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NETWORKS

NETWORKS. Covering High speed switching fabrics Twisted pair Mediums Fiber optics Radio Ethernet Coax. NETWORKS. Logarithms Channel capacity Hartley-Shannon Law Review of the Layers Things you need to get started on a LAN. High Speed Switching Fabrics.

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NETWORKS

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  1. NETWORKS • Covering • High speed switching fabrics • Twisted pair • Mediums • Fiber optics • Radio • Ethernet Coax

  2. NETWORKS • Logarithms • Channel capacity • Hartley-Shannon Law • Review of the Layers • Things you need to get started on a LAN

  3. High Speed Switching Fabrics • Aside from the Bus topologies, there are many others, with higher throughput, like • ring • Transputer Topology • Torus Topology • Cray T3D

  4. The Transputer Topology 4 way connectivity

  5. The Torus Topology 4 way connectivity

  6. Torus Topology 5 way connectivity

  7. Cray T3D, Torus Topology 6 way connectivity

  8. Twisted Pair • Typically a balanced digital line • 2 conductor insulated wire • Twisting the wire minimizes the electromagnetic interference • A primary medium for voice traffic • used as serial cable to hookup networks

  9. Twisted Pair • The repeat coil (transformer) or Op-Amp can be used

  10. Twisted Pair • In telephone modem terms this is known as a DAA (Data Access Arrangement).

  11. Mediums • UTP (unshielded twisted pair) • typical voice line • Generally good for star LAN short haul 10 Mbps • STP (shielded twisted pair) • level 5 data grade (100 Mbps) • RS-422 • balanced serial data communications • RS-232 • unbalanced serial data communications

  12. Mediums • Coax • CATV (community antenna TV) • telephone long line via FDM carries 10,000 voices • LAN-WAN • cable TV

  13. Mediums • Fiber Optics • use total internal reflection • This occurs in a transparent medium whose index of refraction is higher that surrounding medium • optic fiber is a wave guide in the 10 raised 14 to 10 raised 15 hz range

  14. Fiber Optics • multimode • different rays have different path lengths, loss occurs • multimode-graded index • variable core index, focuses rays more efficiently that multimode • single mode • only the axial ray passes, most efficient.

  15. Fiber Optics • LED (light emmiting diode) • inexpensive • ILD (injection laser diode ) • more expensive (more efficient and higher bandwidth that LED). • Detectors • Photo Diodes

  16. Fiber Optics • light propagates best at 850, 1300 and 1500 nm • 640 nm = wavelength of HE-NE red = .64 micro meters • ultra pure fused silica is best, plastic is cheapest and worst

  17. Fiber Optics • bandwidth - 2 Gbps (typical) • smaller size and weight than copper • lower attenuation than coax • electromagnetically isolated • greater repeater spacing, 5 Gbs over 111 km w/o repeater • phasing out cable.

  18. Radio • Microwave • line-of-sight • parabolic dish

  19. Ethernet Coax • For Ethernet coax • ASIC’s which give a digital interface to a bus topology LAN • For example, the Crystal Semiconductor Corporation CS83C92 is a Coaxial Transceiver Interface on a chip

  20. Ethernet Coax

  21. Ethernet Coax • CS83C92 • Balanced serial inputs • Uses Manchester codes • All operations with IEEE 802.3 of the 10Base5 (Ethernet) and 10Base2 (Cheapernet) standard

  22. Ethernet Coax • CS83C92 have • equalizers • amplifiers • idle detectors, receiver squelch circuits • collision testers • oscillators • differential line drivers • (with other stuff too!!!) • A manchester code convert chip is also needed

  23. Logarithms • Log Review

  24. Logarithms • For example

  25. Logarithms

  26. Logarithms • Laws of Logarithms

  27. Intermodulation noise • results when signals at different frequencies share the same transmission medium

  28. the effect is to create harmonic interface at

  29. cause • transmitter, receiver of intervening transmission system nonlinearity

  30. Crosstalk • an unwanted coupling between signal paths. i.e hearing another conversation on the phone • Cause • electrical coupling

  31. Impluse noise • spikes, irregular pulses • Cause • lightning can severely alter data

  32. Channel Capacity • Channel Capacity • transmission data rate of a channel (bps) • Bandwidth • bandwidth of the transmitted signal (Hz) • Noise • average noise over the channel • Error rate • symbol alteration rate. i.e. 1-> 0

  33. Channel Capacity • if channel is noise free and of bandwidth W, then maximum rate of signal transmission is 2W • This is due to intersymbol interface

  34. Channel Capacity • Example w=3100 Hz C=capacity of the channel c=2W=6200 bps (for binary transmission) m = # of discrete symbols

  35. Channel Capacity • doubling bandwidth doubles the data rate if m=8

  36. Channel Capacity • doubling the number of bits per symbol also doubles the data rate (assuming an error free channel) (S/N):-signal to noise ratio

  37. Hartley-Shannon Law • Due to information theory developed by C.E. Shannon (1948) C:- max channel capacity in bits/second w:= channel bandwidth in Hz

  38. Hartley-Shannon Law • Example W=3,100 Hz for voice grade telco lines S/N = 30 dB (typically) 30 dB =

  39. Hartley-Shannon Law

  40. Hartley-Shannon Law • Represents the theoretical maximum that can be achieved • They assume that we have AWGN on a channel

  41. Hartley-Shannon Law C/W = efficiency of channel utilization bps/Hz Let R= bit rate of transmission 1 watt = 1 J / sec =enengy per bit in a signal

  42. Hartley-Shannon Law S = signal power (watts)

  43. Hartley-Shannon Law k=boltzman’s constant

  44. Hartley-Shannon Law assuming R=W=bandwidth in Hz In Decibel Notation:

  45. Hartley-Shannon Law S=signal power R= transmission rate and -10logk=228.6 So, bit rate error (BER) for digital data is a decreasing function of For a given , S must increase if R increases

  46. Hartley-Shannon Law • Example For binary phase-shift keying =8.4 dB is needed for a bit error rate of let T= k = noise temperature = C, R=2400 bps &

  47. Hartley-Shannon Law • Find S S=-161.8 dbw

  48. ADC’s • typically are related at a convention rate, the number of bits (n) and an accuracy (+- flsb) • for example • an 8 bit adc may be related to +- 1/2 lsb • In general an n bit ADC is related to +- 1/2 lsb

  49. ADC’s • The SNR in (dB) is therefore where about

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