George Pajari
2003-Sep-04 12:48 UTC
[Asterisk-Users] Traffic Modelling (was IVR only system with scalibility...)
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.
PJ Welsh
2003-Sep-04 13:53 UTC
[Asterisk-Users] Traffic Modelling (was IVR only system with scalibility...)
Nice goin'!! I will use this for a reference point to establish baseline numbers of phone lines. The good news is that the equation is not linear (eg 45 people need 5 lines, 100 need 10 lines). So I can double my potential users and ONLY need 2 more lines (qty 7). The bad news is that I don't 100% think I will have purely random connections. On Thu, Sep 04, 2003 at 12:48:58PM -0700, 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@lists.digium.com > http://lists.digium.com/mailman/listinfo/asterisk-users
Leo Ann Boon
2003-Sep-04 16:44 UTC
[Asterisk-Users] Traffic Modelling (was IVR only system with scalibility...)
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@lists.digium.com > http://lists.digium.com/mailman/listinfo/asterisk-users >