Re: Re: [OT] Asterisk at home help + XAP integration

[Kevin Hawkins <lists@xxxxxxxxxxxxxxxxx>]

Patrick Lidstone wrote:

>>>        Chris Purves wrote:   I always struggle to understand
the
difference between xap and xpl.

Put very simply, xPL can be thought of as a "light" version of
xAP.

___________________________________________________________________________________

Well - not sure even I as a 'xAP' person would simplify it that far
!      xAP vs xPL is a highly emotive topic   -  inevitable with any
open projects like these. The xPL founders were members of the xAP
specification committee and the split ocurred due to differing
objectives,  technical disagreements and subsequent personality
clashes.  I'm trying not to stir the embers here but as I use both I
thought I might be best placed to impartially address the above , (but
do bear in mind I am xAP allied).

xPL originally took the xAP protocol and adapted it , essentially
reducing the addressing capacity (address length), defining a fixed
number of key message types  and removing some of the more advanced
ideas - the rationale being that xPL was a solution for home HA
enthusiasts rather than 'commercial' and so some of the extra xAP
features weren't needed, xPL could achieve capable solutions for the
developers own HA setups and that was the objective. xPL also stated
they would never change their core protocol to preserve total future
compatability. Also reducing the addressing lengths would enable xPL to
be implemented on smaller processors.  (actually  a xAP device can
recognise any other device using a 4 byte address so both are now very
tight here) .  Hence xPL adopted the 'lite on the wire' tag line . In
practice as smaller devices eg PIC's have become more and more capable
(for very low cost), implementing either protocol on such tiny devices
is very achievable and indeed there are commercial PIC based xAP
products on the market complete with inbuilt Ethernet support (eg the
Netiom). The applications that are available for both xAP and xPL have
tended to be running on desktop machines and using Ethernet too so the
capacity issue goes away.  It is quite desireable though for HA users to
not be dependent on a desktop OS for their home to operate hence the
thrust towards embedded solutions. In relative terms xAP and xPL are
very compact although there are even smaller protocols like CAN SNAP
C-Bus etc, which suit low speed communication eg slow radio / RS232
serial links.

Since the split both xAP and xPL have extended their capabilities.
Typically this is done via adding policy layers on top of the base
protocol. Hence all applications still work but new aspects can be added
like 'discovery' 'configuration' 'plug and play' etc and many
"schema"
have been defined which address concepts rather than devices eg 'whole
house audio'  'on screen display'  'caller id' 'weather' etc. These
schemas are a way of abstracting a  device such that you actually
control a virtual device eg an 'mp3 player' rather than a Rio or a DDAR
or Slimp3 - theoretically then when you swap your Slimp3 for a Netgear
101 player it all continues to works as it did before. It is important
to support these abstract devices rather than implementing a schema for
a specific piece of hardware.  In all these areas the two protocols have
significantly diverged and hence become increasingly incompatible. There
is some ability to 'bridge' between the two but it is not always
achievable.

xAP has looked to include support in the typical commercial HA
applications available today to blend with your existing setup,  whereas
xPL focusses on  their own xPL HAL as a free centralised management /
controller application. xPL also tends to be  a practical solution
created for the needs of it's users whereas xAP has tried to market to ,
and get more involvement and support with the outside world and
commercial developers. For xAP (or xPL) to survive this is important.
xAP has some  glitzy 'user interface' applications too like xAP Desktop,
xAP TouchScreen and xAP Floorplan  (AJAX web based) and also works via
XLobby or MainLobby etc.  xPL has less 'eye candy' here (but that is
being addressed) but has better  support for scripting and supports
'determinators' (sort of templates/wizards) for helping new users create
scripts, it has inbuilt support within xPLHAL for configuration too.
Both xAP and xPL offer free VBscript based control environments.

As such neither solution can I feel be seen as a subset of the other,
xPL has addressed several concepts that xAP hasn't and vica versa.. They
are both based on the same core 'protocol' and the xPL implementation is
tighter here (imposes length restrictions and excludes certain
parameters which arguably could make it easier to implement) but the
important fundamentals are all there and almost anything can be achieved
in either protocol.   I have always been disappointed that both exist,
because it causes confusion, duplication of effort and more importantly
we are both small groups trying to offer solutions - if we were both
pulling in the same direction we would have twice as much impact.
Incidently UPnP (Universal Plug and Play)  is a  similar concept backed
by big industry names , and I think it will become quite ubiquitous in
the next few years. You will be able to buy consumer goods with UPnP
inbuilt , indeed Sonos, Escient, Netgear, Roku etc all offer it already.
However 'easy' or 'lite' it certainly is not, being maybe two orders of
maginitude more 'bulky' than xPL or xAP, which puts  it well outside the
capabilities of most enthusiast programmers and small embedded devices.
This is what is so great about xPL/xAP - for the first time they offer a
way of networking / interacting with all your devices and it is
achievable with relatively little programming aptitude. Neither are yet
truly accessible to every 'end user' - you need a bit of programming
expertise - but not a lot beyond simple VB scripting - and both are
slowly getting better in this regard. I have achieved so many things in
my own home using xAP as it provided the methodology to link it all
together.  The xPL'ers have done likewise.  xAP and xPL enable it.

Kevin



>
>