Should I aim for a blocking rate of zero, or is that unreasonable?
A very low blocking rate is possible and reasonable if you have adequate trunks
and staffing and appropriate call patterns. Some call centers strive to not block calls (not give out busy signals), especially if they are a revenue center, have relatively flat traffic (no extreme peaks) and have a high customer accessibility focus. If you get any significant peaks, a blocking rate of zero may be difficult (and expensive) to achieve.
13 Mar 2008