Timers and Scheduling

Timers and scheduling are integral to SIP application development, enabling reliable handling of time-dependent operations such as managing timeouts, resending SIP messages, or cleaning up inactive sessions. These capabilities are important in SIP, where adherence to timing protocols, such as those outlined in RFC 4028 for session timers, is critical for maintaining session integrity and service reliability.

The SIP Servlet API provides a timer service, a container-managed feature that allows applications to schedule timers and receive notifications upon their expiration. Timers are treated as managed resources by the container, and for enhanced reliability, they can be made persistent—stored alongside session data to survive server restarts.

Timers can be configured to execute either as a one-time event after a specified delay or at repeating intervals, making them adaptable to various application scenarios. The timer functionality in the SIP Servlet API revolves around three key interfaces:

• TimerService: Used to create and manage timers.
• ServletTimer: Represents individual timers and provides access to details such as expiration time.
• TimerListener: A callback interface implemented by the application, invoked by the container when a timer expires.

These tools enable developers to implement scheduling in their SIP applications, ensuring efficient management of timeouts, retries, and other periodic tasks.