RE: xAP xPL EIB C-BUS X10 - choice overload!

["Ian Lowe" <ian@xxxxxxxxxxxxxxxxxx>]

-----Original Message-----
From: matt_miles_uk [mailto:m_miles@xxxxxxx]=20
>Hey all,
>
>Stupid question I know (well, it's me asking it so...).  What is the=20
>difference between xAP and xPL?=20=20

=3D=3D=3D=3D=3DDISCLAIMER=3D=3D=3D=3D=3D=3D
I'm part of the xPL Project - this is *my opinion* of the differences
betwe=
en xAP and xPL. It may also be based on an out of date view of xAP, as the
=
protocol seems to still be changing. I am 110% certain that the guys
involv=
ed in xAP will not agree with this interpretation of things, but I'm sure
s=
omeone will be along presently to present the other viewpoint.

I'm intending to make a single post, not start a flamb=E9 war, so please
xA=
P guys, don't do a "point by point reasons why you suck" reply ;)
=3D=3D=3D=3D=3DDISCLAIMER=3D=3D=3D=3D=3D=3D

xPL and xAP have common roots - xAP initially developed from a bunch of
dis=
cussions here in ukha_d about a common protocol for HA purposes.=20

At the very start, xAP was intended as a protocol that was viewed as
connec=
tionless, broadcast based protocol that would essentially have everything
s=
imply announce it's status. The usefulness comes about when other devices
i=
nterpret this information in an intelligent way - acting on the status of
o=
ther devices, displaying info etc.

xAP went through a few rapid changes, and a lot of serious discussion took
=
place about the benefits of certain approaches - a committee formed up to
d=
iscuss these options. Somewhere along the way, people started talking
about=
using the protocol less as a pure status broadcast environment, and more i=
n a control sense.

After a *lot* of discussion/argument/debate, Tony Tofts and I droppedd
from=
the xAP committee. xPL started life as our own "private" version
of the xA=
P concept, and went public as we became more convinced that the xPL
approac=
h was technically superior. (note: our opinion)

The conceptual differences are small, but significant -=20

In the xAP environment, all messages are created equal - essentially
tellin=
g the world about me and leaving them free to do what they will with that
i=
nfo.

In the xPL environment, we have Status, Trigger and Command messages -
stat=
us for xap style status info, triggers for an actionable event, like
flicki=
ng a switch, pressing a button, an IR event, that sort of thing and
command=
s for controlling devices.

>I know it sounds silly but most of the details on xAP/PL are WAY=20
>over my head - even though I think they will do what I want! :)

To be honest, all of the big technical reasons for xPL and xAP being
differ=
ent are down to the low level nuts and bolts of protocol design - issues
su=
ch as the purpose of headers and message bodies.

Anyways, this is mostly ancient history now - The main thing I guess is
"Wh=
at can I use for my specific needs". xPLHal is a pretty solid looking
engin=
e for HA control - there is, however, a specific xPL list so I'd suggest
jo=
ining that (ukha_xpl-subscribe@xxxxxxx ) rather than clogging the m=
ain list with "howto" info.

Ian.



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