Introduction to Transport-Layer Protocols

 

Transport-Layer Protocols

Introduction

A Transport-Layer Protocol defines the set of rules that govern how data is transferred between two application processes running on different hosts. It specifies how data is encapsulated, transmitted, received, acknowledged, and delivered between the sender and receiver.

In the previous section, we discussed various transport-layer services such as:

• Process-to-process communication
• Port addressing
• Multiplexing and demultiplexing
• Flow control
• Error control
• Congestion control
• Connection-oriented service
• Connectionless service

By combining these services in different ways, we can design different transport-layer protocols.

For example:

Protocol	Connection	Flow Control	Error Control	Congestion Control
Simple Protocol	No	No	No	No
Stop-and-Wait Protocol	No	Yes	No	No
Stop-and-Wait ARQ	No	Yes	Yes	No
Go-Back-N	Yes	Yes	Yes	No
Selective Repeat	Yes	Yes	Yes	No
TCP	Yes	Yes	Yes	Yes
UDP	No	No	No	No

We will learn these protocols from the simplest to the most complex, so that each new protocol builds upon the features of the previous one.

Note: For simplicity, these protocols are first explained as simplex (unidirectional) protocols, where data flows only from the sender to the receiver. Later, they can be extended to full-duplex (bidirectional) communication, where both sides can send and receive data simultaneously.