1. Explain how multiplexing is so cost-effective?
Ans:
Multiplexing is cost-effective because the higher data rate. The data rates up to 2Mbps over
two twisted pair. Multiplexing is a popular networking technique that integrates multiple
analog and digital signals into a signal transmitted over a shared medium. Multiplexers and
de-multiplexers are used to convert multiple signals into one signal. Multiplexing can be
charge effective as the increased your data price, the more price good the actual transmittal
ability. Occasion-split multiplexing has developed into a price tag-effective technique that
is not simply suited for trunk area build 'tween switch facilities nevertheless is nowadays
also starting to be suited for nearby circuits towards the client. The fundamental user
interface from the ISDN is definitely a demonstration of this kind of tendency. Because,
the higher the data rate, the more cost effective the transmission facility. That is, for a given
application and over a given distance, the cost per kbps decline with an increase in the data
rate of the transmission facility.
How is interference avoided by using frequency division multiplexing?
Ans:
Interference is prevented underneath frequency partition multiplexing by means of guard
bands, which can be abandoned helpings on the volume range concerning subchannels.
Frequency-partition multiplexing (FDM) is often a plan by which numerous signals are
usually blended for transmitting for a passing fancy devices series or maybe distribution
channel. Each and every transmission can be assigned an alternative rate of recurrence
(subchannel) from the briny channel. Interference is avoided by the use of guard bands,
which are unused portions of the frequency spectrum sub channels. At the receiving end,
the single composite signal is received by the FDM receiver. There are different kinds of
modulation such as amplitude modulation, pulse modulation, frequency modulation etc.
As the name suggests, the modulation done here is frequency modulation by the FDM
transmitter. These modulated signals are then added up using a linear adder or a mixer,
forming a composite signal which gets transmitted over a communication channel (single
channel). FDM is possible when the useful bandwidth of medium exceeds required channel
bandwidth. A number of signals can be carried simultaneously if each signal is modulated
onto a different carrier frequency. Carrier frequencies must be sufficiently separated so that
signals do not overlap. Each modulated signal requires a certain bandwidth cantered on its
carrier frequency, referred to as Channel. To prevent interference, the channels must be
separated by guard bands, which are unused portions of the spectrum. Channel is allocated
even if no data is to be sent.
A.
1. List and briefly define some of the requirements for effective communications over a
data link.
2. Define flow control.
3. Describe stop-and-wait flow control.
4. What are reasons for breaking a long data transmission up into a number of frames?
Ans:
1) Because of the possibility of transmission errors, and because the
receiver of data may need to regulate the rate at which data arrive, synchronization and
interfacing techniques are insufficient by themselves. It is necessary to impose a layer of
control in each communicating device that provides functions such as flow control, error
detection, and error control. This layer of control is known as a data link control protocol.
Flow control enables a receiver to regulate the flow of data from a sender so that the
receiver’s buffers do not overflow.
In a data link control protocol, error control is achieved by retransmission of damaged
frames that have not been acknowledged or for which the other side requests a
retransmission.
High-level data link control (HDLC) is a widely used data link control protocol. It contains
virtually all of the features found in other data link control protocols.
2) Flow control is a set of procedures that tells the sender how much data it can transmit
before it must wait for an acknowledgement from the receiver.
3) Stop-and-wait flow control is the simplest form of flow control. In this method the
message is broken into multiple frames, and the receiver indicates its readiness to receive
a frame of data. The sender waits for a receipt acknowledgement (ACK) after every frame
for a specified time (called a time out).
4) In order to track the frames transferred and to resend only those frames which are not...