The data link layer is concerned with local delivery of frames between nodes on the same level. The network layer is interested in getting messages to the corresponding network layer module on an adjacent machine. The data link layer s first sublayer is the media access control mac layer. General data link layer frame structure computer networking. Lecture notes data communication networks electrical.
Responsible for reliable transmission of packets over a link. A link isthe communication channels that connect two adjacent hosts or routers. As shown on the above representation of the frame, the header and trailer are added to the already formed pdu, which is packet that contains data coming from the application layer down to the network layer. The datalink layer has responsibility of transferring datagram from one node to adjacent node over a link goto top link layer and local area networks 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.
Data packets are framed and addressed by this layer, which has two sublayers. It is called segment at transport layer, packet at the network layer, and it is referred to as frame in the data link layer. Computer networking and management lesson 5 the data link layer. Data link layer dlc responsible for reliable transmission of packets over a link framing. The data link and physical layer is where network abstractions are implemented. Datalink layer protocols, such as ppp, format the ip datagram into a frame.
Elec3030 el336 computer networks s chen framing data link layer is responsible for making physical link reliable and, to do so, it breaks up network layer data stream into small blocks, a process called segmentation, and adds header and frame. The data link layers primary duty is to carry network layer l3 datagramspackets inside frames to a next hop neighbor through a physical wiredwireless link. Elec3030 el336 computer networks s chen data link layer. What sets of bits constitute a frame where is the beginning and the end of frame. Transmission link may cause errors in frames, finite buffer at the receiver ack frames may now be lost 40 problems introduced by a noisy line problem 1. The data link layer is used for the encoding, decoding and logical organization of data bits. Media access control and llc logical link controlsub layers.
Framing blocks of data exchanged between nodes we know how to transmit sequence of bits over a link challenge. Eytan modiano slide 4 character based framing standard character codes such as ascii and ebcdic contain special communication characters that cannot appear in data entire transmission is based on a character code. The ethernet a local area network data link layer and physical layer specifications digital equipment corporation intel corporation xerox corporation maynard, ma santa clara, ca stamford, ct version 2. Framing notes from csc 6520 at georgia state university. These protocols attach a third header and a footer to frame the datagram.
The senders data link layer inserts an ascii dle character just before the dle character in the data. Data link layer silvia giordano ica, epfl the datalink layeris responsible for transferring a datagram across an individual link. We said in the previous lessons that data has different names at different layers. The remote network layer peer should receive the identical message generated by the sender e. This lecture notes explores data link layer dlc which is responsible for reliable transmission of packets over a link 1. Data link layer is the second layer in osi reference model and lies above the physical layer. Provides a welldefined service interface to the network layer.
The data link layer provides data reliability and provides tools to establish, maintain, and release data link connections among the network nodes. Data link layer data link layer objectives specific. May 16, 2018 data link layer design issues framing i. Find materials for this course in the pages linked along the left. Data link layer takes the packets from the network layer and encapsulates them into frames. The physical layer provides only a raw bitstream service between computers. The main task of the data link layer is to transform a raw transmission facility into a line that appears free of undetected transmission errors to the network layer. Thats why an optimized frame size has been defined for the.
The receivers data link layer removes this dle before this data is given to the network layer. Hdlc stands for highlevel data link control protocol. Data link layer protocols the data link layer provides service to the network layer above it. Data link layer is responsible for converting data stream to signals bit by bit and to send that over the underlying hardware. Link channel complexity causes the logical link and mediaaccess control sublayers split. Data link layer, part 1 introduction and framing these slides are created by dr.
Frame relay is a layer 2 protocol and commonly known as a service from. 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. Codes all these codes add redundancy to the information that is sent. Whenever the sender encounters five consecutive 1s in the data, it automatically stuffs a 0 bit into the outgoing bit stream. 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. Frames have headers that contain information such as errorchecking codes. Error control deliver frames without error, in the. Media access control and llc logical link controlsublayers.
Ethernet frame the data link layer frame is then organized into the physical layer as shown below. Data link layer of osi reference model studytonight. This post briefly describes the general format of a data link layer frame. Framing is a pointtopoint connection between two computers or devices consists of a wire in which data is transmitted as a stream of bits. Allows the upper layers to access the media using techniques such as framing. If the frame size becomes too large, then the packet may be divided into small sized. Data link layer objectives specific responsibilities of the data link layer include. Frames are the small data units created by data link layer and the process of creating frames by the data link layer is known as framing. Well consider three approaches, byteoriented framing, bitoriented framing, and the inclusion of a length eld. Data link control framing free download as powerpoint presentation. Determines how the bits of the physical layer are grouped into frames framing. It provides a way for a sender to transmit a set of bits that are meaningful to the. Types of services provided to the network layer, unacknowledged connectionless service acknowledged connectionless service acknowledged connection oriented service framing translation of physical layers raw bits into a larger. Data link protocols data link protocols are sets of rule and regulations used to implement data link layer.
Af it f dt bit d d d ta frame consists of m data message bits and r redundant. The link layer protocoldefines the format of the units of data frames exchanged between the nodes at the ends of the link, as well as the actions taken by these nodes when sending and receiving. Aug 29, 2016 the data link layer is the second layer in the osi model, above the physical layer, which ensures that the error free data is transferred between the adjacent nodes. In the physical layer, data transmission involves synchronised transmission of bits from the source to the destination. It accomplishes this task by having the sender break up the input data into data frames typically a few hundred or few thousand bytes and transmit the frames sequentially. The ethernet a local area network, data link layer and. Jan 15, 2015 issues in data link layer services provided to network layer virtual communication actual comunication 3. The endtoend argument becomes clear at the data link layer. Framing the data link layer, needs to pack bits into frames, so that each frame is distinguishable from another.
Loss of a data or ack frame since the transmission link is not errorfree, a data or ack frame may be lost, causing the sender to wait indefinitely for an ack. Huangs courses at gmu can make a single machinereadable copy and print a single copy of each slide for their own reference, so long as each slide contains the. The receivers link layer removes this special byte before the data are given to the network layer. The data link layer, needs to pack bits into frames, so that each frame is distinguishable from another. The data link layer offers transmission service to the network layer. Almost all linklayer protocols encapsulate each networklayer datagram within a link layer frame before transmission onto the link. View data link layer from cse 201 at american international university bangladesh campus 5. Since this can interfere with the framing, a technique called character stuffing is used. Ethernet, token ring, frame relay, and other data link layer technologies have their own frame structures.
940 1603 973 1622 2 1600 1437 954 271 589 241 1238 1400 813 865 859 33 1537 1146 531 898 172 617 156 415 642 1295 1526 626 1039 1109 495 1471 131 114 646 563 462 123 1263 612 358 356 456 419 423 886 470