PRI sizing for 150 remote locations

[Ion Cristian Radescu]

Hi all,

We have a customer(a bank) with the following situation:

- 150 remote locations with PBX and 4 local analog PSTN lines in each location;

- 2 x HQ locations with Cisco IP Telephony solution;

We want to integrate all 150 remote branches with the IPT solution. We want to eliminate all local lines and install PRI lines in HQ locations insteed.

We studied the detailed invoice report from voice provider and we saw a medium of 39 minutes talked from one branch during working hours.

Also we observed the traffic in the busiest hour of the day and we calculated Erlang as 0.15.

After that we used the tools at the following links and we obtained from both tools the same number of lines needed: 2(so 4 lines in site is too much anyway):

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

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

Now, my question is: what model should I use to calculate the number of channels needed in HQ in order to replace all lines from all remote locations and eventually to cut some costs?

If we use 150 * 2 = 300 channels, it seems too much for me compared with the general rule of thumbs "1 channel per 10 users"(I have 1600 users so I'll need 160 channels according to this rule).

Maybe I should start with 5 x E1 connections and equipment capable to scale up to 10 x E1 connections.

What do you think? What would you do?

Thanks for your ideas,

Cristian

[paolo bevilacqua · Accepted solution]

I would use a 2951 or 3925 with 4 PRI initially, that can scale up to 8.

Withe the performances of today ISR G2, even a 2911 may do actually.

[David Hailey · Accepted solution]

How would I do it?  I would probably go with a minimum of a 2811/2911 per site depending on size.  Larger sites would start to move into 2821/2921 and up.  I would also work within the recommended user to channel sizing (i.e., 10 channels per user) guidelines.  Of course, your organization's tolerance for potential blocking may drive you to start lower than that (e.g., 15 channels per user) and see what happens before increasing capacity.  The user to channel number can vary from 7 (per user) to 15 (per user)  depending on who you talk to (whether it is an Engineer or a Telco, for  that matter).

Hailey

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[Ion Cristian Radescu]

Thank you both for your time and answers.

Very good info as always.