Serial Infrared Physical Layer Specification, Version 1.4, Infrared Data Association,30 th May 2001.
http://en.wikipedia.org/wiki/Infrared_Data_Association Follow the linux links for chipsets implementing IRDA phy
Interface PDA with http://www.clarinetsys.com/en/pdf/EthIR_LAN_ESB5001_Data_Sheet_v1.7.pdf IRDA LAN Ethernet. The concept is obvious but was patented by Clarinet Systems which is why Altech SA can't commercialize such an innovation to us at a reasonable price. The concept can be extended to create upto 200m range(Longer?) IRDA LAN Ethernet hotspots by using the RonjaChips transmitter design , replacing their Lumileds LED with a RCLED - FiberLed. Hack the patent http://www.patentstorm.us/applications/20050010694/fulltext.html and resell via a FrontingCompany. Type Clarinet Systems in the Assignee box of http://www.patentstorm.us/search/advanced.html to obtain all the patents assigned to Clarinet.
The advantage of IRDA is the extremely low cost of around $3/chip(plus peripherals). A Ronja solution is around $150.