Voicmail ports

[stuzzy]

Is there a ratio for calls recieved and voicemail ports?

We have an auto attendant that answers all calls 24/7 (VMPro) and we are expecting an increase in volume in about a month and I am trying to determine if we need extra voicemail ports so I'm wondering if there is somekind of ratio I can use as a base for projecting our needs.


Thank you.

 

[sizbut]

Its all going to be very subjective.

?How long on average is any caller going to be in a voicemail callflow before the auto-attendant hands them off to a real user.

?How burstie (new word) is that traffic. Some call center suffer big peaks at the at the start of the day, just before lunch and then at the end of the day with a lot of idle time between.

?To what extent are you prepared to balance losing some calls in return for not paying for channels that are rarely used. (factor likely earnings per call if doing sales).

?Over what period are you prepared to write off the cost of the extra channels (at least its a one of cost rather than lease).

?Is the voicemail also used for mailboxes. If yes, then you have to factor in the usage time for messages being left and for users collecting messages.

?What control unit are you on, that sets the ultimate limit for channels that can be used for voicemail (IP403 = 10, IP406 = 20, IP412 = 30)


It takes some interpretation but the SMDR log output does indicate when voicemail channels are in use, so you could plot a graph for how many channels are use at any time with your current usage and then interpolate that for an expanded system.

 

[Morrack]

All of what sizbut mentioned above is all true. To take it step further though, you can use a tried and true scientific method of determining ports referred to as Erlang B. Basically, using the guidelines sizbut mentioned determine an acceptable 'blocking rate' - ie how often are you prepared to have VMPro unavailable (0.01% is a common choice, but the more tolerant you are the less ports you will need). Then determine average call length in the VMS - again if you don't have CCC use the smdr data. Run these numbers for the busiest hour of your typical day through any of the myriad of free Erlang B calculators on the internet - ex.

http://www.erlang.com/calculator/

Note: Erlang B is typically used to size trunk groups, so don't let that throw you. The same principle applies for a VMS group - think of the ports as trunks, the IPO is the CO and the VMS is the PBX.

Peter

PS you may find the Call Minutes calculator on the erlang.com site easier to understand and use... but it's also powered by the Erlang B formula.