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  Select one of the categories you may need to make clear. The sample questions which are being addressed are as follows.
  1. Communication can be categorized into two. i.e. Public and Personal communication. Explain the characteristics of each. 1. Explain Analog and Digital type of signaling 1. Discuss the quality factors used in the Telephone Network.
  2. Telecommunication is a powerful tool of personal communication. Why is it powerful? 2.What is Forward and Backward error correction? 2. Prove the following
a. Answer / Bid = Answer / Seizure (1-Congestion)
b. Average Holding Time = ~ (Answer / Seizure ) * (Average Conversation Time)
(Approximately equal)
  3.Explain Four layers of SS7.
3. How do you nameplate each communication node? (Numbering of a telecommunication terminal)

4.In SS7 signaling backward error correction is deployed. Explain the difference between basic method and preventive cycle retransmission of error correction. Clearly explain the sequence control field.


4. Telephone network will have the following major elements;Explain them. 3. In a Telecom Network the observation with regard to two routes of a telephone exchange where 15,000 Customers are connected is given as follows.....

a. Geographical location of the customer

b. Access network

c. Local switch/s

d. Domestic Transport Network

5. In the basic method of error correction station A is sending 5 messages to station B.Draw the signaling diagram that you may observe from station A to station B to show the above transaction. Clearly explain the sequence control field.

e. International Gateway

e. International Gateway

g. Other country’s Domestic Transport Network

7. Error control plays a vital role in transmitting data from one station to another station. In CCITT No. 7 signalling, for error control Cyclic Redundancy Code of 16 bits are used. Explain how CRC is applied for error control in No. 7 signalling. 1.Transmission essentially involves transporting of information from one place to another.Explain why digital transmission cannot be achieved by merely following the Sampling Theorem.
5. Domestic transport network includes how a call is routed via many hierarchical
Telephone exchanges. Explain in detail the characteristics that you can find in a hierarchical switching network in Sri Lanka.
8. Design a circuit 1.2.Explain the basic process of Pulse Code modulation.
  9. Show an instant where CRC is failed to identify errors in the bit stream.

1.3 In practice, non-linear quantizing is deployed as against linear quantizing, explain the reasons behind. 256 levels are used for non-linear quantizing and there are 8 segments each positive and negative sample. Explain the basic characteristics of non-linear quantizing used for European system (the A-law signal compression of 13 linear segments)


1.1 Explain the major components of a telephone exchange and explain their limiting
1.2 Explain the difference between Strict and Wide sense of Non Blocking.

1.4Each quantized level will be converted to binary before transporting the quantized level
(related to the sample) into the transmission media. Assuming a telephone will generate a
maximum of +3072 mV calculate the encoded format that will be sent in the transmission
media for the following sample values.
i. + 2210mV
ii. + 128mV
iii. – 14mV
iv. –416mV


1.4 A ‘T’ switch will connect two subscribers in two different locations as follows.
1.5 C is the Master Switch, where as D and E are Remote Switches. Each remote switch
will connect to Master Switch by 16 PCM systems namely P0 to P31. A is speaking
with B on P0 TS8, where as B is speaking to A on P18 TS20.
(i) Explain clearly how A and B is in conversation with respect to the Master
(ii) Assuming only these RSU are connected to this MSU, calculate the
maximum traffic that this switch can handle.

2.1.Time Division Multiplexing (TDM) is deployed in the PCM system in order to maximize the utilization of the transmission media. Explain briefly the TDM systems deployed in the Europe and America / Japan.



2.1Explain the basic elements of a fixed telephone network.


2.2.In practice, non-linear quantizing is deployed as against linear quantizing, explain the reasons behind.


2.2 Basic demarcation of telephone network can be categorized as follows.
Out-side plant
Explain the physical demarcation of each of the above and the functions that
we have to achieve from the each above.

2.3. 256 levels are used for non-linear quantizing and there are 8 segments for each positive and negative sample. Explain the basic characteristics of non-linear quantizing used for European system (the A-law signal compression of 13 linear segments)


2.3 A digital telephone exchange contains a single stage ‘T’ switch, which can
accommodate 512 PCM systems. Assuming all the 512 PCM systems can be utilized
for telephone conversation, what is the maximum traffic in Earlangs that this switch
can carry.

3.1 .Draw a block diagram of PCM clearly explaining how a basic frame structure is achieved in each block.


Two RSUs connected to the exchange are connected with PCM0 to PCM15 to one
RSU, while the other RSU is connected with PCM385 – PCM400. Total number of
PCMs to the Master switch will be 512 (assume all these PCMs are used for RSUU).
Two customers connected from these two RSUU are connected via PCM1 TS5 and
PCM386 TS10 to the main switch. If this ‘T’ switch is working as an output
controlled ‘T’ switch, explain clearly how the ‘T’ switch works when these two
customers are in conversation with respect to the elements of buffer memory,
controller memory and microprocessor.
Note: TS = Time Slot

3.2. A PCM system will comprise of sampling, quantizing and encoding. Explain each block. clearly.


3.1Explain the difference between Analogue & Digital switching.

3.3 Three consecutive voice samples in a 30 channel PCM system are identified as follows.
+50V, 0V, -68V
Draw the wave forms that you can observe in the transmission media, assuming HDB3 transcoding.
(Assuming A-Law compression for non-linear quantizing


3.2 What are the basic components of a Telephone exchange explain the functions of each.
3.3 Design 3-stage strict sense of non-blocking 49 inputs, 49 outputs. How
many middle switches you use? Prove the total number cross points are
4.1 Explain the following with reference to PCM.
3.4 If you have to design 48 input 48 out 5 stage switching Network, how do
you design to obtain minimum number of cross points? Calculate the
number of cross points in that network.

4.2 What are the applications of TS0 and TS16 in the PCM frame.


4.1Today the telephone exchanges use packet switching technology, named Next
Generation Networks. Explain the basic advantage of utilizing NGN networks.

4.3 .Briefly explain why higher order multiplexing is necessary in telecommunication.In SMW4 submarine cable system, STM-64 is used which is equivalent to 10Gbit/s. Briefly Explain how a bit in a sample is multiplexed and de-multiplexed if used SMW4


  4.2The following is a part of digital switching network deployed in Sri Lanka. Each
Remote Subscriber Unit is connected to Master exchange by 8 PCM systems.

5. .Digital transmission is essential in today’s telecommunication as it is the most efficient way of reproducing the transmitted signal at the receiving end.”
Explain the above statement with reference to different stages in digital transmission.


  From the diagram what is your assessment of the number of customers that
can be connected to each RSU.
  5.2 .What are the different types of repeaters?

Assuming that there are no customers connected at Ratmalana Master
exchange, what is the maximum traffic that the Master exchange can
handle. (Assume no other connections from Master exchange to other
exchanges and this will work as a closed Switching network.)

5.3 .Repeaters are extensively used in Pulse Code Modulated (PCM) transmission links in Cable PCM transmission systems.Explain different sections of a repeater with reference to the functions of each unit.
If A customer speaking to B customer on P03 TS05 and P14TS10. Clearly
explain how digital switching is achieved at Ratmalana Master exchange.
  6.0 .Explain the basic difference between SDH and PDH transmission.


6.1 Clearly explain the difference between PDH and SDH multiplexing methods.



7.1 STM-1 Frame structure is defined by 9x270 Matrix, each point of the Matrix is a byte (8 bits).Show that STM-1 will carry 155.52 Mbps.



7.2 The following shows the STM-1 frame. Explain the importance of each area shown.

7.3 SDH will use the following 3 processes.
v. Mapping
vi. Aligning
vii. Multiplexing
Briefly explain the applications of above when a PDH 2.048 Mbps, 34.368 Mbps, 139.264
Mbps is converted to STM-1. Draw the relevant diagram.
7.4 Draw the SDH multiplexing hierarchy from STM-1 to STM-256 and show the basic information of
1 bit is shrink from 6.4 ns to 25 ps when the multiplexing is achieved up to STM-256. Clearly show
the bit speed of each SDH hierarchy