[Tinyos Core WG] Fwd: [Tinyos-devel] message_t

[Philip Levis]

On May 6, 2009, at 7:22 AM, culler wrote:

> I think that it is time we allowed ourselves more room to maneuver.  
> The active message concept was important to establish how  
> communication and computation need to be efficiently integrated.   
> The key elements of that are (i) event-driven dispatch on receipt  
> and when the transmit buffer can be reclaimed, (ii) handler  
> namespace, and (iii) not requiring arbitrary buffering in the  
> communication subsystem.  The traditional sockets API and parallel  
> program message passing interface, e.g., MPI, do not have these  
> properties.  However, an event driven UDP interface can be created  
> that does.  It means that Port serves as the AM handler ID.  It also  
> means that we think about encapsulation from the beginning -  
> transport / routing / link.  I realize that the message_t discussion  
> can be had without taking a position that it is time to eliminate AM  
> in favor of something that looks like sockets, but I think that it  
> would serve us well to make that step and gain some focus.  Things  
> like group_id were hacks we through in for the first TinyOS bootcamp  
> in 2001.  It was not well architected.  Ports is a sufficiently  
> large name space for tiny devices.

AM ids are a link-layer dispatch mechanism for different layer 3  
protocols. UDP provides transport layer dispatch for different  
presentation, session, and application layer protocols. The former  
does not preclude the latter, as blip demonstrates. As a lot of TinyOS  
users want to operate at the link layer, eliminating access to it is  
problematic. The term "port," after all, comes from "transport."

What the UDP interfaces look like is a wholly different question, and  
something which net2 covers. Hammering out those interfaces so they  
are simple and effective, such that systems and protocols migrate to  
using them, is a more effective way to promote their use than removing  
access to the link layer.

Phil