How to Add BLF Support to a Software SIP Client

In the realm of SIP communication, BLF (Busy Lamp Field) support is an essential feature for improving user experience and call management efficiency. BLF is widely used in enterprise environments to monitor the status of other lines or extensions, providing a real-time visual indicator for line statuses, such as “busy”, “idle”, or “ringing”.
For SIP-based VoIP solutions, incorporating BLF support into a software SIP client can enhance productivity, streamline call handling, and improve overall efficiency for users. In this article, we’ll walk through the steps to add BLF support to your software SIP client, covering both the technical setup and practical considerations for smooth implementation.

What is BLF in SIP Communication?

SIP (Session Initiation Protocol) is a widely used signaling protocol that enables the initiation, management, and termination of real-time communication sessions, such as voice and video calls over IP networks. In the case of a door-phone video system, SIP enables communication between the door-phone and a remote client — such as a smartphone, tablet, office intercom system, or application running on desktop computer — allowing users to interact with visitors at the door.
Using SIP, these systems can initiate video calls, establish connections, and terminate the session once the communication is complete. This transforms what was once a simple doorbell into a sophisticated audio-visual intercom system.

Key Benefits of BLF:

• Improved Call Handling. Users can see if colleagues are busy before transferring calls, reducing the chances of misrouting.
• Better Collaboration. Visual indicators allow team members to respond appropriately, whether it’s taking a call or assisting in urgent situations.
• Enhanced Productivity. By minimizing wait times and missed connections, BLF can streamline communication and save time.

Steps to Add BLF Support in a Software SIP Client

Step 1: Configure BLF on the SIP Server. Enable Presence Subscription and ensure the server is set to notify clients about the status changes of monitored extensions.

Step 2: Modify the SIP Client to Support BLF. Implement sending SUBSCRIBE requests. Siprix library does this when client app invokes method ‘Subscription_Create’. Once subscribed, the client will receive SIP NOTIFY messages when there’s a change in the status of a monitored extension.
The client needs to handle and process these messages to update the status indicators (e.g., green for idle, red for busy, flashing for ringing) on the user interface.
Design the UI to clearly show the status of each monitored extension. You may want to add icons or colored indicators beside each contact or extension.
Consider a clean, intuitive display that uses color-coding or labels like “Idle”, “Busy”, and “Ringing” to communicate statuses.

Step 3: Configure User Settings for Flexible BLF Control. Allow users to enable or disable BLF monitoring based on their role or preference. Provide options for users to add or remove extensions from their BLF list, allowing for greater flexibility in choosing which colleagues they monitor. Adding sound alerts for changes, such as when a monitored extension starts ringing, can enhance awareness and improve response times.

Step 4: Test and Optimize BLF Functionality. After configuring the SIP client for BLF support, it’s crucial to test and fine-tune the functionality. Monitor how quickly the SIP client reflects status changes and confirm that notifications are accurate. Ensure the SIP client’s interface remains responsive even when handling multiple BLF notifications. Evaluate the visual layout to make sure status indicators are clear and intuitive.

Why Add BLF Support to Your SIP Client?

• Enhanced Call Management. Users can monitor colleagues’ statuses, avoiding disruptions and unnecessary waiting time.
• Better Collaboration and Communication. Teams can quickly see each other’s availability, leading to more effective collaboration.
• Productivity Gains.BLF helps users focus on active calls and efficiently handle call transfers and responses.

Example application

Here is example how it works in Flutter application available on pub.dev.

Conclusion

BLF is a powerful feature for SIP clients, particularly in business and enterprise environments where managing calls efficiently is a priority. By configuring BLF support through your SIP server and implementing subscription and notification handling in your client, you can deliver a more robust, feature-rich software SIP solution. This guide provides a foundational approach to getting started with BLF, ensuring that your users have an intuitive, productive experience when using the software SIP client.
By following these steps, you can add BLF support to your software SIP client, giving users a clearer, more efficient way to manage calls and collaboration across your organization. For additional resources and tools, explore our SIP client solutions at SIPrix.