HKT, Hong Kong’s largest operator, and Chinese equipment vendor Huawei said they completed the industry’s first home subscriber server (HSS)/VoLTE cutover, to prepare for the integration of the HKT and CSL mobile networks into a single core network.

HKT acquired CSL from Telstra for $2.4 billion in May 2014.

HKT said the cutover was the most difficult part of the integration as a live, dynamic database of several million CSL subscribers had to be transferred from the HSS of the original vendor to that of HKT’s existing partner Huawei.

Wang Yongde, Huawei’s VP of core networks, said the migration project required the convergence of packet switched, circuit switched and IP multimedia subsystem (IMS) domains. “The huge amount of data involved and the tight timeframe made network migration extremely challenging,” he added.

The integration, which HKT expects to complete this year, will allow it to offer advanced services and more extensive roaming coverage, the operator said in a statement.