Best Way to handle Overlapping DNs

[mumbles202]

Have an existing CUCM cluster that has multiple sites with VGs.  Currently all sites DNs are in the same partition, with 5XXXX being used for DNs.  Also have inter-cluster trunks to other sites that utilize 2-4XXXX and 6-7XXXX.  Currently have 11122256XX ringing in on a PRI on a VG at 1 location.  Another carrier is bringing in a new block of numbers, 33344456XX, so wondering what the best way to handle this would be.  I figured I could create a translation for the new block of numbers and then translate them to say 566XX or something in a range that isn't in use in CUCM and have that ring in on people phones.  Then fix the external mask so that when they call out it shows their correct number. 

My concern w/ this approach is the end users seeing 56625 for example on their phone, but then having to tell everyone their DID is 3334445625.  Maybe that isn't a real concern and users will be fine, but wondering if there is a better way to accomplish this. I could label their DID on the button as well. 

My other thought was to create a separate partition for these new 56XX numbers, but then thought it might be confusing for users to have to dial a prepend code to dial other users in the company.  Also considered using 55XXXX, but thought that might get confusing.  

I was given the option of having the new numbers just ring in as the full DID and make that an extension, but didn't see that as a viable option (not for the CUCM side but more for end users as they'd need to know how to reach the new numbers internall).

[Roger Kallberg]

The absolute best and recommended way is to use full +E.164 numbers for your directory numbers. That way you do not have to deal with any overlapping numbers. In general you should by effort avoid situations where you have overlapping dial plans as that introduces dialling delay.

[mumbles202]

I could certainly try for that.  I'd have to get buy-in from end users for dialing internally as people are used to their 5 digit dialing. 

[Roger Kallberg]

You can overlay a 5-digit dial plans on top of the +E.164 numbers. Based on the information you provided you would not have a five digit overlap as you’d have 256XX and 456XX. These are not overlapping. But at some point you’ll get into a situation where you have a potential overlap, so you’ll need to come up with a plan to not get into that trap. It may be that a 5-digit overlay won’t cut it, so maybe you should look at a longer overlay number plan.

[mumbles202]

Thanks.  2XXXX-4XXXX and 6XXXX-7XXXX are actually existing route patterns that route to other locations, but I think I understand what you mean.  I'll see if I can work out an overlay that works.  

[Elliot Dierksen]

I agree with @Roger Kallberg about using +E.164 numbers. User dialing behavior is another thing. You would use translation patterns to expand 2XXXX to +1.202.555.XXXX (or whatever). My suggestion is to try and preserve as many digits on the right as possible. Otherwise your translation patterns can get messy.

[mumbles202]

Thanks for the feedback from both of you.  I'll try to implement and see how it works.  Can I do a staged migration to +E.164?  So start with just the new numbers for now and then migrate the rest remaining users over time?  I only ask as I need to determine timeline and downtime that will be associated with migrating all the DNs over and the impact on user behavior.

[Roger Kallberg]

Sure that’s absolutely doable.