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Day 8

Day 8. Multiplexing. More than 1 signal per cable. Typically a single cable can carry a single connection Not good if you want a cable to be able to send lots of separate Telephone calls TV channels Data connections. Multiple ways to slice things. By Frequency

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Day 8

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  1. Day 8 Multiplexing

  2. More than 1 signal per cable • Typically a single cable can carry a single connection • Not good if you want a cable to be able to send lots of separate • Telephone calls • TV channels • Data connections

  3. Multiple ways to slice things • By Frequency • Frequency Division Multiplexing • By time • Synchronous Time Division Multiplexing • Statistical Time Division Multiplexing • Other special application • Wavelength Division Multiplexing • Discrete Multitone • Code Division Multiplexing

  4. Frequency Division Multiplexing • Examples • FM Radio • TV/Cable TV • D-AMPS (old cellular) • 802.11b/g (3 channels)

  5. Frequency Division Multiplexing

  6. Guard Bands • Used to prevent “cross talk” between the channels. • Empty frequencies between channels.

  7. Synchronous time division • Each station gets a chance to talk. • If a station has anything to say, their data is inserted into their block. • If nothing to say, the block is left empty • Everyone gets equal time.

  8. Synchronous Time Division Multiplexing

  9. T1/DS1 – 1.544Mb/s • The T1 is a high speed data line designed to interconnect phone switches. • Also available to end users to provide high speed data or lots of phone lines • It uses synchronous time division multiplexing • 24 Channels • Each frame gets 1 byte from each of 24 devices • 8000 frames per second are transmitted • 56k/channel for voice, 64k for data. • Extra control bit is used giving 7 bits which is all that is necessary for voice. • ~$400/month + install

  10. ISDN • 2 B channels (64k) • 1 D channel (16k) • Signal • Control bits • 8 bits from B1 • Control bits • D bit • Control bits • 8 bits from B2

  11. SONET • Synchronous Optical Network • Single clock • Atomic clock • Synchronous Transport Signals • OC 1 – 51.84Mbps • 8000 frames/second 6480 bits/frame • OC 3 = 3*OC1 = 155.52Mbps • ~ $40k/month • OC48 = 2.5Gbps • ~$80k/month • OC192 = 192 OC1 =~ 10Gbps • ~$1/4million per month • 1, 3, 9, 12, 18, 24, 36, 48, 96, 192 • Gige ~$15k/month

  12. Statistical Time Division • Not everyone has something to say at all times. • Why not give the traffic to those who do • If so, we need to add addresses so we know who said what. • Multiplexer must be smart

  13. Size of frames • Either they must be set in stone • Or you must transmit the size so the other side can tell where one frame ends and the next starts

  14. Wavelength Division Multiplexing • Using laser color to differentiate streams • You can now multiplex multiple OC192’s together on a single cable. • Has been used to create up to 1.6Tbps over a single fiber pair

  15. Discrete Multitone Multiplexing • Examples • DSL • Digital FM Radio • 802.11a/g • A specific example of frequency division multiplexing • Data in a particular channel is transmitted on multiple different frequencies at once. • Frequencies are chosen to avoid interference with other data

  16. Code Division Multiplexing • Each user has a code: • A: 10111001 • B: 01101110 • C: 11001101 • If you want to send a 1 you send your code, if you want to send a 0 you send the inverse of your code (flip all 0’s and 1’s) • Receiver gets the sum of all this, adds each code (1= 1 or 0= -1). • +8 means they sent a 1, -8 means they sent 0

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