More super-fast 3G mysteries revealed

JUDGING FROM our mailbag, there's obviously great interest in the technology behind super-fast 3G (HSDPA). In particular with regard to running Skype over HSDPA. The answer is, yes, it does work well.

This email is fairly typical: "I work for a large corporation and have just sat through a presentation about HSDPA. Apparently, it's not supposed to be able to do VoIP because it's got latency problems.

In your story you said, "the BBC (British Broadcasting Corporation) became the first commercial user of Manx Telecom's super-fast 3G network…using Skype." (See BBC is accidentally first super-fast 3Guser).

So can you tell us a little bit more about how Skype worked? You wouldn't have happened to check ping times would you?"

Actually reduced end to end delay (latency) was one of HSDPA's advantages which O2's CTO, Dave Williams, highlighted. His graph showed HSDPA suffering delays of around one quarter of those experienced with GPRS. And you can run Skype over GPRS.

Operators like O2 aren't interested in promoting Skype/VoIP because their 3G networks are built to handle voice calls very efficiently - each one consuming 12 Kbit/s whereas a single user's Skype session might consume 64 Kbit/s.

So Skype does work and Manx Telecom videoed the Beeb using Skype efficiently.

More intriguing is the problem of 'network backhaul speeds'. The Internet connexion to a single HSDPA 3G base station is running at 8 Mbit/s and Williams admitted that the network is architected to support 70 users per base station. One journo pointed out that means each user gets 117 Kbit/s.

But real life doesn't work like that. You're not likely to get 70 users simultaneously trying to stream video. And even if you did - say with everyone trying to watch a TV news clip - the network operator can throttle back data users so the whole network doesn't fall over.

As Dave Williams admitted, by around 2009 operators are going to have to think about using Gigabit Ethernet for their backbone networks.

Manx Telecom is supplying Sierra Wireless' PC card so users could run a Skype connexion via that route. The INQ suspects that O2 will eventually offer a HSPDA card from Novatel as well. Williams claimed that at least two major laptop manufacturers would offer models with HSDPA built in.

That would imply the likes of Sony, IBM and Toshiba supplying such laptops but the INQ remembers Panasonic producing a laptop with a built-in GSM modem for Vodafone.

Finally, with regard to Ping times - Nope, the INQ didn't run any Ping tests. But rival hack Rupert Goodwins captured some speed data. See here. He saw a burst speed of around 1.3 Mbit/s as Manx was claiming. µ