Technicolor TB30, Administrator'S Manual

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TB30s SIP Administrator Guide v1.3
Page 91 of 259
BLF
The objective of this section is to present the way TB30 SIP uses backlit
function keys to monitor the state of other extensions. The backlit function
keys will indicate if an extension is idle, in use, or ringing. This feature is
known as BLF or Monitoring Extension function.
TB30 extension module can be used to have more programmable keys on
board. There are basically two scenarios:
-
Server-to-phone scenarios : there is a SIP proxy which controls the
state of each extension and sends the appropriate messages to the
supervisor phone. Asterisk is an example and the reference followed for
implementation.
-
Phone-to-phone scenarios : each phone is responsible for notifying its
own state to supervisor phones
TB30 supports three types of BLF – two types of BLF based on “dialog” event
package: User and List-oriented, third BLF: Presence basesd BLF. Please
note default mode for BLF is User-Based.
User-oriented BLF
Mechanism used for BLF is SUBSCRIBE/NOTIFY messages described in RFC-
3265.
The device will subscribe to the state of the extension of interest and receive
status notifications from this extension or from the proxy in order to drive
the LEDs.
High level technical description
When the phone is initialized, it will send out a SUBSCRIBE message to the
proxy for each extension it would like to monitor. This is to subscribe to the
state of the other extension. The proxy (and in some cases the other
extension) needs to support these subscriptions. At this point 2 things can
happen depending on the Proxy, which correspond to the scenarios listed
above:
• Phone-to-phone scenarios : the proxy will forward the SUBSCRIBE to
the far phone. Then the phone needs to log all extensions which subscribed,
and send out NOTIFY messages when changes happens in its state.