• When a pulse of 'Tb' secs duration is transmitted through a band limited channel, the pulse appearing at o/p is dispersed or expanded having duration greater than 'Tb'.

• As the received pulses are extended, when a train of pulses gets transmitted, each pulse interference with the adjacent pulse transmitted over the channel.

• This interference is over the adjacents symbols, hence the name Inter symbol Interference.

• Due to ISI, determination of a symbol as 1 or 0 is difficult at receiving end.

• In multiplexed systems such TDMA, cross talk can take place due to over lapping of adjacent pulses, i.e. ISI.

- ISI Removal:

Since pulse dispersion is the property of the channel, it cannot be completely eliminated.

• To avoid the effects of ISI, elements with negative dispersion can be added to the channel, i.e. change the channel property.

• Use of Repeaters will allow system to reconstruct the pulses.