RE: xAP-485 Bridge Software

[Kevin Hawkins]

Hi Paul,

Great stuff - will be very interested to hear how you get one - I am
VB based (or embedded C even now) but haven't yet stepped up to Stuarts
.Net
stuff. I do hope to do this though eventually.

BTW There is a fantastic upgrade offer for VS.NET 2002 users to move
to 2003 - IIRC it is just £19.95 from Microsoft's site delivered to your
door. Can't grumble at that.. .

UID's : Yes different networks that are bridged / routed in some
form require different network ID's (The first two digits of the UID). As
you are indicating you would like some form of filtering this is especially
important as there is an implicit understanding that whenever the first two
digits are the same then everyone can hear everyone else. The hop value
should also increase by one as you say. The main purpose of the hop value
is
to determine how local a node is to you and also to avoid looping in
networks where a packet could go around forever being forwarded in a loop.
You have to make an arbitrary decision how many hops are valid - most
people
would probably drop if the count exceeded 9 but if you have only 3 networks
then two 'hops' is the most you should see. Cant remember if local hubs
increment hop ?? I am guessing not .

You make a comment in a later post about RS232, RS485 and Ethernet,
as you RS485 is essentially an extension of the RS232 out the PC I take it
your bridge is between Ethernet and the RS232 port ?? Or might you be using
several RS232 ports on one PC. There are some hubs that already support
RS232 but I think they do just that - i.e. all traffic is on both
interfaces
- as you said you may want to filter the traffic down on the serial links
due to bandwidth. We don't have any policy within xAP or indeed any
indicators in packets to 'instruct' re forwarding so your filters will have
to be carefully constructed (as the essential xAP tenet where everyone
hears
everyone else will be compromised). I have thought that maybe we should
have
some form of parameter in a xAP header to indicate 'must bridge' to allow
you to forcibly traverse bridges e.g. for discovery but we haven't as yet.
(However you could trial your own adoption of this if you wish with the
TEST00= names, in the header). As a first guess at what to filter I would
have thought that targeted messages could be blocked (unless they had an
appropriate receiver on the other side of the bridge - and you could
determine this in your software), plus you could filter specific named
sources... and maybe heartbeats - although I would pass all low speed
heartbeats back to the high speed network I think - to allow discovery. I
think you must pass all fully qualified targeted messages back to the low
speed network - and then basic status and control will work correctly :-)
Bear in mind that if you do filter anything that the essential way xAP
operates is compromised but this will be acceptable if implemented
appropriately.


Welcome to xAP btw... any Q's ask away


Kevin



> -----Original Message-----
> From: Paul Barrett
> Sent: 08 November 2003 11:09
> To: <a
href="/group/xAP_developer/post?postID=0qhBm36zxnpyWhyNGjfyMmz8LZY1eBd47KwXAK438A4VJ5AnDDu7DmM6f2q5k4lAobLWSTVIK08mOQtwJaF5Q1O5DhU">xAP_developer@xxxxxxx</a>
> Subject: [xAP_developer] xAP-485 Bridge Software
>
> Hi
>
> Now that I have my xAP-485 Connector which connects to a PC Serial
port
> and
> converts the messages to RS485 for the PIC nodes to process. I am
> looking to
> make the xAPplication (using Stuart's xAPFramework) to bridge the two
> networks.
>
> Could you please give me some advise as to how you would go about
> implementing this. Also should I be incrementing the hop value in the
> header
> of the messages been passed through and how are the UID's handled for
> the
> two networks.
>
> I was looking to get a basic bridge built and then at a later stage
add
> filtering so that I could limit the amount of traffic on the low spec
> network.
>
> I have a working knowledge of Visual Basic and have just started
> working
> with the .NET Framework.
>
> Any Ideas / Commands / Suggestions / etc let me know
>
> Thanks
> Paul
>