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2. Key systems overview
Key telephony systems are defined through the arrangement of phone buttons with line
selection function for each available analog telephony line. This means that all the analog
lines on the device will be shown as a registered BLF
functions assigned. With such configuration, inbound calls on analog lines, don't have a
specific destination. On key systems, inbound calls are ringing the inbound line which
activates the BLF keys subscribed to that line.
First few BLF keys will be occupied by line monitoring and calling functionalities, then
comes the Intercom button, which is followed by all the users on the system. If there are
numerous users on the system, each phone should provide their own way of pagination of
users on BLF keys.
By default with no calls on the system, BLF keys on the phones either do not show any
activity like on VVX600, or they are illuminated with green light like on T42G phone.
When the call comes in through the analog lines, or there is a call made from the extension
on the system, BLF keys on other phones monitoring the status of the line or the extension
will blink with either red color (Yealink T42G) or the green color (Polycom VVX600).
Generally speaking, blinking BLF light shows that the line or extension is being called, and
is ringing.
If the call is answered, BLF keys on phones will show that line and the extension that
answered as busy, by showing a constant red light (physical keys), or just showing a red strip
next to the extension or line (VVX600 touchscreen).
2.1
Supported phones
The software supporting the key systems device enables the usage of a wide array of phones,
but for simplicity and management reasons, the system is optimized for Yealink and Polycom
1
Busy Lamp Field is a custom/additional button key on the phone with integrated background light, which
in most cases can be used to monitor and/or call other extensions.
1
keys with monitoring and calling
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