Computer Networks Summary

Layered Architecture

• Each layer has its responsibility


• It achieves the separation of concerns

Each layer does the following

1. It takes input from the layer above it


2. It communicates with the layer below it to process the input


3. After processing, it gives output back to the layer above it.

OSI Model(The Open Systems Interconnection Model)

• A conceptual model that enables data communication


• Consists of 7 layers: physical layer, data-link layer, network layer, transport layer, session layer, presentation layer, and application layer

TCP/IP Protocol Suite

• A set of protocols used on the Internet


• Maintained by IETF(Internet Engineering Task Force)


• Consists of 4 layers: data access layer, internet layer, transport layer, and application layer

Data-Link Layer(Layer 2)

• Responsible for point-to-point reliable data transfer within the same network


• HDLC(High-Level Data Link Control) is the most commonly used protocol on this layer

Key Features

• Error Recovery: error detection and correction


• Flow Control: the sender trasmits data at which the receiver can receive

Error Detection Techniques

• Parity bits


• CRC(Cyclic Redundancy Check)


• Checksum

Error Correction Techniques

• Hamming Code

Error Correction && Flow Control Techniques

• ARQ(Automatic Repeat Request)


• Stop-and-wait ARQ


• Go-back-N ARQ


• Selected Repeat ARQ

Flow Control

Key Features

Transport Layer(Layer 4)

• Responsible for end-to-end reliable data transfer across multiple networks


• TCP(Transport Control Protocol) and UDP(User Datagram Protocol) are most commonly used protocol on this layer

Key Features

• Error Recovery: Error detection and correction


• Flow Control: The sender trasmits data at which the receiver can receive


• Congestion Control: