Abstract-.Deployment of 802.11 Wireless LANs is increasingly

on the rise leading to new service scenarios in which users are connected everywhere – everytime. However the IEEE 802.11 standard was designed for short range wireless data transmissions and does not natively provide any support for roaming amongst different access networks. In the more general case, a mobile user should be expected to be able to roam into a visited domain and gain access to the network on the basis of some credentials shared with his home domain or WISP. There are several mechanisms that can be involved in providing such access control and roaming functionality but no any standard has overcome. In this paper1 a new SIP based solution is proposed. SIP-based authentication is provided end-to-end between user-to-network and network-to-network. The proposed solution realizes full proxy-to-proxy authentication at SIP level, enabling dynamic and secure WISP-to-WISP interworking. The proposed solution has been also implemented and successfully tested in a demonstrating testbed. I