In the
mid/late 2000s, one corner of the mobile universe
was focused on (some might say obsessed with) the seamless, in-call handover
over a voice session to (or from) Wi-Fi
from (or to) the cellular network.
At the time, this was known as “
fixed-mobileconvergence”. There were companies
trying to solve this from the network angle (
Bridgeport, Outsmart, NewStep, Convergin,…),
others from the enterprise side (DiVitas, Tango, Agito,…). There were even industry associations like
the FMCA and MobileIGNITE. Nearly all of
these companies/approaches are dead and gone.
In the end, there was and continues to be, only one
technology which supports seamless handover,
3GPP GAN (aka UMA) technology.
Then in 2010, T-Mobile re-launched their GAN-based service
under the brand name
Wi-Fi Calling geared towards smartphones – with one
technical difference, Android devices with Wi-Fi Calling did not support
handover.
Outrage ensued!
Well, not really. In
fact there was almost no
public
comment (e.g. Twitter complaints) from T-Mobile’s user base. While
thrilled with the benefits of Wi-FiCalling (specifically coverage), users were ambivalent to handover.
Let me offer some insight as to why this may be the case:
- Dramatically larger
Wi-Fi coverage area. Ironically when a
phone needs to worry about handover, any dip in Wi-Fi signal immediately
becomes cause for concern. The signal
strength threshold for deciding to hand over needs to be sufficiently high so
the call doesn’t drop, resulting in a rather modest range (or radius) from the
Wi-Fi AP. People found their phones
handing out to cellular in corners of the house/office – sometimes in places
where there wasn’t sufficient cellular coverage to ‘catch’ the hand-off. Whoops.
By eliminating handover, the phone is forced to focus on maintaining a
connection to the Wi-Fi signal, thus dramatically increasing the effective
coverage area.
- Differentiated billing.
By inserting a ‘seam’ between Wi-Fi and cellular, T-Mobile was able to
bill differently for calls over Wi-Fi.
In fact, with the new service, domestic calls over Wi-Fi aren’t billed
at all. This enables T-Mobile to be
competitive in locations (like the home) where there is a lot of telecom
competition – from fixed lines to Skype and other Wi-Fi-based calling services
– and maintain a premium for outdoor/cellular service. (A billing benefit also provides incentive
for users to turn on and connect to Wi-Fi, which drives more data offload, but
that’s a different story…)
- More devices supported at a lower cost. It stands to reason that handover is more
complicated than no handover. The
millisecond timing required for handover requires low level of
integration. GAN handover is implemented
at the silicon layer, GAN without handover is implemented in the OS layer. The result is much faster time to market for a
broader range of devices ultimately at a lower cost.
To sum up the state of Wi-Fi/cellular handover today? 3GPP GAN supports it in the specification, it’s
been proven in the field, but it seems that from a commercial perspective, it’s
time has passed.