LTE has its own complications, notably because of the current lack of voice support, and the highly fragmented spectrum picture round the world. But it has its advantages too – in particular, operators can use local break-out to deliver the same speeds to roamers as native subscribers.
This was demonstrated earlier in the month by Hong Kong's CSL and its parent, Telstra of Australia. The test used Telstra's GRX (GPRS Roaming Exchange) to transport network signalling, using the Diameter protocol commonly used for LTE, between the two networks. Telstra customers used the CSL network for applications such as HD videoconferencing and video streaming, and the results were compared with existing 3G roaming experiences.
The key difference was that roamers obtained the same speeds as local subscribers because the cellcos were harnessing the local break-out (LBO) capabilities of the LTE standards. Latency was also reduced by 90% compared to 3G roaming.
Using LBO, data traffic is offloaded to the roaming network, rather than being routed first back to the home system, adding to time and cost. In fact, LBO is enabled in GPRS and 3G standards, but has rarely been used for commercial and billing reasons, and sometimes to protect security. However, the volumes of data and signalling seen among LTE users are likely to push operators to use LBO more extensively to reduce network strain.
“With 3G, there is no local break-out because operators want the traffic sent back home to them so that they can charge for it,” CSL's CTO Christian Daigneault told the recent GSMA Mobile Asia conference. “LTE brings signaling into the picture, so you can still charge for data even with local break-out.” He cautioned that the system is currently only in test form, and that there are several issues, mainly surrounding the best way to do signalling, still to be resolved.