Based on the IP technology, the Next Generation Networks (NGN) must overcome the main drawbacks of this technology consisting in the lack of Quality of Service (QoS), security and mobility management. To ensure a service offer in an NGN environment, a protocol for negotiating a service level can be used. However, most of the existing negotiation protocols allow the establishment of a service level which includes only QoS. As for security and mobility, they were often not covered by these negotiations, and therefore managed independently. However, securing a service can cause degradation of the QoS, and the mobility of a user can change the service needs in terms of QoS and security.