This layer is also responsible for logical mac addressing and llc processing, creating logical topologies, and controlling media access. Data link layer protocol tutorial with example tutorialwing. Data packets are framed and addressed by this layer, which has two sublayers. Data link layer data link layer protocols create, transmit, and receive packets. Computer networking and management lesson 5 the data. It is responsible for delivering messege between network host. Other responsibilities or functions of the data link layer include the following. Data link layer is the second layer in osi reference model and lies above the physical layer. What are the functions of a data link layer in a computer. When you open a web browser or an instant message window, an application is started, and. The physical layer is the lowest layer of the osi model and is closest to the physical medium. Typically, the network layer adds its own header to the packets received from the transport layer.
Many of these protocols are originally based on the internet protocol suite tcpip and other models and they often do not fit neatly into osi layers. The data link layer is also called as the layer 2 of the osi model. Specific functions of the transport layer are as follows. This list is not exclusive to only the osi protocol family. The data link layer provides services to the network layer. Allows a device to access the network to send and receive messages offers a physical. Some definitions needed in the protocols to follow. Refer to bridges and bridging and switching and switched networks for more information. Data link layer protocols require control information to enable the protocols to function. The data link layer introduction link layer and local area networks link layer.
The data link layer divides the stream of bits received from the network laye. The logical link control llc sublayer provides the logic for the data link. High level data link control hdlc synchronous data link. At the receiving end, data link layer picks up data from hardware which are in the form of electrical signals, assembles them in a recognizable frame format, and hands over to upper layer. In this protocol, the contents of the acknowledgement frame are. Data link protocols data link protocols are sets of rule and regulations used to implement data link layer. For effective data communication between two directly connected transmitting and receiving stations the data link layer has to carry out a number of specific. Following is the list of protocols from the reference. The data link layers primary function is to ensure data is received by the correct device in a network using hardware addresses, called mac address, and then convert that. Similar techniques to transport layer ack and retransmit. Control information can be inserted as bits depending on the information to be contained in the frame bitoriented protocol can pack more information into shorter frames. In this lesson we examine the data link layer its services, the principles underlying its operation, and a number of important data link layer protocols.
The data link layer is concerned with local delivery of frames between nodes on the same level of the network. Data link layer transforms the physical layer, a raw transmission facility to a reliable link. The data link layers first sublayer is the media access control mac layer. The core functions of network layer is given below. Defines the methods and provides addressing information for communication between network devices. The data link layer or layer 2 is the second layer of the sevenlayer osi model of computer networking. The data link layer ensures that all packets of information are passed on free of errors. Data link layer silvia giordano ica, epfl the datalink layeris responsible for transferring a datagram across an individual link. Data link layer is responsible for moving from one hop node to the next.
In the previous tutorial, we have studied about the physical layer and the various functions performed at this layer. Data link layer, layer 2 in the tcpipbased layered network, layer 2 is the data link layer. Communication at the data link layer protocol is nodetonode. Data link layer is responsible for converting data stream to signals bit by bit and to send that over the underlying hardware. The data link layer is the protocol layer in a program that handles the moving of data in and out across a physical link in a network. The application layer is the top most layer of osi model, and it provides that directly support user applications such as database access. An upper layer refers to the layer just above another layer.
It also synchronizes the information which is to be transmitted over the data. The actual protocols encompassed in the link layer are numerous, and the implementation details can be found in various documents throughout the internet and in trade texts. We will now move ahead to the next layer in iso osi stack i. Computer networking and management lesson 5 the data link layer. Data link layer it is responsible for nodetonode delivery of data. In the data link layer some sets of rules and procedures are made to carry the control functions in the data link layer. Transport layer is the 4th layer in tcpip model that deals with logical communication between process.
The physical layer of the osi model is only part of a lan local area network. A node constructs a framefrom a single packet message. This layer is one of the most complicated layers and has complex functionalities and liabilities. Responsible for encoding and decoding of the electrical signals into bits. The network layer is interested in getting messages to the corresponding network layer module on an adjacent machine. About data link layer protocol with its function and services. That is, sender sends at a speed on which the receiver can process and accept the data. Datalink layer protocols that are reliant on a specific physical layer may be limited to the transmission medium involved, but, in some cases e. In the osi model, the data link layer is a 4 th layer from the top and 2 nd layer from the bottom the communication channel that connects the adjacent nodes is known as links, and in order to move the datagram from source to the destination, the datagram must be moved across an individual link. The tcpip network access layer is the equivalent of the osi. The remote network layer peer should receive the identical message generated by the sender e. Computers often run many programs at the same time.
The data link layer performs the following functions. Allows a device to access the network to send and receive messages offers a physical address so a devices data can be sent on the network. The data link layer is concerned with local delivery of frames between devices on the same lan. Router 3layer physical, datalink, network device, with 3 key functions. A top down approach featuring the internet, 2nd edition. Data link layer 6 data link layer model assume the sending host has infinite supply of messages. In this paper we integrate the energy models of all the components of the data link layer of a wireless sensor network into a single framework, which interacts with the abstracted models of the. In 1st part, data link layer has a number of specific functions. The data link layer is layer 2 in the open systems interconnect osi model for a set of telecommunication protocols. Data link layer hides the details of underlying hardware and represents itself to upper layer as the medium to communicate. When a data frame layer2 data is sent from one host to another over a single medium, it is required that the sender and receiver should work at the same speed.
The seven layers of osi model their protocols and functions. The physical layer provides only a raw bitstream service between computers. The data link layer s first sublayer is the media access control mac layer. Data link layer devices include bridges and switches. In the osi model, the data link layer is a 4 th layer from the top and 2 nd layer from the bottom the communication channel that connects the adjacent nodes is known as links, and in order to move the datagram from source to the destination, the datagram must be. The network layer is the middle layer between the transport layer and the data link layer. The data link layer provides data reliability and provides tools to establish, maintain, and release data link connections among the network nodes. Many of these protocols are originally based on the internet protocol suite tcpip and other models and they often do. It makes sure the appropriate physical protocol is assigned to the data.
The lower layer of the osi model deals with the data transport issues. Data link frames, as these protocol data units are called, do not cross the boundaries of a local area network. There are numerous protocols in place to assist with this responsibility. The data link layer is used for the encoding, decoding and logical organization of data bits. Internetwork routing and global addressing are higher layer functions, allowing data link protocols to focus on local. This layer is the protocol layer that transfers data between adjacent network nodes in a wide area network wan or between nodes on the same local area network lan segment. As the second layer in the osi model, the data link layer is very strict on protecting the data that is passed to the network. Obtaining data from the session layer, divide it into segments and transmit to the network layer. Almost all linklayer protocols encapsulate each networklayer datagram within a. The protocols are developed in increasing complexity to help students understand the data link layer issues. This layer can handle connectionoriented transmissions unlike the mac sublayer below it, although connectionless service can also be provided by this layer. Data link layer is second layer of osi layered model. The physical layer is simply responsible for sending bits from one computer to. It then provides the addressing information by adding header to each frame.
Examples of linklayer protocols include ethernet, token ring, fddi, and ppp. This article lists protocols, categorized by the nearest layer in the open systems interconnection model. The data link layer and the physical layer are implemented in hardware and software. The llc sublayer provides a way for the network layer to communicate with one of these protocols. It forms frames from the packets that are received from network layer and gives it to physical layer. Provide user interface to send and receive the data. Functions of transport layer in the osi model computer. The functions associated with the application layer protocols in both the osi and the tcpip models enable the human network to interface with the underlying data network.
Data link layer works between two hosts which are directly connected in some sense. For the functioning of the communication protocols, every layer exchanges information with the corresponding layer on the other side of the connection, apart from the application data. We learn that the basic service of the data link layer is to move a networklayer datagram from one node host or router to an adjacent node. Actual protocols are developed for specific use for the communication network. Data link layer performs the most reliable node to node delivery of data. We will exam how various data link layer protocols deal with these issues. Sliding window protocols window set of sequence numbers to sendreceive sender window sender window increases when ack received packets in sender window must be buffered at source sender window may grow in some protocols. Pdf data link layer design for wireless sensor networks. The osi model provides the guidelines for the data link layer.
We learn that the basic service of the data link layer is to move a network layer datagram from one node host or router to an adjacent node. The result of this standardization will provide a standard data model, communications protocol and management functional areas that are applicable to osi and non osi applications. The data link layer s primary function is to ensure data is received by the correct device in a network using hardware addresses, called mac address, and then convert that data into bits for the physical layer to transmit. Here are the basic functionalities of the data link layer. In addition, the data link layer can perform some type of flow control. The data link layer or layer 2 is the second layer of the seven layer osi model of computer networking. It is responsible for moving frames from one hop node to the next i. Protocols can be defined as these are called as set of rules.
Datalink frames, as these protocol data units are called, do not cross the boundaries of a local network. This header provides the information needed for routing e. Data networks lecture 1 introduction mit opencourseware. Some of the data link controls used in data link layer are. By adding grouping to the seemingly arbitary bits beeing placed on and extracted from the network media, the data link layer protocols provides meaningful data between the upper layers of the sending and receiving nodes. The data link layer provides service to the network layer above it. A link isthe communication channels that connect two adjacent hosts or routers. Sdlc synchronous data link protocol hdlc highlevel data link control. Internetwork routing and global addressing are higher layer functions, allowing datalink protocols to focus on local delivery, addressing.
199 1315 526 1239 1284 214 1391 1562 1014 856 593 710 351 1368 782 269 496 1306 1232 1454 161 850 329 855 596 975 448 576 263 1102 971 1450 520 429 187 685 1079 964 1124 994