[coherence-dev] Send discovery response delayed

[Frank Scholz]

Hi Caleb,

> I’m evaluating Coherence for use as a discovery service on a networked
> vision system for industrial automation.
very interesting!

> I’ve gotten Coherence working in my
> testbed environment (Debian 3.1—Sarge), and the test discovery seems to
> work, but it’s inconsistent. Oftentimes when I start the program for the
> first time, I get something along these lines:
[...]
> 192.168.1.102 is the IP address of the computer I’m using to browse
> available UPnP devices.
you fire up Coherence with a MediaServer backend and you see here
responses upon an M-Search request.

They are delayed as the spec requests it:

http://upnp.org/specs/arch/UPnP-arch-DeviceArchitecture-v1.0.pdf

Page 20, 1.2.3 Discovery: Search: Response


> When I see these messages, it delays the discovery of the Coherence service,
> sometimes for minutes at a time. Occasionally, discovery never occurs until
> I restart Coherence. Does anyone have any idea why that might be? I suspect
> it has to do with the underlying routing mechanisms in Linux, but I don’t
> know exactly how or what.

SSDP announces and M-Search requests are routed via Multicast. It could
be that your router or switch prevents that from proper working.

Sometimes you have to set the multicast route manually

route add -net 239.0.0.0 netmask 255.0.0.0 eth0 (replace with your
                                                 interface)

in case the gateway your default route is pointing to doesn't
send the multicast packages back into the network.

Regards,
Frank