Network Model Illustration

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Layered Tasks in a Network Model

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We use the concept of layers in our daily life. As an example, let us consider two friends who communicate through postal mail. The process of sending a letter to a friend would be complex if there were no services available from the post office. Figure 2.1 shows the steps in this task.


Tasks involved in sending a letter is just like Network Model
Figure 2.1

Tasks involved in sending a letter is just like Network Model




Sender, Receiver, and Carrier

In Figure 2.1 we have a sender, a receiver, and a carrier that transports the letter. There is a hierarchy of tasks in a network model.


At the Sender Site :


Let us first describe, in order, the activities that take place at the sender site.

Higher layer.

The sender writes the letter, inserts the letter in an envelope, writes the sender and receiver addresses, and drops the letter in a mailbox.

Middle layer.

The letter is picked up by a letter carrier and delivered to the post office.

layer.

The letter is sorted at the post office; a carrier transports the letter.


On the Way :



The letter is then on its way to the recipient. On the way to the recipient's local post office, the letter may actually go through a central office. In addition, it may be transported by truck, train, airplane, boat, or a combination of these.


At the Receiver Site :


Lower layer.

The carrier transports the letter to the post office.

Middle layer.

The letter is sorted and delivered to the recipient's mailbox.

Higher layer.

The receiver picks up the letter, opens the envelope, and reads it.


Network Model Hierarchy

According to our analysis, there are three different activities at the sender site and another three activities at the receiver site. The task of transporting the letter between the sender and the receiver is done by the carrier. Something that is not obvious immediately is that the tasks must be done in the order given in the network model hierarchy. At the sender site, the letter must be written and dropped in the mailbox before being picked up by the letter carrier and delivered to the post office. At the receiver site, the letter must be dropped in the recipient mailbox before being picked up and read by the recipient.


Network Model Services

Each layer at the sending site in network model uses the services of the layer immediately below it. The sender at the higher layer uses the services of the middle layer of the network model. The middle layer uses the services of the lower layer. The lower layer uses the services of the carrier.

The layered network model that dominated data communications and network modeling literature before 1990 was the Open Systems Interconnection (OSI) network model. Everyone believed that the OSI network model would become the ultimate standard for data communications, but this did not happen. The TCP/IP protocol suite became the dominant commercial architecture because it was used and tested extensively in the Internet; the OSI network model was never fully implemented.


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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