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

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

3. Frequency-Division Multiplexing

4. 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

5. 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

6. Time-Division Multiplexing

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

8. 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

9. 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

10. TDM Link Control (cont)

11. 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

12. DS-1 Transmission Format

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

14. Digital Carrier Systems (cont)

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

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

17. 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

18. SONET/SDH Signal Hierarchy

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

20. 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

21. 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

22. Statistical TDM (cont)
(HDLC)  or

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

24. 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

25. 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