Multiple messages/signals on a single (shared) channel
Roles:
Multiplexer (MUX) - combines the messages/signals
Demultiplexer (DEMUX) - splits the messages/signals
Multiplexing on Circuits
Frequency-Division Multiplexing (FDM):
A frequency band is devoted to each connection (e.g.,
analog cable television)
Time-Division Multiplexing (TDM):
Each connection is allocated a time slot
Multiplexing on the Internet
Network/Internetwork Layer (IP):
Responsible for routing and delivering frames/datagrams
Transport Layer:
Responsible for (among other things) delivering the
segments to the appropriate process/application (which is
identified by fields in the segment's header)
The receiver identifies the process/application
and delivers the segment (i.e., demultiplexes)
The sender includes the destination process/application
fields in the
header and hands the segment off to the network layer
(i.e., multiplexes)
An Analogy
The Setting:
Several people live at the same address
Multiplexing:
The local post office bundles all mail to the same
address
Delivery:
The letter carrier delivers the bundle to the address
Demultiplexing:
Someone at the address divides the bundle and
puts it into different stacks
Ports
Types:
Source - used to identify the process/application that
sent the segment
Destination - used to identify the receiving
process/application