OSI Layering Concepts and Benefits

Many benefits can be gained from the process of breaking up the functions or tasks of networking into smaller chunks, called layers, and defining standard interfaces between these layers. The layers break a large, complex set of concepts and protocols into smaller pieces, making it easier to talk about, easier to implement with hardware and software, and easier to troubleshoot. The following list summarizes the benefits of layered protocol specifications:

■ Easier to learn—Humans can more easily discuss and learn about the many details of a protocol specification.

■ Easier to develop—Reduced complexity allows easier program changes and faster product evolution.

■ Multivendor interoperability—Creating products to meet the same networking standards means that computers and networking gear from multiple vendors can work in the same network.

■ Modular engineering—One vendor can write software that implements higher layers— for example, a web browser—and another can write software that implements the lower layers—for example, Microsoft's built-in TCP/IP software in its operating systems.

The benefits of layering can be seen in the familiar postal service analogy. A person writing a letter does not have to think about how the postal service will deliver a letter across the country. The postal worker in the middle of the country does not have to worry about the contents of the letter. Likewise, layering enables one software package or hardware device to implement functions from one layer, assuming that other software/hardware will perform the functions defined by the other layers. For instance, a web browser does not need to think about what the network topology looks like, the Ethernet card in the PC does not need to think about the contents of the web page, and a router in the middle of the network does not need to worry about the contents of the web page or whether the computer that sent the packet was using an Ethernet card or some other networking card.

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