Sunday, October 4, 2015

Comparison of OSI and TCP/IP model

Both are based on the concept of a stack of independent protocols. Also,the functionality of layers is roughly similar.
3 concepts are central to OSI model:

1.Services-performs some services for the layer above it,tells what layer does.It defines the layer's semantics.

2.Interfaces-tells processes above it how to access it.

3.Protocols-layer's own business.

The protocols in the OSI model are better hidden than in the TCP/IP model and can be replaced relatively easily as the technology changes.
Data Link Layer originally dealt with point-to-point networks. The committee originally expected that each country would have one network, run by govt. and using OSI protocols, so no thought was given to internetworking.
With TCP/IP the reverse was true:the protocols came first and the model was just a description of existing protocols. The only trouble was that the model did not fit any other protocol sticks.
An obvious difference between the 2 models is the number of layers:the OSI model has 7 layers and the TCP/IP has 4 layers.Both have (inter)network, transport and application layers,but other layers are different.
The OSI model supports both connectionless and connection oriented communication in the network layer.The TCP/IP model has only one mode in the network layer (connectionless)but supports both modes in the transport layer,giving the users a choice.