Core Session and Message Handling

There are several critical classes and interfaces. The SipServlet class is central to application logic, acting as the base class for all SIP servlets and defining methods for processing requests and responses. The SipServletMessage interface, along with its specialized subinterfaces SipServletRequest and SipServletResponse, provides a comprehensive framework for interacting with SIP messages, accessing headers, and managing message content. 

Session handling is another cornerstone of the API. The SipSession interface represents individual SIP dialogs, allowing developers to manage dialog-specific attributes and state transitions, while the SipApplicationSession interface facilitates broader application-level session management, coordinating interactions that span multiple dialogs or protocols.