ECEN5553 Telecom Systems Dr. George Scheets Week #2 Read [3] "A Roadmap to 100G Ethernet at the Enterprise Data Center" Exam #1 Lecture 15, 21 September (Live) No later than 28 September (Remote DL) Outline 7 October 2015, Lecture 22 (Live) No later than 14 October (Remote DL)

Outlines Received due 7 October (local) 14 October (remote) 0 %

Fiber Optic Cable 1 1/4 inch SC

Physical Layer Ailments... Attenuation Signal power weakens with distance Attenuation Signal power weakens with distance Distortion Pulse shapes change with distance Distortion Pulse shapes change with distance Copper cabling High frequencies attenuate faster Pulses smear Copper cabling High frequencies attenuate faster Pulses smear Fiber cabling Frequencies propagate at different speeds Dispersion (Pulses change shape) Fiber cabling Frequencies propagate at different speeds Dispersion (Pulses change shape)

Generating a Square Wave Hz + 15 Hz + 25 Hz + 35 Hz cos2*pi*5t - (1/3)cos2*pi*15t + (1/5)cos2*pi*25t - (1/7)cos2*pi*35t)

Effects of Dispersion Hz + 15 Hz + 25 Hz + 35 Hz cos2*pi*5t + (1/3)cos2*pi*15t + (1/5)cos2*pi*25t + (1/7)cos2*pi*35t) In this example the 15 and 35 Hz signals have suffered a phase shift (which can be caused as a result of different propagation speeds) with respect to the 5 and 25 Hz signals. The pulse shape changes significantly.

Smearing (a.k.a. Inter-symbol Interference) z k z2 k 1270k output input Pulse energy is no longer confined to a T second time interval. Makes receiver symbol detector's life more difficult.

Examples of Amplified Noise Radio Static (Thermal Noise) Radio Static (Thermal Noise) Analog TV "snow" Analog TV "snow" 2 seconds of White Noise

SNR = Average Signal Power = Infinity Average Noise Power Binary Signal Sequence =

SNR = 100 Signal a sequence +1 and -1 volt pulses For your info, SSD BER ≈ 0.0

SNR = 10 Signal a sequence +1 and -1 volt pulses For your info, SSD P(BE) = = 1/1277

SNR = 1 Signal a sequence +1 and -1 volt pulses For your info, SSD P(BE) = = 1/6.3

SNR =.1 Signal a sequence +1 and -1 volt pulses For your info, SSD P(BE) =

Single Sample Detector: SNR = k Threshold is placed midway between nominal Logic 1 and 0 values. Detected sequence = at the receiver, but there were some near misses.

Fall 2002 Final 'Average' based on 1 test chosen at random out of 150 'Average' based on 1 test chosen at random out of 150 Analogous with "Single Sample" Detector Analogous with "Single Sample" Detector 'Average' based on 10 tests chosen randomly out of 150 'Average' based on 10 tests chosen randomly out of 150 Analogous with "Multiple Sample" Detector Analogous with "Multiple Sample" Detector Average based on 10 samples tends to be more accurate than "Average" based on 1 sample Average based on 10 samples tends to be more accurate than "Average" based on 1 sample Actual Midterm Average out of 150 Actual Midterm Average out of 150

Matched Filter Detector: SNR = k Orange Bars are average voltage over that symbol interval. Averages are less likely to be way off the mark. SSD P(BE) = , MFD P(BE) = (10 samples/bit)

Receiver Detection SNR tends to worsen with distance SNR tends to worsen with distance Digital Receiver Symbol Detectors Digital Receiver Symbol Detectors Examine received symbol intervals (T sec.) Examine received symbol intervals (T sec.) Decide which of M symbols was transmitted Decide which of M symbols was transmitted Single Sample Detectors Sample each symbol once Compare sampled value to a threshold Single Sample Detectors Sample each symbol once Compare sampled value to a threshold Matched Filter Detectors (Optimal) Sample each symbol multiple times & generate an average Compare the average value to a threshold Matched Filter Detectors (Optimal) Sample each symbol multiple times & generate an average Compare the average value to a threshold

Channel Capacity Bandwidth affects usable symbol rate Bandwidth affects usable symbol rate Rapidly changing symbols need hi frequencies Rapidly changing symbols need hi frequencies Baud rate too high? Distortion!! Baud rate too high? Distortion!! M-Ary allows increased bit rate M-Ary allows increased bit rate Each symbol can represent multiple bits Each symbol can represent multiple bits SNR SNR Affects RCVR ability to tell symbols apart Affects RCVR ability to tell symbols apart Bandwidth & SNR affect usable bit rate Bandwidth & SNR affect usable bit rate

Channel Capacity (C) Bandwidth, Bit Rate, SNR, and BER related Bandwidth, Bit Rate, SNR, and BER related Channel Capacity defines relationship C = Maximum reliable bit rate C = W*Log 2 (1 + SNR) bps Channel Capacity defines relationship C = Maximum reliable bit rate C = W*Log 2 (1 + SNR) bps Bandwidth sets the maximum Baud rate If move too many Baud, symbols will smear. SNR sets the maximum number of different symbols (the "M" in M-ary) you can reliably tell apart.

Channel Capacity (a.k.a. Shannon-Hartley Theorem) Claude Shannon Ralph Hartley

Power Line Communications Image Source Wikipedia Transformers don't pass high frequency signals.

Power Lines act as Antennas Source:

Home Power Line Networks Possible using home wiring Possible using home wiring Outside Step Down Transformer blocks further wired transmission Outside Step Down Transformer blocks further wired transmission Signal radiates off internal house wiring Signal radiates off internal house wiring Netgear claims 500 Mbps Netgear claims 500 Mbps

Normalized Propagation Delay NPD = End-to-End Propagation Delay Average time to inject a Packet NPD = End-to-End Propagation Delay Average time to inject a Packet NPD > 1 1 or more packets can simultaneously be in transit NPD > 1 1 or more packets can simultaneously be in transit If NPD = 5, 5 average sized packets can be physically on the line If NPD = 5, 5 average sized packets can be physically on the line NPD < 1 Packet front end hits far side before back end transmitted NPD < 1 Packet front end hits far side before back end transmitted TransmitterReceiver High Speed Low Speed

Types of Traffic... Computer Data Bursty Highly sensitive to errors Not as time sensitive as voice or video Computer Data Bursty Highly sensitive to errors Not as time sensitive as voice or video Interactive Voice/Video Fixed Rate (if not compressed) *Not very sensitive to errors Fixed or Variable Rate (if compressed) *Sensitive to errors Time Sensitive Interactive Voice/Video Fixed Rate (if not compressed) *Not very sensitive to errors Fixed or Variable Rate (if compressed) *Sensitive to errors Time Sensitive

IEEE Institute for Electrical & Electronics Engineers Institute for Electrical & Electronics Engineers Largest Technical Organization in the World Largest Technical Organization in the World Promotes betterment of Electrical Engineering Promotes betterment of Electrical Engineering Journals & Magazines Journals & Magazines Conferences Conferences Standards Standards

IEEE Ethernet Based on late 1970’s technology Based on late 1970’s technology Covers OSI Layers 1 & 2 Covers OSI Layers 1 & 2 10 Mbps Line Speed 10 Mbps Line Speed Logical Bus Logical Bus Designed to move Computer Data Designed to move Computer Data The various flavors dominate the wired LAN The various flavors dominate the wired LAN

Serial Bit Stream: NRZ Coding time +1 volts 0 T 00 Logic One Logic Zero Called ‘Non Return to Zero’ because voltage never dwells on zero volts. T

Ethernet Uses Manchester Coding time +1 volts 0 T 00 Logic One Logic Zero All symbols have a transition in the middle.

Ethernet Uses Manchester Coding time +1 volts 0 T High Pass Filters Emphasize Change

High Pass Filter Output time +1 0

Rectify (Absolute Value) time +1 0 T Result always has pulses T seconds apart. Useful for receiver synchronization.

What is CSMA/CD? n Polite Conversation u One node active at a time u No deliberate interruptions u Collisions sometimes occur after a pause

802.3 Back-Off Algorithm n choose random number 1st Collision0, 1 2nd Collision0, 1, 2, 3 3rd Collision0, 1,..., 6, 7 4th Collision0, 1,..., 14, 15 10th Collision0, 1,..., 1022, th Collision0, 1,..., 1022, th CollisionPunt n Wait (Random Number* ) seconds