Every good Voice Engineer I know has seen them, however, very few notice or even pay attention to it, until… it’s a problem for the customer.  Today I had just such an event pop up in a handy little trouble ticket from one of our customers.  The ticket went a little something like this “When I dial 9, I hear silence until I dial a second digit.”

Any thoughts?

This is a very common problem for a lot of people when they have dial plan overlap.  What I mean by this is after examining the customers dial plan for several minutes I noticed that their route patterns were all 9.@ and were assigned route filters.  This wasn’t so bad, actually when I can do so, I prefer route filters to traditional patterns as it creates more room for flexibility in your dial plan.  As I was scrolling down the route plan report I noticed something that caught my eye, someone had configured a phone with extension 9001 on it.  Not a problem you say, I beg to differ!

Call Manager or Cisco Unified Communications Manager has a very strict set of rules for digit interpretation and call routing.  Each time you dial a digit Communications Manager will evaluate that digit against all possible route patterns, DN’s, CTI RP’s, etc until it finds a possible match or an exact match.  The kicker is when there is a tie, so in our example above the 9.@ and 90 would match, and it wasn’t until the user would dial a second or third character that CUCM could rule out the 9001 extension for the remaining patterns would it present outside dial tone to the user.

This is a very common mistake in a lot of deployments, one that won’t really affect any system functions, but is more of a nuisance to the end user.  This very problem is one of the items we look for while performing our UC Assessment and Health Checkups.  Contact us today for more information this service if you feel your organization could benefit from a UC Health Check!