Last week I attended 1st UBI Summer School in Oulu, Finland. It was organized as a part of Ubiquitous Oulu Project. Its main topic was ubiquitous and urban computing. The School comprised of six workshops. I took part in workshop E - “IP-based sensor networks” by Zach Shelby. It was the most geeky and technical workshop of all - other workshops were much more human and application oriented.
The main focus of the IP-based WSN workshop wasn’t 6LoWPAN (as one could expect), but CoAP - Constrained Application Protocol. CoAP is an application protocol (ISO OSI layer 7) designed for WSN operation - it’s RESTful, it features subscribe/notify mechanism and service discovery and it has a very small header. HTTP has neither of these. CoAP is still only an IETF draft, but taking into consideration the absence of open standards in the area it might really catch on.
I’ve got to admit that two weeks ago I didn’t know what REST really was, but I like the RESTful approach very much - it’s not based on some complicated messages, but rather on availability and state of resources. I find this philosophy coherent with Unix/Linux systems, where every device, or process is represented by a file in a system tree.
Other features of CoAP: subscription and discovery are even more interesting. Subscription is a must for communication with WSN nodes that are asleep most of the time. Service discovery makes application deployment for such nodes much easier - and it also makes maintenance and network expansion a lot simpler (maybe someday Google will start to index your WSN nodes too :) ).
According to other participants of the UBI school the REST way is the only way for WSN (except one guy who did research into SOAP and EXI, but stupid airlines lost his luggage, and he was forced to leave the school before he could show us the results). But some of the people weren’t convinced that new protocol is really necessary - people will still use old and clumsy (but more diverse and supported) protocols, and not a specialized thing like CoAP. Being more of a hardware guy I still can’t present my own opinion in the area. Time will tell.