Multiplexing Techniques 1/6
Applied Network Research Group Department of Computer Engineering, Kasetsart University
Multiplexing techniques
Surasak Sanguanpong nguan@ku.ac.th http://www.cpe.ku.ac.th/~nguan
Last updated: 11 July 2000
Multiplexing Techniques 2/6
Applied Network Research Group Department of Computer Engineering, Kasetsart University
Why multiplexing
z
share a use of common channel
DEMUX
Multiplexer Demultiplexer
shared channel MUX
Multiplexing provides a mechanism to share the use of a common channel or circuit by two or more devices. Multiplexing minimizes number of transmission lines required to connect communication devices.
Multiplexing Techniques 3/6
Applied Network Research Group Department of Computer Engineering, Kasetsart University
Type of multiplexer
z
FDM (Frequency Division Multiplex)
z
TDM (Time Division Multiplex)
Major multiplex techniques can be categorized into two types:
- Frequency division multiplex - Time Division Multiplex
Multiplexing Techniques 4/6
Applied Network Research Group Department of Computer Engineering, Kasetsart University
Frequency Division Multiplex
CH2 CH1
CH3
original bandwidth CH1
CH2
CH3
bandwidths raised in frequency
MUX
bandwidths multiplexed into one channel
CH1 CH2 CH3
f
FDM is a broadband analog transmission technique. Each data signal is modulated onto a carrier with a different frequency and all signal travel simultaneously over a channel.
Multiplexing Techniques 5/6
Applied Network Research Group Department of Computer Engineering, Kasetsart University
Time Division Multiplex
A2 A1
A3
original signal
D2 D1
D3
digitized signal
data filled in time slot
time slot
1 2 3 4
MUX
TDM is a baseband technique in individuals circuit are identified by their position in a stream. Analog inputs are digitized using PCM and the digitized information are insert into the fixed timing called timed slot.
Multiplexing Techniques 6/6
Applied Network Research Group Department of Computer Engineering, Kasetsart University
Statistical TDM
A B C D
Data to be sent
t
1t
2t
3A
1B
1C
1D
1A
2B
2C
2D
21stcycle 2ndcycle Synchronous TDM
waste bandwidth
A
1B
1B
2C
21stcycle 2ndcycle Statistical TDM
extra bandwidth available
TDM uses preallocated and fixed time slot. Each time slot will be allocated even there is no data transfer.
Statistical TDM, also known as asynchronous TDM dynamically allocate time slots on demand. The statistical multiplexer does not send empty slots if there are any other data to send. [Stallings, p.219]
