Extension Number, Phone Device, or User?
September 6th, 2010
Is a phone, an Extension Number (e.g. DN) and a User the same entity?   Does the User define the Extension number?  Does the User define the Phone?   What is the difference and why would you care?   You care when you have to separate the concept of a “function” from the concept of a “Person”.    Is there a function named “Receptionist”?    Or do we have a  User who is the Receptionist?   Does the Person who is the Receptionist get a personal Voice Mailbox?  Or is that User also the General Delivery mailbox for the Receptionist function?     The answers to these questions are not necessarily complex, but they will define the implementation strategy.  The implementation strategy, in turn will be dictated to by the manner in which  the system architecture handles the phone, extension number and user entity definitions.     Lets assume you are deploying a solution for a Theme Park.   The Theme park will have many employees, some of which are part of the office staff and management team and others that are part of the campus Park staff.     The Office staff has a more formal structure with specific Users and assigned workspaces.  The Park staff, however,  consists of employees who work at different hours and on different days.   For example, there is a phone at the “Snack Bar” but who knows who will answer that phone?   That phone is a “function” not a person.    CISCO will allow phones to register with the “Mother Ship” (e.g. Call Manager) without requiring either an Extension Number  or an assigned User.  ShoreTel will also allow a phone to register with the Mother Ship without an Extension number or User.  Both solutions require that the device be assigned a “line number” or “extension number” before the device can be called, though the phone might have some limited out dialing capabilities without an Extension number.     T he ShoreTel model, however, assumes that every device has both a Unique Extension number and a Unique User.  In  the ShoreTel model, a  User can not exist without an Extension number.  In the CISCO model, Users are optional?  I get to work with both systems and  the difference are both subtle and  interesting.  Not that one strategy is any better than the other, it  is just a matter of how you have to organize the entities to achieve a particular application solution.  Lets assume the “Snack Bar” is very long and has 10 phone devices distributed up and down the counter.    In the ShoreTel model, each phone would be required to have a unique Extension number.  License issues aside,  what number do you dial to call the Snack Bar?    Remember, we are calling a “function” not a “person”.    In the  ShoreTel model,  each phone must have a unique extension number.    Additionally,  each extension number must have a unique User defined in the system administration portal.   In the ShoreTel model we end up with something like SnackBar  Phone1,  SnackBar Phone2……….ShackBarPhone9  etc.      Given that all the ShoreTel devices at the Snack Bar have different Extension numbers we have to organize either a “hunt group” or create a “bridged line appearance” if we want to call the “Snack Bar” with a single extension number. In the traditional TDM world, you would have taken the 9 phones in the Snack Bar  an punched them down on the same Extension!   That seems to be the way CISCO deals with this situation.  You can create the phones, give them all the same Extension number and publish that number  as the “Snack Bar” in the Directory.    This scenario is not unique to a Theme Park.   Separating  a  “function” from a “person” or User is often a requirement in a phone system deployment.   The scenario could  have easily been a  “Sales Counter” at an Auto dealership; or the Admissions desk at a hospital  rather than a Snack Bar.  Another subtle ramification of being able to separate Users from the Devices they use is the subject of calling permissions.    Do we restrict or grant calling permissions to phones, Extension numbers or to  Users?   In the ShoreTel model, we generally grant calling permissions based on the User.  A User is placed into a particular Group that defines privileges.    In the CISCO world we generally grant calling permission based on the Extension numbers and the Partitions that contain them.    Again, it is not a matter of one strategy being better than another.  They are just different strategies and as a result your deployment will have to be planned accordingly.    At the Snack Bar, we have lots of different employees using the phone, so we are more likely to want to restrict the Extension number assigned to the “function” rather than restrict the Users assigned to work at the Snack Bar!