Originally Posted by
underfire
it allows for iPad and other smart device integration.
That could be good. It could also be bad. If the system is implemented with a private address space (not connected to the Internet at large), the issues of security and denial of service could be minimized. In addition, using the IP protocol allows for flexibility in integrating with future communications systems that support it. An onboard router could easily select the best available link (IP over VHF, satcom, or air to ground) and switch the link without the using systems having to handle the switch.
But it's that security thing that could bite. An iPad could connect to an isolated onboard network and interrogate ACARS. But not fetch or send e-mail (for example) unless it was logged off and connected to a general purpose Internet link. Even isolated, a compromised device could still interfere with the secure system even if it can't connect to a botnet command and control server (see StuxNet). And I have the feeling that once monies are spent on air to ground IP connectivity, the temptation will be to sell a part of that bandwidth to the passengers for web surfing in flight. And some hand-waving will be done to promise appropriate safety in the system (see 787 FAA special conditions for combined passenger/avionics network busses).