Concept relationship between extension and phone

[petewatterschats]

I an trying to understand the relationship Between a Phone (PC, VOIP Phone, Smart Phone, Tablet, Intercom, Camera etc.) and an EXTENSION.

Does each Phone have a unique extension?

A individual person can have multiple phones is the extension for that person the same for all his/her phones ?

Any direction to explanation of this relationship would be appreciated

 

[leejor]

A SIP device (phone, tablet running a phone App, Smart phone running a Phone app, etc.) can be assigned an extension number. In fact many devices can be assigned more than one extension number at a time (think multi-line phones).
In many cases an extension number is assigned to one device, and that device might sit on your desk, so that extension number is yours. However, that extension number could be assigned to more than one device (called SIP forking). Your desk phone could have the same number as the App on your mobile phone, so, a call to your number will ring both devices at the same time. Someone could easily have an extension at home (or anywhere), with the same number as the phone on their desk at work. You could assign the same number to all of that persons devices, so if they were all on, they would all ring on an incoming call. When a device is first turned on, it registered with the PBX telling it where it can be reached (IP address and port number), it will repeat this every 30 minutes, or less, depending on what the PBX requests. Most VoIP providers act in the same manner although some do not permit more than one device to be registered at a time.