CS601 Short Notes

Short Notes: · CS 601 Data Communication & Networking · TOPIC 124 – 125 · Chap….#...9 · Data link Layer + Nodes & 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

The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. 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.

Example of data link protocols are Ethernet for local area networks (multi-node), the Point-to-Point Protocol (PPP), HDLC and ADCCP for point-to-point (dual-node) connections. In the Internet Protocol Suite (TCP/IP), the data link layer functionality is contained within the link layer, the lowest layer of the descriptive model, which is assumed to be independent of physical infrastructure.

Nodes & Links:

As we study before that communication in data link layer is nod to node. We also know about data unit from one point to another point in Internet needs to pass through many networks like (LANs and WANs) 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.

Topic 126 - 127. Serves provided by Data link Layer:

Data link layer provides the following services:

•  framing
•  flow control
•  error control
•  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. Flow Control: Second Services flow control the transmission of frames from the source Host to the destination it actually needs some sort of control .Whenever your sender is transmitting data and your receiver is consuming the data we need to make sure some sort of control between sender and receiver. So that the speed of Data transmitting and the speed of data consuming they are same and data get not loss.

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.

Error Control: 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 two types of DLL

There are two types of DLL:

•  Point-to-point link
•  Broadcast link

Point -to-point link: A point-to-point link refers to a communications connection between two communication endpoints or nodes. An example is a telephone call, in which one telephone is connected with one other, and what is said by one caller can only be heard by the other.

The term is also used in computer networking and computer architecture to refer to a wire or other connection that links only two computers or circuits, as opposed to other