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ECEN4533 Data Communications Lecture #9 28 January 2013 Dr. George Scheets Read: 4.4 Problems: 4.1, Web 6.1 Design #1 due 1 February (Live) 8 February (Async DL) Late = -1 per working day Quiz #1 Lecture 12, 4 February (Live) < 11 February (Async Distance Learning) ECEN4533 Data Communications Lecture #10 30 January 2013 Dr. George Scheets Read: 5.1 - 5.4 Problems: 5.1 - 5.3 Design #1 due 1 February (Live) 8 February (Async DL) Late = -1 per working day Quiz #1 Lecture 12, 4 February (Live) < 11 February (Async Distance Learning) ECEN4533 Data Communications Lecture #11 1 February 2013 Dr. George Scheets Read: 5.7 - 5.8 Problems: None Design #1 due 1 February (Live) 8 February (Async DL) Late = -1 per working day Quiz #1 (open book & notes) Lecture 12, 4 February (Live) < 11 February (Async Distance Learning) POTS at the CO Switch Band Pass Filter suppresses energy outside voice bandwidth (300 - 3,400 Hz) Twisted Pair Cable 64 Kbps A/D Converter Band Pass Filter (.3 - 3.4KHz) Code 8 bits/sample Sampler Fs = 8 KHz Quantize 256 levels Nyquist's Sampling Theorem Want to have a shot at perfectly reconstructing a sampled signal? Sample at a rate > twice the maximum frequency. Example: Phone system Maximum frequency around 3.5 KHz, fs = 8 Ksps Example: Compact Disk Maximum frequency around 20 KHz, fs = 44.1 Ksps Video undersampling 30 video stills/second 27 wheel revs/second 0.9 wheel revs/still time t=0 time = 1/30 Spoke would appear to be moving backwards. time = 2/30 PC Dial-Up Modems & POTS PC Bit Stream has a significant amount of energy below 0.5 KHz Modems shift the energy into the pass band of the filter PC Twisted Pair Cable 64 Kbps A/D Converter Band Pass Filter (.3 - 3.4 KHz) Code 8 bits/sample Sampler Fs = 8 KHz Quantize 256 levels Sources of POTS delay Source CO Local Loop PCM Coder POTS TDM Trunk TSI ... Trunk resources are dedicated to each voice call via TDM. PCM Coder POTS Local Loop TDM Trunk TSI Destination CO Intermediate Digital Voice Switches Example) Coding a Microphone Output m(t) volts (air pressure) time (sec) Energy from about 300 - 3,400 Hz. A/D Convertor m(t) volts (air pressure) 1/8000 second time (sec) Step #1) Sample the waveform at rate > 2*Max Frequency. Telephone voice is sampled at 8,000 samples/second. A/D Convertor. 1 bit/sample. Example) N = 2. Assign 0 or 1 to voltage. 3.62 v, output a 1 t1 time (sec) 0 < Voltage < +5v, Assign Logic 1 -5v < Voltage < 0, Assign Logic 0 Bit Stream Out = 1111110000111... A/D Convertor. 1 bit/sample. Example) N = 2. Assign 0 or 1 to voltage. 0 < Voltage < +5v, Assign Logic 1 -5v < Voltage < 0, Assign Logic 0 Far side gets... 1111110000111 (13 samples) Need to output 13 voltages. What does a 1 represent? A 0? Receive a 1? Output +2.5 v (mid-range) Receive a 0? Output -2.5 v (mid-range) Hold the voltage until next sample A/D Convertor. 1 bit/sample. Input to the transmitter. Output at the receiver. +2.5 v -2.5 v Considerable Round-Off error exists. A/D Convertor. 2 bits/sample Example) N = 4. Assign 00, 01, 10 or 11. 3.62 v, Assign 11 +2.5 v time (sec) t1 -2.5 v 2.5 < Voltage < 5 , Assign 11 0 < Voltage < 2.5, Assign 10 -2.5 < Voltage < 0, Assign 00 -5 < Voltage < -2.5, Assign 01 Bit Stream Out = 11111011111100 000000101011... A/D Convertor. 2 bits/sample. Input to the transmitter. Output at the receiver. +3.75 v +1.25 v -1.25 v Receive 11? Output 3.75v Receive 10? Output 1.25v Receive 00? Output -1.25v Receive 01? Output -3.75v Reduced Round-Off error exists. -3.75 v Circuit Switched Voice (POTS) Telephone System uses Pulse Code Modulation Equal length code word assigned to all voltages N = 256 voltage levels Log2256 = 8 bits per code word A/D Converter samples voice 8,000 times/second rounds off voice to one of 256 voltage levels transmits 8 bits to far side D/A Converter receives 8 bit code word outputs one of 256 voltage levels for 1/8000th sec. 1/8th Second of Voice 1/8th Second of Voice 1/8th Second of Voice Sampling & Quantizing Examples fs = 16 KHz 4096 quantiles 256 quantiles (approximate phone quality) 32 quantiles 4 quantiles (generally 2 levels used!) 4096 fs quantiles = 16 KHz fs = 8 KHz (some interference) fs = 2 KHz fs = 1 KHz SONET Hierarchy Basic Building Block: 51.84 Mbps STS-1 Frame 8,000 frames/second 810 bytes/frame, 36 bytes for OA&M Optical Carrier-N? N byte interleaved STS-1 signals (TDM) OC-1 51.84 Mbps OC-3 155.52 Mbps OC-12 622.08 Mbps OC-48 2.48832 Gbps OC-192 9.95328 Gbps OC-768 39.81312 Gbps T Carrier & SONET Technology used in Leased Lines Mid-1960’s (T Carrier) & Late-1980’s (SONET) technology Covers OSI Layers 1 & 2 (not packet-aware!) Guaranteed Bandwidth using Circuit Switching & TDM End-to-End path mapped in advance Provides fixed number of bytes, 8000 times second, for customer use As they arrive, switches repetitively move input bytes to appropriate output & TDM slot Leased Line Networks Last Mile Connectivity Fractional T-1 (4 Wire Twisted Pair) N*64 Kbps, N = 1 - 23 T-1 (4 Wire Twisted Pair) 1.536 Mbps (24*64 Kbps) Fractional T-3 (Coax) N T-1's, N = 1 - 27 T-3 (Coax) 28 T-1's + Overhead (45 Mbps) Last Mile or Long Haul Connectivity OC- N, N = 1, 3, 12, 48, & 192 (SONET) N*51.84 Mbps (Fiber) ISO OSI Seven Layer Model Leased Line (Circuit Switched, TDM) Organized around Frames:1/8000th second entity Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 Layer 2 Layer 1 Application Presentation Session Transport Network Data Link Physical SONET, T-Carrier (PPP) SONET, T-Carrier Carrier Switches are byte-aware, NOT packet-aware. Leased Line Packet Format 7 Point-to-Point Protocol 20 20 IP TCP 6-1460 Data + Padding Leased Line Backbone Cross-Connect Leased Line ‘Cloud’ Trunk capacity shared via TDM & Circuit Switching Carrier Leased Line Network LAN Cross-Connect LAN Nailed up end-to-end connectivity (a Circuit). Bit pipe. No packet processing between Routers. Circuit Switched connections waste bandwidth for bursty traffic. traffic 1.536 Mbps Line Speed 146 Kbps Average time Idle Time >> Active Time Load = 9.456% Carrier Leased Line Network ATM Frame Relay Router TDM Switch Route once (circuit setup). Path through Network nailed down. Switches forward based on Time Slots per 1/8000th sec. Long Haul U.S. Traffic Primarily carried on fiber Running SONET or OTN Generally OC-48, 192, & 768; some 100 Gbps Wavelength Division Multiplexing common Each OC-N drives a laser lasers tuned to different frequencies injected onto same fiber strand SONET BW parceled out to users Circuit TDM Switching WDM: 32 OC-768’s (1.274 Tbps) #1 STS-768 Laser Detector #1 STS-768 #1 @ f1 #2 STS-768 Laser Detector #2 STS-768 #2 @ f2 Fiber in the ground #32 STS-768 Laser @ f32 Optical Combiner Optical Splitter Detector #32 STS-768 #32 Systems are also available that can map an arbitrary input (doesn’t have to be SONET or OTN based) onto an optical wave. Leased Lines Covers OSI Layers 1 & 2 64 Kbps - 10 Gbps Line Speed TDM, Circuit Switched Based on 1960 & 1990 technology Switches are byte aware Common: Corporate Connectivity Very Common: ISP Connectivity Page Info Nov 2007 IEEE 802.3 Ethernet Covers OSI Layers 1 & 2 10 Mbps Line Speed Packet Switch, StatMux Based on late 1970’s technology Computing Power & Memory was Expensive Initially Shared System Polite Conversation (CSMA/CD) One Node talks at a time Need to talk? Wait til line quiet Nobody deliberately butts in Switched Ethernet now more common ISO OSI Seven Layer Model Ethernet (Packet Switched, StatMux) Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 Layer 2 Layer 1 Application Presentation Session Transport Network Data Link Physical 802.3 802.3 802.3 Ethernet Frame Format Bytes: 7 1 6 MAC Destination Address 6 2 MAC Source Address 20 20 6-1460 4 IP TCP Data + Padding CRC Duplex: We're not talking apartments Simplex Only one node can talk (one way traffic) Commercial Radio Station Half Duplex Only one node can talk at a time Walkie-Talkie Full Duplex Both nodes can talk at same time Telephone 802.3 Flow Chart (NIC) 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 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 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 PC Hub PC PC Logical Bus & Physical Star Shared hub (OSI Level 1) copies input bits to all outputs. All nodes monitor traffic. 10BaseT & Shared Hub PC Twisted Pair Cabling PC Hub PC PC Logical Bus & Physical Star Each PC gets 2.5 Mbps on average. 10BaseT & Switched Hub PC PC Switched Hub PC PC Logical Bus & Physical Star Switched Hub (OSI Level 1 & 2) copies packet to proper output. Only the destination monitors traffic. 10BaseT & Switched Hub PC PC Switched Hub PC PC Logical Bus & Physical Star This system can move up to 20 Mbps 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. Full Duplex System PC PC Switched Hub PC PC All 10 Gbps, most 1 Gbps, & many 100 Mbps systems are Full Duplex. NIC’s are designed to simultaneously transmit & receive. Line no longer shared. No Collisions. No need for CSMA/CD. Campus Network 1993 Ethernet Switched Hubs 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) Desination Packet MAC address not in table? MAC address in table? shipped to proper output Ethernet Switched Hubs Look-up Table updated as packets arrive Ethernet MAC Address : Port # Flooding does not scale well on WAN OK on LAN with a probably a few hundred addresses Too much unnecessary traffic on WAN with millions of addresses Ethernet is making way into MAN & WAN Requires modified protocols Ethernet Flavors 802.3 10 Mbps 802.3u 100 Mbps (Fast Ethernet) 802.3z 1 Gbps Ethernet 802.3ae 10 Gbps Ethernet 802.3ba 40 & 100 Gbps Ethernet Shared Ethernet PC Hub PC PC Hub PC PC PC Hub PC Hub PC All nodes share the system's 10 Mbps. Multiple paths = feedback loop = mess. PC Switched Ethernet PC PC Switched Hub PC Switched Hub PC PC PC PC Switched Hub Switched Hub PC PC Each node shares 10 Mbps with its switch. Network can move > 10 Mbps at any instant. Multiple paths usually not used. Ethernet & Switched Hub Server Server PC PC Server Switched Hub PC Different speeds are used for different connections. PC PC To the rest of the world. 10/100 Mbps 1 Gbps 10 Gbps Two Types of Addresses Local (Layer 2 MAC) End-to-End (Layer 3 IPv4) Link Transmitter Link Receiver MAC Destination Address MAC Source Address Information Sink (Destination) Exception: NAT Information Source IP TCP Data + Padding CRC Whose Address goes where? Generally, PC's don't directly connect to Router Usually connected to Switched Hub Using IPCONFIG /ALL ... Ethernet MAC address (hard-wired) 00 50 04 C1 73 50 (6 Bytes, Base 16) Last byte is 0101 0000 Alpha-Numeric IP Address (usually fixed) es303f-2.ceat.okstate.edu host name - network name Domain Name Server Converts alpha-numeric IP address to numeric Whose Address goes where? Numeric IP Address (assigned on Power Up) Dynamic Host Configuration Protocol (DHCP) 139.78.79.157 (4 Bytes, Base 10) on 31 Jan 2004 Default Gateway (assigned on Power Up) Dynamic Host Configuration Protocol (DHCP) 139.78.79.254 Router IP Address Where to send packets when destination not part of your network ceat.okstate.edu Generally, Router sets the network boundary Packet to Print? Must know destination IP Address At my computer's IP Layer... Adds 20B IP Header to each packet Source IP address = My computer (Terminating) Destination IP address = Printer Is Information Sink IP address on my network? Yes? Tell Layer 2 to use Information Sink's MAC address No? Tell Layer 2 to use Router's MAC Address Shared 802.3 Ethernet R PC PC Hub Pr Hub PC PC PC Hub Hub PC 10 Nodes Share 10 Mbps Printer part of "ceat.okstate.edu". PC PC Whose address goes where? Printer MAC MAC Destination Address PC MAC MAC Source Address Information Sink (Printer IP) Information Source (PC IP) IP TCP Data + Padding CRC Hub ignores packet contents, copies bits to all outputs. Shared 802.3 Ethernet R PC PC Hub Pr Hub PC PC PC Hub Hub PC All nodes will see packets from PC to Printer. PC PC Switched Ethernet R PC PC Switched Hub Pr Switched Hub PC PC PC PC Switched Hub Switched Hub PC PC Packet formatting same as before. Only the Printer will see packets from the PC. Switched Ethernet PC R PC Pr Switched Hub PC PC PC PC Switched Hub Switched Hub PC PC Packets need to cross a network boundary. Whose address goes where? Connection from PC to Router Router MAC MAC Destination Address PC MAC MAC Source Address Information Sink (Printer IP) Information Source (PC IP) IP TCP Data + Padding CRC IP addresses don't match MAC addresses. Whose address goes where? Printer MAC MAC Destination Address Router MAC MAC Source Address Information Sink (Printer IP) Information Source (PC IP) IP TCP Data + Padding CRC Connection from Router to Printer Whose address goes where? MAC addresses change when router crossed. Stay same through an Ethernet Switch. MAC Destination Address MAC Source Address IP addresses remain unchanged end-to-end. IP TCP Data + Padding CRC Frame Relay Early ‘90’s technology Covers OSI Layer 2 N*64 Kbps or N*1.54 Mbps connections Virtual Circuits Route once on circuit set up. Packet Switch, StatMux Backbones Accessed by Routers with proper interface Being replaced by the Internet Frame Relay Backbone FR Switch Frame Relay ‘Cloud’ Trunk capacity shared via StatMux & Packet Switching Frame Relay Backbone Corp. LAN FR Switch Corporate Routers or FRAD's usually attached to FR backbones. Corp. LAN ISO OSI Seven Layer Model Frame Relay Switch (Layer 1 & 2) Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 Layer 2 Layer 1 Application Presentation Session Transport Network Data Link Physical Word Perfect Windows API TCP, Windows TCP, Windows IP, Windows Frame Relay, T Carrier or SONET T Carrier or SONET Frame Relay Packet Format (Assuming Ethernet LAN) 3 20 20 0-1460 3 FR Header IP TCP Data FR Trailer Header includes 10 bit DLCI Locally Unique Address (Valid between I/O ports) Trailer includes 2 byte Frame Check Sequence Only checks for errors in FR header TCP error checking should catch any payload error Frame Relay Connectivity Server LAN #2 LAN #1 VC #2 PC VC #1 FR Switch Suppose we need to connect to three LAN's. LAN #3 Server Frame Relay VC Set Up Client requests connectivity from Carrier Carrier arranges for Leased Line to nearest Point of Presence Technician runs Routing Algorithm on a Work Station Paths through network generated Appropriate Switches Notified DLCI's Assigned I/O mappings updated in Switch Look-Up Tables Source Router ships all FR traffic down same leased line FR switches use DLCI to properly output Note LAN #2 & #3 can communicate with each other thru edge router of LAN #1 Frame Relay Backbone Server LAN LAN PC FR Switch Look Up tables map Input DLCI and Port to Output DLCI and Port. Reverse path DLCI's not shown. LAN Server Moving Packets PC1 > Ethernet (Switched) Hub > Router1 > FR1 > FR2 > Router2 > Ethernet (Switched) Hub > Server PC1 injects Ethernet Packet Destination IP Address of Server (info sink) Router Ethernet MAC Address Router1 Examines, processes, strips off Ethernet Header Examines Destination IP Address & Routing Table Sees best path is over FR network Router1 injects FR Packet DLCI 375 carrying Layer 3-7 info Frame Relay Backbone Server 2 LAN 1 LAN 2 PC 1 FR Switch Look Up tables map Input DLCI and Port to Output DLCI and Port. LAN Server Moving Packets PC1 > Ethernet (Switched) Hub > Router1 > FR1 > FR2 > Router2 > Ethernet (Switched) Hub > Server FR Switch 1 Examines FR Look Up Table DLCI 375 on input from Router1 maps to DLCI 177 on output to FR Switch 2 FR Switch 1 injects FR packet DLCI 177 carrying Layer 3-7 info Frame Relay Backbone Server 2 LAN 1 LAN 2 PC 1 FR Switch Look Up tables map Input DLCI and Port to Output DLCI and Port. LAN Server Moving Packets PC1 > Ethernet (Switched) Hub > Router1 > FR1 > FR2 > Router2 > Ethernet (Switched) Hub > Server FR Switch 2 Examines FR Look Up Table DLCI 177 on input from Switch1 maps to DLCI 177 on output to Router2 FR Switch 2 injects FR packet DLCI 177 carrying Layer 3-7 info Frame Relay Backbone Server 2 LAN 1 LAN 2 PC 1 FR Switch Look Up tables map Input DLCI and Port to Output DLCI and Port. LAN Server Moving Packets PC1 > Ethernet (Switched) Hub > Router1 > FR1 > FR2 > Router2 > Ethernet (Switched) Hub > Server Router 2 Strips off FR Header Examines Destination IP Address & Routing Table Sees best path is over Internal LAN Router 2 injects Ethernet Packet Server Ethernet MAC (Assuming Server is on same subnet as Router) ATM Mid ‘90’s technology Covers OSI Layer 2, Line Speeds < OC-48 Virtual Circuits Route once on circuit set up. Five classes of service Cell Switch (53 bytes), StatMux or TDM Failed at desktop OK on Carrier WAN & Corporate Backbone Fading from the scene Being replaced by Internet ISO OSI Seven Layer Model ATM Switch Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 Layer 2 Layer 1 Application Presentation Session Transport Network Data Link Physical Word Perfect Windows API TCP, Windows TCP, Windows IP, Windows ATM, SONET or T Carrier T Carrier, or SONET ATM Cell #1 Format AAL5 5 20 20 8 ATM Header IP TCP Data Header includes 24 or 28 bit VPI & VCI Follow on cells carry remainder of the packet. Carrier ATM Network LAN ATM Switch What appears to be nailed up end-to-end connectivity (a Virtual Circuit). Switch I/O mappings similar to Frame Relay. LAN StatMux ATM Version Different channels use all of the frequency some of the time, at random, as needed. frequency 1 empty cell 2 1 3 empty cell 1 Can also use TDM. OSU Campus Network ('95 - '01) OneNet 802.3 LAN 802.3 LAN 802.3 LAN LAN ATM Switch ATM-Ethernet Switch LAN LAN ATM Network Frame Relay Routers ATM Switch All kinds of boxes are typically hanging off carrier ATM Switches. ATM PVC Set Up Client requests connectivity from Carrier Carrier arranges for Leased Line to nearest Point of Presence Technician runs Routing Algorithm on a Work Station Paths through network generated Appropriate Switches Notified VPI's and VCI's Assigned I/O mappings updated in Switch Look-Up Tables Switch Resources reserved, depending on CoS requested Corporate ATM switch (or Router with a plug-in ATM compatible card) ships all traffic down same leased line ATM switches use VPI & VCI to properly output ATM Connection Admission Control Procedure for setting up VC’s End user requests call set-up Provides destination, CoS, parameters Switches determine if resources are available Sufficient Buffer Space? Sufficient unreserved trunk bandwidth? Call is rejected if insufficient resources ATM Connection Admission Control CBR VC’s VBR VC’s Reserve Average Trunk BW Reserve Buffers to cover bursts ABR VC’s Reserve Peak Trunk BW Reserve Minimal Buffer Space Reserve Minimum Trunk BW Reserve Buffers to cover bursts UBR VC’s Reserve Nothing Allow VC establishment if spare BW & Buffers above some minimum The Internet VAST collection of interconnected networks Mid ‘70’s technology Key Building Block: Routers running IP (Layer 3) Packet Switch, StatMux Designed for data Internet Service Provider Backbone Router Packet Switched Statmux Network. Full duplex trunks. Washington D.C. Area - 2000 ISO OSI Seven Layer Model IP Router Layer 7 Layer 6 Layer 5 Layer 4 Layer 3 Layer 2 Application Word Perfect Presentation Windows API Session TCP, Windows Transport TCP, Windows Network IP, Windows Data Link Ethernet, FR, ATM SONET, OTN, T-Carrier, PPP, WiFi Layer 1 Physical Ethernet, SONET, OTN, T-Carrier, DSL, Cable Modem, WiFi Internet Service Provider Network LAN LAN Router LAN Corporate Routers & Other ISP Routers attached. ISP trunks could be... Leased Lines ISP Router ISP Router Cross-Connect Nailed up end-to-end connectivity (a Circuit). Bit pipe. No packet processing between Routers. Light Path (Wave) Connectivity (OC-48, OC-192, or OC-768) ISP Router ISP Router Optical Switch Nailed up end-to-end connectivity (a Circuit). Light Path. No packet processing between Routers. Internet Packet Format ?? Layer 2 Header 20 IP 20 TCP 0-1460 Traffic ?? Layer 2 Trailer? Probably originated on an Ethernet. Internet Router Line Speeds generally T1 to OC-768 on the WAN, some 100 Gbps (Mostly Leased Line or Light Waves) 10/100/1,000/10,000 Mbps (Ethernet) on the LAN Some Ethernet making it into MAN Hierarchical Alpha-Numeric Names [email protected] Datagrams Independent I/O decisions on every packet Not guaranteed to follow same path