A radio system where the channel is allocated on demand by user is called “trunked” system.
In this concept large number of users will be sharing limited number of resources provided by system.
HOW IT WAS DONE:
There will be pool of channels available for users . When user request for channel then on the basis of channel per cell concept a channel is allocated to him.
when user finish his conversation and cut the call the occupied channel is again returned to the pool of available channels .
Thus limited number of channels can be used to accommodate large number of users .
PROBLEM WITH THIS CONCEPT:
All though it’s a good system to accommodate large users but it has got some problems with it …
1) Suppose we have got a pool of 50 channels , numbers of customers at this time requesting for call or other service are more than 50 .
2) In this situation a channel cannot be allocated to user or the call will be in blocked state.
3) The user has to wait untill a channel become free and it is again returned to the pool of available channels.
4) Some times the calls are queued to keep the users on waiting.
GRADE OF SERVICE(GOS):
To measure the efficiency of trunked system a term is coined i e GOS .
Its like a “benchmark” for trunked system.
” It’s a measure of the ability ot a user to access a trunked system during the busiest hour”.
The busiest hour may be based on end of year , month, week, and also based on timings i e between 4 p.m and 6 p.m .
It is duty of system designer to consider all these concepts and create a good system.