The Wiki of Unify contains information on clients and devices, communications systems and unified communications. - Unify GmbH & Co. KG is a Trademark Licensee of Siemens AG.
A telephones is normally associated with a directory number (or in general with SIP: AoR) for taking calls and for displaying its identity when placing calls. This number is also used when more than one call appearance is supported due to additional features like call waiting CW.
A keyset denotes a telephone that is associated with more than one number - this allows a given telephone to act on behalf of different phone numbers. Just as with traditional telephony systems, people sometimes refer to lines instead of number, hence keyset phones are also referred to as multiline phones. The main line (i.e. the line/directory number for user associated with a given physical telephone) is called primay line, while all other lines that can be handled on other phones are denoted shared lines.
At a given time, one telephone can handle only one call appearance for connecting to the handset, and the same applies to keyset / multiline telephones. Similar to single line telephones, features like CW may increase the number of call appearances that can be handled, but on a keyset telephone, these appearances may refer to different lines / numbers. The programmable feature keys are used for handling the lines and their call appearances, supported by the associated LEDs to reflect the line/call status.
The number of lines that can be shared may depend on the phone model.
This feature can be used for different use cases, like chief / secretary.
This feature requires specific support by the softswitch / application server. Depending on the selected system, a specific set of features for handling call appearances is available.
Similar features are named Bridged Line Appearance (BLA) and Shared Call Appearance (SCA).
Pls. refer also to DSS keys.