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calculating the ratio of required trunks to phone users

Is there a rule of thumb for calculating the ratio of required trunks to phone users?

Assuming a small environment, where I don’t have any measured value of BusyHours, Erlangs,

i.e. if I only have 25 phone users – not very busy – it’s not a call center. What’s a reasonable number of trunks?

What about if I have 50 phone users?

3 REPLIES
Silver

Re: calculating the ratio of required trunks to phone users

The short answer is that there is no easy answer. A through answer to your question needs to take into account a number of variables (size of the telco switch, calling patterns of the subscribers and size of the local metropolitan area).

Try:

http://www.cisco.com/en/US/products/sw/iosswrel/ps1839/products_feature_guide09186a0080087acf.html

Re: calculating the ratio of required trunks to phone users

Any estimate will vary wildly based on your type of business. If most of your business is done on the web or face to face, 2 trunks may be sufficient for 25 users. If however, most of your business is done on the phone and your 25 users each spend 75% of the day on the phone, you might need a PRI. I would recommend estimating the busy hour traffic and using an Erlang calculator such as the one below.

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

Hope this helps. If so, please rate the post.

Brandon

Re: calculating the ratio of required trunks to phone users

you better have a look here:

http://www.cisco.com/en/US/tech/tk652/tk701/technologies_white_paper09186a00800d6b74.shtml

(IP Telephony/Voice over IP (VoIP) Traffic Analysis)

also look at the CallManager capacity tool

http://www.cisco.com/cgi-bin/CT/CCMCT/ct.cgi

normally you use 4 BHCA for a normal user,

but you need to know how long the average calls are,

i.e. 3/5/10 minutes

HTH

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