Why layering is required in OSI model?

Answer 1

The simple answer is that a networking system is simpler, cheaper, and more reliable if it is implemented in terms of layers. Each layer accepts responsibility for a small part of the functionality. Having a clean separation of function between layers means that multiple layers do not need to duplicate functionality. It also means that layers are less likely to interfere with one another.

A simple example: in the TCP/IP protocol suite, the IP layer is very simple. All it does is (a) provide a uniform format for messages to be passed between computers that will work from anywhere on the internet (regardless of what kind of link layer is being used), and (b) provide a uniform addressing model for computers on the Internet. IP does not ensure that messages are delivered correctly or reliably, it doesn't ensure that messages are not duplicated, and so forth. That's the job of higher layers. TCP, which is layered on top of IP, allows two computers to exchange messages of arbitrary length. Essentially, TCP takes care of fragmenting the messages into IP packets (which have a maximum size) and making sure that the entire contents of those messages arrive at their destination and are reassembled, in order, without duplicated or missing fragments. The TLS protocol (formerly known as SSL) is layered on top of TCP and provides encryption, digital signatures, and assures the integrity of the message against deliberate or accidental modification. Application protocols layered on top of TCP and/or SSL provide higher-level functions, such as delivery of email or a web page.

Similarly, protocol layers underneath IP are used to deliver messages on specific kinds of data links. Wireless LAN is somewhat different from a DSL circuit, cable TV Internet, point-to-point fiber optic link, or a wired Ethernet.

Answer 2

For large and complex systems that are constantly being updated,the ability to change the implementation of a service without affecting other components of the system is an important reason why layering is required and also different services can be implemented at each layer
layered architecture is easy to make changes ,
for example service provided by a layer can be modified or replaced this will not affect the service of the layers above or below .

Answer 3

Whenever messages are passed in network, it doesn't happen as easily as we think. The message has to pass through different layers and each layer has its own function. As we think logically, the message should be broken up into smaller packets because huge data can cause more traffic. There must be a source and destination address for the reliable transmission of messages. Error detection and controlling must also be there in order to control the flow of packets within the network. For security purposes, encryption must also be there in order to provide security for the messages. So to do these different jobs, each layers in network has its own responsibility. That is why we need different layers.

Answer 4

That is a long answer. Your best bet is to look up "The OSI Model"...it is the layers that information has to go thru before it is sent out on the web.