In what language is VoIP written?

ANSI-C. 

Should I use Erlang-B or Poisson models?

Question:
I am trying to determine the best traffic modeling formula to use for VoIP, such that we wish to know necessary bandwidth when converting to VoIP.

Answer:

1) Decide if your source population is

• (F) FINITE (e.g. an office with a known number of phones/employees) or
• (I) INFINITE (e.g. a call center receiving VoIP calls from a 1-800 number).

2) Decide what happens to calls that cannot get 'service' (e.g. talk) immediately. Do they

• (A) Just disappear and don't try again. [eg overflow from VoIP network to PSTN]
• (B) Keep trying or go onto a HOLD queue, but if the wait is too long...hang up
• (C) Go onto a queue and NEVER leave until they get service.

3) Choose model:

• (F) + (A) = Erlang B
• (F) + (B) = Poisson
• (F) + (C) = Erlang C
• (I) + (A) = Engset
• (I) + (B) = Binomial
• (I) + (C) = Delay

4) Use a tool (such as our Erlang-G program) to decide how many voice trunks you need. At this point - it is irrelevant if they are VoIP or non-VoIP trunks.

5) Take the result from step (4) and use the VoIP too to calculate the required bandwidth for your VoIP network.

Generally - Erlang-B is often used in VoIP calculations for infinite populations (or Engset for finite populations) BECAUSE there is often an overflow path (to PSTN?) so loosing a call is not critical; just a little more expensive.

But if there is no overflow path, then the Poisson model (infinite populations) or the Binomial model (finite populations) should be used.

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Last modified: March 07, 2001