ECEN5553 Telecom Systems Week #3 Read: [3] "A Roadmap to 100 Gbps Ethernet" [4a] "What if Ethernet Failed?" thru [4d] "Showdown Coming on Ethernet Standard" Exam #1: Lecture 14, 16 September (Live) No later than 23 September (Remote DL) Outline: Lecture 22, 5 October (Live) No later than 12 October (Remote DL)

Outlines Received due 5 October (local) 12 October (remote) 0 %

Power Lines act as Antennas Source: http://www.doobybrain.com/2008/02/03/electromagnetic-fields-cause-fluorescent-bulbs-to-glow/

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

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

Normalized Propagation Delay NPD = End-to-End Propagation Delay Average time to inject a Packet NPD > 1 1 or more packets can simultaneously be in transit 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 High Speed Low Speed Transmitter Receiver

Types of Traffic... 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

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

IEEE 802.3 Ethernet Based on late 1970’s technology Covers OSI Layers 1 & 2 10 Mbps Line Speed Logical Bus Designed to move Computer Data The various 802.3 flavors dominate the wired LAN

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

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

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

High Pass Filter Output +1 time -1

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

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

802.3 Back-Off Algorithm choose random number 1st Collision 0, 1 2nd Collision 0, 1, 2, 3 3rd Collision 0, 1, ..., 6, 7 4th Collision 0, 1, ..., 14, 15 10th Collision 0, 1, ..., 1022, 1023 15th Collision 0, 1, ..., 1022, 1023 16th Collision Punt Wait (Random Number*.0000512) seconds

802.3 MAC Flow Chart No Packet to Send? Drop Packet. Notify Higher Layer Yes Yes No Set Collision Couter = 0 16th Collision? Back-Off Yes Traffic on Network? Bump Collision Counter by +1 No Send Packet Yes Collision? Jam No

Major Drawbacks of CSMA/CD MMAT equals infinity (No guaranteed Bandwidth) No Priorities These make 802.3 Ethernet marginal, at best, for Multimedia Traffic.

802.3 Packet Format Bytes: 7 1 6 6 2 Pre SFD Destination Address Source Len 46-1500 4 CRC Data + Padding

Preamble Logic Logic One Zero Series of pulses generated at receiver T seconds apart & in middle of each symbol. volts +1 time -1 T

Transmitting a File Broken into smaller packets Initial packets from Layer 5 Open Logical Connection Packets from Layer 7 “Data” Contains Layer 7 traffic “Data” Contains Layer 3-6 info Packets from Layer 4 Acknowledgements Final packets from Layer 5 Close Logical Connection

All nodes monitor traffic 10Base5 & 10Base2 (Obsolete) Coax Cable PC PC Printer Logical & Physical Bus All nodes monitor traffic Nodes share 10 Mbps 10Base2 "T" connection 10Base5 "Vampire Tap" Images from Wikipedia

10BaseT & Shared Hub PC PC Twisted Pair Hub PC PC Logical Bus & Physical Star Shared hub (OSI Level 1) copies input bits to all outputs. All nodes monitor traffic. 4 nodes share 10 Mbps.

10BaseT & Switched Hub Switch PC PC PC PC Logical Bus & Physical Star Switched Hub (OSI Level 1 & 2) copies packet to proper output. Only the destination monitors traffic. This example system can move up to 20 Mbps provided the packet source & destinations differ.

Logical Bus & Physical Star with the Switched Hub if Half Duplex. 10BaseT & Switched Hub PC PC Switched Hub PC PC Logical Bus & Physical Star Each node shares 10 Mbps with the Switched Hub if Half Duplex.

10BaseT & Switched Hub PC PC reception is screwed up Switched Hub PC Using Half Duplex 10BaseT, a collision occurs if PC & Switched Hub simultaneously transmit.

IEEE 802.3u 100 Mbps Fast Ethernet Preserves CSMA/CD Preserves Packet Format Maximum End-to-End Lengths (a.k.a. Collision Domain) reduced to keep Normalized Propagation Delay low Sales exceed 10 Mbps as of ‘98

Ethernet Switch Port Sales "A Roadmap to 100G Ethernet at the Enterprise Data Center" IEEE Communications Magazine, November 2007 Source:

Back around 1994 to 1995… Two 100 Mbps "Ethernets" introduced Version A CSMA/CD MAC, Ethernet Frames Version B Demand Priority MAC, Ethernet Frames IEEE said Version A is Ethernet IEEE 802.3u Fast Ethernet IEEE said Version B is not Ethernet IEEE 802.12 100VG-AnyLAN 802.12 is currently Dead RIP

IEEE 802.3z 1 Gbps Ethernet (1998) Uses an extended version of CSMA/CD, including "Frame Bursting" Best performance uses full duplex connections & switched hubs CSMA/CD included so it can be called Ethernet Collision Domain same as Fast Ethernet Preserves Packet Format Fiber or Cat6 Cables

Full Duplex System PC PC Switched Hub PC PC All > 10 Gbps, most 1 Gbps, & many 100 Mbps systems are Full Duplex. Net IC’s are designed to simultaneously transmit & receive. Line no longer shared. No Collisions. No need for CSMA/CD.

IEEE 802.3ae 10 Gbps “Ethernet” (2002) Standard as of June 2002 Does not use CSMA/CD Uses switched hubs & full duplex connections Uses Ethernet frame format Initial available products used fiber Copper cabling now an option

IEEE 802.3ba 40 & 100 Gbps “Ethernet” (2010) Standard as of June 2010 Does not use CSMA/CD Uses switched hubs & full duplex connections Uses Ethernet frame format Copper cabling an option 7-10 m, 10 twisted pairs required Mostly uses fiber

IEEE 802.1p Priority Tags 8 priorities MAC protocols remain unchanged Used by 802.1p enabled switches Allows interactive voice or video to receive preferential treatment on an Ethernet LAN

Many Ethernet Physical Layer Standards Exist source: "Evolution of Ethernet Standards in the IEEE 802.3 Working Group", IEEE Communications Magazine, August 2013

LAN Throughput Average bit transmission rate actually available for use Throughput = Efficiency * Line Speed Shared Half Duplex Network No Load Efficiency: ≈ 100% Actually a little less since frames can't be transmitted back-to-back Heavy Load Efficiency: ≈ 1/(1+5*NPD) Shared network: apply to entire network Switched network: apply between switched hub & end device Switched Full Duplex Network Efficiency ≈ 100% These are Estimates.

10BaseT & Shared Hub PC 53 m PC 8 m Hub PC PC 26 m 17 m Logical Bus & Physical Star Shared hub (OSI Level 1) copies input bits to all outputs. All nodes monitor traffic. 4 nodes share 10 Mbps. Max end-to-end distance is 79 meters.

10BaseT & Switched Hub Switch PC 53 m PC 8 m PC PC 26 m 17 m Logical Bus & Physical Star Switched hub (OSI Level 1 & 2) is packet & MAC aware. Nodes don't see all traffic. Line shared between node & switch. η Distance to use is PC to Hub specific.

Ethernet Performance Simulations show CSMA/CD is very efficient for slow speed Networks. Shared Ethernet efficiency equation reasonably accurate. Simulations also show that Average Delay to move a packet at head of queue is usually small, even under heavy load conditions.

Shared 802.3 LAN Efficiencies 500 m end-to-end Heavy Load Conditions 100 B packets: Formula = .8809 efficiency 5 nodes: .9986 simulated 50 nodes: .6980 simulated 1500 B packets: Formula = .9911 efficiency 5 nodes: .9953 simulated 50 nodes: .9532 simulated Conclusion: Heavy Load η reasonably accurate

Head of Line Performance 185 m end-to-end, 130 byte packets 5 nodes > 90% of packets do not collide Average collisions/packet = .05 Average delay to transmit = 51 microsec. Maximum delay to transmit = 11.3 msec. 50 nodes > 45% collide one or more times (2% 16x) Average collisions/packet = .93 Average delay to transmit = 340 microsec. Maximum delay to transmit = 236 msec

LAN History IEEE 802.5 Token Ring Based on early 1980’s technology Covers OSI Layers 1 & 2 4 or 16 Mbps Line Speed Logical Ring A ‘Token’ is passed around the ring Node must have the Token to transmit Guaranteed Bandwidth Has Priorities

IEEE 802.5 Token Ring Technically Superior to shared Ethernet Similar evolution to Ethernet Logical & Physical Ring Logical Ring, Shared Physical Star Logical Ring, Switched Physical Star 100 Mbps products available in ’98 3 years after Fast Ethernet Sales have crashed. 802.5 is dead. RIP

Ethernet & Token Ring Shared Network Efficiency 1.0 Efficiencies Token Ring 1/(1 + NPD) Ethernet 1/(1 + 5*NPD) 0.5 0.0 .01 .10 1.0 10.0 100 NPD

Shared Network Performance Issues Slow Speed Network? Both Ethernet & Token Ring work well Borderline Network? Token Ring offers clearly superior performance High Speed Network? Both stink. Token Ring and Ethernet MAC’s don’t scale well to long distances or high speeds

Shared Ethernet Efficiency Designed to operate as "Low Speed" 1.0 Standard CSMA/CD 0.5 0.0 .01 .10 1.0 10.0 100 NPD