All Trunks Busy

All trunks busy, abbreviated as ATB, is the state in which all telephone lines of a PBX (or PABX) are in use. When all telephone lines are busy no more telephone calls can start until one of the current calls complete.

The problem

Imagine that you run a business, if all trunk lines are busy no more outgoing calls can be made. Perhaps worse, no more incoming calls from customers can be received either. Unable to receive phone calls means poor customer service, or loss of business.

To determine the number of trunk lines used businesses typically use a call accounting program. Running an 'All Trunks Busy' or 'Trunk Utilization' report below shows the number of telephone lines in use for each minute of the day.

all trunks busy - trunk utilization report

Saving money

When starting a business the number of telephone lines required is often unknown. To be safe businesses often buy, or are sold, more trunks than necessary. It is certainly in the telephone company's interest to sell as many lines as possible. If the number of telephone lines used is less than required significant savings can be made.

For example: say you rent 30 ISDN lines at $30 per trunk per month. After running a call accounting system for a while you might discover that most of the time you use less than 20 lines. Reducing the number of lines rented from 30 to 20 saves $300 per month - $3600 per year.

Call accounting software

Not all call accounting software is equal.

The basics of a call accounting system can be simple, creating a system that can run a 'all trunks busy' report fast can be an issue. At least one call accounting software manufacturer has a warning in its user guide that running the 'all trunks busy' / 'trunk utilization' report can take a long time.

Designed to be fast, the TIM4biz trunk utlization report is included on the default home page, and the public demonstration page.