Assignment # 2
Waleed Raza
F-43088
Bs(Se) 22-B
CNDC

Q1(A) Answer the following short questions
• Differentiate between the three multiplexing techniques (FDM, WDM, and TDM) and write down advantage and disadvantage of each technique (at least one in each).
Difference
Frequency Division Multiplexing (FDM) * Divides the available frequency into non-overlapping bands with guard spaces between to avoid overlapping (adjacent channel interference) * Receiver has to know the frequency to tune

Advantage:
All the Receivers,such as cellular telephones,do not need to be at same location
Disadvantage:
Noise problem due to analog signal and wastes bandwidth
Time Division Multiplexing (TDM) * Allows access to entire frequency bandwidth but for a limited amount of time * All senders use same frequency in at different time * If two transmissions overlap known as co-channel interference
Advantage:
Digital Signals
Disadvantage:
wastes bandwidth
Wavelength Division Multiplexing(WDM) * In WDM, all signals will arrive at the same time * WDM takes multiple optical signals, maps them to individual wavelengths, and multiplexes the wavelengths over a single fiber.
Advantage:
Very high capacities over fiber.
Disadvantage:
Cost Complexity

(B) Differentiate between the two TDM schemes. Synchronous Time Division Multiplexing * Accepts input from attached devices in a round-robin fashion * Transmits data in a never ending pattern
Statistical Time Division Multiplexing * transmits only the data from active workstations * Accepts incoming data streams * Creates a frame containing only the data to be transmitted

(C) Define DSSS and differentiate between FHSS and DSSS.
Direct Sequence Spread Spectrum (DSSS) is a technique in which original data is multiplied by a pseudo random noise spreading code. they transmit the message bearing signals using a bandwidth that is in excess of the bandwidth that is actually needed by the message signal.
Differnce Between FHSS and DSSS
Frequency Hopping Spread Spectrum (FHSS)
When using FHSS, the frequency spectrum is divided into channels. Data packets are split up and transmitted on these channels in a random pattern known only to the transmitter and receiver.
Direct Sequence Spread Spectrum (DSSS)
The DSSS encoder spreads the data across a broad range of frequencies using a mathematical key. The receiver uses the same key to decode the data.

Q2. We have 10 sources, each creating 600 8 bits character per second. Since only some of these sources are active at any moment, we use statistical TDM to combine these sources using character leaving. Each frame carries 6 slots at a time, but we need to add four bit addresses to each slot. Answer the following question
a) What is the size of an output frame in bits?

b) What is the output frame rate?

c) What is the duration of output frame?

d) What is the output data rate?

Solution :
1st: ( 2500 K / 2× 108 /) +4+6+20 =42.5
2nd:( 9700K/ 2× 108 /) +4+8+20 =80.5
3rd:( 13100 K/ 2× 108 /) +4+8+6+20 = 103.5
4th:( 8500K/ 2× 108 /) +4+6+20 = 72.5
5th:(10200 K/ 2× 108 /) +4+8+6+20 =89
The order of the arrival is 3 → 5 → 2 → 4 → 1

(A)Find the output port and output VCI for packets with the following input port and input VCI addresses * Packet 1:3, 78 * Packet 2:2, 92 * Packet 3:4, 56 * Packet 4:2, 71

Solution: * Packet 1: 2, 70 * Packet 2: 1, 45 * Packet 3: 3, 11 * Packet 4: 4, 41

B) Can a switching table in a virtual-circuit network have two entries with the same input port number? With the same output port number? With the same incoming VCIs? With the same incoming Values (port, VCI)? With the same outgoing values (port. VCI)?
Solution:
In a virtual circuit network,the VCIs is unique to a port.so,we can have the same input port and output port number and also we can have two entries with same VCIs but we cannot have same (port,VCI) for the two entries

Q5 .In table of switch or router, the minimum number of column in a datagram network is two; the minimum number of column in virtual circuit switch is four. Can you explain the reason? Is the difference related to the type of address carried in the packet of each network?
Solution: