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Logsv2

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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 Topology4 way connectivity
  • 5. The Torus Topology 4 way connectivity
  • 6. Torus Topology 5 way connectivity
  • 7. Cray T3D, Torus Topology 6 way connectivity
  • 8. Diagram of a typical packet radio setup TNCMac ASYNC SYNC Modem Radio Serial Serial CPU Memory We left out the redundant curcuitry in the gray box to make poor mans packet
  • 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 S+I S + S+I-(-S+I)=2S - -S -S+I I
  • 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. core, one or more strands cladding, one for each fiber Jacket
  • 19. Radio • Microwave – line-of-sight – parabolic dishd = 7.14 kh = distance to horizond in metersh = height of antenna in metersk = adjustment factor, microwaves bend with the curature of the earth
  • 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 CS83C92 TX- GND TX+ TXO CD- CDS CD+ RXI RX- RX+ Shi el d
  • 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 if x = a y then y = log a x so if x = 210 then 10 = log 2 x
  • 25. Logarithms• For example find log 2 4096 4096 = 2 y ln 4096 = y ln 2 ln 4096 = y = 12 ln 2
  • 26. Logarithmsso ln xlog 2 x = ln 2if base = B then ln x log10 xlog B x = = ln B log10 B
  • 27. Logarithms• Laws of Logarithms log a (xy) = log a x + log a y log a (x / y) = log a x − log a y log a x n = n log a x
  • 28. • Intermodulation noise – results when signals at different frequencies share the same transmission medium
  • 29. • the effect is to create harmonic interface at f 1 + f 2 and / or f 1 − f 2 f 1 = frequency of signal 1 f 2 = frequency of signal 2
  • 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) C = 2Wlog 2 m m = # of discrete symbols
  • 36. Channel Capacity• doubling bandwidth doubles the data rate if m=8 c = 2(3100 hz)log 2 8 = 18, 600 bps
  • 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 signal power (S / N)dB = 10log noise power
  • 38. Hartley-Shannon Law• Due to information theory developed by C.E. Shannon (1948) C:- max channel capacity in bits/second S C = w log2 (1 + ) N w:= channel bandwidth in Hz
  • 39. Hartley-Shannon Law• Example W=3,100 Hz for voice grade telco lines S/N = 30 dB (typically) Ps 30 dB = 10 log Pn
  • 40. Hartley-Shannon Law Ps 3 = log Pn Ps log10 =3 Pn Ps 10 3 = = 1000 Pn C = 3100 log 2 (1 + 1000) = 30,898 bps
  • 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 / secEb =enengy per bit in a signal
  • 43. Hartley-Shannon Law S = signal power (watts)T b = the time required to send a bit 1R= TbEb = ST bEb = energy per noise power density per hertzN0
  • 44. Hartley-Shannon LawEb S / R S = =N0 N0 kTR k=boltzman’s constantbyEb = ST b EbS= ∴S / R = Eb TbN0 = kTR
  • 45. Hartley-Shannon Law assuming R=W=bandwidth in Hz In Decibel Notation:Eb = S −10 log R + 228. 6dbW − 10 logTN0
  • 46. Hartley-Shannon LawS=signal power R= transmission rate and -10logk=228.6 So, bit rate error (BER) for digital data Eb is a decreasing function of N0 Eb For a given N0 , S must increase if R increases
  • 47. Hartley-Shannon Law• Example For binary phase-shift keying Eb =8.4 dB is needed for a bit error rate N0 of 10 −4 let T= k = noise temperature = C, R=2400 bps & Pe = 10 −4 = BER
  • 48. Hartley-Shannon Law• Find S Eb −S = − −10 log R + 228. 6dbW − 10log T N0 −S = −8. 4 − 10 log2400 + 228.6dbW −10 log 290 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 S SNRdB = 10 log10 N where S = 2n 1 −n −n −1 N = 2 =2 2 2n+1 SNRdB = 10 log10 2 = (20n +10)log10 2 about SNRdB = 6n + 3
  • 51. Review of the Layers• Physical Layer (bits)• The Link Layer (frames)• The Network Layer (packets)• The Transport Layer• Session Layer• The Presentation Layer• The Application Layer
  • 52. Physical Layer• The function is to send & receive bits (marks & spaces)• deals with – Physical connections (duplex or half duplex) – Physical service data units (PSDU’s) one bit in serial xmission, nbits in parallel xmission
  • 53. Physical Layer– circuit identification– bit sequencing– notification of false conditions– deriving quality of service parameters– modulation and demodulation– signaling speed
  • 54. Physical Layer– transmission of data and handshaking signals– characterization of communication media– maintains an actual electrical connection with its peers. Other layers uses virtual connections
  • 55. The Link Layer• The Link Layer of data link control arranges the bits into frames• Most common protocol is ISO high-level Data Link Control Procedures (ISO 3309)
  • 56. The Link Layer• This layer – Establishes and releases one or more link connections – exchanges data-link service data units (DLSDUs)-frames – identifies end-points – keeps DLSDUs / frames in proper sequence
  • 57. The Link Layer– notifies the network layer when errors are detected– controls data flow– selects optional qualityof service parameters
  • 58. The Network Layer• Arranges data into packets – Adds the network information to the frames to form packets• SLIP – Serial Line Internet Protocol is network layer protocol – uses the EIA-232 Physical layer – Internet protocol is a network layer protocol
  • 59. The Network Layer– keep track of the network node address while routing outgoing packets and recognizing packets that are intended for the local node
  • 60. The Network Layer• ARP – Address Resolution Protocol provides addresses form required by IP – User may specify the datagram route – APR will stay aware of manually generated routing tables for the datagram routing function
  • 61. The Network Layer•in CCITT x.25 protocol the network layer is called the packet layer.
  • 62. The Network Layer• The function provided by the network layer are – network addressing and identifiers – network connections and release – transmission of network service data units NSDU’s (packets) – quality of service parameters
  • 63. The Network Layer– notifies the transport layer of errors– flow control– expedited service network– may provide sequenced delivery
  • 64. The Network Layer• Two types of network layer protocols – connection oriented – connectionless
  • 65. Connection Protocol• set up a virtual circuit (VC) between two end points• Advantage is that since each packet does not contain complete addressing information, the overhead is lower
  • 66. Connectionless Protocol• Uses a datagram (DG) which contains complete addressing information in each packet so that it can use any variable route through the network
  • 67. Connectionless Protocol• The advantage is that packets may freely choose the best available routes for the transfer rather than being stuck on a VC with variable quality
  • 68. The Transport Layer• uses transport protocol data units (TPDU)• TPDU = packets + transport layer data• TCP = transmission control protocol
  • 69. The Transport Layer• This layer ensures that – all data send is received completely – is sequenced – transmission of TPDU messages – multiplexing and demultiplexing to share a net connection between two or more Xport connections
  • 70. The Transport Layer– error detection– error recovery– connection establishment– data xfer– release of connections
  • 71. The Transport Layer• CCITT transport protocol in X.224 says there are 5 classes of transport classes – 0. simple class – 1. error recovery – 2. multiplexing – 3. error recovery and multiplexing – 4. error detection and recovery class
  • 72. The Transport Layer• The amount of work done is dependent on the protocol (VC or datagram) used at the network layer
  • 73. The Transport Layer• Datagrams may arrive out of sequence, in a connectionless net, and buffers may be needed to resequence• connection nets allow a leaner transport layer
  • 74. Session Layer• Organizes data into SPDU (session protocol data units)
  • 75. Session Layer• This layer does – dialog management – Data flow control – mapping address with name (domain name service) – graceful or abrupt disconnection – buffering data until delivery time
  • 76. Session Layer• has phases of service – connection establishment – data xfer – connection release
  • 77. Presentation Layer• responsible for the terminal management• Performs – transfer of syntax for character sets, text strings data display format, graphics file organization and data types
  • 78. Presentation Layer– data encoding, decoding and compacting– interpret character sets ( i.e. ASCII)– code conversion
  • 79. Application Layer• The only layer which does not interface with a higher one• It does – log in identification of communication partners – password checking and authority to communicate
  • 80. Application Layer– determine adequacy of resources– determine acceptable quality of service– synchronization of application programs– selecting the dialog procedures– agreement on error-recovery responsibility– procedures for control of data integrity– identifying data syntax constraints
  • 81. Application Layer• has 5 groups – 1. System management protocols – 2. Application management protocols – 3. System protocols – 4. Industry specific protocols – 5. Enterprise protocols
  • 82. Things you need to get started on a LAN• IP ADDRESS – this a 32 bit number issued by your local IP coordinator – it is expressed as 4 numbers separated by periods – looks like 44.112.0.200.
  • 83. Things you need to get started on a LAN• HOST TABLE – A file that list all the folks around you that also have IP addresses – It must have your IP address and hostname (call sign) at least
  • 84. Things you need to get started on a LAN• HOST TABLE – you can get this from your coordinator – It looks like this 44.112.0.1 unix.n3cv1 44.112.0.2 w3vc 44.112.0.3 darth.wa3yoa

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