Network Performance: Why CPS is the Wrong Measure

One of the most common questions asked by customers of VoIP networks is “What level of CPS can your network handle?” CPS, or Calls Per Second is a term used widely in today’s telecoms industry; you’ll hear it in business meetings, presentations, sales pitches and in the conversations between technical network staff. But as it turns out, the number of calls per second is not actually the best indicator of network performance or call capacity. We got together with Simon Sharman, Technical Director at Nexbridge, to get the facts straight.

Why would CPS be the wrong measure of network performance?

Simon:Screen Shot 2015-03-03 at 12.31.52
“The issue lies in the fact that the number of live calls that a network can handle at any one time is never fixed. In fact it depends greatly on a number of factors, including how many call attempts are being made (these have to be processed of course), how many calls are being answered (Answer Seizure Ratio), and how long these answered calls are lasting (Average Call Duration), among other things. Which means a given value for CPS for a network doesn’t mean much on its own.”

So how should we measure the performance or capacity of a communications network when there are so many variables involved?

Simon:
“As it turns out, the number of call attempts per second (CAPS) is the most appropriate measure. This is because the most difficult tasks a network must perform concern the set up and disconnection of calls, rather than the supporting of multiple calls at once.

If we imagine a scenario where there are two networks, with one having significantly more processing power than the other, the more capable network might still be supporting fewer calls per second, if it is having to deal with a higher number of call attempts per second.  It is therefore much more appropriate (especially for VoIP customers) to be talking in CAPS, not CPS.”

Some VoIP network providers restrict customers by putting hard limits on the CPS or CAPS per customer. Other networks however, work with their customers to come to an appropriate soft limit. Make sure that you have the right conversations with your VoIP provider if you are going to be routing high volumes of call traffic.