Data link layer, part 1 introduction and framing these slides are created by dr. Codes all these codes add redundancy to the information that is sent. Data link layer silvia giordano ica, epfl the datalink layeris responsible for transferring a datagram across an individual link. 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. Hdlc stands for highlevel data link control protocol.
Frames have headers that contain information such as errorchecking codes. Data link layer dlc responsible for reliable transmission of packets over a link framing. Data link layer data link layer objectives specific. Media access control and llc logical link controlsub layers. Well consider three approaches, byteoriented framing, bitoriented framing, and the inclusion of a length eld. 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. Ethernet, token ring, frame relay, and other data link layer technologies have their own frame structures. It provides a way for a sender to transmit a set of bits that are meaningful to the receiver.
If the frame size becomes too large, then the packet may be divided into small sized. What sets of bits constitute a frame where is the beginning and the end of frame. View data link layer from cse 201 at american international university bangladesh campus 5. General data link layer frame structure computer networking. Data link layer of osi reference model studytonight. Af it f dt bit d d d ta frame consists of m data message bits and r redundant. Data link layer provides a welldefined service interface to the network layer.
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. 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. Find materials for this course in the pages linked along the left. 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 remote network layer peer should receive the identical message generated by the sender e. The data link layer s first sublayer is the media access control mac layer. In the physical layer, data transmission involves synchronised transmission of bits from the source to the destination. Almost all linklayer protocols encapsulate each networklayer datagram within a link layer frame before transmission onto the link. The data link layer, needs to pack bits into frames, so that each frame is distinguishable from another. The data link layer is used for the encoding, decoding and logical organization of data bits. Computer networking and management lesson 5 the data link layer. These protocols attach a third header and a footer to frame the datagram. The fields for the diagrams above are described below. Link channel complexity causes the logical link and mediaaccess control sublayers split.
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. However, these bits must be framed into discernible blocks of information. 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. The data link layer offers transmission service to the network layer. 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.
Jan 15, 2015 issues in data link layer services provided to network layer virtual communication actual comunication 3. Lecture notes data communication networks electrical. Error control deliver frames without error, in the. Media access control and llc logical link controlsublayers. This post briefly describes the general format of a data link layer frame. 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. Data link control framing free download as powerpoint presentation.
Data link protocols data link protocols are sets of rule and regulations used to implement data link layer. 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. Whenever the sender encounters five consecutive 1s in the data, it automatically stuffs a 0 bit into the outgoing bit stream. Determines how the bits of the physical layer are grouped into frames framing. Data link layer is responsible for converting data stream to signals bit by bit and to send that over the underlying hardware. Elec3030 el336 computer networks s chen data link layer. Framing the data link layer, needs to pack bits into frames, so that each frame is distinguishable from another. The senders data link layer inserts an ascii dle character just before the dle character in the data. The frame header includes a cyclic redundancy check crc field that checks for errors as the frame travels over the network media. The physical layer provides only a raw bitstream service between computers. We said in the previous lessons that data has different names at different layers. Data link layer is the second layer in osi reference model and lies above the physical layer. When a packet reaches the data link layer, it is encapsulated with a header and a trailer which you will see later to be called a frame.
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. Datalink layer protocols, such as ppp, format the ip datagram into a frame. The network layer is interested in getting messages to the corresponding network layer module on an adjacent machine. Since this can interfere with the framing, a technique called character stuffing is used. The receivers link layer removes this special byte before the data are given to the network layer. 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. 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. The data link layer is concerned with local delivery of frames between nodes on the same level. Data link layer takes the packets from the network layer and encapsulates them into frames. The ethernet a local area network, data link layer and.
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. 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. Data link layer objectives specific responsibilities of the data link layer include. Frame relay is a layer 2 protocol and commonly known as a service from. Framing notes from csc 6520 at georgia state university.
This lecture notes explores data link layer dlc which is responsible for reliable transmission of packets over a link 1. It provides a way for a sender to transmit a set of bits that are meaningful to the. A link isthe communication channels that connect two adjacent hosts or routers. Responsible for reliable transmission of packets over a link. Provides a welldefined service interface to the network layer. May 16, 2018 data link layer design issues framing i. Allows the upper layers to access the media using techniques such as framing. Framing blocks of data exchanged between nodes we know how to transmit sequence of bits over a link challenge. Thats why an optimized frame size has been defined for the. Examples of linklayer protocols include ethernet, token ring, fddi, and ppp. Data link layer protocols the data link layer provides service to the network layer above it. The endtoend argument becomes clear at the data link layer. Ethernet frame the data link layer frame is then organized into the physical layer as shown below. Data packets are framed and addressed by this layer, which has two sublayers.
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