Mike Puchol

Wi-Fi Direct explained for those who think it is ad-hoc mode revisited

While it does contain most of the ad-hoc stack, the recently announced Wi-Fi Direct standard is actually an attempt to become more like Bluetooth. Ever since Wi-Fi was invented, ad-hoc mode allowed two or more adapters to form a peer-to-peer network without an access point (AP) running the show. In certain scenarios, there would be connectivity problems when adapters were not configured for automatic IP assignment in the auto-discovery range, or had static IPs setup. Saving these, the user would then have to make sure his operating system had enabled the appropriate sharing protocols so that meaningful things could happen, such as sending files from one machine to the other.

Ever since Bluetooth was invented, it provided a communications stack, and a protocol stack, which encompassed a growing number of profiles. An application only had to talk to the right profile in order to establish communication with another Bluetooth device supporting the same profile, for example, serial port, audio gateway or FTP. During device discovery, a Bluetooth device would query the other about its available profiles, and would then choose the right one as needed. As a practical and recent example, the iPhone initially supported the handset profile, which provides very rudimentary headset functionality and leaves out things like address book access. Over time, the iPhone has been upgraded with more profiles, some as complex as A2DP which allows highish-definition audio to be sent to stereo headphones or speakers. I say “highish” as it uses an audio bandwidth of 16kHz, way below the normal audio response of a set of headphones, leading to a noticeable decrease in quality. But I digress.

In my view, the press release was very badly worded, making it appear as a re-branding of old-time ad-hoc, when it really implies adding a number of protocol stacks and profiles to the standard ad-hoc mode. It is also an attempt to take Bluetooth head-on, with the argument that Wi-Fi is a gateway to a bigger number of services – Bluetooth DSL router, anyone? no? I rest my case. Having such a set of profiles would obviate the need to have Bluetooth chipsets on top of Wi-Fi, which are always an added cost and source of radio interference. We would then have to see how audio accessories cope with this, but then again, I’ve not seen many people carrying Bluetooth headsets around, while car kits can accommodate a Wi-Fi chipset thanks to their board space and bigger battery.