Csc339 – lecture 2a network fundamental

05/02/2023Jahan University 1

CSC339 – NETWORK

FUNDAMENTAL Jahan University

Computer Science Department

Lecturer: Islahuddin Jalal

Master in Cyber Security


Class Policy

A student must reach the class-room in time. Late comers may join the class but are not entitled to be marked present.

Attendance shall be marked at the start of the class and students failing to secure 75% attendance will not be allowed to sit in final exam.

The assignment submission deadline must be observed. In case of late submission, ten percent may be deducted from each day.

Those who are absent on the announcement date of the assignment/test. Must get the topic/chapter of test/assignment confirmed through their peers.

Mobile phones must be switched-off in the class-rooms.


Grading Evaluation for Network fundamental

Internal Evaluation Midterm Exam 20% Attendance 5% Assignment/Presentations 5% Quizzes/Tests 10% Total Internal Evaluation 40% Final-term Examination Final-term Exam 60% Total Marks 100%


Topics to be discussed

Baseband transmission Broadband transmission Modes of channel operation Attenuation


Digital signal vs Analog signal

Signals can be analog or digital Analog signals can have an infinite number of values in a range. Digital signals can have only a limited


Baseband Transmission

Baseband transmission Digital signals are used Time Division Multiplexing is possible Baseband is bi-directional transmission Short distance signal travelling Entire bandwidth of the cable is consumed by a single signal in a baseband

transmission. Using dedicated medium


Baseband transmission

In baseband transmission, the required bandwidth is proportional to the bit rate; if we need to send bits faster, we need more bandwidth.

Baseband transmission of a digital signal that preserves the shape of the digital signal is possible only if we have a low pass channel with an infinite or very wide bandwidth.

Baseband transmission


Example of Baseband transmission

LAN uses a dedicated channel for two stations communicating with each other. In a bus topology LAN with multipoint connections, only two stations can

communicate with each other at each moment in time, the other stations need to avoid from sending data.

In a star topology LAN, the entire channel between each station and the hub is used for communication between these two entities.

Etc.


Broadband transmission

Broadband: Analog signals are used Transmission of data is unidirectional Signal travelling distance is long Frequency division multiplexing is possible The signals are sent on multiple frequencies and allow all the multiple

signals are sent simultaneously in broadband transmission. Modulator is used

Modulation of a digital signal for transmission on a bandpass

channel


Example of Broadband Transmission

Sending computer data over a telephone line Digital Cellular telephone.

The digital cellular phones convert the analog audio signal to digital and then convert it again to analog for transmission over a bandpass channel.


Attenuation

Loss of energy When a signal travels through a medium, it loses some of its energy due

to the resistance of the medium. Some wire or medium carrying electric signals get warm after some

time it is converted into heat

Attenuation


Data Transmission Rates

How fast we can send data Bit per second over a channel


Data Transmission rate

Depends of three factors The bandwidth available The level of the signals The quality of the channel (the level of noise)


Theoretical formulas for data rate

There are two formulas for calculating data rate Noiseless Channel formula by Nyquist

BitRate = 2 * bandwidth * log2L Noisy Channel formula by Shannon

Capacity = bandwidth * log2 (1+SNR) SNR = signal to noise ratio = average signal power average noise power


Example of Noiseless channel formula Consider a noiseless channel with a bandwidth of 3000Hz

transmitting a signal with two signal levels. The maximum bit rate can be calculated as: BitRate = 2 * 3000 * Log22 = 6000 * Log22 = 6000 * 1 = 6000 bps


Example of noisy channel formula

We can calculate the theoretical highest bit rate of a regular telephone line. A telephone line normally has a bandwidth of 3000 Hz (300 to 3300) assigned for data communications. The signal-to-noise ration is usually 3162. for this channel the capacity is calculated as:

C= B log2 (1+SNR) = 3000 log2 (1+3162) =3000 log2 (3163) =3000 * 11.62 =34860bps


Modes of Channel Operation

Three types of modes of Channel Operation Simplex Half duplex Full duplex


Simplex

Data in a simplex channel is always one way. Simplex channels are not often used because it is not possible to send back error or control signals to the transmit end.

E.g Television, radio transmission


Half duplex

A half-duplex channel can send and receive, but not at the same time.

E.g one-lane bridge, walkie-talkie In some aspects, you can think of Internet surfing as being half-

duplex, as a user issues a request for a web document, then that document is downloaded and displayed before the user issues another request

In addition, it is possible to perform error detection and request the sender to retransmit information that arrived corrupted.

http://physinfo.ulb.ac.be/cit_courseware/datacomm/dc_005.htm#internet


Half Duplex


Full duplex

Data can travel in both directions simultaneously. There is no need to switch from transmit to receive mode like in half

duplex. Its like a two lane bridge on a two-lane highway. E.g Mobile

END

Thanks for hearing…………………….

Csc339 – lecture 2a network fundamental

Technology

Transcript of Csc339 – lecture 2a network fundamental