PHY layer ethernet
See SoftwareDefinedRadio for Ethernet phy layer development by Ettus.
optical switching networks http://www.amazon.com/Optical-Switching-Networks/dp/0521868009/ref=pd_sim_b_1
Passive optical network
Serial latency: how many devices? Up to 32 devices in a daisy-chain can be sensibly deployed in an industrial setting. Theoretically there could be dozens of device deployed in a chain through use of store and forward technology ¨C used by both daisy-chain devices and standard Ethernet switches. This assures that each packet is checked for accuracy before being forwarded on the network. The cost of that accuracy is 20-40¦Ìs latency for the average automation protocol message passing through each device. This means that the total time it takes for a message to travel from the first device in a chain of 32 to the last device would be less than 1.3ms absolute worst case.
http://www.hardforum.com/showthread.php?p=1033085451 Hardware forum
http://www.freepatentsonline.com/6240082.html routers for daisy chained components
http://www.windowsbbs.com/hardware/32244-can-routers-daisy-chained.html 4 switches will result in latency
* http://www.tomshardware.com/forum/19527-42-switch-question-daisy-chain-home * comp.dcom.lans.ethernet