ONVIF : How to form the device web service address from the IP address of an NVT

My question is about the ONVIF specification. http://www.onvif.org/imwp/download.asp?ContentID=18006 In section 5.10, it says :

A service is a collection of related ports. This specification does not mandate any service naming principles.

Lets say that I have the IP address of an NVT (Network Video Transmitter like an IP camera for example), how do I form the address of the device management web service? This service is the entry point of the whole system.

Thank you.