[Asterisk-Users] Traffic Modelling (was IVR only system with scalibility...)

[Leo Ann Boon]

For IVR or call center, you will need to the Erlang C model to calculate 
how many IVR lines/agents are required.

Using George's assumptions, 4 lines are required to service the calls 
with a service level of 98.7%, assuming each call should be answered 
within 10 seconds. Average speed of answer (ASA) is 0.8s. Actually 5 
lines would be better, but would bump up the hardware cost since most 
voice cards are available in 4s or 8s.

For comparison:
1 line - ASA=2250s SLA=6.6% (a caller may have to wait up to 2/3 an hour 
for call to be answered!)
2 line - ASA=42.2s SLA=72.1%
3 line - ASA=5.6s SLA=93.2%
5 line - ASA=0.1s SLA=99.8%

Just my $0.02.

George Pajari wrote:

> The question was posed:
>
> "incomming calls for 45 or so people that will call in 3 or 4 time 
> each day during (approx) normal business hours"
>
> The comment was made (taken out of context):
>
> "The quick math says that 45 people with 4 calls is 180 calls a
> day. In a 8 hour day you have 480 minutes. From 480 minutes 1 port could
> handle the load if the call was under 2.5 minutes long and everyone
> waited till it became available."
>
> Unfortunately as we all know, asking callers to guess when the line is 
> free and equally spacing their calls is not terribly realistic (as the 
> author of the comment above goes on to imply).
>
> So how does one analyse such a situation? Using statistical traffic 
> modelling!
>
> For more information, see http://www.erlang.com/calculator/erlb/
>
> Plug in:
>     Busy Hour Traffic: 0.937 Erlangs
>     (based on 45 * 4 * 2.5 / 480)
>
>     Acceptable Blocking Factor: 1%
>     (we will accept 1 in 100 calls receiving a busy signal)
>
> Result:
>     you will need 5 incoming lines.
>
> If you are willing to tolerate (say) 3% of calls receiving a busy 
> signal, you can get by with 4 lines etc. and etc.
>
> Hope you find the above useful in planning your Asterisk installation.
>
> _______________________________________________
> Asterisk-Users mailing list
> Asterisk-Users at lists.digium.com
> http://lists.digium.com/mailman/listinfo/asterisk-users
>