CS601 Final Term Short Notes by Amir

CS601 · Short Notes(Handouts) · Composed By Amir

These notes will cover all Final term topics. Including all concepts of PPT slides

Topics 124-127

Data link Layer , Nodes and Links

The Internet is a combination of networks glued together by connecting devices (routers or switches) If a packet is to travel from a host to another host, it needs to pass through these networks Data Link layer controls node-to-node communication

Data link layer:

The data link layer is the second layer of the seven-layer OSI model .This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer. The data link layer provides the functional and procedural means to transfer data between network entities and might provide the means to detect and possibly correct errors that may occur in the physical layer. Data link layer control Node-to-Node communication.

Nodes and Links:

Communication in data link layer is node to node. We also know about data unit from one point to another point in Internet needs to pass through many networks to reach another point. We refer to the two endpoints that are called hosts and the router as notes and the networks in between as links.

Services provided by Data link Layer

Data link layer provides the following services:

1. framing 2. flow control 3. error control 4. congestion control

Framing:

First and foremost function of data link layer is framing. Date link layer divides data packets into small frames. Framing is a primary service of data link layer.

In case of framing we gone talk about two processes encapsulation and de capsulation, both combined are call framing. We know that data travel in the form of packets. Data link layer encapsulate this Packets into multiple frames. Encapsulation means breakdown of a packet into multiple frames which is stream of bit for transmission. Data Link Layer is also add its own header to each off frame .When data receive data link layer de-capsulate these frames. It Takes multiple frames and combined it in form of packet.

Example of Encapsulation & De Capsulation:

Suppose you have to travel from one city to another, the first thing you will do is you will take taxi for railway station and get off here for the train, and get on the train and go to another city. After landing in another city, you will take the taxi again and reach your destination. In data communications, flow control is the process of managing the rate of data transmission between two nodes to prevent a fast sender from overwhelming a slow receiver. It provides a mechanism for the receiver to control the transmission speed, so that the receiving node is not overwhelmed with data from transmitting node.

Flow control is important because it is possible for a sending computer to transmit information at a faster rate than the destination computer can receive and process it. This can happen if the receiving computers have a heavy traffic load in comparison to the sending computer, or if the receiving computer has less processing power than the sending computer.

Data link layer is the layer where deploy some sort of error correction first of all detection and then error correction as well.

Congestion control is a method used for monitoring the process of regulating the total amount of data entering the network so as to keep traffic levels at an acceptable value. This is done in order to avoid the telecommunication network reaching.

Topic 128

Types of data link layer(DLL)

There are two types of DLL: