1.What is a protocol?
Ans: It is a set of rules that governs data communication. A protocol defines what is
communicated, how it is communicated, and when it is communicated. The key elements of
protocol are syntax, semantics and timing.
2.What is TCP/IP protocol model?
Ans: It is a five layered model which provides guidelines for the development of universally
compatible networking protocols.
The five layers are physical, data link, network, transport and application.
3.Describe the functions of five layers?
Ans: Physical- It transmits raw bits over a medium. It provides mechanical and electrical
Data link- It organizes bits into frames. It provides hop to hop delivery.
Network-It moves the packets from source to destination.It provide internetworking.
Transport-It provides reliable process to process message delivery and error recovery.
Application-It allows ti access to network resources.
4.What is ISO-OSI model?
Ans: Open Systems Interconnection or OSI model was designed by the International
Organization for Standardization (ISO) .It is a seven layer model. It is a theoretical model
designed to show how a protocol stack should be implemented.
It defines two extra layers in addition to TCP/IP model.
Session -It was designed to establish, maintain, and synchronize the interaction between
Presentation-It was designed to handle the syntax and semantics of the information exchanged
between the two systems. It was designed for data translation, encryption, decryption, and
4. What is multiplexing?
Ans: Multiplexing is the process of dividing a link, the phycal medium, into logical channels for
better efficiency. Here medium is not changed but it has several channels instead of one.
5.What is switching?
Ans: Switching in data communication is of three types
6.How data is transmitted over a medium?
Ans: Data is transmitted in the form of electromagnetic signals.
7. Compare analog and digital signals?
Ans: Analog signals can have an infinite number of values in a range but digital signal can have
only a limited number of values.
Ans: The range of frequencies that a medium can pass is called bandwidth. It is the difference
between the highest and lowest frequencies that the medium can satisfactorily pass.
9.What are the factors on which data rate depends?
Ans: Data rate ie.how fast we can send data depends upon
i) Bandwidth available
ii) The levels of signals we can use
iii) The quality of the channel (level of noise)
10.Define bit rate and bit interval?
Ans: Digital signals are aperiodic.so instead of using period and frequency we use bit interval
and bit rate respectively.Bit interval is the time required to send one single bit.Bit rate is the
number of bit intervals per second.
11.What is Nyquist bit rate formula?
Ans: For a noiseless channel, the Nyquist bit rate formula defines the theoretical maximum bit
Where Bandwidth is the bandwidth of the channel
L is the number of signal level used to represent the data
Bitrate is the bit rate in bits per second.
12.Define Shannon Capacity?
Ans: Shannon Capacity determines the theoretical highest data rate foe a noise channel.
Capacity= Bandwidth * log2 (1+SNR)
Bandwidth is the bandwidth of the channel.
SNR is the signal to noise ratio, it is the statical ratio of the power of the signal to the power of
Capacity is the capacity of the channel in bits per second
13.What is sampling?
Ans: It is the process of obtaining amplitude of a signal at regular intervals.
14.Define pulse amplitude modulation?
Ans: It is an analog to digital conversion method which takes analog signals, samples it and
generates a series of pulse based on the results of the sampling. It is not used in data
communication because the series of pulses generated still of any amplitude. To modify it we use
pulse code modulation.
15.Define pulse code modulation?
Ans: Pulse code Modulation modifies pulses created by PAM to create a completely digital
For this PCM first quantizes the PAM pulse. Quantization is the method of assigning integral
values in a specific tange to sampled instances.PCM is made up of four separate processes:
PAM, quantization, binary encoding and line encoding.
16.What is Nyquist Theorem?
Ans: According to this theorem, the sampling rate must be at least 2 times the highest frequency
of the original signal.
17.What are the modes of data transmission?
Ans: Data transmission can be serial or parallel in mode
In parallel transmission, a group of bits is sent simultaneously, with each bit on a separate line.In
serial transmission there is only one line and the bits are sent sequentially.
18.What is Asynchronous mode of data transmission?
Ans: It is a serial mode of transmission.
In this mode of transmission, each byte is framed with a start bit and a stop bit. There may be a
variable length gap between each byte.
19.What is Synchronous mode of data transmission?
Ans: It is a serial mode of transmission.In this mode of transmission, bits are sent in a
continuous stream without start and stop bit and without gaps between bytes. Regrouping the bits
into meaningful bytes is the responsibility of the receiver.
20.What are the different types of multiplexing?
Ans: Multiplexing is of three types. Frequency division multiplexing and wave division
multiplexing is for analog signals and time division multiplexing is for digital signals.