[Bacnet4linux-developer] BACNet4Linux TimeSync

[Steve K. <sk...@us...>]

Hello Heiko,

You have been added to our developer list.  Welcome!

>>> For this we are using NTP (the Network Time Protocol) and when some 
>>> customer told me about BACNet today, I wanted to find out how a 
>>> BACNet network dealing with time synchronization.
>>
>> You are at the right place!
>>
> That's good :-) I am not quite sure about the market chances we have 
> with such a device. What do you think, could a native BACnet UTC time 
> source be of interest to end users of this system? And, what do you 
> think about the market shares of BACnet in the Building Automation 
> market? I heard of something called LONWorks which looks like a 
> competiting system and cannot really determine at the moment which 
> system is the most wanted in the BA world..

Yes, LON is the competition.  BACnet is the better system :-)

>>> Can you shed some light on this for me? I would like to find out if 
>>> it would make sense to add BACNet support to our time servers which 
>>> then could be used in a BACNet installation. Because they are 
>>> stand-alone appliances, the time synchronization could be taken off 
>>> the shoulders of the workstation and this could add stability and 
>>> (maybe accuracy, too) to the time base of such a network. For this it 
>>> would probably make sense to use your BACNet4Linux and add support 
>>> the four BIBBs I mentioned earlier.
>>
>> It should be trivial to add BACnet support for TimeSync and 
>> UTCTimeSync under Linux using the BACnet4Linux code as a baseline.  In 
>> fact, we already have support for TimeSync in the core code.  You 
>> would probably want to strip out some things, like the HTML and the 
>> query new device code.
>>
> That would make sense. I did not look into your code but I guess it is 
> possible.
> 
>> Also, to be a good BACnet citizen, you need to have a BACnet Device 
>> Object with a unique BACnet ID.  The current code has this using 
>> command line parameters when starting the daemon.
>>
> That's something we have to ask for someone I guess.

It's really just a matter of configuration.  The unique BACnet ID is 
just like an IP address in that it is unique on the LAN and needs to be 
configured in the device.  There is also a special BACnet address that 
acts like a DHCP kind of thing.

If you are going forward to making a BACnet device, you would also get a 
unique Vendor ID, which is free.  A link to the request form is at:
http://www.bacnet.org/VendorID/

>> The BACnet Ethernet layer is working well, but the BACnet/IP layers 
>> needs a little attention.
>>
> Can you specify "needs a little attention" ? :)

With the current code base, BACnet/IP seems to send out messages, but I 
couldn't get it to receive any messages (when I disable the BACnet 
Ethernet layer).  Coleman swears that it used to work, and also has 
given me his latest code which he says works, but I haven't taken the 
time to compare the two to find out why the current BACnet4Linux 
BACnet/IP is not receiving (or possibly not sending with the right 
network layer data).

>> The UTCTimeSync would need to be added, but it should be trivial as it 
>> would mostly be a copy/paste from the TimeSync function.
>>
>> Most of the time the TimeSync is sent out as a global or local 
>> broadcast, but occasionally it is sent out as unicast to a specific 
>> device.  Our current code only has the broadcast.  There is a time 
>> sync reception list in the Device Object, which can contain a 
>> broadcast address or the address of a specific device, and can be 
>> writeable.  I don't think we have that list in our current code.
>>
> How does this work? A "-B" device tells the "-A" device that it wants to 
> receive unicast time synchronization messages at a specific interval? Or 
> on request? Or is the -A device responsible for querying the network and 
> finding devices which need TS messages in unicast form?

Usually the specific interval is a configuration issue and doesn't come 
from an A or B side device.  But it is possible to have a writeable 
recipient list where the B side device requests to be added to the list. 
  In the Lithonia Lighting BACnet device, I have the list configured to 
send out local or global broadcast of time sync at a specific interval 
if it is enabled.  But since that list is not writeable, I don't even 
support the recipient list property of the device object.

Coleman has been doing some work with the 
time-synchronization-recipients property lately.  Perhaps he can chime in.

Best Regards,

Steve
-- 
http://www.kargs.net/