I was wondering what is the effect of sending continuos SIP registrations in the smartphones battery duration, to compare that solution (SIP register and proxy) with an Apple Push Notification alternative.
From my point of view, SIP registrations should be very expensive specially in NAT environments where typical SIP REGISTER expiration time is in the 30secs-2mins range to avoid expiration of mappings in the routers handling the NAT.
I did a quick test with a new iPhone 4 (without any background application) and the battery level at 100%.
12 hours without SIP registrations -> battery level 98%
12 hours with SIP registrations every 60 secs-> battery level 70%
Note: The SIP registrar was an asterisk with peers qualifying activated. Disabling that feature should reduce a bit the battery consumption.
The tests are done using Wifi connectivity (in fact the iPhone is running without SIM).
I repeated the tests during 24 hours and disabling the asterisk peer qualifying:
24 hours without SIP registrations -> battery level 99%
24 hours with SIP registrations every 60 secs -> battery level 40%