Voip Blog
7 Digit Versus 10 Digit Dialing
Friday, May 23, 2008
7 digits versus 10 digits. How can three little digits be so problematic? When you're trying to write dial plans, of course!
A traditional telco Central Office only has to worry about crafting a dial plan for a specific community. For example, in the Central Office my landline connects to, it's possible for me to dial--via 10 digit dialing--two different area codes: 253 and 360. Other area codes would be considered "long distance."
On a VoIP analog terminal adapter or IP phone, there are four possible types of dial plans you could do for North America. Assume all dial plans below also permit 11 digit dialing, X11, and 011 for international calls. The inter-digit timeout--the time allowed between button presses on your touch tone keypad--is 4 seconds.
The dial plans are:
7 Digit Dialing Required: If the first digit is not one or zero, the VoIP device will expect 6 more digits to be dialed before the call is connected.
10 Digit Dialing Required: If the first digit is not one or zero, the VoIP device will expect 9 more digits to be dialed before the call is connected,
10 Digit Dialing with 7 Digits Permitted: If the first digit is not one or zero, if you dial 6 more digits and wait for the inter-digit timeout to expire (4 seconds), the call will be connected. Otherwise, if you dial 10 digits in total, the call will be connected. This is how voip.com handles both 7 and 10-digit dialing.
7 Digit Dialing with Smart 10 Digit Dialing: In areas where 7 and 10 digit dialing is permitted, in reality, only a few area codes can be dialed with 10 digits, others will require 11. In my example above, only 253 and 360 can potentially be dialed 10 digits. If the first three digits I dial are either 360 or 253, expect 7 more digits. Otherwise, assume only 7 digits will be dialed.
While the last method is perhaps the most clever, it creates the most overhead in terms of management.
