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07: Transport layer - Multiplexing and demultiplexing part 6


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While using a computer, one may open many applications to connect to a multitude of serves or other computers at the same time. Multiplexing and demultiplexing are just concepts which describe the process of the transmission of data generated by different applications simultaneously, and when arriving at the Transport layer, each data segment is independently processed and sent to its appropriate application in the destination machine.

Let us assume that you are using Google chrome browser to view news online, Microsoft outlook to send e-mails, and chat application to chat with your friends. All that takes place simultaneously. Whatever remote network device sees your computer merely as an IP. Here is the problem ! if your computer is seen as one IP address, how the exact application can be found to receive data, and what will happen if the incoming data for Microsoft outlook is forwarded to chat application. The resolution to this problem is port numbers as demystified in the preceeding lesson. Each network application will bind itself to an available port number so that the application can be identified based on port numbers.

The process of assigning port numbers to each type of data coming from the Application layer, dividing them into small segment in such a way that each segment is designated a port number, and putting the segments of different applications on wire for transmission is what paves the way for multiplexing and demultiplexing. Consider the following figure.

Obviously, one chief aim of multiplexing and demultiplexing is allowing us to use a multitude of applications concurrently.  The above figure reveals source computer is using Google, Outlook, and Chat application at the same time. All data is forwarded to Destination computer. As you see, each application has a segment put on wire to be transmitted. That signifies that all applications are running simultaneously ; conversely, if no multiplexing/demultiplexing exists, a user can use only one application at a time on the grounds that only the segments of that application are put on wire and transmitted. Take a look at the following figure for more clarification.

 
As you already know, multiplexing/demultiplexing  occurs at the Transport layer and application programs reside within the Application layer. Besides, port numbers are assigned to each application at the same layer. To clarify the above figure, applications at the Application layer have generated data, then handed down to the Transport layer to be segmented. After segmenting the data, port numbers are given to each segment to be ready for transmission. Lastly, segmenets are put on wire to travel across the network to the destination. This process is called ‘multiplexing’. When the transmitted segments reach the Transport layer of the destination, They are automatically sent up to their appropriate applications. This process is called ‘demultiplexing’.
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07: Transport layer - Multiplexing and demultiplexing part 6 Reviewed by BOUFTIRA on 7:25:00 AM Rating: 5

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