Winter 2018 Q.1 Solution - Grad Plus

Winter 2018 Q.1 Solution

Q.1 a) Discuss similarities and differences in TCP/IP and OSI model. Also explain OSI model. [ 09 M]

Ans :

1 Model : Both TCP/IP Are logical models.  
2 Structure : Both are arranged as layered wise which is also called an architectural model. These models have a stack of protocols it means the protocol is arranged in every layer. Both the models have some set of protocols.  
3 Networking : Both TCP/IP define standards for networking  
4 Framework : Both TCP/IP provide a framework for creating and implementing networking standards and device  
1 TCP/IP has 4 layers. OSI has 7 layers
2 TCP/IP helps you to establish a connection between different types of computers. OSI Model helps you to standardize router, switch, motherboard, and other hardware.
3 TCP Model is developed by ARPANET ( Advanced Research Project Agency Network) OSI Model is developed by ISO ( International Standard organization )
4 TCP/IP model is both connection oriented and connectionless OSI model, the Transport layer, is only connection oriented.
5 TCP/IP helps you to determine how a specific computer should be connected to the internet and how you can be transmitted between them. The OSI Model is logical and conceptual model that defines network communication used by systems open to interconnection and communication with other systems.
6 TCP/IP header size is 20 bytes. OSI header is 5 bytes
7 TCP/IP refers to transmission Control Protocol OSI refers to Open System
8 TCP/IP follows a horizontal Approach. Interconnection whereas OSI follows a vertical approach.

OSI Model

1) The OSI model is shown in fig. This model is based on a proposal developed by the International Standards Organization (ISO) in 1983. The model is called the ISO OSI (Open Systems Interconnection) Reference Model because it deals with connecting open systems which means systems that are open for communication with other systems.

2) The OSI model has seven layers.

Osi model 2 - Grad Plus
Fig. OSI Reference Model

Layer 1 – The Physical Layer : The physical layer is responsible for transmitting raw bits over a communication channel. In this layer, when one side sends a 1 bit, it is received by the other side as a 1 bit, not as a 0 bit.

Layer 2 – The Data Link Layer : The main task of the data link layer is to take a raw transmission facility and transform it into a line, it seems to be free of undetected transmission errors to the network layer. It accomplishes this task by having the sender break the input data up into data frames, it transmit the frames sequentially and process the acknowledgement frames sent back by the receiver.

Layer 3 – The Network Layer :  The network layer is responsible with controlling the operation of the subnet. The key design issue is determining how packets are routed from source to destination. Routes can be based on static tables that are “wired into” the network and rarely changed.

Layer 4 – The Transport Layer : The basic function of the transport layer is to accept data from the session layer and split it up into smaller units and then pass these to the network layer and also to ensure that the pieces all arrive correctly at the other end.

Layer 5 – The Session Layer : The session layer allows various users on different machines to establish sessions between them. A session also allows ordinary data transport and also provides enhanced services useful in some applications. A session layer also used to allow a user to log into a remote timesharing system or to transfer a file between two machines.

Layer 6 – The Presentation Layer : The presentation layer performs certain functions that are requested sufficiently to guarantee the finding a general solution for them rather than letting each user solve the problems. In general, the presentation layer is concerned with the syntax and semantics of the information transmitted.

Layer 7 – The Application Layer : The application layer deals with a variety of protocols that are commonly needed. It includes transferring a file between two different systems requires handling incompatibilities can be done by application layer, as in electronic mail, remote job entry, directory lookup, and various other general purpose and special-purpose facilities.

Q.1 b) Explain different physical topologies that are used in the Network. [04 M]

Ans :

The various different physical topologies that are used in the Network are as follows:

1. Bus Topology :

i) In bus topology all computers are connected to a long cable called a bus. A node that wants to send data puts that data on the bus which carries it to the destination node.

ii) In this topology, any computer can data over the bus at any time. Since, the bus is shared among all the computers. When two or more computers wants to send data at the same time, an arbitration mechanism is needed to prevent simultaneous access to the bus.

iii) A bus topology is easy to install but it is not flexible. It is difficult to add a new node to bus. In addition to this, the bus stops functioning even if a portion of the bus breaks down. It is also very difficult to isolate fault from it.

Bus Topology Page 2 - Grad Plus
Fig. Bus Topology

2. Ring Topology :

i) In ring topology, computers are connected in the form of a ring. Each node is having exactly two adjacent neighbors.

ii) To send data to a distant node on a ring, it passes through many intermediate nodes to reach to its ultimate destination.

Ring Topology Page 3 - Grad Plus
Fig. Ring Topology

i) A ring topology role is as to install and reconfigure. In this topology, fault isolation is very easy because a signal that circulates all the time in a ring helps in identifying a faulty node. Here, the data transmission takes place in only one direction.
ii) A node when fails in ring, it breaks down the whole ring. To overcome this drawback some ring topologies use dual rings.

3. Star Topology :

i) In star topology, all the nodes are connected to a central node called a hub. A node wants to send some six data to some other node on the network, send data to a hub which in turn sends it the destination node.

ii) A hub plays a major role in such kind of networks.

Star Topology Page 4 - Grad Plus
Fig. Star Topology

4. Tree Topology :

i) Tree topology is the hierarchy of various hubs. The entire nodes are to be connected to one hub or the other.

ii) There is the central hub to which only a few nodes are connected directly.

Tree Topology Page 5 - Grad Plus
Fig.Tree Topology

i) The central hub also called active hub as looks at the incoming bits and regenerates them so that they can traverse over longer distances.
ii) The secondary hubs in tree topology is active hubs or passive hubs. The failure of a transmission line separates the node from the network

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