Network Model Illustration

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Network Model :: Data Link Layer

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The data link in a network model layer transforms the physical layer, a raw transmission facility, to a reliable link. It makes the physical layer appear error-free to the upper layer (network layer). Figure 2.6 shows the relationship of the data link layer to the network and physical layers of network model.


Data link layer in a network model
Figure 2.6

Data link layer in a network model



The data link layer in a network model is responsible for moving frames from one hop (node) to the next.

Other responsibilities of the data link layer in a network model include the following:

Framing.

The data link layerin a network model divides the stream of bits received from the neteork Jayer into manageable data units called frames.

Physical addressing.

If frames are to be distributed to different systems on the network model, the data link layer in network model adds a header to the frame to define the sender and/or receiver of the frame. If the frame is intended for a system outside the sender's network, the receiver address is the address of the device that connects the network to the next one.

Flow control.

If the rate at which the data are absorbed by the receiver is less than the rate at which data are produced in the sender, the data link layer in network model imposes a flow control mechanism to avoid overwhelming the receiver.

Error control.

The data link in network model layer adds reliability to the physical layer by adding mechanisms to detect and retransmit damaged or lost frames. It also uses a mechanism to recognize duplicate frames. Error control is normally achieved through a trailer added to the end of the frame.

Access Control.

When two or more devices are connected to the same link,data link layer protocols in network model are necessary to determine which device has control over the link at any given time.

Figure 2.7 illustrates hop-to-hop (node-to-node) delivery by the data link layer.


Hop-to-hop delivery by the data link layer
Figure 2.7

Hop-to-hop delivery in network






As the figure shows, communication at the data link layer in a network model occurs between two adjacent nodes. To send data from network model A to network model F, three partial deliveries are made. First, the data link layer at network model A sends a frame to the data link layer at network model B (a router).

Second, the data link layer at network model B sends a new frame to the data link layer at network model E. Finally, the data link layer at network model E sends a new frame to the data link layer at network model F. Note that the frames that are exchanged between the three nodes have different values in the headers. The frame from A to B has B as the destination address and A as the source address. The frame from B to E has E as the destination address and B as the source address. The frame from E to F has F as the destination address and E as the source address. The values of the trailers can also be different if error checking includes the header of the frame.


Next

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Network Model

Layered Tasks in a Network Model

Network Model: THE OSI MODEL

Network Model :: Physical Layer

Network Model :: Data Link Layer

Network Model :: Network Layer

Network Model :: Transport Layer

Network Model :: Session Layer

Network Model :: Presentation Layer

Network Model :: Application Layer

TCP/IP protocol suite in a Network Model

Addressing system in a Network Model

Important Points about Network Model


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