Core features are network features that operate independently of the User Agent appliance used by the customer. These features include Calling Line Identification features, Call Forwarding, Call Blocking, and Call Screening.
You might ask yourself, “Why implement features on a Feature server; why not just add them to the functionality of the phone?” While some features belong on the endpoint, there are several reasons it is desirable to implement some of your features within the network. For example, in the case of the Call Forward No Answer feature, what happens if your phone is down? And your phone may be down for various reasons such as a power failure or a connectivity problem with the local network. Having a dead phone doesn’t eliminate your need to have calls forwarded to voice mail.
As for call blocking, you can’t trust the phone to block the calls properly, and some users can’t be trusted with 1-900 numbers or whatever numbers are being blocked. The same thing goes for Calling Party ID Blocking: you don’t want to send the ID to the phone and then hope that the phone doesn’t display it to the end user. Also, if the user changes her set, the new phone may not support the same features as the old phone did. For stability and consistency, it is better to have some core system features implemented on a server within the system.
Calling Line Information features are the calling features that appear in a call display device: