[nSLUG] Linux, HDLC and a traffic variable message sign

Rich budman85 at eastlink.ca
Tue Jul 25 15:08:55 ADT 2006


On Tue, 2006-07-25 at 08:59 -0300, Scott Syms wrote:
> Hi, folks-
> 
> I'm stumped with an interface issue and hoped to draw on the awesome
> collected wisdom of the group.
> 
> I'm trying to talk to a variable message sign that uses NTCIP, a
> protocol that leverages HDLC and SNMP developed as a standard to
> interface to traffic field devices. 
> 
> My first inclination was to attempt a synchonous PPP connection, but
> nada.  I looked at IPPP, which seemed to indicate that you could use a
> standard serial port as a device, but it complained that there was no
> ippp0 device. 
> 
Need to load the module.  I think a few kernels back, in the 2.4 series,
the ppp process was broken into two separate modules.  There will always
be the generic module, then the module to handle the synch type

# assume 2.4 or newer

#  # This module is for PPP support:
#  /sbin/modprobe ppp_generic

Then load one of these depending on the synch type

standard dialup modems
#  # This PPP plugin supports PPP over serial lines:
#  /sbin/modprobe ppp_async

synch lines like 56K/T1 anything leased (load this one)

#  # Use this plugin instead for HDLC 
#  (used for high-speed leased lines like T1/E1)
#  # /sbin/modprobe ppp_synctty

that should get you rolling.


> I'm assuming that since I'm connected to the sign on the serial
> interface, it should just be a matter of creating a PPP-like interface
> and assigning IP's to the remote/local ends of the interface.  Then I
> talk to the remote interface with the vendor-supplied MIB. 
> 
> The sign vendor supplies a windows gui control program written in .NET
> (I can't get the source) so I know that the protocol works under
> regular serial hardware.  
> 
> Any ideas?
> 
> tks
> 
> Scott Syms
>  
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-- 
Rich <budman85 at eastlink.ca>

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