Part- 2 Network Physical Layer

 Physical Layer

1. Digital Transmission

2. Transmission Media

3. Guided Media

4. Multiplexing

5.Switching

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Switching techinique

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Multiplexing  :- transmission medium is used to send the signal from sender to receiver.

Frequency-division Multiplexing (FDM) :-is a technique in which the available bandwidth of a single transmission medium is subdivided into several channels. 

Wavelength Division Multiplexing (WDM)- optical signals. 

Time Division Multiplexing

    1. Synchronous TDM :-Synchronous TDM, each device is given some time slot irrespective of the fact that the device contains the data or not.

      

    2. Asynchronous TDM :-  technique in which time slots are not fixed as in the case of Synchronous TDM. Time slots are allocated to only those devices which have the data to send.

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1. Digital Transmission :-

Data Can be represent either analog or digital Form .

    1. Digital to Digital Conversion:-     

            1 Unipolar

            2. Polar

            3. Bipolar

    

1. Unipolar : Send Voltage Pulse over the Medium link (Wire or Cable) , in this Voltage represent (1 and 0) so pulse determine whether it Positive or negative. it contain two problem 

            1. DC component :-

            2. Synchronization:- 

2. Polar : encoding scheme that uses two voltage levels: one is positive, and another is negative.

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• NRZ stands for Non-return zero.
• RZ stands for Return to zero.

3. bipolar : 

• Bipolar encoding scheme represents three voltage levels: positive, negative, and zero.
• AMI stands for alternate mark inversion
• B8ZS stands for Bipolar 8-Zero Substitution.
• HDB3 stands for High-Density Bipolar 3.

ANALOG-TO-DIGITAL CONVERSION

 analog signal is digitalized, this is called an analog-to-digital conversion.

Techniques for Analog-To-Digital Conversion

• PAM stands for pulse amplitude modulation. :-generates a series of digital pulses based on the result of sampling where sampling means measuring the amplitude of a signal at equal intervals.
• PCM stands for Pulse Code Modulation. :- is used to modify the pulses created by PAM to form a digital signal.

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Transmission Media

Guided Media : 

    1. Twisted Pair :- a. Unshielded Twisted pair 2. Shielded Twisted pair

Unshieled Twisted Pair :- 

• Category 1: Category 1 is used for telephone lines that have low-speed data.
• Category 2: It can support upto 4Mbps.
• Category 3: It can support upto 16Mbps.
• Category 4: It can support upto 20Mbps. Therefore, it can be used for long-distance communication.
• Category 5: It can support upto 200Mbps.

 

Coaxial Cable:- 

Coaxial cable is of two types:

1. Baseband transmission: It is defined as the process of transmitting a single signal at high speed.
2. Broadband transmission: It is defined as the process of transmitting multiple signals simultaneously.

Fibre Optic :-

Core: The optical fibre consists of a narrow strand of glass or plastic known as a core.

Cladding: The concentric layer of glass is known as cladding.

Jacket: The protective coating consisting of plastic is known as a jacket. The main purpose of a jacket is to preserve the fibre strength, absorb shock and extra fibre protection.