8/18/2019 Blocking Probability

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Blocking Probability 

Based on our experiences either calling or receiving calls from a cellular phone, most of us

know that not every call works. It may not reach the person we are calling, it may drop theconnection, and so on.

Because designing coverage that is flawless 100% of the time is not a realistic goal, R!esigners design their systems according to a specified blocking probability  and grade of

 service.

 Blocking Probability Defined 

Blocking pro"a"ility is the fraction of time a trunk re#uest is denied "ecause all channels are

"usy. $his pro"a"ility is usually specified for a given system. It is typically desired to be2%.

trunk group with a "locking pro"a"ility of 0.0& means that all trunks are simultaneously

"usy &% of the time or a total of ' minutes an hour.

(ell site "locking pro"a"ility is the fraction of time a call setup attempt at a particular cell

site is re)ected "ecause all channels are "usy.

Grade of Service (GOS)

*ost telephone networks, are designed to provide a specified grade of service +GOS duringthe "usy hour. $he -/ is expressed as the percentage of call attempts that are "locked

during peak traffic periods "ecause of a lack of network resources +such as radio channels incellular systems.

$ypically, landline telephone networks are engineered to a % grade of service. *ost cellularsystems are designed to a "locking rate of 1% to &% during the "usy hour, with % "eing

the most common. utside of peak hours, the "locking rate is much lower.