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Physical Layer

Outline Signal Propagation Media The Calculation of Signal Delivery Time The Evaluation of End-to-end Delay Signal Encoding and Modulation Wired Signal s Encoding, Decoding and Decoding Error Wired Signal s Propagation Wireless Signal s Modulation, Demodulation and Demodulation Error Wireless Signal s Propagation Summary Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 2

Media for Delivering Signals Wired Media Copper wire for delivering electrical signal Optical fiber for delivering optical wave etc. Wireless Media Air for delivering electromagnetic wave Air for delivering optical wave etc. Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 4

Sending Host Transmission Time & Propagation Delay Receiving Host User Network Applications Network Applications User TCP / UDP TCP UDP Segment gram TCP UDP TCP / UDP Kernel v4 / v6 Packet v4 / v6 Kernel ARP Device Driver ARP Device Driver Hardware Network Interface Card (NIC) Network Interface Card (NIC) Hardware Tx Start Tx End T Bit T2 Rx Start Transmission Time = T2 T = T4 T3 Rx End Propagation Delay = T3 T = T4 T2 Delivery Time = Rx End Tx Start = T4 T = Transmission Time + Propagation Delay T3 T4 Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 6

Sending Host The Calculation of Transmission Time Receiving Host User Network Applications Network Applications User TCP / UDP TCP UDP Segment gram TCP UDP TCP / UDP Kernel v4 / v6 Packet v4 / v6 Kernel ARP Device Driver ARP Device Driver Hardware Network Interface Card (NIC) Network Interface Card (NIC) Hardware Tx Start Tx End T Bit T2 Sending Host s Interface Rate = X Mbps = (X * ^6) bps Size = Y bytes = (8 * Y) bits Transmission Time = T2 T = (8*Y)/(X * ^6) sec E.g., If X = and Y =, Transmission Time = (8*)/( * ^6) =.8 sec 7 Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved..

Sending Host The Calculation of Propagation Delay Receiving Host User Network Applications Network Applications User TCP / UDP TCP UDP Segment gram TCP UDP TCP / UDP Kernel v4 / v6 Packet v4 / v6 Kernel ARP Device Driver ARP Device Driver Hardware Network Interface Card (NIC) Network Interface Card (NIC) Hardware Tx Start T Bit Rx Start T3 Signal Speed over the Medium = S meter/sec Distance between Sending Host and Receiving Host = D meters Propagation Delay = T3 T = D/S sec E.g., If S = (2 * ^8) and D = 2, Propagation Delay = (2)/(2 * ^8) =. sec Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 8

Transmission Time > Propagation Delay Sending Host Receiving Host User Network Applications Network Applications User TCP / UDP TCP / UDP Kernel v4 / v6 v4 / v6 Kernel ARP ARP Device Driver Device Driver Network Interface Card (NIC) Network Interface Card (NIC) Hardware Hardware Tx Start Rx Start Tx End T Rx End T3 T2 T4 Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 9

Sending Host Transmission Time < Propagation Delay Receiving Host User Network Applications Network Applications User TCP / UDP TCP UDP Segment gram TCP UDP TCP / UDP Kernel v4 / v6 Packet v4 / v6 Kernel ARP Device Driver ARP Device Driver Hardware Network Interface Card (NIC) Network Interface Card (NIC) Hardware Tx Start Tx End T Bit T2 Rx Start Rx End T3 T4 Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved..

Sending Host End-to-end Delay A B Receiving Host User Network Applications Network Applications User TCP / UDP TCP UDP Segment gram TCP UDP TCP / UDP Kernel v4 / v6 Packet v4 / v6 Kernel ARP Device Driver ARP Device Driver Hardware Network Interface Card (NIC) Network Interface Card (NIC) Hardware Bit End-to-end Delay = Sending Host s Kernel/User Processing Delay (e.g., Protocol, Scheduling, Queuing, etc.) + Transmission Time + Propagation Delay + Receiving Host s Kernel/User Processing Delay (e.g., Protocol, Queuing, etc.) Round Trip Time (RTT) = End-to-end Delay from Host A to Host B + End-to-end Delay from Host B to Host A Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 2 2

Sending Host Transmission Time < Propagation Delay Receiving Host User Network Applications Network Applications User TCP / UDP TCP UDP Segment gram TCP UDP TCP / UDP Kernel v4 / v6 Packet v4 / v6 Kernel ARP Device Driver ARP Device Driver Hardware Network Interface Card (NIC) Network Interface Card (NIC) Hardware Tx Start Tx End T If ignoring kernel/user space processing delay and transmission time << propagation delay, propagation delay dominates end-to-end delay. Bit T2 Rx Start Rx End T3 T4 Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 3

Transmission Time > Propagation Delay Sending Host Receiving Host User Network Applications Network Applications User TCP / UDP TCP / UDP Kernel v4 / v6 v4 / v6 Kernel ARP ARP Device Driver Device Driver Network Interface Card (NIC) Network Interface Card (NIC) Hardware Hardware Tx Start Rx Start T Tx End If ignoring kernel/user space processing delay and transmission time >> propagation delay, transmission time dominates end-to-end delay. Rx End T3 T2 T4 4 Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved..

End-to-end Delay across Other Network Devices Sending Host Router Receiving Host User Network Applications Network Applications User TCP / UDP TCP UDP Segment gram TCP UDP TCP / UDP Kernel v4 / v6 Packet v4 / v6 Kernel ARP Device Driver Plane ARP Device Driver Hardware Network Interface Card (NIC) ASIC ing Fabric & L3+ Function Network Interface Card (NIC) Hardware Bit End-to-end Delay from Sending Host to Receiving Host = Point-to-point Delay from Sending Host to Router + Router s Forwarding Delay + Point-to-point Delay from Router to Receiving Host Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 5

Think about different end-to-end delays in the following network VM VM VM VM VM VM VM VM VM VM VM VM VM VM VM (VM) Internal Server (VM) Internal Server 2 (VM) Internal Server 3 (VM) Internal Server 4 (VM) Internal Server 5 (VM) Internal Server 6 (VM) Internal Server 7 (VM) Internal Server 8 Sensor 5G Cellular Network Core Sensor Backbone Router Backbone Router Backbone Router Mobile Communication ISP Backbone ISP Backbone ISP Backbone Camera Display AP Router Router SDN Router Router SDN SDN TOR Router SDN Controller Router ISP Edge Cloud Center SDN Cloud Center Router SDN Controller Router Router Router SDN Controller SDN SDN (VM) NAT (VM) NAT 2 (VM) Firewall Server 4 Server (VM) Firewall 2 Campus / Enterprise Sensor Sensor Sensor IoT SDN TOR Server Router Server 5 Server 6 SDN SDN Server 2 Server 3 Router ISP Gateway ISP Gateway ISP Gateway ISP Gateway AP AP AP AP AP AP AP TV AP TV TV TV AP AP AP AP TV TV TV TV TV TV TV TV Home Office / Shop Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 6

Encoding and Decoding If some data (analog or digital) have to be transmitted in the form of digital signal, the data have to be encoded into digital signals at the sender site. At the receiver site, the received digital signals are decoded to retrieve the original data (analog or digital). Analog Encoding / Decoding Analog Digital Signal Digital Encoder Decoder Digital Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 8

Modulation & Demodulation If some data (analog or digital) have to be transmitted in the form of analog signal, the data have to be modulated into analog signals at the sender site. At the receiver site, the received analog signals are demodulated to retrieve the original data (analog or digital). Carrier Signal Modulation / Demodulation Analog Analog Analog Signal Digital Modulator Demodulator Digital Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 9

Wired Signal s Encoding and Decoding 2 3 Host Host 2 Encode digital data into digital signals Encode Encode Encode 4 5 6 7 Decode digital signals into digital data Decode Decode Decode Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 2

Wired Signal s Decoding Error 2 3 Host Host 2 Encode digital data into digital signals Encode Encode Encode 4 This segment of digital signal is corrupted due to interference 5 6 7 Decode digital signals into digital data Decode Decode Decode Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 22

How to check if the decoded data are corrupted? A frame is usually composed of header field, data payload field, and frame check sequence (FCS) field. The value filled in the FCS field is calculated by the Cyclic Redundancy Check (CRC) algorithm. The input data for the algorithm are the contents of header field and data payload field. Before a frame is transmitted at the sender site, a CRC value is calculated and filled in the FCS field. When the frame is received at the receiver site, another CRC calculation is done and the new CRC value is used to compare with the value of the FCS field. If the two values are different, the received data are considered corrupted. Sender Site Receiver Site Payload FCS Payload FCS CRC CRC =? Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 23

When wired signals enter a network device like hub or repeater, the signals directly pass through the device without experiencing signal decoding. 2 Before signals enter the hub Signals are directly broadcasted to other ports Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 25

When wired signals enter a network device like switch or router, the signals have to experience signal decoding and the decoded data have to be stored and processed for determining the outgoing interface/port. Before signals enter the switch 2 Signals are received by the switch for finding out the destination 3 Signals are forwarded only to the port which the destination is connected to 26 Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved..

Wired signals could collide with other signals while being transmitted on a wire. If, on a wire, only one direction is allowed to transmit signals simultaneously, it is called half duplex. If signals are transmitted from both directions simultaneously, a signal collision occurs and that results in no successful signal reception. If, on a wire, both directions are allowed to transmit signals simultaneously, it is called full duplex. No collision occurs on a full-duplex wire. Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 27

Wireless Signal s Modulation and Demodulation 2 3 Host Host 2 Modulate 4 Modulate digital data into analog signals Modulate Modulate 5 6 7 Demodulate analog signals into digital data Demodulate Demodulate Demodulate Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 29

Wireless Signal s Demodulation Error Host 4 5 Host 2 2 Modulate digital data into analog signals Modulate Modulate This segment of analog signal is corrupted due to interference 6 Demodulate analog signals into digital data Demodulate 3 Modulate 7 Demodulate Demodulate Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 3

How to check if the demodulated data are corrupted? A frame is usually composed of header field, data payload field, and frame check sequence (FCS) field. The value filled in the FCS field is calculated by the Cyclic Redundancy Check (CRC) algorithm. The input data for the algorithm are the contents of header field and data payload field. Before a frame is transmitted at the sender site, a CRC value is calculated and filled in the FCS field. When the frame is received at the receiver site, another CRC calculation is done and the new CRC value is used to compare with the value of the FCS field. If the two values are different, the received data are considered corrupted. Sender Site Receiver Site Payload FCS Payload FCS CRC CRC =? Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 3

Wireless Signal s Propagation < Simulation Case > antenna_gain_pattern.xtpl wireless_link_recv_sensitivity.xtpl wireless_signal_collision.xtpl Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 32

Isotropic Antenna Factors to determine the transmission range of wireless signals:. Antenna gain patterns of both sender site and receiver site 2. Signal transmission power on sender site 3. Signal receiving sensitivity on receiver site 4. Signal frequency and environmental parameters (e.g., terrain, surface object, weather, interference, etc.) Directional Antenna (horizontal angle 6, point to the right) 6 The point with half the energy (-3dB) The point with half the energy (-3dB) Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 33

The transmission power of signal is gradually attenuated along with the signal emission path. When the power is lower than the receiving sensitivity of a receiver, no signal is received. Sender Receiver The receiver is moving within the coverage of transmitted signals, it receives the signals successfully. Once the receiver moves beyond the coverage of the transmitted signal, no signal is received. Sender Receiver Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 34

When wireless signals are transmitted on the air, collisions could occur among different signals. Sender Sender Receiver Different signals collide with each other at the receiver Sender Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 35

Review of Points In terms of signal delivery time, what is transmission time? And what is propagation delay? What are the factors to determine the end-to-end delay? What are the procedures of signal encoding/decoding and modulation/demodulation? Why are there errors during the procedures of signal decoding and demodulation? What are the characteristics of wired signal propagation? What are the characteristics of wireless signal propagation? Copyright 2-28, EstiNet Technologies Inc. All Rights Reserved.. 37