SECURITY FEATURES OF SIP

...  Proxy Server – Provides services like authentication,authorization,routing etc  Redirect Server – Informs to client about next server hop  Registrar Server – Registers user location information ...

Should SIP be modified for per call billing?

... SIP is not just for voice, we don’t need to mimic the POTS behavior. Billing network resource is better handled by network protocols, RSVP. ...