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ECEN5553 Telecom Systems Week #3 Read [4a] "High Speed Ethernet: A Planning Guide" [4b] "What If Ethernet Failed?" [4c] "8 Ethernet Predictions for 2014" [5a] "Is Your Ethernet Fast Enough?" [5b] "Showdown Coming on Ethernet Standard to Serve Faster Wi-Fi" [6a] "Browse at Your Own Risk" [6b] "The Data Brokers: Selling Your Personal Information" 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% 802.3 MAC Flow Chart No Packet to Send? Drop Packet. Notify Higher Layer Yes Set Collision Couter =0 Traffic on Network? No Back-Off Yes 16th Collision? Yes Bump Collision Counter by +1 No Send Packet Yes Collision? No Jam 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 Pre 1 6 6 SFD Destination Address Source Address 46-1500 Data + Padding 2 Len 4 CRC Preamble Logic One 0 Logic Zero 0 volts +1 Series of pulses generated at receiver T seconds apart & in middle of each symbol. 0 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 10Base5 & 10Base2 (Obsolete) Coax Cable PC PC Printer Logical & Physical Bus All nodes monitor traffic Nodes share 10 Mbps 10Base5 "Vampire Tap" 10Base2 "T" connection Images from Wikipedia 10BaseT & Shared Hub PC Twisted Pair PC 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 PC PC Switch 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. 10BaseT & Switched Hub PC PC Switched Hub PC PC Logical Bus & Physical Star Each node shares 10 Mbps with the Switched Hub. 10BaseT & Switched Hub PC reception is screwed up PC PC 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 Source: "A Roadmap to 100G Ethernet at the Enterprise Data Center" IEEE Communications Magazine, November 2007 Ethernet Switch Port Sales Back around 1994 to 1995… Two 100 Mbps "Ethernets" introduced Version A CSMA/CD Version B Demand 802.3u Fast Ethernet IEEE said Version B is not Ethernet IEEE Priority MAC, Ethernet Frames IEEE said Version A is Ethernet IEEE MAC, Ethernet Frames 802.12 100VG-AnyLAN 802.12 is currently Dead 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% These are Actually a little less since frames Estimates. 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% 10BaseT & Shared Hub 53 m PC 8m PC Hub PC 26 m 17 m 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. Max end-to-end distance is 79 meters. 10BaseT & Switched Hub 53 m PC 8m PC Switch PC 26 m 17 m PC 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. 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 NPD 10.0 100 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 NPD 10.0 100 Low Speed Network? This configuration... PC Server Hub PC PC 10BaseT & Shared Hub ... is as good as this one... PC Server Switched Hub PC PC 10BaseT & Switched Hub ...IF traffic mostly going to/from same machine Switched Hub better if diverse traffic flow This configuration is even better. PC 10 Mbps 1 Gbps Server Switch 100 Mbps PC 10 Mbps PC Server on a higher speed line. Shared Ethernet Efficiency Gbps has higher NPD 1.0 0.5 0.0 .01 .10 .1 1.0 NPD 1 10.0 10 100 High Speed Network? This configuration has horrible throughput. PC Server Shared Hub PC PC 1 or 10 Gbps & Shared Hub Under heavy load, too much time spent recovering from collisions. Ethernet (Shared) Hub Operates at OSI Level 1 ‘Electric Cable’ Traffic arriving at an input is immediately copied to all other ports on a bit-by bit basis. Used on LAN's. Pretty much obsolete. Repeater = single input & single output hub Not used much on Ethernet any more Generally now only used on WAN long haul May be different protocol than Ethernet Black Box Performance... From Node A Node B Node C To Node A OSI Level 1 LAN Hub Node B Node C Two packets simultaneously show up at input... Black Box Performance... From Node A Node B Node C To Node A OSI Level 1 LAN Hub Node B Node C ... will overwrite each other, i.e. garbage out. a.k.a. Shared Hub Black Box Performance... OSI Level 1-2 (Switch) or 1-3 (Router) Two packets simultaneously show up at input... Black Box Performance... OSI Level 1-2 (Switch) or 1-3 (Router) ... one will be transmitted (when allowed by MAC), the other momentarily buffered... Black Box Performance... OSI Level 2/3 Switch or Router ... and then transmitted. 10BaseT & Shared Hub 53 m PC 8m PC Hub PC 26 m 17 m One big collision domain. PC 10BaseT & Half Duplex Switch 53 m PC 8m PC Switch PC 26 m 17 m PC Four smaller collision domains. Example If Box 1 & 2 are Level 1 Hubs One Big Collision Domain 15 Nodes share 10 Mbps Each node gets average of 10/15 Mbps World 10BaseT 7 Hub 1 Users Hub 2 7 Users Right Side to World gets 7/15th of available BW, on average. Example If Box 1 & 2 are Level 2 Switches Each node shares 10 Mbps with Switch Right Hand Side is on one 10 Mbps line. World 10BaseT 7 Users Sw 1 Right hand side sees increased delays. Can be alleviated with 100 Mbps Box 1 ↔ Box 2 link. Sw 2 7 Users Right Side to World gets 1/8th of available BW. _____ (Was 7/15th) Switched Hubs or Bridge On Power Up know nothing When a packet arrives at an input port... Look-Up Table consulted Source MAC address not in table? Table Updated: MAC address & Port matched Destination Packet broadcast to all outputs (a.k.a. flooding) Destination Packet MAC address not in table? MAC address in table? shipped to proper output Look-up Table update is dependent on packet arrivals Router Operates at OSI Layers 1, 2, & 3 Capable of making complex routing decisions ‘peers into’ packets and examines Layer 3 address Very useful on Large Networks with multiple end-to-end paths Routers frequently exchange connectivity info with neighboring Routers Routing Algorithms used to update Routing (Look-Up) Tables Tables updated independently of traffic Bridging versus Routing Ethernet Bridge, Switch, or Switched Hub Uses Layer 2 MAC Address Unknown Destination? Flooded Look-up Table updates are packet dependent Router Uses Layer 3 Internet Protocol Address Unknown Destination? Default location Look-up Tables updated independently of traffic Small Network? Doesn't matter Big Network? Floods not a good idea. Ethernet Switch Uses MAC Source Address to populate Look-Up Table Uses MAC Destination Address & Table for I/O Decision Bytes: 7 1 6 6 2 Pre SFD Destination Address Source Address 46-1500 Data + Padding Len 4 CRC Router Populates Look-Up table independently of traffic. Uses Destination IP Address & Table for I/O Decision Bytes: 7 1 6 6 2 MAC Destination Address MAC Source Address 20 20 6-1460 4 IPv4 TCP Data + Padding CRC