Answer the following questions: 1) What is the different between OSI reference m

Question

Answer the following questions: 1) What is the different between OSI reference model and TCP/IP protocol stack? 2) What are the advantage of disadvantage of OSI reference model? 3) For a point-to-point link, whether network layer is necessary? 4) What is the different of the error controls performed at data linklayer and transport layer? 5) If each packet has been verified by data link layer in each hop, why does the whole message, consisting of multiple packets, need to be checked again by transport layer?

Explanation / Answer

Ans:

1) OSI(Open System Interconnection)

1. OSI is a generic, protocol independent standard, acting as a communication gateway between the network and end user.

2. In OSI model the transport layer guarantees the delivery of packets.

3. OSI model has a separate Presentation layer and Session layer.

4. OSI is a reference model around which the networks are built. Generally it is used as a guidance tool.

5. Network layer of OSI model provides both connection oriented and connectionless service.

6. OSI model defines services, interfaces and protocols very clearly and makes clear distinction between them. It is protocol independent.It has 7 layers

TCP/IP(Transmission Control Protocol / Internet Protocol)

1. TCP/IP model is based on standard protocols around which the Internet has developed. It is a communication protocol, which allows connection of hosts over a network.

2. In TCP/IP model the transport layer does not guarantees delivery of packets. Still the TCP/IP model is more reliable.

3. TCP/IP does not have a separate Presentation layer or Session layer.

4. TCP/IP model is, in a way implementation of the OSI model.

5. The Network layer in TCP/IP model provides connectionless service.

6. In TCP/IP, services, interfaces and protocols are not clearly separated. It is also protocol dependent.It has 4 layers

2)

Advantages of OSI model :

-->Since the protocols are hidden, any protocols can be implemented in this model. So I call it as a generic model. It has all flexibility to adopt with many protocols.

-->It supports connection-oriented as well as connectionless services. So we can use connection oriented model when we need reliability and connection-less services when we need a faster data transmission over the internet.

-->It follows the divide and conquer technique. All the services are distinguished in various layers. So administration and maintenance for these OSI model architecture are straightforward and easy.

-->This layered architecture follows abstraction principle. Change in one layer does not impact much on other layers.

--> It is more secure and adaptable than having all services bundled in a single layer.

Disadvantages of OSI Model:

-->It may find sometimes difficult to fit a new protocol in this model. This is because this model was created before the invention of any of these protocols.

-->The session layer is used for session management. Presentation layer deals with user interaction. Though they are useful, not as much as other layers in the OSI model.

-->There is also interdependence among the layers. These layers can not work in parallel. They have to be in wait to receive data from its predecessor.

3) Yes

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