PART A: Short Answer Questions (5 x 8 = 40 Marks) 1. Explain the difference between switch and a hub. Please justify your answer with appropriate visuals and diagrams. (8 marks) 2. Draw in chart form...

PART A:
1. Difference in the switch and Hub are:-
    Switch
    Hub
    Switch is operated on a data link layer of the OSI model .
    Hub is operated on physical layer of the OSI model.
    Switch is operated with software so it acts as active device
    Hub is operated without software so it acts as passive device.
    Data in switch is transferred as Frames and packets
    Data in hub is transferred as electrical signal or bits.
    Data in switch is transferred in Full duplex mode
    Data in hub is transferred as electrical signal or bits
    Multiple devices can send data on same time in switch
    only one device can send data at same time
    switch stores media access control(MAC) addresses in look up table
    hub cannot deal with MAC addresses
    Switch is expensive
    Hub is cheaper than Switch.
Figure 1 Switch and Hub
2. Voltage representation of 11001010 using different digital encoding schemes:-
3. Circuit Switching:-It establish physical connection between sender i.e source and receiver i.e destination device for the committed duration of time. Landline telephone system utilizes circuit switching. There are three phases of circuit switching circuit establishment of connection, transfer of data and disconnection of circuit.
Advantages of circuit switching are:-
a. It uses the fixed Bandwidth.
b. It is better for continues and long transmission.
c. Data is transferred at steady Data rate.
d. Once connection is made no lag in transmission.
e. Since it give continues transmission so it provides high quality service.
Disadvantages of circuit switching:_
1. Once connection is made another data cannot be transferred even channel is free so resources are not implemented well.
1. Time required to make connection in two devices is long.
1. Each connection need more bandwidth.
1. Link will continue until discontinued by user.
Figure 2 Circuit Switching
Packet Switching:- It divides data into small pieces are known as packet than transmit across the different networks. There is virtual connection made between sender and receiver. Every packet carry address of sender and receiver, number of pieces and sequence number that will be used during reassembly. Acknowledgment is transmitted by receiver to sender if it received the packets and in case of missing packet receiver transmit message to sender to resend it.
Advantages of Packet Switching:-
1. It implement resource in efficient manners such that no wastage of bandwidth.
1. Less time required for the connection establishment.
1. Since it does not require physical connection so it can even works in disaster or crises.
1. It uses small disk space.
Disadvantages of Packet switching:-
1. Packets of data can lost.
1. Specific protocols are required for transfer.
1. It is inefficient in heavy use.
1. It ineeficient in real time stream of data.
Figure 3 Packet switching
4. Various type of substitution cipher techniques are:
1. Caeser cipher:-In this set of texts are replaced by other character,symbol and numbers.Each alphabet in message is replaced by alphabet which comes after 3 place after. Example if message text is ABC then A in the message replace by D,B by Eand C by F so encrypted text is DBE
.
Figure 4 Caeser cipher
1. Monoalphabatic cipher:- In this each alphabet in text is replaced by any of the other alphabet except itself. Example in message text ABC ,A can be replaced by any other alphabe from B to Z except A.Similar for B and C.
1. Homophonic Subsitution cipher:In this each alphabet in text is replaced by fixed set of alphabet. Example in message text ABC , each alphabet have fixed set of alphabet for replacement.
1. Polygram substitution cipher:-In this block of alphabet is replaced by another block of alphabet,Example ABCDE can be replaced by QGTHS.
1. Polyalphabetic substitution cipher:-It utilizes the diferent substitution alphabets for encryption. The table carry 26 alphabets that are written in different lines; every alphabet is cyclically shifted to the left in accordance with the previous alphabet, corresponding to 26 possible Caesar ciphers. The cipher uses a different alphabet from one of the lines at different points in the encryption process.
1. Play fair Cipher:-Play fair cipher technique can be used to encrypt or encode a message. It works exactly like typical encryption. The only difference is that it encode a digraph, or a pair of two alphabet, as opposed to a single alphabet. An initial 5x5 matrix key table is created. The plaintext encryption key consists of the alphabetic characters of the matrix. Keep in mind that you should not repeat letters. There are 26 alphabets, but only 25 spaces in which we can place a letter. The matrix deletes the extra letter because there is one extra letter.
1. Hill cipher: It is a polygraphic substitution cipher that works based on linear algebra. Each alphabet is donated by a number modulo 26. A simple scheme A = 0, B = 1, …, Z = 25 is often used, but this is not a basic feature of the cipher. To encrypt a message, each block of m letters is...