BHT(Busy Hour Traffic) and Blocking

This page describes BHT(Busy Hour Traffic) and Blocking basics in a telephone network and mention example calculation of Busy Hour Traffic and Blocking.

BHT(Busy Hour Traffic)

It is used to represent quantity of telephone network traffic in the unit of Erlangs. For calculation, let us assume 1 Erlang as 1 hour of calls. BHT is represented as number of hours of telephone traffic which is available with network trunk group in the busiest hour.


From the call records let us assume that 400 calls are made on some trunk group. Average call duration is 180 seconds. Now Busy Hour Traffic is calculated as per following equation.

BHT = Average call duration(seconds) * Calls per Hour /3600
BHT = 180 * 400 / 3600
BHT = 20 Erlangs


This figure refers to calls which can not be completed due to insufficient telephone lines. Blocking of 0.01 refers to 1% of calls will be blocked. Normally this figure is taken into calculations in telephone traffic engineering.

Useful Links

echo canceller   exchange signaling types   EPABX basics   PDH vs SDH   CAS vs CCS   Erlang and Grade of Service  Busy Hour Call Completions and Attempts

RF and Wireless Terminologies