Chapter 8 Multiplexing FrequencyDivision Multiplexing Synchronous TimeDivision Multiplexing

Chapter 8. Multiplexing • Frequency-Division Multiplexing • Synchronous Time-Division Multiplexing • Statistical Time-Division Multiplexing • Asymmetric Digital Subscriber Loop 1

Multiplexing • Three types of multiplexing techniques – Frequency-division multiplexing (FDM) – Time-division multiplexing (TDM) – Statistical TDM 2

Frequency-Division Multiplexing 3

FDM (cont) m 1(t) m 2(t) m. N(t) Sub-carrier fsc 1 Sub-carrier fsc 2 Sub-carrier fsc. N Ssc 1(t) Ssc 2(t) S mc(t) Transmitter fc s(t) Ssc. N(t) (a) Transmitter 4

FDM (cont) S(t) Receiver Bandpass filter fsc 1 Demodulator fsc 1 Bandpass filter fsc 2 Demodulator fsc 2 Bandpass filter fsc. N Demodulator fsc. N m 1(t) m 2(t) m. N(t) (b) Receiver 5

Time-Division Multiplexing 6

Synchronous TDM m 1(t) buffer m 2(t) Scan operation mc(t) Modem s(t) . . mn(t) (a) Transmitter 7

Synchronous TDM (cont) buffer Frame m 1(t) m 2(t) mc(t). . 1 2. . . N. . . 1 2. . . N mn(t) Time slot: may be empty or occupied (b) TDM frames Scan operation (c) Receiver 8

TDM Link Control • Flow control is not needed as far as the multiplexer and demultiplexer are concerned – data rate on the multiplexed line is fixed • Saturated output device causes the flow of data from the corresponding input device to cease (per-channel) • Error control: per-channel basis 9

TDM Link Control (cont) 10

Digital Carrier Systems • DS-1 transmission format – multiplexes 24 channels – each frame contains 8 bits per channel plus a framing bit for 24*8 + 1 = 193 bits 125 msec Channel 1 Channel 2 F 1 2 3 4 5 6 7 8 Channel 24 1 2 3 4 5 6 7 8 193 bits 11

DS-1 Transmission Format 12

Digital Carrier Systems (cont) • DS-1 Data Rate (North American) – 24 voice channel = 8000*193 = 1. 544 Mbps • DS-3 Data Rate (North American) – 672 voice channels – 44. 736 Mbps 13

Digital Carrier Systems (cont) 14

ISDN Basic Rate • 2 B (64 kbps) + D (16 kbps) = 144 kbps +- +- 15

ISDN Primary Rate • North American – 23 B + D (64 kbps) = 1. 544 Mbps (B 8 ZS) • European transmission structure – 30 B + D = 2. 048 Mbps (HDB 3) 16

SONET/SDH • SONET – Synchronous Optical Network – Proposed by Bell. Core and standardized by ANSI • SDH: Synchronous Digital Hierarchy – compatible version of SONET – by ITU-T • For high-speed digital transmission capability of optical fiber 17

SONET/SDH Signal Hierarchy 18

STS-1 Frame Format • A STS-1 frame is transmitted one every 125 ms 19

Statistical TDM • Also known as asynchronous TDM and intelligent TDM Users t 0 t 1 t 2 t 3 t 4 A B To remote computer C D 20

Statistical TDM (cont) • Synchronous TDM Wasted bandwidth A 1 B 1 C 1 D 1 A 2 First cycle B 2 C 2 D 2 Second cycle • Statistical TDM Address A 1 B 1 First cycle B 2 C 2 extra bandwidth available Second cycle 21

Statistical TDM (cont) (HDLC) or 22

ADSL Channel Configuration POTS 20 k 25 k Upstream 200 k 250 k Downstream 1000 k. Hz Frequency-division modulation 23

Discrete Multitone (DMT) • Uses multiple carrier signals at different frequencies sending some of the bits on each channel – DMT Modem sends out test signals on each sub-channel to determine SNR – Assign more bits to channels with better signal transmission qualities Bits per hertz Frequency Line gain Frequency Bits per hertz Frequency 24

DMT Transmitter x 1(t) a 1 R bps 0 < ai < 1 Sai = 1 fi+1 = fi + 4 k. Hz Binary input x(t) R bps Serial-to-parallel converter xn(t) an. R bps cos 2 pf 1 t QAM cos 2 pf 2 t S DMT signal out y(t) cos 2 pfnt QAM 25

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