We have a new Xerox 6121MFPN laser printer in the office. We use network printing, so this printer is connected to a Linksys WAG320N router (to port 1, if it matters).
When we do not print anything for a while, in 5 minutes the printer goes to sleep. The 5 minutes is a config parameter of the printer.
The problem is that even after we do not print anything for a long while (and no incoming faxes or scan jobs, etc), the printer wakes up every 15 minutes, warms up, waits for 5 minutes (since there's no print job) then goes back to sleep.
We can not figure out why it is waking up, it is quite annoying. If I disconnect the Ethernet cable to the printer, it no longer wakes up. If I connect the network cable but turn off the WAG320N, it no longer wakes up. My guess is that the printer is waking up due to a computer doing some sort of status check or query, but I can not be sure.
All our machines are Win 7 machines, connected wirelessly to the same router.
Update-1 (edit): I added a firewall rule to block all requests from my computer to the printer and make a log of the requests. Turns out, at every HH:MM:55, HH:MM:05 and HH:MM:15, there is a UDP packet transmitted to the printer, from source port 60732 to destination port 161.
And, approximately every 20 minutes, there is a TCP packet from port 60691 to port 139 of the printer, followed by 2 UDP packets from port 137 of the PC to port 137 of the printer. Any ideas of what these might be?