Introduction to Physical Layer Advanced Computer Network by Ravinder Nath Rajotiya - September 25, 2021September 28, 20210 Share on Facebook Share Send email Mail Print Print Role of Physical Layer Physical Layer Signals – bit Bite Rate- no. of bits sent in one seconds Bit length- distance one bit occupies on the transmission medium = propagation speed x bit duration Attenuation- Loss of energy as it travels on the medium. To compensate for loss, we may use different components such as amplifiers, Decible- It is the unit that measure the relative strength (power or voltage) of two signals one signal at two different points. db = 10 log10(P2/P1) or db = 20 log10 (V2/V1) It should be noted that db will be +ve if signal is amplified and –ve if signal is lost/attenuated Nyquist bit rate :For noiseless channel, the nyquist bit rate define theoretical maximum bit rate as Nyquist bit rate= 2 x bandwidth x log2L Throughput: is a measure of how fast we can send the data through a network. Ex. 12000 frames/min, each fram carrying 10000bits, bandwidth 10Mbps Throughput = (12000X 10000)/60 = 2MBPS, therefore the throughput in this case is 1/5th of the bandwidth Latency: It is the delay and define how long it takes for an entire message to completely reach at the destination from the 1st bit that is sent out from the source Latency = Propagation time+transmission time + queuing time+processing delay Operation at Physical Layer Digital Transmisstion Basic understanding ‘r’ is the ration of number of data elements carried by a signal element Signal rate = data rate / r S = N/ r Line coding- Process of converting digital data to digital signals. Unipolar line coding – Non-return-to-zero(NRZ) Polar Scheme – NRZ, RZ, manchester (biphase and differential) Bipolar – AMI and Pseudoternary Multilevel- 2B/1Q, 8B/6T, 4D-PAM5 Multitransition – MLT3 Block Coding – it changes a block of M bits into a block of N bits referred as mB / nB such as 4B/5B, 8B/10B Analog to Digital Conversion (A-D) Pulse code modulation Delta Modulation Transmission Modes Parallel Serial – Asynchronous, Synchronous, Isochronous Analog Transmission Digital to Analog conversion – ASK, FSK, PSK Analog-to-analog conversion – AM, FM, PM Multiplexing FDM, TDM Spread Spectrum- FHSS (frequency hopping spread spectrum), DSSS(direct sequence spread spectrum) Transmission Medium Guided Medium – Twisted pair cable(TP), Coaxial cable, Fiber-optic cable Unguided Medium – Radio Wave, Microwave, Infrared Switching – Switching can happen at physical layer, at datalink layer, network layer or at application layer Types – Circuit switching, message switching, packet switching Physical Layer – Circuit Switching Data link layer – packet switching, but we will refer them as frames or cell at DLL. Packet switching at DLL is using virtual circuit approach Network layer – packet switching. Virtual circuit or datagram approach is used in network layer Application layer – message switching. E-mail is a kind of message switching Share on Facebook Share Send email Mail Print Print