VTU Module - 4 | Transport Layer

18EC71 | COMPUTER NETWORKS | Module-4 VTU Notes

Transport Layer: Introduction and Services

The Transport Layer serves as a crucial element in the OSI (Open Systems Interconnection) model, positioned above the Network Layer and below the Session Layer. Its primary role is to facilitate reliable communication between devices across a network, ensuring the efficient and error-free transmission of data.

Transport Layer Services

The Transport Layer offers two fundamental services to the upper layers: connection-oriented and connectionless services. In a connection-oriented service, a virtual circuit is established between the sender and receiver before data transmission, ensuring a reliable and orderly delivery of information. On the other hand, connectionless services treat each data unit independently, without establishing a dedicated path in advance.

Connectionless and Connection-Oriented Protocols

Connectionless and connection-oriented protocols represent two distinct approaches to data transmission. Connectionless protocols, such as UDP (User Datagram Protocol), offer a faster and more lightweight communication method but lack guarantees of delivery and order. Connection-oriented protocols, exemplified by TCP (Transmission Control Protocol), establish a reliable connection, ensuring data integrity and sequence.

Transport Layer Protocols

Several protocols operate at the Transport Layer, each designed to address specific communication needs. Among these are:

1. Simple Protocol: A basic, uncomplicated protocol that serves as a foundation for more advanced communication methods.
2. Stop-and-Wait Protocol: An elementary protocol where the sender transmits a single data frame and waits for an acknowledgment from the receiver before sending the next frame. This method ensures sequential and reliable data transmission.
3. Go-Back-N Protocol: This protocol allows the sender to transmit multiple frames before waiting for acknowledgments. If an acknowledgment is not received, the sender resends all frames from the last successfully received acknowledgment.
4. Selective Repeat Protocol: Unlike Go-Back-N, the Selective Repeat Protocol permits the sender to retransmit only the frames that were not successfully acknowledged, resulting in more efficient data transmission.

Understanding the nuances of these Transport Layer protocols is essential for optimizing network communication, balancing the trade-offs between speed, reliability, and resource efficiency.