Routing and Proxying

Routing and proxying are fundamental components of SIP communication, enabling the delivery of SIP messages between endpoints. In SIP servlet applications, these mechanisms are critical for managing the flow of requests and responses, directing them appropriately based on application logic, user preferences, or network policies.

Routing:

Routing determines the path a SIP request should take to reach its intended destination. It involves analyzing the request, inspecting headers like Route or Record-Route, and applying logic to decide the next hop. SIP servlets often rely on the SipApplicationRouter to implement custom routing strategies based on application-specific requirements, such as user-defined rules, geographic location, or service policies.

Proxying:

Proxying involves forwarding SIP messages on behalf of a client. A SIP proxy server can act as an intermediary, relaying requests to the appropriate endpoint or proxying responses back to the original sender. SIP servlets use the Proxy and ProxyBranch interfaces to manage and control the proxying process. Proxying supports features like:

• Forking: Simultaneously sending a request to multiple destinations (e.g., parallel ringing).
• Stateful Proxying: Maintaining transaction state to ensure reliability and proper message delivery.
• Rewriting: Modifying SIP headers to manage routing or comply with application logic.

These mechanisms enable SIP applications to implement advanced features like call routing, load balancing, and failover, as well as to integrate with other systems like presence servers, registrars, or external databases. Together, routing and proxying provide the tools needed for flexible and scalable SIP communication.