Jan Janak jan@iptel.org Jiri Kuthan jiri@iptel.org Bogdan Iancu Bogdan.Iancu@fokus.fraunhofer.de 2001 2002 FhG FOKUS $Revision$ $Date$ The document describes the SIP Express Router internals and algorithms. It describes overall server architecture, request processing, configuration, memory management, interprocess locking, module interface and selected modules in detail. The document is intended mainly for module developers wishing to implement a new module for the server. Other people like developers of SIP related software or students might be interested too.