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💡 Busy Lamp Field (BLF) Overview & Setup

How to Configure BLF and Presence for VoIP Phones

Busy Lamp Field (BLF) allows users — especially receptionists — to see the real-time status of other phones or extensions in your Kiwi VoIP Cloud PBX group. This makes it easier to know who’s available, who’s on a call, or who’s ringing before transferring calls.

👀 What is BLF?

BLF is a feature supported by many VoIP phones. It works by:

  • Monitoring other extensions or numbers in your account

  • Showing their status using LED lights on your phone or reception console:

    • ✅ Green = Available

    • 🔴 Red = On a Call

    • 🔔 Flashing Red = Ringing

    • 🟠 Orange = Error or configuration issue

🔧 How Does BLF Work?

BLF operates using the SIP SUBSCRIBE and NOTIFY protocol:

  • Your phone (the subscriber) sends a SUBSCRIBE message to Kiwi VoIP

  • Kiwi VoIP (the notifier) replies with NOTIFY messages whenever the status of a monitored extension changes

This keeps your phone's display in sync with real-time call activity.

🔐 Important BLF Requirements

To ensure BLF works with Kiwi VoIP, make sure:

  • The subscriber and monitored extensions are:

    • On the same Kiwi VoIP account

    • In the same PBX group (default group = DEFAULT)

    • Behind the same internet connection (NAT/session binding required)

  • Presence & BLF is enabled in the portal:

    • Go to the Advanced > Presence & BLF section

    • Enable presence for the lines or the entire account

☎️ Supported Phones

BLF is supported by many VoIP handsets including:

  • Yealink

  • Cisco (e.g. SPA504G)

  • Polycom

  • Grandstream

  • Fanvil and more

🛠️ Example: BLF Setup for Cisco SPA504G

Assume the user is using extension 093778647 on Line 1 and wants to monitor 093778648.

Step-by-Step:

  1. Line 1 (Ext 1):

    • Configure normally

    • Under Share Line Appearance, set Share Ext: to shared

    • Set Subscription Expires: to 300

  2. Line 2 (Ext 2):

    • Set Line Enable: to no

    • Set Share Ext: to shared

    • Set Subscription Expires: to 300

  3. Phone Tab > Line Key 2 (or desired key):

    • Extension: set to Disabled

    • Share Call Appearance: set to shared

    • Short Name: = label you want displayed

    • Extended Function:

      perl
      CopyEdit
      fnc=blf+sd+cp;sub=093778648@sip.kiwivoip.co.nz;nme=093778648

      (Use nz.tlssip.com if you’re using TLS transport)

  4. Auto Attendant Page:

    • Server Type: = Asterisk

    • Subscribe Expires: = 600

    • Subscribe Retry Interval: = 30

    • Attendant Console Call Pickup Code: = *88 (for group call pickup)

🔁 Call Pickup with BLF

You can use *88 to pick up a ringing call on any BLF-monitored extension in your group — ideal for shared desks or reception roles.