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

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

Frequency-Division Multiplexing

FDM (cont) Ssc1(t) m1(t) m2(t) Ssc2(t) S mc(t) s(t) mN(t) SscN(t) Sub-carrier fsc1 m2(t) Ssc2(t) S mc(t) s(t) Sub-carrier fsc2 Transmitter fc mN(t) SscN(t) Sub-carrier fscN (a) Transmitter

FDM (cont) m1(t) m2(t) S(t) mN(t) (b) Receiver Bandpass filter fsc1 Demodulator fsc1 m2(t) S(t) Receiver Bandpass filter fsc2 Demodulator fsc2 mN(t) Bandpass filter fscN Demodulator fscN (b) Receiver

Time-Division Multiplexing

Synchronous TDM Scan operation buffer m1(t) m2(t) mc(t) s(t) . . . . Modem . . . . mn(t) (a) Transmitter

Synchronous TDM (cont) buffer m1(t) m2(t) mc(t) Frame Frame 1 2 ... N ... 1 2 ... N . . . . mn(t) Scan operation Time slot: may be empty or occupied (b) TDM frames (c) Receiver

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

TDM Link Control (cont)

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 Channel 24 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 F 193 bits

DS-1 Transmission Format

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

Digital Carrier Systems (cont)

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

ISDN Primary Rate North American European transmission structure 23B + D (64kbps) = 1.544 Mbps (B8ZS) European transmission structure 30B + D = 2.048 Mbps (HDB3)

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

SONET/SDH Signal Hierarchy

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

Statistical TDM Also known as asynchronous TDM and intelligent TDM A B Users t0 t1 t2 t3 t4 A B To remote computer C D

Statistical TDM (cont) Synchronous TDM Wasted bandwidth A1 B1 C1 D1 A2 B2 C2 D2 First cycle Second cycle Statistical TDM Address A1 B1 B2 C2 extra bandwidth available First cycle Second cycle

Statistical TDM (cont) (HDLC)  or

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

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 Frequency Bits per hertz Line gain

Serial-to-parallel converter DMT Transmitter cos2pf1t x1(t) a1R bps 0 < ai < 1 Sai = 1 fi+1 = fi + 4 kHz QAM Binary input DMT signal out Serial-to-parallel converter QAM S x(t) R bps y(t) cos2pf2t cos2pfnt xn(t) anR bps QAM