U of I CS 438 - Direct Link Networks (10 pages)

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Direct Link Networks



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Direct Link Networks

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Pages:
10
School:
University of Illinois
Course:
Cs 438 - Communication Networks
Communication Networks Documents
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Direct Link Networks Direct Link Networks Two hosts connected directly No issues of contention routing Key points Physical Connections Encoding and Modulation Framing Error Detection 9 6 06 Internet Protocols User level software Session Transport 2 Outline Application Presentation UIUC CS ECE438 Fall 2006 Hardware building blocks Encoding Framing Kernel software Network Data Link Physical 9 6 06 Framing error detection medium access control Encoding Hardware network adapter UIUC CS ECE438 Fall 2006 3 Hardware Building Blocks 9 6 06 4 Copper based Media Hosts general purpose computers Switches typically special purpose hardware Routers varied Links UIUC CS ECE438 Fall 2006 Links Copper Nodes 9 6 06 Category 5 Twisted Pair ThinNet Coaxial Cable ThickNet Coaxial Cable 10 100Mbps 10 100Mbps 10 100Mbps 100m 200m 500m twisted pair Copper wire with electronic signaling Glass fiber with optical signaling Wireless with electromagnetic radio infrared microwave signaling UIUC CS ECE438 Fall 2006 coaxial cable coax 5 9 6 06 copper core insulation braided outer conductor outer insulation UIUC CS ECE438 Fall 2006 6 1 Links Optical Links Optical Optical Media Multimode Fiber 100Mbps Single Mode Fiber 100 2400Mbps Single mode 2km 40km Lower attenuation longer distances Lower dispersion higher data rates Multimode fiber Cheap to drive LED s vs lasers for single mode Easier to terminate core of single mode fiber glass core the fiber glass cladding plastic jacket optical fiber 1 wavelength thick 1 micron core of multimode fiber same frequency colors for clarity O 100 microns thick 9 6 06 UIUC CS ECE438 Fall 2006 7 Links Optical Higher bandwidths Superior attenuation properties Immune from electromagnetic interference No crosstalk between fibers Thin lightweight and cheap the fiber not the optical electrical interfaces 9 6 06 UIUC CS ECE438 Fall 2006 9 Wireless POTS 64Kbps ISDN 128Kbps ADSL 1 5 8Mbps 16 640Kbps Cable Modem 0 5 2Mbps DS1 T1 1 544Mbps DS3 T3 44 736Mbps STS 1 51 840Mbps STS 3 155 250Mbps ATM STS 12 622 080Mbps ATM 9 6 06 UIUC CS ECE438 Fall 2006 AMPS PCS GSM 3G 13Kbps 300Kbps 2 3Mbps 3km 3km 3km digital data a string of symbols Infrared 900Mhz 2 4GHz 2 4GHz Bluetooth 4Mbps 2Mbps 2Mbps 11Mbps 700Kbps 10m 150m 150m 80m 10m Satellites Geosynchronous satellite 600 1000 Mbps Low Earth orbit LEO 400 Mbps continent world UIUC CS ECE438 Fall 2006 11 9 6 06 modulator demodulator a string of signals digital data a string of symbols Problems with signal transmission 9 6 06 10 Encoding Wireless Local Area Networks WLAN 8 Cellular UIUC CS ECE438 Fall 2006 Leased Lines Advantages of optical communication 9 6 06 Attenuation Signal power absorbed by medium Dispersion A discrete signal spreads in space Noise Random background signals UIUC CS ECE438 Fall 2006 12 2 Analog vs Digital Transmission Encoding Goal The physical medium is used to propagate signals Data is encoded in the signal UIUC CS ECE438 Fall 2006 13 RS 232 Electronic Industries Association EIA standard RS 232 C International Telecommunications Union ITU V 32 9600 bps modem standard 9 6 06 UIUC CS ECE438 Fall 2006 14 RS 232 Timing Diagram Communication between computer and modem Uses two voltage levels 15V 15V a binary voltage encoding Data rate limited to 19 2 kbps RS 232 C raised in later standards Characteristics Calculate measure effects of transmission problems Periodically interpret and regenerate signal Simpler for multiplexing distinct data types audio video e mail etc Two examples based on modulator demodulators modems Modulate electromagnetic waves Vary voltage frequency wavelength 9 6 06 Reasonably low error rates over arbitrary distances Idea Advantages of digital transmission over analog Understand how to connect nodes in such a way that bits can be transmitted from one node to another Serial one signaling wire one bit at a time Asynchronous line can be idle clock generated from data Character based send data in 7 or 8 bit characters 15 Voltage 15 idle start 1 0 0 1 1 0 0 stop idle Time 9 6 06 UIUC CS ECE438 Fall 2006 15 RS 232 9 6 06 16 Common binary voltage encodings initiates send by pushing to 15V for one clock start bit Minimum delay between character transmissions 0V is a dead disconnected line 15V is both idle and 1 UIUC CS ECE438 Fall 2006 Voltage Encoding One bit per clock Voltage never returns to 0V 9 6 06 Idle for one clock at 15V stop bit One character leads to 2 voltage transitions Total of 9 bits for 7 bits of data 78 efficient Start and stop bits also provide framing UIUC CS ECE438 Fall 2006 17 9 6 06 Non return to zero NRZ NRZ inverted NRZI Manchester used by IEEE 802 3 10 Mbps Ethernet 4B 5B UIUC CS ECE438 Fall 2006 18 3 Non Return to Zero Inverted NRZI Non Return to Zero NRZ High Low Signal to Data Signal to Data Comments Bits Bits Transitions maintain clock synchronization Long strings of 0s confused with no signal Long strings of 1s causes baseline wander Both inhibit clock recovery 19 XOR NRZ data with clock High to low transition Low to high transition UIUC CS ECE438 Fall 2006 20 Signal to Data Solves clock recovery problem Only 50 efficient 1 2 bit per transition Bits 9 6 06 1 0 Comments Strings of 0 s still a problem 4B 5B Signal to Data 0 0 1 0 1 1 1 1 0 1 0 0 0 0 1 0 Comments Manchester Encoding 1 0 NRZI NRZ UIUC CS ECE438 Fall 2006 NRZ 0 0 1 0 1 1 1 1 0 1 0 0 0 0 1 0 9 6 06 Transition Maintain 1 0 Symbols 0 0 1 0 1 1 1 1 0 1 0 0 0 0 1 0 NRZ Clock Encode every 4 consecutive bits as a 5 bit symbol At most 1 leading 0 At most 2 trailing 0s Never more than 3 consecutive 0s Transmit with NRZI Comments 80 efficient Manchester 9 6 06 UIUC CS ECE438 Fall 2006 21 Binary Voltage Encodings Amplitude Modulation Significant dispersion Uneven attenuation Prefer to use narrow frequency band carrier frequency Types of modulation 9 6 06 22 Wide frequency range required implying UIUC CS ECE438 Fall 2006 Problem with binary voltage square wave encodings 9 6 06 Amplitude AM Frequency FM Phase phase shift Combinations of these UIUC CS ECE438 Fall 2006 idle 23 9 6 06 1 UIUC CS ECE438 Fall 2006 0 24 4 Frequency Modulation idle 9 6 06 1 Phase Modulation 0 UIUC CS ECE438 Fall 2006 idle 25 Phase Modulation 9 6 06 0 UIUC CS ECE438 Fall 2006 26 Phase Modulation Algorithm Send carrier frequency for one period 108 difference in phase phase shift in carrier frequency 1 collapse for 108 shift 8 symbol example Perform phase shift Shift value encodes symbol 90 135 Value in range 0 360 Multiple values for multiple symbols Represent


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