Anurag RANA

• the role of the data link layer, • Three common error detection and correction methods. • two basic approaches to controlling access to the media, • common sources of error and its prevention, • Several commonly used data link protocols. INTRODUCTION The data link layer sits between the physical layer and the network layer. The data link layer accepts messages from the network layer and controls the hardware that actually transmits them. Both the sender and receiver have to agree on the rules or protocols that govern how their data link layers will communicate with each other. Introduction A data link protocol provides three functions: • Controls when computers transmit (media access control). • Detects and corrects transmission errors (error control). • Identifies the start and end of a message (message delineation). MEDIA ACCESS CONTROL Media access control (MAC) refers to the need to control when devices transmit. MAC becomes important when several computers share

Contents • 1 Introduction • 2 Error Control • 3 Flow Control • 4 MAC • 5 Problems • 6 Further reading Introduction Data link layer is layer 2 in OSI model. It is responsible for communications between adjacent network nodes.It handles the data moving in and out across the physical layer. It also provides a well defined service to the network layer. Data link layer is divided into two sub layers. The Media Access Control (MAC) and Logical Link Control (LLC). Data-Link layer ensures that an initial connection has been set up, divides output data into data frames, and handles the acknowledgements from a receiver that the data arrived successfully. It also ensures that incoming data has been received successfully by analyzing bit patterns at special places in the frames. In the following sections datalink layer's functions- Error control and Flow control has been discussed. After that MAC layer is explained. Multiple access protocols are explained in the MAC layer section.

I close my eyes and allow myself to connect to the Divine within. I affirm that within this inner presence are all the answers I need. I allow the truth contained within to saturate my being until I am filled with truth. I imagine myself going through my day stopping often to connect to the Divine wisdom within me. I see myself using this inner wisdom in everything I do. In my mind's eye I see myself making wise decisions and sharing this inner wisdom with others. I imagine myself experiencing the confidence that comes from having access to the wisdom of the universe. I combine these images with the feelings of joy and let them go, knowing that they will create the good things I am visualizing and thinking.

Data Link Layer has number of specific functions to carryout. These functions include:- 1. Providing a well defined service interface to the Network Layer. 2. Determining how the bits of the Physical Layer are grouped into frames. 3. Dealing with transmission errors. 4. Regulating the flow of frames so that slow receiver are not overcome by a fast sender. Services provided to the Network Layer The function of the Data Link Layer is to provide services to the Network Layer. The principle service is transferring data from the Network Layer on the source machine to the Network Layer on the destination machine. On the source machine there is an entity or a process, in the Network Layer that transfers some bits to the Data Link Layer for transmission to the destination machine. The job of the Data Link Layer is to transmit the bits to the destination machine so that they can be handled over, to the Network Layer. The Data Link Layer can be designed to offer various se

Data Link Layer has number of specific functions to carryout. These functions include:- 1. Providing a well defined service interface to the Network Layer. 2. Determining how the bits of the Physical Layer are grouped into frames. 3. Dealing with transmission errors. 4. Regulating the flow of frames so that slow receiver are not overcome by a fast sender. Services provided to the Network Layer The function of the Data Link Layer is to provide services to the Network Layer. The principle service is transferring data from the Network Layer on the source machine to the Network Layer on the destination machine. On the source machine there is an entity or a process, in the Network Layer that transfers some bits to the Data Link Layer for transmission to the destination machine. The job of the Data Link Layer is to transmit the bits to the destination machine so that they can be handled over, to the Network Layer. The Data Link Layer can be designed to offer various se

The first of April, some do say Is set apart for All Fool's Day; But why the people call it so Nor I, nor they themselves, do know, But on this day are people sent On purpose for pure merriment.