The GSM Association has completed trials of SIP-I, a protocol that will make it possible to send circuit-switched mobile traffic over core networks based on Internet Protocol.

As mobile networks become more and more IP-based there will still be a need to support devices that use circuit-switched voice networks, according to Mark Hogan, program director at the GSM Association.

In the trial, SIP-I (Session Initiation Protocol with encapsulated ISUP) was used to control the transmission of voice calls from a conventional circuit-switched mobile network on to an IP-based backbone network and then back onto a conventional circuit-switched mobile network, using equipment from Ericsson and Nokia Siemens.

The goal, which was accomplished, was to show interoperability between mobile softswitches from the two vendors. Besides voice, SIP-I can also be used to support video telephony, fax and data traffic.

The trial was hosted by TeliaSonera, using its Finnish and Swedish laboratories. The company sees the need for the protocol both internally and when interconnecting with other operators, according to Claes Nycander, head of common development and vice president at TeliaSonera Mobility Services.

The SIP-I trials are also part of a bigger picture: the GSM Association's IPX (Internetwork Packet Exchange) initiative to develop a private global IP backbone designed to guarantee quality of service when users connected to different operators communicate with each other. The first IPX networks will see the light of day next year, according to Hogan.

Besides TeliaSonera other operators, including France Telecom, T-Mobile, Telefonica and Vodafone, are involved in the development of IPX, according to the GSM Association.