Re: Re: New to the list- intro

["Ake Hedman" <akhe@xxxxxxxxxxxxx>]

Hi Ian,

the good thing with an XML format is that there are

- Knowledge about it.
- A lot (and I mean a lot) of tools.
- It's a standard.

The last point is essential. It is the most important factor for the
success of every HA solution. X10 is stupid but in some way a defacto
standard. We use it because we can get stuff from others that use it and
the units work together. VSCP will never be a "standard" or a
well adopted
technology. Its just a fun way to make tiny things interact. Someone will
eventually come up with the killer protocol and we will all go for it. xpl
in true XML may well have been that thing IMHO. OK, it's a bit
"politics"
involved in choosing XML but it is so well accepted.  Still, use of
balanced <...> ,,, </...> pares and the XML header is all that
is needed
to make people go for it.

As you say VSCP have a very tiny frame being CAN oriented which originally
was designed for cars. Automotive use and automation use includes loading
codes into devices, real time control with plenty of data. And its all
rock solid. It is perfectly possible (and it is often used) to send large
amount of data using multiple frames.

Still the small frame size can be a problem for some higher level stuff
use. I was looking at xAP to solve this but I did not like the format. I
will take a look at xap. I was not aware of its existence. It can well be
the solution I am looking for the higher levels.

I introduced VSCP level 2 as a solution for this. It is intended for
TCP/IP and can carry much higher payloads. I will probably add a xAP class
on this level that can carry xAP packets. Level 2 events are defined by a
16-bit header where the first 256 classes are the same as for Level 1.

For interoperability what you see on a node is an event with a specific
class and type. If you are interested in events of this class abd type you
know the format of it. You can react on it. Send a new VSCP message or
what ever.

Some examples

- A button on an X10 control is pressed.
- The code is broadcasted as a VSCP message with class=201 and the data.
- A node that is interested in this class receive it. Turn on a relay.

- A temperature/humidity node send out a temperature measurement and a
humidity measurement once a second.
- A node interested in this can receive it. Log it to a database.
- Another node can sound an alarm if the temperature is to low.
- Another can put the temperature out on an LCD display.

- For multi packet

- A phoe rings.
- Several VSCP packet are transmitted with line, number info.
- A node receives it and mute the in-house audio.
- A PC receives it and look the phone number up in a database sending out
a level 2 VSCB event with extended information.

The thought is that a node interested in a message know the format of it.

I can write a lot about this but I think the spec. says it all. If someone
is interested there is a list available at http://can.sourceforge.net

Regards


On Wed, 26 May 2004 09:25:51 +0100, Ian Lowe <ian@xxxxxxx>
wrote:

>
> Welcome to the list Ake,
>
> I'm one of the "splitters" (for all you monty python fans)
;) from the
> xPL Project, discussion group at:
> http://groups.yahoo.com/group/ukha_xpl/
>
> We share some of your concerns about parsing complex xAP messages, and
a
> few of the differences between the protocols come from that desire for
a
> simpler way of doing things - (like much more fixed header structures
> for example).
>
> That being said, I actually agree with Patrick - "proper"
XML would not,
> I feel, have been the best choice for an HA protocol - we also make
> extensive use of XML in the tools supporting xPL, but the message
format
> itself is not XML.
>
> The distributed decision making you describe is very much xAP's
> philosophy (unless the BCS Mapper is a move to centralised decision
> making - Mark?) whilst smaller, more tightly regulated messages is
> ours...
>
> I'd *normally* suggest looking at xPL but in this case, I think you
are
> a long way down the design road - and from a quick look at the VSCP,
you
> are not kidding when you say Very Simple!!
>
> I'm actually wondering more how you can achieve the degree of
> interoperability that xPL/xAP are looking for with only 8 bytes of
data
> in a packet? Are the actual messages delivered across multiple
packets?
>
> Ian.
>
>
>
>
>
>
>
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--
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Ake Hedman (YAP - Yet Another Programmer)
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