1. William Stallings Data and Computer Communications
Chapter 8
Multiplexing
(will cover only basics)

2. Multiplexing

3. Frequency Division Multiplexing
FDM
Useful bandwidth of medium exceeds required bandwidth of channel
Each signal is modulated to a different carrier frequency
channel is divided to carry different signals at different frequencies

4. Frequency Division Multiplexing Diagram

5. Time Division Multiplexing (TDM)
Data rate of medium exceeds data rate of digital signal to be transmitted
Multiple digital signals interleaved in time

6. Synchronous TDM System
Time slots preassigned to sources and fixed
Time slots allocated even if no data
Almost no overhead

7. Statistical TDM In Synchronous TDM many slots are wasted
Statistical TDM allocates time slots dynamically based on demand
Multiplexer scans input lines and collects data until frame full
Overhead
e.g. addresses in frames

8. Asymmetrical Digital Subscriber Line
ADSL
Link between subscriber and network
Local loop
Uses currently installed twisted pair cable
voice uses only 4KHz
Can carry broader spectrum
1 MHz or more

9. ADSL Design Asymmetric Frequency division multiplexing Range 5.5km
Greater capacity downstream than upstream
originally designed for video-on-demand (never used for it)
but later adopted for end-user Internet access
Frequency division multiplexing
Lowest 25kHz for voice
Plain old telephone service (POTS)
only 4 KHz is enough to carry voice but, we need buffer to prevent crosstalk
Use echo cancellation or FDM to give two bands (for two directions)
Use FDM within bands
single bit stream is split into paralel bir streams to be transmitted at different frequencies
Range 5.5km

10. Türk Telekom’s ADSL Tariff

11. xDSL High data rate DSL (HDSL) Single line DSL (SDSL)
late 80s
special coding to deliver upto 2Mbps over two twisted pair cables
symmetric
digital
Single line DSL (SDSL)
same data rate as one copper wire
uses echo-cancellation effectively
symmetric and digital
Very high data rate DSL
analog, asymmetric, short-distance but high data rates