COMMUNICATION SWITCHING TECHNIQUES -...

COMMUNICATION SWITCHING TECHNIQUES

SUBJECT: COMMUNICATION SWITCHING TECHNIQUES

UNIT-I

COMPONENTS AND PRINCIPLES

1. What is meant by telecommunication?

Telecommunication network carry information signals among entities. Entities

may be computers, a human being and data terminals. The process of information transfer

may be file transfer, message transfer in between terminals, etc

2. Define calling and called subscribers?

Calling subscriber:

In telephone conversation, the one who initiates the call

Called subscriber:

The one for whom the call.

3. Define switching system?

The subscribers are not connected directly with others; instead, they are connected

to switching system. When a subscriber wants to communicate with another, a connection

is establishing b/w the two switching system.

Switching system also called as switching office (or) Exchange

4. Define control function?

The function performed by a Switching system in establishing and releasing

connections

5. What are the types of switching system?

Manual Switching system

Automatic Switching system

6. What are the types of Automatic Switching system?

Electromechanical switching system

Electronic switching system

7. What are the types of Electromechanical and Electronic switching system?

Electromechanical: Electronic:

Strowger switching Space division switching

Crossbar switching Time division switching

III YEAR/B.Tech-IT


8. What is meant by Strowger switching?

The control functions are performed by circuits associated with switching system

9. What is meant by Electronic switching?

The control functions are performed by the Processor (or) a Computer.

It also called as Stored Program Control (SPC)

10. Define Space division and Time division switching?

Space division:

A dedicated path is established b/w the calling and called subscriber for

the entire duration of the call.

Time division:

The sampled values of speech signals are transmitted at fixed intervals.

11. Define Trunk?

The Links that run between switching system are called trunks

12. Define Transducer?

Transducers perform the energy conversion. whether optical signal to voice signals (or)

Electrical signal to Voice signals

13. What are the telecommunication networks?

Telegraph networks

Telex networks

Telephone networks

Data networks

14. Basic components of switching system?

Inlets, outlets and switching network

15. Define symmetric network?

Inlets and outlets are equal in a switching (N=M)

16. Define blocking and non-blocking network?

Blocking network:

There is a path free in the network

Non-blocking network:

There is no path free in the network

17. What is meant by Interdigit gap?

Two successive trains are distinguished from one another by a pause in between

them

18. What are the different types of signaling tones?

Dial tone


Ringing tone

Busy tone

Number unobtainable tone

Routing tone

19. What are the design parameters?

Cost of the switching system

Traffic handling capability

Equipment utilization factor

Cost capacity index

20. What are the control functions in switching system?

Event monitoring

Call processing

Charging

Operation and maintenance

21. What are the service information are needed for rates of subscriber?

Call barring

Call priority

Call charging

Origin based routing

No dialing calls

22. What is the procedure for establishing a connection in crossbar switching?

Energize horizontal bar Energize vertical bar

Energize vertical bar (or) energize horizontal bar

De-energize horizontal bar De-energize vertical bar

23. What is the principle of crossbar switching?

To provide a matrix oh n*m sets of contact with only n+m activators (or) less to

select one of the n*m sets of contacts.


UNIT-II

SPACE DIVISION AND TIME DIVISION SWITCHING

1. Define stored program control?

A program or a set of instruction to a computer is stored in its memory and

executed automatically one by one by the processor.

2. What are the electronic space division switching systems?

Electromechanical switching

Electronic switching

3. What are two approaches to organizing stored program control?

Centralized SPC

Distributed SPC

4. Define centralized SPC?

All the control equipment is controlled by a single processor. It must be capable

of processing 10-100 calls per second.

5. What are the modes of dual processor?

Standby mode

Synchronous duplex mode

Load sharing mode

6. Define standby mode?

One processor is active and the other is on standby, both hardware and software.

It is used to determine which of the subscribers and trunks are busy (or) free.

7. Define Synchronous duplex mode?

The hardware coupling is provided between the two processors which execute the

same set of instructions and compare the results continuously.

8. Define availability and unavailability of the processor?

A = MTBF/(MTBF + MTTR)

A= availability

MTBF=Mean time b/w failure

MTTR=Mean time to repair

U=1-A

U= unavailability

9. What are the interrupts in SPC?

Vectored interrupt

Non-vectored interrupt


10. Define Distributed SPC?

The control functions are shared by many processors within the exchange itself.

This offers better availability and reliability.

11. Differance between micro programmed control and hard-wired control?

Micro programmed control Hard-wired control

1. Flexible not flexible

2. Slower faster

3. More expensive for processing functions less expensive

4. Easier to implement complex processing functions difficult to implement

12. Difference between single and multistage networks?

i) Inlet to outlet is through a Inlet to outlet is through a

Single cross point multiple cross point

ii) Use of a single crosspoint per Use of a multiple crosspoint may

Connection results in better quality link degrade the quality of a connection

iii) Time for establishing a call is less time for establishing a call is

more

iv) The network is none blocking the network is blocking

13. Define full availability?

There are k alternative paths for any inlets/outlets pair connection. The network is

said to be full connectivity (or) full availability

14. Define baseline networks?

Networks that support N simultaneous connections but under restricted traffic

distribution conditions

15. When a network is called as analog and digital time division switching?

When PAM samples are switched in a time division manner, the switch is called as

analog time division switching.

When PCM samples are switched in a time division manner, the switch is called as

digital time division switching.

16. Define time division space switching?

A single switching element (bus) is being time shared by N connection, all of

which can be active simultaneously and a physical connection is establishing b/w

inlet and outlet duration of time sample transfer is called time division space

switching.

17. What is the controlling in a time division time switching?

Sequential write / random read


Random write / Sequential read

Random input / random output

18. What are the two modes of time division time switching?

Phased operation

Slotted operation

19. Define time multiplexed switch?

The inlets and outlets are trunks which carry time division multiplexed data

streams. Such a switches called a time multiplexed switch.

20. Define combination switching?

It can be built by using a number of stages of time and space switches according

to time space (TS) and space time (ST).


UNIT-III TRAFFIC ENGINEERING

1. Why we are going for traffic engineering?

The load (or) traffic pattern on the network varies during the day with heavy

traffic at certain times and low traffic at other times. Such a bisis are provides a traffic

engineering.

2. What is meant by busy hour?

In a day, the 60 minute interval in which the traffic is highest is called busy hour

(BH).

3. What are the basic busy hours?

Busy hour

Peak busy hour

Time consistent busy hour

4. Define busy hour calling rate and day-to-busy hour traffic ratio?

Busy hour calling rate = average busy hour calls / total number of subscriber

Day-to-busy hour traffic ratio= busy hour calling rate/average calling rate

5. Define traffic intensity (A0)?

A0 = period for which a server is occupied/total period of observation

Traffic intensity is called erlang(E).

6. Define traffic carried per server?

Traffic carried per server=occupied duration/total duration

7. Define centum call second?

Traffic intensity is also called as centum call second.

This represents a call-time product. One CCS may mean one call for 100 seconds

duration (or) 100 calls for one second duration each or any other combination.

8. How can the overload traffic may be handled?

The overload traffic may be rejected without being serviced (or)

Held in a queue until network become available.

9. Define loss and delay system?

Loss system:

Under overload traffic condition a user call is blocked and is not serviced unless

the user makes retry.

Delay system:

A good operator registers the user request and establishes connection as soon as

network becomes availability without the user having to make another request.


10. What are traffic models in loss system and delay system?

Loss system

Blocking models

Congestion models

Delay system

Queuing models

11. Define Grade of service (GOS)?

The amount of traffic rejected by the network is an index of the quality of the

service offered by the network. This is termed as Grade of service.

Grade of service=Lost traffic/offered traffic.

12. What is meant by random or stochastic process?

One or more quantities vary with time in such a way that the instantaneous values

of the quantities are not determinable precisely but are predictable with certain

probabilities.

13. What are the stochastic processes?

Continuous time Continuous state

Continuous time discrete state

Discrete time Continuous state

Discrete time discrete state

14. Define stationary processes?

Random processes whose statistical parameters do not change with time are

known as stationary processes.

15. Define ergodic processes?

The random processes which have identical time and ensemble average are

known as ergodic processes

16. What are the models in loss system?

Lost calls cleared (LCC)

Lost calls returned (LCR)

Lost call held (LCH)

17. What is meant by lost calls cleared (LCC)?

It assuming infinite number of subscriber. The arrival rate is independent of the

number of subscribers already busy and remains constant irrespective of the state of the

system.

18. Define offered traffic?


Offered traffic=new traffic + retry traffi

19.Define CCR (Call Completion Rate)

CCR is defined as the ratio of the number of successful calls to the number

of call attempts. The number of call attempts in the busy hour is called busy hour

call attempts (BHCA).

20.Define busy hour calling rate.

It is defined as the average number of calls originated by a subscriber

during the busy hour.

21. An exchange serves 2000 subscribers. If the average BHCA is 10,000 and the CCR is

60%, calculate the busy hour calling rate.

Solution:

Average busy hour calls = BHCA × CCR = 6000 calls.

Busy hour calling rate = Average busy hour calls / Total no. of

subscribers

= 3 calls

22. List out the basic performance parameters for a loss system\

a. Grade of service

b. Blocking probability

c. Delay systems.

23. Define congestion models.

The traffic models used for studying loss systems are known as blocking

or congestion models. And the ones used for studying delay systems are called

queuing models.

24.Define grade of service.

It is defined as the ratio of lost traffic to offered traffic. Offered traffic is

the product of the average number of calls generated by users and the average

holding time per call.

GOS = A

AA 0−

Where,

A = Offered traffic

A0 = Carried traffic

A-A0 = Lost traffic

25.Define carried traffic.

The actual traffic carried by the network is called the carried traffic.

26.Define blocking probability (PB).


The blocking probability PB is defined as the probability that all the

servers in a system are busy. When all the servers are busy, no further traffic can

be carried by the systems and the arriving subscriber traffic is blocked.

27.Define delay probability.

The probability that a call experiences delay, termed delay probability.

28.Define flow control.

An easy way of bringing the system back to stable region of operation is to

make it behave like a loss system until the queued up traffic is cleared to an

acceptable limit. This technique of maintaining the stable operation is called flow

control.

29. State random process.

A random process or a stochastic process is one in which one or more

quantities vary with time in such a way that the instantaneous values of the

quantities are not determinable precisely but are predictable with certain

probability. The quantities are called Random Variables.

30. Give the four different types of stochastic process.

1) Continuous time continuous state

2) Continuous time discrete state

3) Discrete time continuous state

4) Discrete time discrete state.

31. Define stationary process

Random processes whose statistical parameters do not change with time

are known as stationary processes.

32. Define Ergodic Processes

The random processes, which have identical time and ensemble averages,

are known as ergotic processes.

33. Define Wide-Sense Stationary Processes.

In some random processes, the mean and the variance alone are stationary

and other higher order moments may vary with time such processes are known as

wide-sense stationary processes.

34. List out the block which is used in delay systems.

a) Message switching

b) Packet switching

c) Digit receiver access

d) Automatic call distribution

e) Call processing.


35. Give the three ways in which overflow traffic handling.

a) The traffic rejected by one set of resources may be cleared by another

set of resources in the network.

b) The traffic may return to the same resource after sometime.

c) The traffic may be held by the resource as if being serviced but actually

serviced only after the resources become available.

36. List out the three analysis aspects of telecommunications.

a) Modeling the system

b) Traffic arrival model

c) Service time distribution

37. Give the three models of loss systems.

a) Lost calls cleared (LCC)

b) Lost call returned (LCR)

c) Lost calls held (LCH)

38. Define Erlang traffic

The system is said to be in state j when j servers are busy. As long as all

the servers in the system are not busy, the entire incoming traffic is carried by the

network and when all the servers are busy no traffic is accepted by the network.

Such a traffic on the network is known as Erlang traffic or pure chance traffic

of type 1.In this case, we have

Ci = λ for 0 < i < R, CR = 0

Where R is the number of servers in the system

λ represents the Poisson arrival rate.

39. Define Delay Systems

A class of telecommunication networks, such as data networks, places the

call or messages arrivals in a queue in the absence of resources, and services

them as and when resources become available. Servicing is not up until the

resource becomes available. Such systems are known as delay systems which are

also called Lost Call Delayed (LCD) systems.

40. List out the few examples of delay systems in telecommunications.

a) Message switching

b) Packet switching

c) Digit receiver access

d) Automatic call distribution

e) Call duration

41. Explain about D.G.Kendall notations

A queuing system is characterized by a set of six parameters. A concise 6-

parameter notation, due to D.G.Kendall, is used to represent different types of


queuing systems. This notation reads as A/B/c/K/m/Z. The parameters

specifications are as follows: A = Arrival process specification

B = Service time distribution

c = number of servers

K = queue capacity

m = number of sources (input population)

Z = Service discipline

Uses: to represent a loss system where the parameter K has a value zero.

42. Give some commonly used Queue Discipline

a) First-come-first served (FCFS)

b) Random selection

c) Priority based selection

43. In a telephone system, there are 20 servers and 100 subscribers. On an average, there

are 10

busy servers at any time. The probability of all the servers being busy is 0.2. calculate

the

grade of service assuming (a) Erlang traffic, and (b) Engest traffic.

Solution:

For Erlang traffic, GOS is the same as PR. Therefore, GOS =0.2.

For Engest traffic, GOS is given by

Carried traffic = Traffic of average busy servers = 10

Therefore, GOS = RPAN

RN

0−

−

GOS = 2.010100

20100×

−

−

GOS = 0.1875

The GOS is lower in the case of LCC model with finite sources.

44. A TASI system has 10 channels and 20 sources connected to it. What is the

probability of

clipping if the activity factor for each source is 0.4?

Solution:

Average number of busy servers = 0.4 * 20 = 8

Clipping occurs if 10 or more sources are in the activity phase simultaneously.

Therefore,

the probability that 10 or more sources are active gives the clipping probability. This

is

determined from the poison equation as:


Prob (clipping) = )8(10

=∑∞

=

tPj

j

= 1- )8(9

0

=∑=

tPj

j

= 1- 8−e (1 + 8 + 2

82

+ …… + )9

89

Prob (clipping) = 0.284

45. List out the analysis assumptions in lost calls returned system

1) No new call is generated when a blocked call is being retried.

2) A number of retry attempts may be involved before a call eventually gets

serviced.

3) Retries are attempted after a random time and each retry time is statistically

independent of the others.

4) Typical waiting time before a retry is longer than the average holding time.

46. Define Engest traffic or pure chance traffic of type 2.

The arrival rate to the system is dependent on the number of subscribers who

are not

occupied as the busy subscribers do not generate new calls. The traffic in this case is

known

as Engest traffic or pure chance traffic of type 2.

47. What is meant by Lost Call Held system.

Lost call held (LCH) systems are distinctly different from delay systems

where the

messages are queued and taken up for service as and when resources are available.

The time

a call spends in a delay system is the sum of the waiting time and the service time.

In the LCH model, the total time spent in the system is independent of the watng

time and

is only determined by the average service time required. Example is TASI System.

48. List out the important Random Variables in a Queuing System.

S.No Random Variable

Notation

1 State of the system (No. of calls present in

the system k


2 Queue length (No. of calls or requests

waiting to be serviced) kq

3 Number of calls in service ks

4 Mean wait time tq

5 Mean service time tk 6 Mean arrival rate λ

7 Mean service rate µ

8 Mean interarrival time τ

9 Probability that there are k calls in the

queuing system Pk

10 Traffic intensity (λ/ µ) ρ

11 Server utilization u

49. Write down the steady state equation of a Birth-Death Process.

Under steady state conditions, the state probabilities reach an equilibrium value

and do

not change with time. i.e., Pk(t1) = Pk(t2) = Pk(ti) = Pk. therefore, the steady state

equations of

a B-D process are,

Pk-1 λk-1 + Pk+1 µk+1 – (λk + µk) Pk = 0 for k 1≥

P1 µ1 – λ0 P0 = 0 for k = 0

50. What is meant by Renewal Process or Pure Birth Process.

The process can be treated as a special case of the B-D process in which the death

rate is

equal to zero. In otherwords, there is no death occurring in the process. Such a

process is

known as renewal process. The equations governing the dynamics of a renewal

process can

be easily arrived at from the B-D process equations by setting µk = 0. Therefore,

)()()(

11 tPtPdt

tdPkkkk

K λλ −= −− for k 1≥

)()(

000 tPdt

tdPλ−= for k = 0

51. Write down the Poisson Process Equation.

If we assume a constant birth rate λ which is independent of the state of the

system, then

we get Poisson process. The governing equations of a Poisson process are


)()()(

1 tPtPdt

tdPkk

K λλ −= − for k 1≥

)()(

00 tPdt

tdPλ−= for k = 0

52. Mention some of the real life examples for Poisson Process.

a) Number of telephone calls arriving at an exchange.

b) Number of coughs generated in a medical ward by the patients.

c) Number of rainy days in a year.

d) Number of typing errors in a manuscript.

e) Number of bit errors occurring in a data communication system.

52. Describe the Poisson Process according to Venn Diagram.

a) A Pure Birth process with constant birth rate.

b) A Birth-Death process with zero death rate and a constant birth rate.

c) A Markov process with state transitions limited to the next higher state or to the

same

state, and having a constant transition rate.

56. What is meant by Pure Death Process.

The system is said to be pure death process in a B-D Process, is setting the

birth

rate equal to zero. Thus the equation of pure death process is given by,

)()()(

11 tPtPdt

tdPkkkk

K µµ −= ++ for k 1≥

)()(

110 tPdt

tdPµ= for k = 0

57. Write down the necessary condition for stable operation of delay system for infinite

queue

Capacity.

1pµ

λ

Where, λ- Mean Arrival Rate, µ- Mean Service Rate

Or 1pc

A

Where, A-Offered Traffic, c- Number of Servers


UNIT-IV DIGITAL SUBCRIBER ACCESS

1. What is the main objective of ISDN?

The main objective of ISDN is to offer new digital transmissions services to

Subscribers.

2. Define ISDN

An integrated services digital network in which the same digital switches and

digital paths

are used to establish different services, for examples, telephony and data.

2. What are the bearer services of ISDN?

The main bearer services are the transport of audio and digitized voice, circuit

Switched digital channels at rate that are multiples of 64 Kbps, Packet switched virtual

Circuits and connectionless service.

3. What are the principles of ISDN?

1. Support voice and non-voice communication

2. Support switched and non switched application.

3. Reliance on 64Kbps connection

4. Intelligence in the network.

4. list out the three factors which are responsible for the developments towards ISDN.

a) Sociological or societal needs

b) Economic necessities

c) Technological developments

4. What are key objectives of ISDN?

The key objectives are:

1. Standardization

2. Transparency

3. Separation of competitive functions

4. Least and switched services

5. Smooth migration

6. Multiplexed support

5. What are the benefits of ISDN?

1. Large scale and low cost production.

2. Enhanced service provider.

6. What are the services offered by ISDN?

ISDN provides number of services such as facsimile, teletex, videotext etc.

7. What are the connections supported by ISDN?


1. Circuit switched calls over B or H channel

2. Semi permanent connection over B or H channel

3. Packet switched connection over B or H channel.

4. Packet switched connection over D channel

5. Frame relay calls over B.

8. State Little’s formula

It states that the mean number of customers in any queuing system is equal to the

product of

the mean waiting time for a customer and the mean arrival rate.

M = λT or T = M/λ

9. List out the analysis assumptions in the case of network and protocol architecture.

a) The total capacities of the integrated and segregated networks are

identical.

b) Input services have identical requirements in both the cases.

c) Service rate distributions are identical.

10. Define Bearer Service functions

In ISDN protocol architecture, the lower three layer functions are known as bearer

service functions.

11. Define Teleservices

Services offered by service providers are known as teleservices. Functionalities of

layers 1-7 are required to offer teleservices which are built over bearer service functions.

12. list out the three fundamental channels in ISDN.

There are 3 types of fundamental channels in ISDN around which the entire

information transmission is organized. These are

a) Basic information channel B channel, 64 kbps

b) Signaling channel D channel, 16 or 64 kbps

c) High speed channel H channels

H0 Channels, 384 kbps



13. Write down the frame size and frame rate equations in the case of transmission

channels.

I = RF × D, R = RF × S

Where, I = Information stream rate in bps.

RF = Frame rate in frames per second

D = number of information bits in each frame.

R = Rate in bps (8,16, or 32 kbps)

14. Give the two multiplexing schemes used in transmission channels.

a) Fixed format multiplexing – It is suitable when the mixture of sub rate

streams is known in advance.


b) Flexible format multiplexing – It may lead to efficient B channel

utilization if the mixture of sub rate streams varies dynamically.

15. Mention the applications of H channels.

a) High speed facsimile

b) High fidelity audio

c) High speed data.

16. Write down the interface access standard used in ISDN.

a) Basic rate access – Caters to low bit rate services

b) Primary rate access – Caters to services that demand high bit rates.

17. what are the basic factors consider before selection of access interfaces in ISDN.

a) Use of much of the existing telephony networks; expensive replacement

is not to

be resorted to except for some special function or locations.

b) Use of low cost VLSI technology to add new functionalities and to

provide

Upgrade capabilities.

18. Define signalling

ISDN uses a common channel signalling scheme. The signalling is done over the

D channel which acts as the common signalling channel for the B channel and H

channels which carry the user information

19. Give the signalling categories of ISDN.

a) User level signalling

b) Network level signalling

20. Define functional terminal

Message based signalling is employed when the user end equipment is an

intelligent terminal. In ISDN parlance, an intelligent terminal is known as functional

terminal.

21.write the functions of addressing

1. Addressing scheme is easy to understand by the user

2. It adapt the existing one

3. It should allow the expansion of sizing bit

4. Number should be a decimal one.

22. List out the messages groups.

1) Call establishment messages

2) Call control messages

3) Call disconnect messages

4) Miscellaneous messages


23. What are the mandatory fields for all the messages?

1) Protocol discriminator

2) Call reference

3) Message type

24. What are the six field’s present messages formats of ISDN?

a) Routing label

b) Circuit identification code

c) Message type

d) Mandatory fixed part

e) Mandatory variable part

f) Optional part.

25. What are the features of physical layer?

1. Encoding of bit stream

2. Full duplexing

3. Multiplexing

4 Activation and deactivation of physical circuit

5. Terminal identification.

26. What are the three types of traffics in collision avoidance?

1. B channel traffic

2. Incoming B channel traffic

3. Outgoing B channel traffic.

27. What are the methods used for the control of supplementary services?

1. Key pad control

2. Feature key management protocol

3. Functional protocol.

28. What are the three types of ISDN services?

Bearer services (layer three function), teleservices (4 to 7 layer),

supplementary

services (conjunction b/w bearer and teleservices).

29. List out the some of the important new services provided by ISDN.

a) Videotext

b) Electronic mail

c) Digital facsimile

d) Telefax

e) Database access

f) Electronic fund transfer

g) Image and graphics exchange

h) Document storage and transfer

i) Document storage and transfer

j) Automatic alarm services, e.g., smoke,fire,police,and medical


k) Audio and video conferencing.

30. What are the services of LAPD?

1. Acknowledgement information transfer service

2. Unacknowledgement information transfer service

31. What is the purpose of SS7

SS7 is used to generalize the common channel signalling.

32. List out the characteristics of SS7

1. Optimizing digital communication

2. Designed reliability

3. Suitable for point to point terrestrial link

33. List out the interactive services

1. Conversational

2. Messaging

3. Retrieval.

34. What is BISDN?

Broad band ISDN evolved from narrow band ISDN. BISDN is used to

increase

the data rate for high data rate application. Its also used for universe communication.

35. List out the distribution service

1. Distribution without service with out user control

2. Distribution with service with out user control.

36. What is Broadband ISDN?

Broadband ISDN (BISDN) is defined as a network capable of supporting data

rates greater than the primary rate (1.544 or 2.048 Mbps) supported by ISDN. The main

aim of BISDN is to support video and image services.

37. give the services of BISDN.

It is broadly classified into two types. They are

a) Interactive services

i) Conversational services

ii) Messaging services

iii) Retrieval services

b) Distribution services

i) Broadcast services

ii) Cyclic services

38. Write down the important requirements of BISDN.

a) Narrowband signals and broadband signals


b) Interactive and distributive services

c) Point – to- point, point-to- multipoint and broadcast connections

d) Different traffic patterns (e.g., for voice, data and video)

e) Value-added services

f) Multirate switched and Nonswitched connections

g) Channel bandwidth (140 Mbps per service)

39. List the channels proposed for BISDN.

a) H2 channel, 30-45 Mbps

b) H3 channel, 60 -70 Mbps

c) H4 channel, 120 – 140 Mbps

These channels are organized to provide a transmission structure at the user

interface.

40. Distinguish between digitized voice and data traffic.

S.No Digitized Voice Data Traffic

1 Periodic bursty in nature Aperiodiic bursty in nature

2 Fxed length burst Variable length bursts

3 Small packet size Large packet size

4 Packetisation time critical Packetisation is not critical

5 Hard bound on delay Soft bound on delay

6 Hard bound on the variance of

delay

Soft bound on the variance of delay

7 Loss of parts of speech

acceptable

Loss of parts of data unacceptable

8 Low overhead as there is no

error recovery

High overhead due to error detection and

recovery

41. How voice data integration schemes are placed.

It placed under two broad classes. They are

a) Random allocation of Basic Bandwidth Units

b) Contiguous allocation of BBUs (Boundary Schemes)

The contiguous allocation schemes can be classified as:

a) Fixed boundary scheme

b) Movable boundary scheme

42. What is the transmission technologies used in providing local digital loop?

Copper wire pairs

Fiber

Coaxial cables

Wireless

43. What are the two levels of digital access in ISDN?

Basic rate access (2B+D interface)

Primary rate access (23B+D interface)

44. Features of ISDN B channels?


1. End-to-end four-wire digital circuits: no loss or echoes for voice circuits

using digital instruments

2. Shared network access for voice, data and leased lines

3. High bandwidth (64 kbps)

4. Lower error rates than voiceband modems

45. Features of ISDN D channels?

1. Signaling simultaneously with active connections

2. Calling number identification

3. Far-end supervision

4. User-to-user message transfer

5. Access to packet switching network

46. Define ISDN basic rate access?

It is a standard copper pair that has been specially conditioned to support a

bidirectional 160kbps data rate. This is also referred as Digital subscriber loop (DSL).

47. Define S/T interfaces?

It is defined as in ITU-T recommendation 1.430 to be supplied by network

termination equipment.

48. Define TCM?

It is a time compression multiplex. It provides full duplex transmission on a single

pair of wires by alternately transmitting bursts of data in each direction. It is also referred

as Ping-Pong

49. Define ISDN D channel protocol?

It is defined in two separate series of ITU-T: the I series and the Q series

50. Define High data rate digital subscriber loops?

This technique allows larger bandwidths on copper wire pairs for the availability

of low cost, high performance digital signal processing.

51. Define ADSL?

ADSL-Asymmetric digital subscriber line

ADSL is allows high data rates to subscriber and moderate to low data rates from

the subscriber to the network. It delivered switched digital video over a copper loop.

52. Versions of digital subscriber lines?

DSL

ADSL

HDSL

SDSL

VDSL

53. What are the two versions of ADSL transmission?

Carrierless amplitude and phase modulation (CAP)


Discrete multitone modulation (DMT)

54. Define DMT implementation?

It utilize an inverse FFT as a modulator as the corresponding demodulator.

55. What is the use of PRS source and POT splitter?

PRS source:

A pseudorandom sequence provides a prescribed sequence for characterizing the

channel during a training period. The characters are determined during attenuation, phase

distortion and noise/interference levels

POT splitter:

It used in both ends of transmission to separate the analog voice from the data.

56. Define VDSL?

VDSL-Version of ADSL to achieve even higher bandwidths on particularly short

lines as would be available from remote terminals of fiber to the curb system

57. Define universal digital loop carrier loop system?

The UDLC can be interfaced to any other system like analog and digital. The

interface b/w local switching system of the public network and the central office terminal

involves individual circuits.

58. Define FITL?

FITL-Fiber in the loop is refers to one of three more specific descriptions of the

use of fiber for local distribution.

The 2nd category of FITL is a fiber-to-the-curb(FTTC). These systems are

designed to reach within 1000feet of a subscriber residence.

59. What is the use of voiceband modem?

1. The availability of economical DSP technology for equalization/echo canceling

2. The improved quality of the network in terms of lower noise and distortion

resulting.

60. Define PCM modem?

The principal source of noise in the end-to-end connection is the quantization

noise of the A/D converters leads to alternative modem implementations that directly

utilize the digital 64-kbps channel and eliminate quantization noise. These modems are

referred as PCM modems.


UNIT-V

CELLULAR WIRELESS NETWORKS

1. What is the use of cellular network?

It is developed to increase the capacity available for mobile ratio telephone

service. It provides high power transmitter/receiver.

2. Define base station?

Each cell is allocated a band of frequencies and served by a base station,

consisting of transmitter, receiver and control unit.

3. Define Crosstalk?

Adjacent cells are assigned same frequencies. It can be avoided by assigning

different frequencies.

4. Define frequency reuse?

In cellular system, each cell has a base transceiver. The objective is to use same

frequency band in multiple cells at some distance from another. This allows the same

frequency band to be used for multiple conversations in different cells.

5. Define frequency borrowing?

Frequencies are taken adjacent cells by congested cells. The frequencies can also

be assigned to cells dynamically.

6. Define cell splitting?

Cells in areas of high usage can be split into smaller cells. The original cells are

about 6.5 to 13km in size.

7. Define cell sectoring?

A cell is divided into a number of wedge shaped sectors, within own set of

channels, 3 (or) 6 sectors per cell.

8. Define handoff?

It is the procedure for changing the assignment of the mobile unit from one BS to another

as the mobile unit moves one cell to another.

9. What are the handoff strategies?

Relative signal strength

Relative signal strength with threshold

Relative signal strength with hysteresis

Relative signal strength with hysteresis and threshold


10. What is the use of cordless systems?

It provides user with mobility within a residence or small office by separating the

handset from the rest of the telephone and providing a simple analog wireless link

11. Define TDD?

TDD- Time division Duplex. It also known as time compression multiplexing,

data are transmitted in one direction at a time.

12. Define TDMA/TDD?

It is used in wired subscriber system but TDD involves transmitter and receiver

on the same carrier frequency but at different time.

13. What is meant by differential quantization?

It is based on the speech signals tend not to change much b/w two signals. Thus

with original PCM, the quantized values of adjacent samples.

14. Define adaptive differential PCM?

The predictor and difference quantize adapt to the changing characteristics of the

speech being coded.

15. What is meant by WLL?

WLL- wireless local loop (or) fixed wireless access.

WLL alternatives narrow band, which offer a replacement for existing telephony

services and broadband. It provide high speed two-way voice and data servicing

16. What is the use of mobile IP?

The network portion of an IPO address is used by routers to move datagram from

the source computer to network to which target computer is attached

17. What the basic capabilities of mobile IP?

Discovery

Registration

Tunneling

18. Define WAP?

WAP- wireless Application protocol- is a universal, it provide mobile users of

wireless phones and other wireless terminals such as pagers and personal digital

assistants(PDA).

19. Define WML?

WML- Wireless Markup language- it is designed to describe content and format

for presenting data on devices with limited bandwidth, limited screen siz

20. What is the use of frequency hopping?

It provides resistance to interference and multipath

It provides a form of multiple accesses among co-located devices in different

piconets

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