T-Mobile has completed German trials using ADSL to backhaul data from 3G base stations by encapsulating HSDPA data in the IP stream. In doing so it has proven the technology is viable for the next generation of mobile services.

The trials have been running for the last six months and included several hundred base stations, which are traditionally connected over leased-line or microwave connections using ATM.

This might seem an obvious development, but ATM doesn't easily fit down ADSL lines. So specialists RAD Communications provided kit to T-Mobile to encapsulate ATM into IP packets, for transmission over the ADSL and reassembly at the other end.

RAD Communications business development director Gaby Junowicz said the cost of backhaul is the limiting factor in most mobile broadband - so using ADSL makes sense.

Given the traffic is probably IP anyway, from users surfing the web or downloading mail, the multiple-encapsulation seems excessive. However, ATM is mandated by the 3GPP and used for both voice and data traffic, in contrast to data-orientated technologies such as WiMAX deployments which have long been using ADSL for their backhaul.

So fitting base stations with ADSL not only provides cheap routing for data today, but also prepares the network for an IP-based future - for better or worse. ®

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