Both through comments on the blog and on the forums I usually participate in LinkedIn I got quite a few feedback and insights on the topic of handover between a cellular technology and also on the different alternatives to femtocells.

As I mentioned previously, Skype and other VoIP calling systems can be a – bad – alternative to femtocells. I wouldn’t even consider it an alternative unless it’s during the time it takes for you to have time to go downtown to your provider store to purchase a femtocell. Another better alternative would be Google Voice – yes, you guessed right, I love Google Voice – , that allows you to have your own “virtual” cell phone number to which forward your incoming/outcoming phone calls when under wifi coverage. Finally, I mentioned as a strong competitor for femtocells the new standards and technologies that allow seamless handover between a cellular networg – say 3gPP, UMTS, LTE… – to wifi and viceversa. The only problem with this alternative, that makes it weak in front of femtocells, is – and I am quoting a colleague from LinkedIn here –

… the issue from a handset side is that for seamless operation it requires special modifications to the protocol stack on a 3G handset (in essence to make a WiFi access point appear like an attractive cell to reselect to). On the network side for 2G there are no new interfaces to the CN needed, increasing its attractiveness there, whilst for 3G there are a number of new interfaces needed to be supported by the Core.

So, in other words, for this seamless handover to be possible, changes in the handsets are required which means that you need a new phone. And here is where I drop the line: in my opinion there is currently not known good alternatives to femtocells. Apart from QoS, one of the attractions of femtocells is that they work with standard, unmodified, handsets.

Now, back to the topic of seamless handover between a cellular technology and wifi, many of you have brought to my attention a standard called UMA or GAN – Generic Access Network – for 3GPP, implemented in the US by T-Mobile and in some places in Europe by Orange. These specifications define how a mobile phone can get mobile service over any broadband IP network – with or without Wi-Fi -.

Looking around a bit I found the actual standard from ETSI for GAN – it is free to register to ETSI and all the standards are available in pdf for download – and an interesting presentation from the Norsk UMTS Forum in 2007 describing UMA/GAN for GSM and UMTS.