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Thursday, April 3, 2014

PCM - Pulse Code Modulation


PCM :- Pulse Code Modulation
It is the digitization process in which analog signal is represented in digital or discrete form .
It use ordinary analog signal which is digitized at the end office with the help of codec (coder decoder) codec produces 7 or 8 bit numbers .

Codec is inverse of modem -True
It code the digital to analog.
CO  DEC -COder (Analog to Digital) DECoder  (Digital to analog)

PCM is based Nyquest theorem:-
               There are various system for digital transmission:-
1.T1 carrier system (handle 24 voice channel)
2.Encoding system

There are three methods of PCM:
1.Differential pulse code modulation ( DPCM)
2.Delta Modulation
3.Predictive encoding

1.DPCM :-
Definition :It does not transmit actual sample .It transmit difference between current and previous value .Errors can ignored for voice or speech.

2.Delta modulation :
It is special care of DPCM it uses only one bit per sample .Each sample differs from its predecessor by either +1 or -1 .This is called as a sampling interval .
Granular noise :- The schema which is used for slow changing signal which gives distortion called as granular noise.

3.Predictive encoding : this preemptive to DPCM .Some sampling values are used to protect the next value,for this transmitter and receiver must uses same prediction algorithm.


Data  communication
   characteristics :
1. Delivery     :  Correct destination
2. Accuracy  :  Correct data
3. Timeliness  :  Fast enough
4. Jitter          :  Uneven  delay


Data  representation
1Ttext        :  email
2.Numbers :  Direct  conversion
3. Images   :  pixels
4.Audio      : continous
5. Video     :  movie

Data  flow :
1.Simplex
2.Half Duplex
3.Full Duplex

Solve Questions on Computer Science Single choice answers


Multiple Choice Questions ( Single Choice) :-


1) In SQL, which of the following is not a data Manipulation Language Commands?

A) Delete
B) Select
C) Update
D) Create
E)None of the above

Answer :- E)None of the above



2) Which of the following is not a type of SQL statement?

A) Data Manipulation Language (DML)
B) Data Definition Language (DDL)
C)Data Control Language (DCL)
D)Data Communication Language (DCL)
E)None of these

Answer :- D) Data Communication Language



3)Which of the following is not included in DML (Data Manipulation Language)

A)INSERT
B)UPDATE
C) DELETE
D)CREATE
E)None of these

Answer :-D)CREATE



4)TRUNCATE statement in SQL is a -

A) DML statement
B) DDL statement
C) DCL statement
D)DSL statement
E)None of these

Answer:- B) DDL statement



5) In SQL, which command is used to add new rows to a table?

A)Alter Table
B)Add row
C)Insert
D)Append
E)None of the Above

Answer :- C)Insert



6) Stack is also called ____

A) First In First Out (LIFO)
B)Last In First Out (FIFO)
C)First In Last Out (FILO)
D)First Come First Served (FCFS)
E)None of the above

Answer :- C)First In Last Out (FILO)



7)The full form of DDL is

A) Dynamic Data Language
B)Detailed Data Language
C)Data Definition Language
D)Data Derivation Language
E)All of these

Answer :- C)Data Definition Language



8) The OSI model consists of ___layers.

A) Nine
B)Eight
C)Seven
D)Five
E)Eleven

Answer :- C)Seven


9)Assembly language is a _____

A) Low Level Language
B)Middle Level Language
C)High level Language
D)User Language
E)None of these


Answer :- A) Low Level Language


10) Which of the following is a type of translator?

A)Assembler
B)Compiler
C)Interpreter
D)All of the Above
E) None of these

Answer:-  C)  Interpreter



11) Which of the following term is related to the stack?

 A) TOP
 B)PUSH
 C)POP
D)Rear
E) A, B and C.

Answer:-E) A, B and C.


12) In Queues, the end from where items inserted is called

A) Rear
B) Front
C) Top
D) Base
E) None of these

Answer:- A) Rear



13)Which protocol is used for browsing website:

A) TCP
B) FITFP
C)FTP
D)TFTP
E)None of these

Answer:-A) TCP



13) Which of the following is a browser?

A) Netscape Navigator
B) Mosaic
C)Mozilla Firefox
D)Google chrome
E)All of these

Answer:- E)All of these



14) Black Box Testing sometime called -

A) Data flow testing
B) Loop testing
C) Behavioral testing
D)Graph based testing
E)None of these

Answer:-D)Graph based testing



15)The Objective of testing is

A)Debugging
B)To uncover errors
C) To gain modularity
D) To analyze system
E) None of these

Answer :-B) To uncover errors



16)Choose the right sequence of SDLC (Software development life cycle) steps

A) Design, Requirement Analysis, Coding, Testing
B) Requirement Analysis, Design, Coding, Testing
C) Requirement Analysis, Design, Testing, Coding
D) Requirement Analysis, Coding, Design, Testing
E) None of these

Answer :-B) Requirement Analysis, Design, Coding, Testing



17) ODBC is based on ___.

A) Structured Query Language.
B) C language
C) C++ language
D) .net
E)None of these

Answer:- A) Structured Query Language.




18)JVM is a virtual machine that can execute ___
 A)C language
B).net programming
 C)RDBMS
 D)C++ Language
E)Java byte Code

Answer : E) Java byte Code


19)Which of the following virus overtake computer system when it boots and destroy in-formation?

A)Trojan
B)System infectors
C)Boot infectors
D)Stealth virus
E) None of these

Answer :- C) Boot infectors



20)The JDBC-ODBC bridge is

A) Three tiered
B)Multithread
C) Best for any platform
D) All of these
E) None of these

Answer :-B) Multithread



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