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VU CS504- SOFTWARE ENGINEERING FinalTerm solved unsolved past papers Spring 2009

VU CS504- SOFTWARE ENGINEERING FinalTerm Solved Unsolved Past Papers Spring 2009




Spring 2009
CS504- Software Engineering _ I


Question No: 31 ( Marks: 1 )
Write the procedure how names representing Abbreviations and acronyms should be describe in
coding style guide.
Abbreviations and acronyms should not be uppercase when used as name.

exportHtmlSource(); // NOT: xportHTMLSource();

openDvdPlayer(); // NOT: openDVDPlayer();

Question No: 32 ( Marks: 1 )
Define a system downtime.
A system downtime is the period in which tremendous pressure is on developers end to fix the problem and make the system running again.

Question No: 33 ( Marks: 2 )
What is layered architecture
As the name suggests, a layered architecture has many different layers. One typical

example of a layered architecture is an operating system where different layers are used

to provide services and functionality and the inner layers are closer to the machine

hardware than the outer layers. In this way, each layer isolates the outer layer from inner

complexities. In order to work properly, the outer layer only needs to know the interface

provided by the inner layer. If there are any changes in the inner layer, as long as the

interface does not change, the outer layer is not affected. This scheme tremendously

portability of the system. The basic layered architecture is depicted in the following


Question No: 34 ( Marks: 2 )
What is Infeasible path?
Infeasible path is a path through a program which is never traversed for any input data.

Question No: 35 ( Marks: 3 )
List three guidelines that can help you in writing portable code.

Question No: 36 ( Marks: 3 )
Describe three coverage schemes related to white box testing.

Question No: 37 ( Marks: 3 )
Wrtie the General Form for documenting pattrens.
The motivation or context that this pattern applies to.

Prerequisites that should be satisfied before deciding to use a pattern.

A description of the program structure that the pattern will define.

A list of the participants needed to complete a pattern.

Consequences of using the pattern…both positive and negative.


Question No: 38 ( Marks: 5 )
Discuss any five the General naming conventions for an object oriented language

General naming conventions for Java and C++

1. Names representing types must be nouns and written in mixed case starting with

upper case.

Line, FilePrefix

2. Variable names must be in mixed case starting with lower case.

line, filePrefix

This makes variables easy to distinguish from types, and effectively resolves potential

naming collision as in the declaration Line line;

3. Names representing constants must be all uppercase using underscore to separate



In general, the use of such constants should be minimized. In many cases

implementing the value as a method is a better choice. This form is both easier to

read, and it ensures a uniform interface towards class values.

int getMaxIterations()// NOT: MAX_ITERATIONS = 25


return 25;


4. Names representing methods and functions should be verbs and written in mixed case

starting with lower case.

getName(), computeTotalWidth()

5. Names representing template types in C++ should be a single uppercase letter.

template<class T> …

template<class C, class D> …

6. Global variables in C++ should always be referred to by using the :: operator. , ::applicationContext.getName()

7. Private class variables should have _ suffix.

class SomeClass


private int length_;


Apart from its name and its type, the scope of a variable is its most important feature.

Indicating class scope by using _ makes it easy to distinguish class variables from local

scratch variables.

8. Abbreviations and acronyms should not be uppercase when used as name.

exportHtmlSource(); // NOT: xportHTMLSource();

openDvdPlayer(); // NOT: openDVDPlayer();

Using all uppercase for the base name will give conflicts with the naming conventions

given above. A variable of this type would have to be named dVD, hTML etc. which

obviously is not very readable.

9. Generic variables should have the same name as their type.

void setTopic (Topic topic) // NOT: void setTopic (Topic value)

// NOT: void setTopic (Topic aTopic)

// NOT: void setTopic (Topic x)

void connect (Database database) // NOT: void connect (Database db)

// NOT: void connect (Database oracleDB)

Non-generic variables have a role. These variables can often be named by combining role

and type:

Point startingPoint, centerPoint;

Name loginName;

10. All names should be written in English.

fileName; // NOT: filNavn

11. Variables with a large scope should have long names, variables with a small scope

can have short names. Scratch variables used for temporary storage or indices are best

kept short. A programmer reading such variables should be able to assume that its

value is not used outside a few lines of code. Common scratch variables for integers

are i, j, k, m, n and for characters c and d.

12. The name of the object is implicit, and should be avoided in a method name.

line.getLength(); // NOT: line.getLineLength();

The latter seems natural in the class declaration, but proves superfluous in use.



Question No: 39 ( Marks: 5 )
What are the Software testing objective? Also define a successful test.
Software testing objective

„h The correct approach to testing a scientific theory is not to try to verify it, but to

seek to refute the theory. That is to prove that it has errors. (Popper 1965)

„h The goal of testing is to expose latent defects in a software system before it is put

to use.

„h A software tester tries to break the system. The objective is to show the presence

of a defect not the absence of it.

„h Testing cannot show the absence of a defect. It only increases your confidence in

the software.

„h This is because exhaustive testing of software is not possible – it is simply too

expansive and needs virtually infinite resources.

Successful Test

From the following sayings, a successful test can be defined

“If you think your task is to find problems then you will look harder for them than if you

think your task is to verify that the program has none” – Myers 1979.

“A test is said to be successful if it discovers an error” – doctor’s analogy.

The success of a test depends upon the ability to discover a bug not in the ability to prove

that the software does not have one. As, it is impossible to check all the different

scenarios of a software application, however, we can apply techniques that can discover

potential bugs from the application. Thus a test that helps in discovering a bug is a

successful test. In software testing phase, our emphasis is on discovering all the major

bugs that can be identified by running certain test scenarios. However it is important to

keep in mind that testing activity has certain limitations.

Question No: 40 ( Marks: 10 )
What should be the sets of inputs that should be used to test the system effectively and efficiently? Give an example.
To answer these questions, we divide a problem domain in different classes. These are

called Equivalence Classes.

Question No: 41 ( Marks: 10 )
Discuss Art and Science of Debugging.

Debugging is taken as an art but in fact it is a scientific process. As people learn about

different defect types and come across situations in which they have to debug the code,

they develop certain heuristics. Next time they come across a similar situation, they apply

those heuristics and solve the problem in lesser time and with a lesser effort. While

discussing the debugging process we discuss the phenomenon of “you miss the obvious”.

When a person writes a code, he develops certain impression about that code. One can

term this impression as a personal bias that the developer builds towards his creation the

 “code” and when he has to check this code, he can potentially miss out obvious mistakes

due to this impression or bias. Therefore, it is strongly recommended that in order to

reach to a defect in the code, one needs “another pair of eyes”. That is, start discovering

the defect by applying your own heuristics and if you could reach to the problem, fine,

otherwise ask a companion to help you in this process. We shall further elaborate this

idea based on the following example.

 Final Term Examination – February 2005

Time Allowed: 150 Minutes


Question No. 1                                                 Marks : 6

What are Loop Errors? Describe briefly. What are symptoms of Loop Errors?

Question No. 2 Marks : 15

Loop Errors

„h Loop errors break down into several different subtypes.

„h They occur around a loop construct in a program.

„h Infinite loops, off-by-one loops, and improperly exited loops.


„h If your program simply locks up, repeatedly displays the same data over and over,

or infinitely displays the same message box, you should immediately suspect an

infinite loop error.

„h Off-by-one loop errors are quite often seen in processes that perform calculations.

„h If a hand calculation shows that the total or final sum is incorrect by the last data

point, you can quickly surmise that an off-by-one loop error is to blame.

„h Likewise, if you were using graphics software and saw all of the points on the

screen, but the last two were unconnected, you would suspect an off-by-one error.

Watching for a process that terminates unexpectedly when it should have




Q- 4                              Marks: 6

What are Boolean Bugs? Describe briefly.What are symptoms of Boolean Bugs?

Boolean bugs

Boolean bugs occur because the mathematical precision of Boolean algebra has virtually

nothing to do with equivalent English words.

When we say “and”, we really mean the boolean “or” and vice versa.


„h When the program does exactly the opposite of what you expect it to. For

example, you might have thought you needed to select only one entry from a list

in order to proceed. Instead, the program will not continue until you select more

than one. Worse, it keeps telling you to select only one value.

„h For true/false problems, you will usually see some sort of debug output indicating

an error in a function, only to see the calling function proceed as though the

problem had not occurred.


2. Write a short note on Data Flow or Pipes and Filter Architecture Configuration.(3 Pts)


This architecture is very similar to data flow diagrams. This is used when the input data is

processed through a series of transformations to yield the desired output. It is also known

as pipes and filters architecture where each processing step is called a filter and the

connecting link from one process to the other is called the pipe through which the

information flows from one process to the other. An important aspect of this model is that

each filter works independently of others and does not require knowledge of the working

of any of the other filters including its neighbours.

If the dataflow has only a single sequence of processes with no alternative or parallel

paths, then it is called batch sequential. These models are depicted in the following



3. How do you differentiate between the responsibilities of Developer and Tester? (3 Pts)


Development is a creative activity Testing is a destructive activity

Objective of development is to show that the program works. Objective of testing is to show that the program does not work


Final Term Examination – August 2004




QuestionNo.3                                       Marks:6

What are the symptoms of pointer errors?

Pointer errors

„h A pointer error is any case where something is being used as an indirect pointer to

another item.

„h Uninitialized pointers: These are pointers that are used to point at something, but

we fail to ever assign them something to point at.

„h Deleted pointers, which continue to be used.

„h An Invalid pointer is something that is pointing to a valid block of memory, but

that memory does not contain the data you expect it to.


„h The program usually crashes or behaves in an unpredictable and baffling way.

„h You will generally observe stack corruptions, failure to allocate memory, and odd

changing of variable values.

„h Changing a single line of code can change where the problem occurs.

„h If the problem “goes away” when you place a print statement or new variable into

the code that you suspect contains the problem.


What are the differences between Thin Client and Fat Client architecture?

(Q 9)

Thin Client Model

This model was initially used to migrate legacy systems to client server architectures.

In this case the legacy system may act as a server in its own right and the GUI may be

implemented on a client. It chief disadvantage is that it places a heavy processing

load on both the server and the network.

Fat Client Model

With advent of cheaper and more powerful hardware, people thought of using the

processing power of client side machines. So the fat client model came into being. In

this model, more processing is delegated to the client as the application processing is

locally extended. It is suitable for new client/server systems when the client system

capabilities are known in advance. It however is more complex than thin client model

with respect to management issues. Since the client machine now also has a

significant part of the application resident on it, new versions of each application need

to be installed on every client.


Following is the list of bugs’ symptoms; identify the bug classes in each case.

a) System slowdowns. Memory Leakage

b) The program doesn’t crash, but the flow of the program takes odd branches

through the code. Logical Error

c) If your program simply locks up, repeatedly displays the same data over and over,

or infinitely displays the same message box. Loop Error




VU CS504- SOFTWARE ENGINEERING FinalTerm Solved Unsolved Past Papers Spring 2009

VU CS605- Software EngineeringII FinalTerm solved unsolved past papers Spring 2009

VU CS605- Software EngineeringII FinalTerm Solved Unsolved Past Papers Spring 2009

Spring 2009
CS605- Software Engineering II


Time: 120 min
Marks: 70

Question No: 1 ( Marks: 1 ) – Please choose one
The purpose of earned value analysis is to

► determine how tocompensate developers based on their productivity
► provide a quantitative means of assessingsoftware project progress
► provide a qualitative means of assessing software project progress
► set the price point for asoftware product based on development effort

Question No: 2 ( Marks: 1 ) – Please choose one
The RMMM plan assists the project team in developing strategy for dealing with risk. In this context, an effective strategy must consider:

► Risk avoidance
► Risk monitoring
► Risk management and contingency plan
► All of the given choices

Question No: 3 ( Marks: 1 ) – Please choose one
The component-based development model is

► only appropriate for computer hardware design.
► not able to support the development of reusable components.
► dependent on objecttechnologies for support.
► not cost effective by known quantifiable softwaremetrics.

Question No: 4 ( Marks: 1 ) – Please choose one
In ___________ representation of CMMI model, consideration is given to improve all the defined processes areas.

► Staged
► Continuous

Question No: 5 ( Marks: 1 ) – Please choose one
If you know the relationship between the use cases, classes, GUIs, Test cases and other artifacts then we can say that requirements are traceable in that project.

True ►
False ►

Question No: 6 ( Marks: 1 ) – Please choose one
There could be multiple GUIs to satisfy one requirement

True ►
False ►

Question No: 7 ( Marks: 1 ) – Please choose one
Check in and Check out is actually one and the same process with two different names

True ►
False ►

Question No: 8 ( Marks: 1 ) – Please choose one
If a new version of a product is released by fixing the bugs in the previous release then it is termed as _________________

Product Update ►
Product Upgrade ►
Defect Removal ►
Product Performance ►

Question No: 9 ( Marks: 1 ) – Please choose one
When an Item is baselined, it becomes frozen, here frozen means, that the item can be changed only by creating an old version

True ►
False ►

Question No: 10 ( Marks: 1 ) – Please choose one
Configuration Itemidentification involves:

Identifying the structure of the s/w system ►
Uniquely identify individual components ►
Uniquely identifying various revisions ►
All of the given ►

Question No: 11 ( Marks: 1 ) – Please choose one
Incomplete Configurationidentification documentsmay result in:

Schedule Product ►
all of the given choices are correct ►
Defective Product ►
Higher Maintenance Costs ►

Question No: 12 ( Marks: 1 ) – Please choose one
If Configuration itemidentification is not identified, it is possible to control changes and establish records.

► True
► False

Question No: 13 ( Marks: 1 ) – Please choose one
Availability and Reliability are concerned with 

► Perceived quality
► Quantitatively measured quality

Question No: 14 ( Marks: 1 ) – Please choose one
Software Availability can be calculated by the following equation:

► Availability = (MTTR/MTTF) x 100
► Availability = (MTBF/MTTR) x 100
► Availability = (MTTF/MTBF) x 100
► Availability = (MTBF/MTTF) x 100

Question No: 15 ( Marks: 1 ) – Please choose one
Phase Index can be calculated by the help of the following formula, where
Ei – the total number of errors uncovered during the ith step in the SE process
Si – number of serious errors
Mi – number of moderate errors
Ti – number of minor errors
PSi – product size at the ith step
ws, wm, wt – weighting factors for serious, moderate, and minor errors

► PIi = ws(Si/Ei) + wm(Mi/Ei) + wt(Ti/Ei)
► PIi = ws(Si/Ei) + wm(Mi/Mi) + wt(Ti/T)
► PIi = ws(Si/Ei) + wm(Mi/Mi) + wt(Ti/Ei)
► PIi = ws(Si/S) + wm(Mi/M) + wt(Ti/E)

Question No: 16 ( Marks: 1 ) – Please choose one
The higher the Error Index, the higher will be the Defect Removal Efficiency

► True
► False

Question No: 17 ( Marks: 1 ) – Please choose one
The goal of quality assurance is to provide management with the data needed to determine whichsoftware engineers are producing the most defects.

► true
► false

Question No: 18 ( Marks: 1 ) – Please choose one
From the following listedsoftware development Model, which one is an object oriented model

► Classical life cycle model
► Fountain model
► Spiral model
► Waterfall model

Question No: 19 ( Marks: 1 ) – Please choose one
The prototyping model ofsoftware development is

► a reasonable approach when requirements are well defined.
► a useful approach when a customer cannot define requirements clearly.
► the best approach to use for projects with large development teams.
► a risky model that rarely produces a meaningful product.

Question No: 20 ( Marks: 1 ) – Please choose one
___________________is a team organization where there is no permanentleader and task coordinators are appointed for short duration. Decisions on problems and approach are made by group consensus and communication among team is horizontal.

► Democratic decentralized (DD)
► Controlled decentralized (CD)
► Synchronous paradigm (SP)
► Controlled centralized (CC)

Question No: 21 ( Marks: 2 )
Discuss the role of program restructuring in softwarereengineering?

Question No: 22 ( Marks: 2 )
Differentiate Change Control Authority (CCA) and Change Control Board (CCB)?

Question No: 23 ( Marks: 2 )
Give the uses of Time Boxing?

Question No: 24 ( Marks: 3 )
Differentiate between organizational maturity and process area capability?

Question No: 25 ( Marks: 3 )
What would you understand by the conventional numbering of the product release?

For Complete Paper Please Download the file 

CS605 Spring 2009_FinalTerm_SoftwareEngineeringII_CS605.doc

VU CS605- Software EngineeringII FinalTerm Solved Unsolved Past Papers Spring 2009

VU CS601 – DATA COMMUNICATION FINALTERM solved unsolved past papers Spring 2009

VU CS601 – DATA COMMUNICATION FINALTERM Solved Unsolved Past Papers Spring 2009


Spring 2009

CS601- Data Communication

Ref No: 656191

Time: 120 min

Marks: 80



For Teacher’s Use Only

Q No.




















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Question No: 1      ( Marks: 1 ) – Please choose one



Which is not an element of protocol



       ► semantics




       ► communication service module




Question No: 2      ( Marks: 1 ) – Please choose one



Layers 5, 6 and 7 also called as network support layers.


       ► True


       ► False




Question No: 3      ( Marks: 1 ) – Please choose one



Fourier transform tells us that any digital signal can be decomposed into infinite number of periodic signals


       ► True


       ► False




Question No: 4      ( Marks: 1 ) – Please choose one



Time domain plot show changes in signal phase with respect to time.


       ► True


       ► False




Question No: 5      ( Marks: 1 ) – Please choose one



Analog to digital conversion is also termed as modulating an analog signal.


       ► True


       ► False




Question No: 6      ( Marks: 1 ) – Please choose one



DC component is also termed as Direct current component or a component with non-zero frequency.


       ► False


       ► True




Question No: 7      ( Marks: 1 ) – Please choose one



Manchester is a type of ____________encoding.


       ► biphase


       ► polar


       ► biphase & polar


       ► none of the given




Question No: 8      ( Marks: 1 ) – Please choose one



The inversion of the level at 1 bit is called as __________


       ► NRZ-L


       ► NRZ-I


       ► RZ




Question No: 9      ( Marks: 1 ) – Please choose one



PCM is the first process of PAM.


       ► True


       ► False




Question No: 10      ( Marks: 1 ) – Please choose one



In 4PSK each phase change represents ______bits.


       ► 3


       ► 6


       ► 2


       ► 4




Question No: 11      ( Marks: 1 ) – Please choose one



In RS 422 Balanced mode two lines carry ________ signals which are not identical to each other.


       ► same


       ► different


       ► digital


       ► analog




Question No: 12      ( Marks: 1 ) – Please choose one



A ______________ converts an analog signal into a digital signal.


       ► Demodulator


       ► Modulator


       ► Digital-to-analog converter




Question No: 13      ( Marks: 1 ) – Please choose one



Which of the following is an example of ITU-T modem standards:


       ► T-series


       ► X-series


       ► N-series


       ► V-series




Question No: 14      ( Marks: 1 ) – Please choose one



The maximum data rate in the uploading direction is still ____________.



       ► 26.6 Kbps


       ► 33.6 Kbps


       ► 36.6 Kbps


       ► 46.6 Kbps




Question No: 15      ( Marks: 1 ) – Please choose one



Which of the following primarily uses guided media


       ► Cellular telephone system


       ► Local telephone system


       ► Satellite communications


       ► Radio broadcasting




Question No: 16      ( Marks: 1 ) – Please choose one



When a beam of light travels through media of two different densities, if the angle of incidence is greater than the critical angle, ____________occurs.


       ► Reflection


       ► Refraction


       ► Incidence


       ► Criticism




Question No: 17      ( Marks: 1 ) – Please choose one



When we talk about unguided media, usually we are referring to _________.



       ► Metallic wires


       ► Nonmetallic wires


       ► The air


       ► Water




Question No: 18      ( Marks: 1 ) – Please choose one



Optical fibers are defined by the ratio of the ___________ of their core to the diameter of their cladding.


       ► Diameter


       ► Radius


       ► Length


       ► Width




Question No: 19      ( Marks: 1 ) – Please choose one



All of popular Fiber optic connectors are ___________ shaped.


       ► Conical




       ► Circular


       ► Rectangular




Question No: 20      ( Marks: 1 ) – Please choose one



Radio wave transmission utilizes ___________ different types of propagation.


       ► Four


       ► Three


       ► Two


       ► Five




Question No: 21      ( Marks: 1 ) – Please choose one



dB is ____________ if a signal is amplified.


       ► Negative


       ► Positive


       ► Null


       ► Zero




Question No: 22      ( Marks: 1 ) – Please choose one



A prism can deflect the light depending upon the angle of ____________ and the frequency.



       ► Deviation


       ► Incident


       ► Refraction


       ► Reflection




Question No: 23      ( Marks: 1 ) – Please choose one



Asynchronous TDM is efficient only when the size of the time slot is kept relatively _______________


       ► Large


       ► Small


       ► Medium


       ► None of the given




Question No: 24      ( Marks: 1 ) – Please choose one



The local loop has ___________ cable that connects the subscriber telephone to the nearest end office.


       ► Twisted-pair


       ► Coaxial


       ► Fiber-optic


       ► None of the given




Question No: 25      ( Marks: 1 ) – Please choose one



Data from a computer are ____________; the local loop handles _________ signals.


       ► Analog; analog


       ► Analog; digital


       ► Digital; digital


       ► Digital; analog




Question No: 26      ( Marks: 1 ) – Please choose one



Which error detection method uses ones complement arithmetic?


       ► Simple parity check


       ► Two-dimensional parity check


       ► CRC


       ► Checksum




Question No: 27      ( Marks: 1 ) – Please choose one



Flow control is needed to prevent ____________


       ► Bit errors


       ► Overflow of the sender buffer


       ► Overflow of the receiver buffer


       ► Collision between sender and receiver




Question No: 28      ( Marks: 1 ) – Please choose one



____________ coordinates the amount of data that can be sent before receiving acknowledgment


       ► flow control


       ► error control


       ► data control




Question No: 29      ( Marks: 1 ) – Please choose one



Error control is both error _________ and error ___________


       ► detection; correction


       ► detection; deletion


       ► detection; avoidance


       ► detection; forwarding




Question No: 30      ( Marks: 1 ) – Please choose one



Addressing is not needed in _______________ configuration.


       Point to Point


       ► Multipoint


       ► Point to point and multipoint




Question No: 31      ( Marks: 1 ) – Please choose one



In a Go-Back-N ARQ, if the window size is 63, what is the range of sequence number?


       ► 0 to 63


       ► 0 to 64


       ► 1 to 63


       ► 1 to 64




Question No: 32      ( Marks: 1 ) – Please choose one



A timer is set when ___________ is sent out.


       ► A data frame


       ► An ACK


       ► A NAK




Question No: 33      ( Marks: 1 ) – Please choose one



Sliding window requires that data frames be transmitted _______________


       ► Sequentially


       ► Frequently


       ► Synchronously


       ► Asynchronously




Question No: 34      ( Marks: 1 ) – Please choose one



In Y-MODEM Multiple files can be sent simultaneously


       ► True


       ► False




Question No: 35      ( Marks: 1 ) – Please choose one



BLAST stands for :


       ► Blocked asynchronous transmission


       ► Blocked synchronous transmission


       ► Barrel asynchronous transmission


       ► Below asynchronous transmission




Question No: 36      ( Marks: 1 ) – Please choose one



HDLC is an acronym for ______________.


       ► High-duplex line communication


       ► High-level data link control


       ► Half-duplex digital link combination


       ► Host double-level circuit




Question No: 37      ( Marks: 1 ) – Please choose one



The HDLC ___________ field defines the beginning and end of a frame.



       ► Flag


       ► Address


       ► Control


       ► FCS




Question No: 38      ( Marks: 1 ) – Please choose one



_________ is the access protocol used by traditional Ethernet.


       ► CSMA/CD


       ► CSMA/CA


       ► Token Ring


       ► CSMA




Question No: 39      ( Marks: 1 ) – Please choose one



Bridges can divide a large ________ into smaller segments


       ► Network


       ► Packet


       ► Frame


       ► Address




Question No: 40      ( Marks: 1 ) – Please choose one



Like VRC, LRC and CRC, Checksum is also based on _______________.


       ► Redundency


       ► Decimal Division


       ► Encryption


       ► Encoding




Question No: 41      ( Marks: 2 )



What are the conditions for the polynomial used by the CRC generator?


CRC generator:

CRC generator (the divisor) is most often represented not as a1’s and 0’s but as an algebraic polynomial.

conditions for the polynomial:

it should have following properties:

It should not be divisible by “x”.

It should not be divisible by “x+1”.

The first condition guarantees that all burst error of a length equal to degree of the polynomial is detected.

The 2nd condition guarantees that all burst error affecting an odd number of bits are detected.



Question No: 42      ( Marks: 2 )



What are intelligent modems?

Intelligent modems:


A modem that responds to commands and can accept new instructions during online transmission. It was originally developed by Hayes.


  • Automatic answering,
  • Dialing etc.


Question No: 43      ( Marks: 2 )



What is the basic purpose of Router?


Basic purpose of Router:

“A router is a device that extracts the destination of a packet it receives, selects the best path to that destination, and forwards data packets to the next device along this path. They connect networks together;

a LAN to a WAN for example, to access the Internet.
“A more precise definition of a router is a computer networking device that interconnects separate logical subnets.”


Question No: 44      ( Marks: 3 )



What are the fractional T Lines?


The fractional T Lines:

Many subscribers don’t need the entire capacity of the T-line.

For example,

A small business may need only one-fourth of the capacity of T-line. if four business of same size lie in the same building, they can share  T-line.DSU/CSU allow the capacity of T-line to be interleaved in to four channels



Question No: 45      ( Marks: 3 )




What are the light sources used for optic fiber?


  • light sources used for optic fiber:
  • The light source can weather be an LED or ILD
  • LED (Light emitting diode) cheaper but provide unfocused light that strikes the boundaries of channel at uncontrollable angles.
  • Limited to short distance use.
  • Can be focused to a narrow range allowing control over angle of incidence.







Question No: 46      ( Marks: 3 )



What is Multi Access Unit (MAU) in Token Ring?




Multi Access Unit (MAU) in Token Ring:

  • Individual automatic switches are combined in to a hub
  • One MAU can support up to 8 stations.
  • Although it looks like a star, it is in fact a ring.




Question No: 47      ( Marks: 5 )



Give characteristics of Dual Ring, if necessary then draw the diagram. [5]







Characteristics of Dual Ring:

A network topology in which two concentric rings connect each node on a network instead of one network ring that is used in a ring topology. Typically, the secondary ring in a dual-ring topology is redundant. It is used as a backup in case the primary ring fails. In these configurations, data moves in opposite directions around the rings. Each ring is independent of the other until the primary ring fails and the two rings are connected to continue the flow of data traffic.
















































Question No: 48      ( Marks: 5 )






What the receiver will receive if the checksum method is applied to the following



10101001  00111001












the receiver will receive the checksum method is applied to the following bit.

10101001  00111001

10101001  00111001

Sum of 2 bits are





00011101       1’s complement



00011110        2’s complement


10101001      00111001    ==>  00011110

So the data transmitted which will receiver get:
10101001 00111001 00011110


Question No: 49      ( Marks: 5 )



What is rafraction in terms of optic fiber? Give one example.




Light travels in a straight line as long as it is moving through a single uniform structure If a ray of light traveling through one substance enters another (more or less dense) substance, its speed changes abruptly causing the ray to change direction. This phenomenon is called Refraction.


Refraction in terms of optic fiber:


the propagation of light in an optical fiber which in its simplest form consists of a circular core of uniform refractive index surrounded by a cladding of slightly lower refractive index. The light is launched into the entrance face of the fiber.

The light is propagated by the total internal reflection at the interface between core and cladding. However the rays incident at angles larger than a certain angle, called the cut-off angle, suffer both refraction and reflection at the interface between the core and the cladding.

They, therefore, are not guided. Due to this the optical fiber has a numerical aperture. The numerical aperture is given by the square root of (n12-n22). Typical values of numerical aperture lie between 0.1 and 0.3.


The refractive indices of the core and the cladding are n1 and n 2 respectively. The fiber is normally in air (n0=1) but could also be in a medium of refractive index n0.




Question No: 50      ( Marks: 10 )



What are the asynchronous protocols in data link layer? Discuss in detail with examples.  [10 marks]



Asynchronous protocols in data link layer:

Asynchronous communication at the data link layer or higher protocol layers is known as statistical multiplexing or packet mode communication,

For example :

Asynchronous transfer mode (ATM). In this case the asynchronously transferred blocks are called data packets,

Async protocols in Data link layer is called statistical multiplexing. for example ATM cells.

The opposite is circuit switched communication, which provides constant bit rate, for example ISDN and SONET/SDH.

The packets may be encapsulated in a data frame, with a frame synchronization bit sequence indicating the start of the frame, and sometimes also a bit synchronization bit sequence, typically 01010101, for identification of the bit transition times. Note that at the physical layer, this is considered as synchronous serial communication.

Examples of packet mode data link protocols that can be/are transferred using synchronous serial communication are the

  • HDLC,
  • Ethernet,
  • PPP and
  • USB protocols.


VU CS601 – DATA COMMUNICATION FINALTERM Solved Unsolved Past Papers Spring 2009

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