1. Discuss the advantages and disadvantages of star, bus, and mesh physical topologies. Provide real examples of each type.
2. Explain encapsulation and decapsulation in a five layer TCP/IP protocol suite. How does multiplexing and de-multiplexing differ from encapsulation and decapsulation?
3. Calculate the approximate bit rate and signal level(s) for a 6.8 MHz bandwidth system with a signal to noise ratio of 132
4. Explain why the OSI model is better than the TCP/IP model. Why hasn't it taken over from the TCP/IP model? Discuss the advantages and disadvantages of both models.
Answers:
The advantages, disadvantages and examples of star, bus, and mesh topologies are,
|
|
Advantages
|
Disadvantages
|
Examples
|
|
Star
|
· Hub is directly connected to the nodes.
· Nodes can be connected and disconnected easily.
|
· Compared to bus topology, it requires more cables.
· If the hub fails, then the entire network may fail.
|
A hub connecting multiple nodes to an Ethernet network.
|
|
Bus
|
· Simple to implement.
· Nodes can be connected and disconnected easily.
· Require lesser cable.
|
· The capacity of the network is limited.
· Performance drops when more number of nodes connected to the network.
· If the backbone cable fails, then the network will fail.
|
An Ethernet LAN connected by wired channels.
|
|
Mesh
|
· Nodes are directly connected to one another.
· The communication is faster.
· The expansion of the network is not restricted to the number of nodes connected to it.
|
· Require more cable than a bus and a star network.
· Complex structure.
|
A LAN where each node is connected directly with the other nodes.
|
The TCP/IP protocol suit has four layers of protocols. When a message is sent through the application layer, then the application layer adds some header information with the actual message. The header information is encapsulated and the encapsulated message is sent through the Transport layer, Internet layer and the physical layer. Each layer adds header information and encapsulate the header information with the message it has received from the previous layer. The final encapsulated message is received on the receiving end. Then it goes through the physical layer, Internet layer, Transport layer and the application layer. Each layer decapsulate the header information and the message and passes the message part only to the next layer. In this way, the application layer separates the header information and the actual message.
On the other hand, multiplexing and demultiplexing is used for sharing a communication channel. When multiple transmission share a common channel, then the frequency or bandwidth of the channel is divided into slots and shared among the transmissions. From the sending end, multiple data packets are multiplexed and sent. On the receiving end, the packets are demultiplexed and forwarded to the recipients separately.
The signal to noise ratio is, 132.
The bandwidth of the channel is, 6.8 MHz.
Hence, according to the formulas,
Where, B is the bandwidth, is the signal to noise ratio and M is the number of levels. C is the channel capacity.
And the channel capacity is,
OSI and TCP/IP protocol suite both are used for networking and the Internet. OSI model is a widely used standard for any network. It gives an abstraction of the complexities of the implementation part. As a result, a developer can implement the services of each layer and connect those with one another. The implementation details of a layer does not affect the implementation details of another layer. On the other hand, the TCP/IP protocol is used for IP based networks only and it gives details of the protocols rather than the services. So, OSI is applicable for any network and it is required for implementation of any network. On the other hand, TCP/IP protocol suite is used for only IP based networks and focuses on the protocols only.
The advantages and disadvantages of both models are,
|
|
Advantages
|
Disadvantages
|
|
OSI Model
|
· Suitable for any network
· Transparent and flexible.
|
· Complex than TCP/IP model
· Has more number of layers.
|
|
TCP/IP Model
|
· Simpler than OSI model
· Has lower number of layers
|
· Suitable for only IP based network
· The protocols for each layer are limited. Even the combinations of protocols from different layers are also restricted.
|
According to the formula,
Total delay
= Propagation delay + Transmission delay + Queuing Delay + Processing Delay.
From all the given information,
=( + + +
= () + + ( + seconds
= 0.633693 Seconds
The dominant parts are, Propagation delay and Transmission delay. The negligible parts are, Queuing Delay and Processing Delay.
POP3 stands for the Post Office Protocol 3. POP3 can be implemented based on the RFC 1939. POP3 is a client/server based protocol for exchanging, archiving and retrieving emails. It is an application layer protocol in the TCP/IP protocol suite. A local email client can use the protocol and can connect to a remote POP3 server. It also requires a TCP/IP based communication link.
Reference
Forouzan, B. A. (2015). Data Communications and Networking: McGraw-Hill Education.
