Showing results for 
Search instead for 
Did you mean: 

Debra Chittick

Extension Plan for International Companies

I'm looking for information on extension plans that used by other enterprise level companies who have multiple sites in multiple countries.  We have a 5 digit extension plan that no longer suits our purposes and I'd like to hear how other multi-national companies handle their extension plans.  I am currently considering a 8 digit plan (steering code + last 7 digits of the DID phone number -- steering codes will be 9 for off net and 8 for on net.) 

Thank you in advance for taking the time to read and reply.


We are migrating to E.164 and dropping the private dial plans.  It seems with BYOD and mobile devices and especially with SIP, E.164 is the simplest way to proceed.  Most of the numbers are now obscured with directories anyways so much of the benefits around the short dialing are lost.


Couple of good presentations that cover this in some detail.


Hi Debra,

As Ian pointed out, the use of internal dial-plans is (for many companies) less important these days, with internal directories and click to dial functionality etc being more and more commonplace.  However if you have a multi-vendor environment, you may not be able to get away from having a dial-plan in place to point to various sites.

I have administered multiple clusters across Europe, Asia and Latin America all joined together by Inter-cluster trunks, and for our organisation we tended to allow shortdialing between sites within a city or even smal country, but then used full E.164 dialing only between countries.

Our infrastructure was at one point 14000 extensions in about 80 sites over 17 countries, so what we did was this:

All DID and non-DID extensions were based on E.164 format (so full number like 12125551212 in USA, 441234654321 in UK, 3225555444 in Belgium etc.).  If the user was non-DID, we made up an equivalent length extension the same as another one in the same country, so for example in UK we would use 441000005000, 441000005001 etc).  As there is no area code in UK starting (0)1000, it could never clash with a real PSTN number, so the number would always be 'unique.

All numbers in UK have become 12 digits long starting 44, and all numbers in Belgium are 10 digits long, starting with 32 (the Belgium country code)

This does mean that your overall dialplan is variable in length, but this doesn't really matter as within a site you can use 4 or 5 digit local extensions (with translation up to E.164 to hit the local phone DN).

Between sites in the same country, you can then put in an access and site prefix code if you wish, but all that would really do is translate up to the E164 for the remote site's extension range.

If for example you had two European main offices (in my example UK and Belgium) that were always calling eachother, you could have inter-site short dialing between the two, but all those shortdials would do is convert up to 44xxxxxxxxxx or 32xxxxxxxx.   AAR can easily be used in case of intersite network failure to prefix with PSTN access code (9) plus the 00 international code, meaning that in the case of WAN outage, the call could be prefixed easily and sent out to PSTN for routing direct to the remote site without the use of complex translation within the dial-string.

I don't know the size of your company, so can't tell if it would be possible (or usable) to use intersite short-dial codes within a country, or how widely intersite dialiing is used.  However one thing I would recommend from my experience - having multple 'site' or 'location' codes assumes that everyone knows them or can refer to them quickly and easily, so their use is dependent on the knowledge and confidence of the staff.

With the advent of click-to-dial and apps like Jabber, Lync etc, using full E.164 for extensions is really a 'must-do' especially when your corporate structure is international. It will give you a solid structure with guaranteed uniqueness of DN, and also allows integration with other systems.

I could share details of how we structured our dial-plan and naming convention in more detail but probably best not on this forum as it would require diagrams etc and is not 'forum' style material.

Debra Chittick

All very helpful answers.  I would like to hear if anyone is still using private dialing plans, much like Cisco explains in their SRND for 8.x  under Abrreviated Dialing


"For example, Cisco employees at any Cisco office can dial the San Jose reception number as 8 526 4000. The digit 8 serves as the inter-site access code, and 52 serves as the site code for San Jose.


This form is shorter than the alternative of using an off-net form to route the calls on-net (for example, allowing Cisco employees in Canada to reach the Cisco reception in San Jose by dialing 9 1 408 526 4000 while routing the call on-net). Even though the dialing form is similar to that used to reach an off-net destination, the system is configured to keep calls to on-net destinations dialed in the off-net form within the system."


Even though 52 is called a "site code" it's also part of the actual DID phone number.    So in their example they are using a steering code plus 7 digits of the phone number.  I'm looking names other enterprises that use this type of dial plan. 

I believe we can use the Application Dial Rules within CUCM for Jabber and other idevices, so having the entire extension plan E164 is not necessary, IMO. I have not seen a benefit that motivates me to use +based dialing and DN's that look like: \+1724779XXXX.

I know that it is used by a large (global) US-based motor manufacturer across all of their sites around the world.  Their format is 8-7xx yyyy  where 8 is the access number for intersite calls, 7xx is the site number then yyyy is the local subscriber number.   They use this across multiple platforms (not just Cisco), and local dialing within site is then just yyyy.  One drawback that I see is that within a large site of say 15000 users they may have multiple site codes, i.e. they require two site codes like (8)730 and (8)742 within one physical site.  Local dialing within the site then becomes 4 or 8 digit depending on whether the remote party is is one part of the site or the other.  There is no option but to send the full CLI (either 7xxyyyy or 87xxyyyy) across for all calls.  Re-dialling a missed call (using 'missed calls' on the phone) is easiest using the full 8 digits.  It is likely on such a site to have 2x extn 1111 for example, and they have not used a 5 digit plan so cannot differentiate between 1111 on the west side of a location and 1111 on the east side.  They have to use the full 8 digits or they risk getting the wrong extension 1111 when they call.

One drawback to using this method is really outside the scope of telephony - all of their email signatures and business cards have to show an external DDI number as well as an internal (8)7xxyyyy number.  If you use E.164 throughout, what you put on the business card is what anyone dials, external or internal.

In the Cisco example you show, they used '52' for a site code, but it is part of the actual DID number...  That is not always possible.  If you have two sites with area codes ending 52, then what do you do ??

We're using E.164 on all platforms and have no complex translations for using Jabber, MOC or Lync.

All we do when sending calls out to PSTN (to send CLI) is mask down the length of CLI outbound to the last 4 or 6 digits (in the UK) or 8 digits in Belgium etc.  Calls on the way in are just prefixed in the opposite way, so for example:

In UK extn 441908882222 calling out to PSTN sends 882222 to the carrier.  Inbound calls come in with a destination of 882222, and we just prefix with 441908  and send the call to the phone.

Recognize Your Peers
Content for Community-Ad