The IMS: IP Multimedia Concepts And Services, Second Edition

26.1. Introduction

Many applications enable access to information about a user. This can be in the form of presence information or location information, which reveals personal details about the user's status and whereabouts. The richness of such detailed information is both an extraordinary opportunity for enabling communications as well as a considerable threat to privacy. So, as a result of such applications, there needs to exist a robust and similarly rich system to control the privacy settings of information.

Common Policy [Draft.ietf.geopriv-common-policy] defines an authorization policy markup language that can be used to describe the detailed access rights pertaining to an application. Its origins lie in describing privacy settings that relate to geolocation information but, in the spirit of reuse, Common Policy is also the basis for describing presence authorization policies.

In fact, any application that deals with access to a resource – be it in the form of a subscription, a fetch or an invitation of sorts – can take the basic tools of Common Policy and extend its permission statements to suit the application's special needs.