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Dial Plan Design - very large organization growing VOIP Deployment

Hello Everyone,

I need help in designing a Dial plan that will fit our growing VOIP network.

We have a very large organization spread across the globe. Office size varies from 10 people to 500 +

We have call manager 5.13 deployed in NA with UNified messaging. We currently have 7 sites deployed with Cisco MGCP gateways with PRI lines. We have one CME deployed in South America (H323) and will be deplying another Call manager cluster in Europe with Unified Messaging. We have also just integrated an Avaya G3 V11 Definity with CCM using H323. I had to use a site code for the Avaya in London because of over lap on the existing Dial Plan.

So now that you know the lay of the land.

Problem is:

1) Currently we have 4 digit dial plan that is starting to overlap.

2) 2 digit site code is not good enough(too many offices)

3) 3 digit is too long (end user will not like it)

I like site code becuse I don't have to worry about what DID are availble from the Telco and overlap

It was suggested that 5 digit dialing would solve the problem.

I look forward to your collective wisdom or point me to good docuement where someone has implemented such a plan



paolo bevilacqua
Hall of Fame Master

Yes, it seems your case does fit anymore into 4 digits, and you might need to go to 5, with a prefix digit to indicate that it is an inter-site call.

However, I can suggest that you make the site code to be variable between 1 and 3 digits. Why is that, it allows intra-site calls to be kept short, without using the site code.

I think you've understood what I mean, but let's make an example:

Main site, with potentially more that 1000 extensions, has site code 2. Intra-site calls can be dialed 4 digits, or 8 plus 5 digits

Digit 9 is outside line, 0 is operator, 1 reserved for emergency and other things.

Regional sites, let's say 20 of them, have site codes from 30 to 49 with up to 600 extensions extensions each. Intra-site can be dialed 3 digits, or 8 + 5 digits as above. 0, 1 and 9 same for big site.

Smaller sites, have 3 digits code, from 500 to 799, so it's a lot of them. Each has up to 60 extensions. You dial intra-site with 2 digits or again 8 + five digits.

Hope that makes sense so you. I understand is a deviation from the fixed length way of thinking, but just like in IP networking, and many countries telephone network, it's simply the bast way to utilize a numbering space and keep things short and simple. And the beauty is that if you pick the numbers sensibly, you can grow and shorten sites as necessary.

Hope this helps, please rate post if it does!

Thanks P, Sorry for late reply. I have been digging around and you have the best example. I have not seen an real world examples on the Web.

Can you have some site with 4 digit dial plans while others have 5.

I see your Intersite prefix bing a varible.

Problem is how messy is the route pattern going to be? Can you give me some examples that you would see in CCM.

Thanks for very usefull post.


I'm sorry, I cannot make examples for CCM but I know it can be done.

This is similar to what some country do in their national plans, large cities have short area code but long number, opposite for the smaller.

I have thta in place using 'intrasite prefix' + 4 digits and users like it. We're usng ccme.

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