number and a source port

number, which are used to distinguish the correct receiver and for the receiver to send a reply.

Like TCP, UDP uses the underlying Internet Protocol to transport a message from one machine to

another, and provide unreliable, connectionless datagram delivery. It does not use

Acknowledgement (ACK) to make sure messages arrive, and it does not order the received

messages. That is mean the application program that using UDP to send datagrams have to accept

full responsibility for handling the problems of reliability, such as message loss, duplication, delay,

out-of-order delivery, and loss of connectivity. Figure 4.3 shows the conceptual organization.

(Comer, 2000)