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Planning for Dial Plans

Tristan Walker | Systems Administrator | September 6, 2017

We use them every day and if you’re a business you likely have one set up, though what a dial plan actually is and what it accomplishes is something many don’t have a working understanding of. The topic of and understanding dial plans are important if you are a business considering a VoIP solution in context of the great flexibility allowed compared to landline service – both in regard to the specificity and implementing changes to the dial plan.

Dial plans are a core part of any telephone system regardless if it’s landline or VoIP. At its most basic, a dial plan establishes the valid sequences of digits dialed for both those placing calls and those receiving calls. In the context of digital telephone systems and networks as well as VoIP, dial plans also include the parsing and logical routing for both numbers dialed, special inputs like needing to press a specific digit in order to call outside the office, and automated menu prompts. When calls are placed or received, it is the dial plan that analyzes the number dialed and makes sense of what to do with it exactly. What it “does” varies from removing digits and modifying them based on patterns and rules.

The dial plan is also what makes sense of any digits input at an auto attendant menu. It might not seem so obvious, but for each valid input there is a distinct routing action and for each invalid input nothing unexpected occurs – typically a response that the input is incorrect. For example, if your auto attendant menu prompts the caller “press 1 for billing, 2 for support, and 3 if you’d like to speak to a representative. Alternatively, if you know the direct extension of the person you are trying to reach you may input it now” then pressing 1, 2, or 3 are interpreted to route the call to the appropriate department. Our example auto attendant menu also allows for direct extensions, which would recognize the caller providing 3 or 4 digits rather than a 1, 2, or 3 – the logic even accounts for the circumstance someone in the company has an extension numbered 123.

What’s being touched upon in the above are practical examples of “patterns” defined in the dial plan to achieve a desired routing behavior. Without the dial plan implemented to make sense of these various patterns, there would be no reliable behavior and the system to place calls and interact with menus would be terribly rigid and ineffective. So a bit of complexity goes a long way to enabling behaviors that are generally accepted as just part of the phone system and expected to work  (but now we all know better than that, right?).

With this high level understanding in tow, it becomes obvious the dial plan is something to be mindful of when subscribing to telephone service for your organization – even more so if the organization spans multiple buildings, states, or even countries. While you may never need to develop the underlying logic of a dial plan, you do have a measure of control over what inputs get fed into it and the expected behavior. The goal of an effective dial plan for any organization is to prevent confusion and frustration for those within the organization reaching those outside and across the organization as well as those trying to reach individuals and departments from the outside. Without an effective dial plan, extensions and numbers for your organization are just a mixed bag of numbers and a lot of notes reminding callers what to dial to reach a specific individual or department.

NocTel offers the following recommendations when considering dial plan design for organizations:

Use Distinct Extension Numbers to Act as the “Face” of the Organization or Departments

This means the organization as a whole should be blanketed under a base number like +1-555-555-xxxx or several distinct sequence extension numbers. With multiple locations one office’s main line might be +1-555-555-1000 while another’s is +1-555-555-2000. The idea here is to give outside callers a simple, consistent way of reaching a main office line or department.

Setting aside a 3 digit series for extensions within the x000 range from 1000 to 1999 and 2000 to 2999 in the example above, typically gives enough breathing room internally for further granularity. This would be something like ext 1000 is main office for location, ext 1100-1199 for first floor and ext 1900-1999 facilities or on-call response personnel. However, what ranges and subdivisions that are most effective varies with each organization.

Use Auto Attendant Menus to Help Guide Callers Appropriately

Often times outside callers to your organization do not know a specific individual’s direct extension or even fully sure of which department they’re trying to reach. Worse, if an employee is still with the company but has shifted roles or location, their extension number and possibly desk phone number may have changed. Auto attendant menus with NocTel allow the same digit prompt style along with the ability for callers to specify an individual’s direct extension so secretaries and other front line staff do not need to act as operators for calls coming in. NocTel’s auto attendant menus also allow spoken directory lookup for departments and even specific staff. Couple an auto attendant menu with the company directory through LDAP/Active Directory ensures that the most current information for reaching employees needs to only be maintained in one place.

The benefits of thoughtfulness with auto attendant menus are that callers can be directed appropriately without needing to hang up and call into a different number or the caller reaching the wrong department only to be transferred…potentially multiple times. For example, if the organization has multiple buildings and someone calls the main line of the wrong building, then  the auto-attendant menu for the other building (the one the caller is trying to reach) may include an option for the other building which redirects the call appropriately meaning a caller who dials into the wrong building can reach where they need to just as well as the caller who dials the right building. Alternatively, if the auto attendant menu used NocTel’s spoken directory lookup, the caller could say “NocTel Portland Office” and be directed correctly – this even works for specific individuals within the organization!

Plan Your Extension Needs for the Reasonable Future

Following the above recommendation, if your organization has a good idea how many employees and departments need extensions your dial plan should account reasonable future use and need. Today your organization might be alright with 3 digit extensions, though within the next 12 months due to large growth or organizational changes, it may necessitate using 4 digit extensions instead. For staff in organization technical support roles, it’s much easier to keep things tidy than provision whatever extension number happens to be free. 

While impacts to dialing plan usually occur shifting extension length from 3 to 4 or vice versa, NocTel’s support engineers are always available to consult the impact of changes and assist in minimizing disruption to the organization’s ability to place and receive calls. It’s a good practice for the technical services staff to identify the horizons of the organization to plan expansion or retraction into the foreseeable future.

Use Groups of Extension Numbers for Organization

Regardless if your organization is a large one with multiple locations and thousands of employees or a smaller shop with distinct departments, it’s always a good idea to plan groups of extension numbers for certain use.

For example, placing all technical staff extensions within a certain extension range or for schools placing all teachers in a specific range. For the latter, this could work even across buildings such as having the teachers on extension x20 through x70 where x differentiates the school building through the hundreds digit. That is, teachers in building A are extensions 120 through 170, those in building B are 220 through 270, etc.. The human brain is a pattern seeking thing – take advantage of it!

In larger organizations this may require looser groupings as employees enter and leave the company causing extensions provisioned and available to fluctuate. NocTel’s extension management makes it easy to default or re-provision extensions as staff changes over time whether it’s to accommodate a few employees entering or leaving or many. However, the framework for what extension ranges belong to what within the organization need to be defined and faithfully put into practice to be effective.

Be Aware of Restricted or Special Use Extensions Within the Organization

While extensions extensions are generally available across the organization, there may be special extensions that are reserved for specific routing behaviors or are restricted to avoid dialing conflicts. The most typical side effect is using a 9 to dial out and the inevitable occurrence someone accidentally dials 911.

Avoid Using 9 to Dial Out

Odds are you have worked at an organization that used a 9 to dial out of the organization leading to some mistaken emergency calls and possibly a couple nastygrams from the office manager advising everyone to be careful. If there are alternatives to using 9 to dial out that are not reserved or otherwise unavailable, NocTel strongly recommends using it.

 

While the above are general practices to improve the behavior of your dial plan and make it more flexible to changes in the organization, it is by no means comprehensive. Work with your provider, which may be NocTel, to ensure the dial plan accomplishes everything you need it to while mitigating design and operational difficulties. Customers of NocTel typically work with engineers to identify the most effective dial plan for the organization while retaining it is by no means set in stone – we understand things change. 

 

An Oregonian all his life except for a year spent so far east he flew west to get there, Tristan has grown up and lived alongside computers and networks (and the deer, possums, raccoons, and other indigenous Oregonian fauna), so it comes as no surprise his daily duties center around them. His professional history includes working in web development, wireless automation, and validation engineering ...[More]

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