1.What is FDM?
Ans: In frequency division multiplexing each signal modulates a different carrier frequency. The
modulated carrier combines to form a new signal that is then sent across the link.
Here multiplexers modulate and combine the signal while demultiplexers decompose and
Guard bands keep the modulating signal from overlapping and interfering with one another.
2.What is TDM ?
Ans: In TDM digital signals from n devices are interleaved with one another, forming a frame of
Framing bits allow the TDM multiplexer to synchronize properly.
3.What are the different transmission media?
Ans: The transmission media is broadly categorized into two types
4.What are the different Guided Media?
Ans: The media which provides a conduct from one device to another is called a guided media.
These include twisted pair cable, coaxial cable, and fiber-optic cable.
5.Describe about the different Guided Medias.
Ans: Twisted pair cable consists of two insulated cupper wires twisted together. It is used in
telephone line for voice and data communications.
Coaxial cable has the following layers: a metallic rod-shaped inner conductor, an insulator
covering the rod, a metallic outer conductor (shield), an insulator covering the shield, and a
plastic cover.Coaxial cable can carry signals of higher frequency ranges than twisted-pair cable.
Coaxial cable is used in cable TV networks and Ethernet LANs.Fiber-optic cables are composed
of a glass or plastic inner core surrounded by cladding, all encased in an outer jacket.Fiber-optic
cables carry data signals in the form of light. The signal is propagated along the inner core by
reflection. Its features are noise resistance, low attenuation, and high bandwidth capabilities.
It is used in backbone networks, cable TV nerworks, and fast Ethernet networks.
6.What do you mean by wireless communication?
Ans: Unguided media transport electromagnetic waves without using a physical conductor. This
type of communication is referred as wireless communication.
Here signals are broadcaster through air and thus available to anyone who has a device to receive
7.What do you mean by switching?
Ans: It is a method in which communication devices are connected to one another efficiently.
A switch is intermediary hardware or software that links devices together temporarily.
8.What are the switching methods?
Ans: There are three fundamental switching methods: circuit switching, packet switching,
And message switching.In circuit switching, a direct physical connection between two devices is
created by space division switches, time division switches or both.
In packet switching data is transmitted using a packet switched network. Packet switched
network is a network in which data are transmitted in independent units called packets.
9.What are the duties of data link layer?
Ans: Data link layer is responsible for carrying packets from one hop (computer or router) to the
next. The duties of data link layer include packetizing, adderssing, error control, flow control,
medium access control.
10.What are the types of errors?
Ans: Errors can be categorized as a single-bit error or burst error. A single bit error has one bit
error per data unit. A burst error has two or more bits errors per data unit.
11.What do you mean by redundancy?
Ans: Redundancy is the concept of sending extra bits for use in error detection. Three common
redundancy methods are parity check, cyclic redundancy check (CRC), and checksum.
12.Define parity check.
Ans: In parity check, a parity bit is added to every data unit so that the total number of 1s is even
(or odd for odd parity).Simple parity check can detect all single bit errors. It can detect burst
errors only if the total number of errors in each data unit is odd.In two dimensional parity checks,
a block of bits is divided into rows and a redundant row of bits is added to the whole block.
13. Define cyclic redundancy check (CRC).
Ans: C RC appends a sequence of redundant bits derived from binary division to the data unit.
The divisor in the CRC generator is often represented as an algebraic polynomial.
14. What is hamming code?
Ans: The hamming code is an error correction method using redundant bits. The number of bits
is a function of the length of the data bits. In hamming code for a data unit of m bits, we use the
formula 2r >= m+r+1 to determine the number of redundant bits needed. By rearranging the
order of bit transmission of the data units, the hamming code can correct burst errors.
15.What do you mean by flow control?
Ans: It is the regulation of sender’s data rate so that the receiver buffer doesn’t become
overwhelmed.i.e. flow control refers to a set of procedures used to restrict the amount of data
that the sender can send before waiting for acknowledgement.
16.What do you mean by error control?
Ans: Error control refers primarily to methods of error detection and retransmission. Anytime an
error is detected in an exchange, specified frames are retransmitted. This process is called
automatic repeat request (ARQ).
17.Define stop and wait ARQ.
Ans: In stop and wait ARQ, the sender sends a frame and waits for an acknowledgement from
the receiver before sending the next frame.
18.Define Go-Back-N ARQ?
Ans: In Go-Back-N ARQ, multiple frames can be in transit at the same time. If there is an error,
retransmission begins with the last Unacknowledged frame even if subsequent frames arrived
correctly. Duplicate frames are discarded.
19.Define Selective Repeat ARQ?
Ans: In Selective Repeat ARQ, multiple frames can be in transit at the same time. If there is an
error, only unacknowledged frame is retransmitted.
20.What do you mean by pipelining, is there any pipelining in error control?
Ans: The process in which a task is often begun before the previous task has ended is called
pipelining. There is no pipelining in stop and wait ARQ however it does apply in Go-Back-N
ARQ and Selective Repeat ARQ.