Exploring High-Speed Networks: Topologies, Fiber Optics & More

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

9. 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

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

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

12. 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

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

14. 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

15. 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.

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

17. 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

18. 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.

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

20. 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

21. Ethernet Coax

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

23. 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

24. Logarithms • Log Review

25. Logarithms • For example

26. Logarithms

27. Logarithms • Laws of Logarithms

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

29. the effect is to create harmonic interface at

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

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

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

33. 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

34. 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

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

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

37. 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

38. 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

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

40. Hartley-Shannon Law

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

42. 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

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

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

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

46. 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

47. 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 &

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

49. 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

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