Mac layer protocol data unit

Internally, the data transmission starts from the Application layer of one device and travels to the Physical layer while adding some information to the data packet.

Transport Layer

When the data packet reaches the Physical layer, it is transferred as modulated bits on the medium, which may be wired or wireless. As you may know, OSI model has seven layers, each layer appends some information to the data that is transmitted from the Application layer Layer 7 to the Physical layer Layer 1. At the Network layer Layer 3 , an IP header is prepended to the data that is received from the upper layers.

Once the frame moves to the Physical layer, PHY information is prepended to the frame.


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Finally, data is transferred as bits, which are binary digits: 0 and 1, at the Physical layer. Now, the MPDU data frame is sent to the Physical layer from where the data frame is forwarded further to reach at the destination device. The Frame aggregation was introduced after the An analogy for frame aggregation is carpooling that is implemented to reduce traffic and subsequently reduce traffic jams.

Similarly, frame aggregation is used to reduce medium contention overhead by combining several service data units SDUs.

Memorize Quickly the OSI and TCP IP Models with Mapped PDU

The medium contention overhead is minimized by using the following methods of frame aggregation, which are:. An In the next blog, we will take a look at different types of Till then happy reading!! The interface between an application layer protocol and a transport layer protocol is defined with reference to port numbers and sockets more about this later. The application layer effectively combines the functionality of the application , presentation and session layers of the OSI model. Each of the lower three layers provides services to the layer immediately above it, while the application layer provides an interface between the user application above it and the communication-oriented layers below it.

As the raw data moves from the application itself down through the various layers, it is wrapped up or encapsulated within protocol data units PDUs created by each of the protocols it encounters. The names commonly used to refer to these protocol data units tend to vary. At the internet layer, for example, they are called packets or datagrams.

Difference Between Segments, Packets and Frames

At the link layer, they are more often called frames. The diagram below illustrates how successive headers are added by protocols working at each layer. Data from an application is passed down to the appropriate application layer protocol, which encapsulates the data within a protocol data unit PDU by adding some header information. The entire PDU is then passed down to the transport layer protocol, and undergoes a similar process here.

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This encapsulation is repeated for the internet layer and the link layer. The frame that is built by the link layer is then sent on the first leg of its journey to a network switch or router, for example via some physical transmission medium as a stream of bits. The Internet - indeed any large internetwork - consists of a number of autonomous networks connected together by gateways. A gateway is a special kind of computer called a router.

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Each router has connections to at least two networks, including its own home network. The router's main function is to examine incoming datagrams from its own and other networks, and send them out again along the correct path according to the network number indicated by the each datagram's destination IP address. A computer on any of the networks in an internetwork should be able to send data to, or receive data from, any other computer, whether on the same network or on a different network. Datagrams must often pass through many gateways before getting to their final destination.

The datagrams may follow various routes from one computer to another, depending on the best routing options available at any given time. Routers constantly gather information about the routes available to other networks, and they use this information to decide where to send an incoming packet on the next leg or hop of its journey.


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  5. A client application wishing to send a request to a server somewhere on the internetwork does not need to know how to get to that network, it only needs to know the destination computer's IP address and the hardware MAC address of its own local network gateway router. Consider a client-server process in which a user types the IP address of a Web server into the address box of a Web browser we will be looking at URLs and domain names in due course, by the way.

    The TCP/IP Protocol Stack

    All being well, the document that is retrieved and displayed in the browser window will be the default document from the Web root directory on the server in question, usually a file named "index. But how does this happen?

    Once the server's IP address has been entered into the address box and the user has hit the ENTER key, the browser software asks the TCP protocol to establish a connection with port 80 the HTTP port on the server any available port number on the client computer can be used for the client end of the connection. The connection must be established before any data can be sent.