[cisco-voip] Dial-Plan Advice

[James Brown]

All,

Could I ask for some recommendations on designing a firm-wide dialplan 
please?

We're looking to roll out Cisco IPT to potentially 100 branches (ranging 
5 - 1000 handsets) over the next few years. Where possible, branches 
will have a regional cluster, with SRST configured at the local site.

The goal is to have a dialplan which permits users at each site to call 
other sites over the MPLS WAN, reverting to AAR when necessary and using 
TPs under SRST to expand the short dial number into PSTN format.

Cisco have recommended using:

* 7 digit DNs with TPs to permit 4-digit local calling
* Global dialplan 8 XXX YYYY. X=Site DDI Digit, Y=Extension

I think this is good, but on our scale we're bound to get conflicts if 
we only use three digits from the DDI.

My preference is to instead allocate a random three digit unique number 
to each site that is unrelated to the DDI. Could anyone explain what 
disadvantages having a short dial that is unrelated to DDI could have 
please? Is AAR still configurable? Are there any other dial-plan models 
that you would recommend?

Many thanks for your time.

Regards

James.