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MODEL QUESTION PAPER- COMPUTER NETWORKS I (EC3003) -2013
Question 1
(20 Marks)
1.1 An analog signal is having a 5 kHz – 35 kHz bandwidth which required to be converted to a
digital signal using Pulse Code Modulation process.
i. What is the minimum sampling rate?
(2 Marks)
ii. If 200 quantization levels are used, what is the output digital bit rate?
(3 Marks)
1.2 What do you understand by non-linear quantization? What is the advantage of non-linear
quantization?
(3 Marks)
1.3 Data is to be transmitted over the PSTN using 16 QAM modulation scheme.
i. How many bits are represented by each signaling element in 16 QAM?
(1 Mark)
ii. If the bandwidth of the PSTN is 3000 Hz what is the maximum bit rate that can be send using
16 QAM modulation scheme in the above question?
(3 Marks)
iii. What is the modulation efficiency in the above transmission?
Note: Modulation Efficiency is given by following equation.
𝑀𝑜𝑑𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 =
𝐵𝑖𝑡 𝑅𝑎𝑡𝑒
𝐵𝑎𝑛𝑑𝑤𝑖𝑑𝑡ℎ
(1 Mark)
1.4 State the Shannon’s Law. If particular media has a bandwidth of 5 MHz, signal to noise ratio
is 511, then what is the channel capacity (maximum bit rate that the media can support)?
(5 Marks)
1.5 What do you understand by the term ‘NEXT cancellers’ in relation to data transmission?
(2 Marks)
Question 2
(20 Marks)
2.1 With the aid of sketches, explain the effect on a transmitted binary signal of the following,
i. Attenuation
ii. Limited bandwidth
iii. Delay distortion
iv. Line and system noise
(4 Marks)
2.2 Briefly explain the following terms
i. Signal Propagation Delay (TP)
(2 Marks)
ii. Transmission Delay (TX)
(2 Marks)
2.3 Use the given information to answer the following questions.
Velocity of propagation of an electrical signal in a cable = 3×108 ms-1
Cable length = 100 m
Data transmission rate = 10 Mbps
Amount of data to be transmitted = 5000 bytes (1 byte = 8 bits)
i. Find the Signal propagation delay
(1 Mark)
ii. Find the Transmission delay
(1 Mark)
iii. Find the ratio of the signal propagation delay to the transmission delay, ‘a’
(1 Mark)
iv. Find the Link utilization, U
Note: Link utilization, U is given by following equation
𝐿𝑖𝑛𝑘 𝑈𝑡𝑖𝑙𝑖𝑧𝑎𝑡𝑖𝑜𝑛, 𝑈 =
𝑊ℎ𝑒𝑟𝑒,
𝑎=
1
1 + 2𝑎
𝑆𝑖𝑔𝑛𝑎𝑙 𝑃𝑟𝑜𝑝𝑎𝑔𝑎𝑡𝑖𝑜𝑛 𝐷𝑒𝑙𝑎𝑦
𝑇𝑟𝑎𝑛𝑠𝑚𝑖𝑠𝑠𝑖𝑜𝑛 𝐷𝑒𝑙𝑎𝑦
(1 Mark)
2.4 Physical layer define four main characteristics. State them by giving example values/
diagrams for each. (you may take USB interface as the example)
(4 Marks)
2.5 Draw a diagram to illustrate the light signal propagation in the following cases. (Clearly label
the core and clad typical diameters).
i. In the single mode fiber
(2 Marks)
ii. In the multimode fiber (step index)
(2 Marks)
Question 3
(20 Marks)
3.1 Parity check and Cyclic Redundancy Check (CRC) are used in error detection at the data link
layer. Compare the advantages and disadvantages of those two error detection methods.
(4 Marks)
3.2 State the error detection capabilities of CRC-32, a standard divisor. Name two more standard
divisors.
(4 Marks)
3.3 If the data to be transmitted from station A is 1 1 1 0 0 1 1 0
The divisor is 1 1 0 0 1
i. Write them in polynomial format.
(1 Mark)
ii. Show that Frame Check Sequence (FCS) is X2 + X
(3 Marks)
iii. What is the bit stream that is transmitted in polynomial format?
(2 Marks)
iv. How does CRC detect errors at the receiving end?
(2 Marks)
3.4 Draw timing diagrams to illustrate the following ARQ methods,
i. Selective Repeat method
(1 Mark)
ii. Go-back-N method
(1 Mark)
3.5 In Idle ARQ method, if any of the ACK frames (acknowledgements) or NAK frames
(negative acknowledgements) is lost in the media due to noise or any other reason,
transmission comes to a hold where transmitter and receiver both are waiting for each others’
transmissions. What are the methods used to avoid such situations?
(2 Marks)
Question 4
(20 Marks)
4.1 Application layer send 2500 bytes of data to the Transport layer. TCP segment size is 1580
(TCP segment means without the TCP header. Need to add the TCP header before sending to
Network layer). If the data link layer protocol can accommodate 1500 data bytes, show all
packets, frames which goes through layers. Clearly show all header sizes and calculations.
You may assume the standard header sizes.
(6 Marks)
4.2 Write short notes on the following. You should indicate the ISO-OSI layer it operates,
number of broadcast domains, number of collision domains etc.
i. Router
(2 Marks)
ii. Bridge
(2 Marks)
iii. Switch
(2 Marks)
4.3 MAC addresses are given in the hexadecimal format in the figure Q 5.3. Answer the
following questions referring figure Q 4.3
MAC address
AAAA:BBBB:1111
PC 1
MAC address
AAAA:BBBB:2222
MAC address
AAAA:BBBB:3333
PC 2
PC 4
MAC address
AAAA:BBBB:4444
PC 3
PC 5
MAC address
AAAA:BBBB:5555
Figure Q 5.3
i. PC 1 sends a frame to PC 5 with 1000 bytes received from network layer. Draw the IEEE
802.3 Ethernet frame for that transmission. Clearly indicate all field values. (state any
assumptions)
(3 Marks)
ii. PC 2 sends a frame to PC 4 with 40 bytes received from network layer. Draw the IEEE 802.3
Ethernet frame for that transmission. Clearly indicate all field values. (state any assumptions)
(3 Marks)
iii. If PC 3 sends an ARP broadcast, what is the destination MAC address?
(2 Marks)
Question 5
(20 Marks)
5.1 Name three (3) types of transmission media available. Indicate what the limitations you
encounter in those.
[4 Marks]
5.2 Briefly explain the noise, attenuation, and dispersion with respect to fiber optics.
[6 Marks]
5.3 What do you understand by multiplexing?
[1 Mark]
5.4 With the help of diagrams, briefly explain the Time Division Multiplexing (TDM) and
Frequency Division Multiplexing (FDM).
[4 Marks]
5.5 Draw the first order multiplexer, second order multiplexer and third order multiplexer.
Clearly indicate the data rates, number of channels etc.
[3 Marks]
5.6 Draw the Synchronous Digital Hierarchy (SDH)
[2 Marks]
Question 6
(20 Marks)
6.1 Satellite transmission is used widely, for long distance transmissions. Briefly explain what is
geo-stationary orbit and advantage of it with respect to satellite transmission?
[4 Marks]
6.2 FDMA, TDMA, CDMA are three (3) multiple access methods; briefly explain.
[6 Marks]
6.3 State the Shannon’s equation.
[1 Mark]
S
6.4 N of a particular transmission media is 1023. Bandwidth is 4 kHz. If the 8PSK modulation is
used, what is the maximum bit rate of signal can be send through this media?
[4 Marks]
6.5 CRC is used for error detection in data transmission.
If the data to be transmitted is 1 1 1 0 0 1 1 0
The divisor is 1 1 0 0 1
i.
ii.
iii.
Show that Frame Check Sequence (FCS) is 0 1 1 0
What is the bit stream that is transmitted?
If the received bit stream is 1 1 1 0 0 1 1 0 1 1 1 1, show that received bit stream
is in error.
[5 Marks]
Question 7
(20 Marks)
7.1 What are the four (4) main physical layer characteristics? Briefly explain each of those with
example values.
[4 Marks]
7.2 Token and Carrier Sense Multiple Access/ Collision Detection (CSMA/CD) are two methods
used for Media Access Control. Briefly explain.
[4 Marks]
7.3 IEEE 802.3 is a widely used protocol in data transmission. Draw the IEEE 802.3 frame
structure, clearly indicate each field size and state the importance of each of those fields.
[5 Marks]
7.4 IP packet of 1520 bytes is to be transmitted from the network layer. Data link layer protocol
is IEEE 802.3. How many data link layer frames will be there? Clearly draw all frames
indicating each and every field with amount of bytes in each field.
[5 Marks]
7.5 What are the advantages and disadvantages of using datagram and virtual circuit as network
layer transmission method?
[2 Marks]
Question 8
(20 Marks)
8.1 State
i.
ii.
iii.
Three (3) protocols used at Application layer
Two (2) protocols used at Transport layer
One (1) protocol used at Network layer
[4 Marks]
8.2 Write shot notes on the followings,
i.
Bridge operation and router operation (notes should include the ISO-OSI layer it
operates, how the frames/ packets are handles, how many broadcast domains, how
many collision domains are there etc)
[6 Marks]
ii.
Leased Circuit
iii.
Dial up connection
[2 Marks]
[2 Marks]
iv.
ADSL Connection
v.
ISDN Connection
[2 Marks]
[2 Marks]
vi.
HSDPA Connection
[2 Marks]