Explain the Osi Reference Model and Tcp/ip Protocol Architecture

Computer Networks

* Explain the OSI reference model and TCP/IP protocol architecture.

The Open Systems Interconnection reference model is made up of seven layers to establish reliable communication between nodes. The first layer, the physical layer, controls how the digital information is transmitted between nodes while things such as encoding techniques, connector types, and data rate are established. The second layer, the data-link layer, is responsible for framing data, error detection and maintaining flow control over the physical connection. The third layer, the network layer, takes care of routing protocol-specific packets to their proper destination using IP addressing. The fourth layer, the transport layer, is the first of the seven layers that doesn't care about how the data actually gets from location to location; instead this layer concentrates on providing correct communication between applications. The fifth layer, the session layer handles communication between processes running on two different nodes. The sixth layer, thee presentation layer, deals with text compression, conversion and encryption. The seventh layer, the application layer, is where the user program executes and makes use of the lower layers. This program interfaces directly with the operating system to perform all network related activities. (Piscitello,1993)

TCP/IP or transmission control protocol/internet protocol is the most popular suite of network protocols providing network connectivity for both private and public networks. (Davies,2003) All TCP/IP data are packaged in units called datagram's, all protocols except for address resolution, are encapsulated inside of an IP datagram for delivering on a network.

* Explain the similarities and differences between them.

The foremost differences between the OSI model and TCP/IP relate to the layers before the transport layer and those at the network layer. OSI has both the session layer and the presentation layer, where TCP/IP combines both into an application layer. (Rose,1990) The requirement for a connectionless protocol also requires TCP/IP to combine OSI's physical layer and data link layer into a network level.

For the physical layer Either OSI protocols and TCP/IP protocols build on the same physical layer standards, thus there is no difference between OSI and TCP/IP in this aspect. For ethernet based networks the data link protocol LLC is equally used in OSI and TCP/IP networks.

* Explain the importance of using a layered model.

Layering is a common technique to simplify networking designs by dividing them into functional layers, and assigning protocols to perform each layer's task. Also Protocol layering produces simple protocols, each with a few well defined tasks. These protocols