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I have an existing TI Voice PRI module on a 1760 Router. This is my gateway to the public side. The PRI is supporting 100 block range of DIDs. I will be opening a new campus soon and will be needing to route another 100 block range of DIDs through. So we will have a total of 200 DIDs that will need to be routed. My question is, will the one PRI be sufficient to handle both ranges? What is the general rule for load on phones per PRI.

Obviously adding an additional PRI will be the best solution, but can I avoid it?

Is there a way for me to pull a report on the peak usage for my phone system in CCM.

CCM 4.1(3), Unity4.0(1)

Thanks in advance.

VIP Purple


It's very difficult to give a general rule regarding phones per PRI. It really depends on your usage. For example, a call center would have a much lower phone to PRI density than some other business. The best measure is the number of calls attempted during your busies hour or the BHCA.

One way to get a report on usage is with the Serviceability Reports Archive. The Call Activities Report will give you cluster wide information on calls attempted, PRI channels active, etc. See the link below.

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


Hall of Fame Super Red


Hey Carlos,

Brandon is correct in that the number of required PRI's or channels varies from one deployment to the next. The general "Telco" rule of thumb is referred to as "1 in 10 Trunking Rule" wherein there is 1 Trunk (in your case channel) per every 10 users So

100 users = 10 channels

200 users = 20 channels

You can also use RTMT to monitor your PRI's and send you email alerts when defined thresholds have been exceeded.

As you can see this is not an exact science for example;

For our Student Residence we use 5 PRI's for 1000 student phones.

For our Staff we use 3 PRI's for well over 1500 phones.

Hope this helps!


Please remember to rate helpful posts........

Community Member


It really depends on the amount of calls both outbound and inbound. You may have a problem. If you have 10 outbound calls and 13 inbound your PRI, at that point your PRI is full. Callers will start to get busy on both inbound and outbound calls. Spend the extra money

and do it right. It will save you headaches later.

Regards JR

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