ASTRI

Mobile voice communication has become an indispensable part of our daily lives. With the advances in communication technology, other than the designated cellular wireless network, mobile phones can now tap into other access networks such as Wi-Fi. This opens up a huge opportunity for the mobile device to link up with the Internet and to host a new generation of IPbased applications. In particular, VoIP (Voice-over- IP) is a worthy alternative to the conventional mobile voice communication. Mobile device users then expect the voice session can be switched easily between Wi-Fi and cellular networks. However, cellular network still makes use of the circuit-switched transport for the voice session. This type of transport is inherently not compatible with the IP transport used by the Wi-Fi network and the Internet. ASTRI Mobility solution solves the challenge of transitioning a voice session from the IP domain over the Wi-Fi network to the circuit-switched domain over cellular network.

The ASTRI Mobility solution is designed to co-exist harmoniously with other subsystems of the mobile device. It offers two modes of operation:

i)	manual transition initiated by the user,
ii)	automatic transition based on the user preference and access network conditions.

Even though the ASTRI Mobility solution primarily addresses the Wi-Fi and cellular access networks, it can be extended to accommodate other access networks. For the IP domain, it can support WiMAX, 3G/IMS, and Ethernet. For circuit-switch-based network, in addition to the cellular mode such as GSM/WCDMA/CDMA2000/TD-SCDMA, it can handle DECT/proprietary indoor cordless mode, analog and digital (ISDN) fixed telephone.

The ASTRI Mobility solution consists of the following functional blocks:

i)	"Mobility Module": This module handles the voice session transition from the IP network to the circuit-switch-based network. Based on the access network information collected from the "IP Network Management Module" and the "Cellular Adaptor" together with the user preference, it decides when to initiate the switch. The transition is facilitated by both "VoIP/SIP Module" and "Cellular Adaptor".
ii)	"VoIP/SIP Module": This module implements the SIP-based VoIP client side features and the SIP-based enhancement for the mobility operation.
iii)	"IP Network Management module": This module consolidates the management of all the IP-based access networks. For example, for the Wi-Fi access network, the tasks include network discovery, association and authentication.
iv)	"Cellular Adaptor": This is the software component for accessing and managing the circuit-switch-based cellular access network. Instead of re-implementing all the management functionalities, it is only necessary to instrument thin 'plug-in' software layer to realize selected transactions with the existing cellular related software components.
v)	“Audio Adaptor": For a convergent communication device, there will be some diversified needs for the audio resource. This module resolves the resource contention between different applications. It also facilitates the audio path switching between the VoIP and cellular applications to ensure a consistent user experience.