Don't quote me (and don't know if it'll help to much) but I think if I remember correctly it has port 1720 is some kind of VoIP, maybe that was on a Windows system.
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OK had me thinking if I remembered correctly and I found the following information from http://www.voipvoice.com/faq.html (hope it's OK to post the link ) - it's the 3rd last question asked and might provide you with a little more information.

For H.323 (MS Netmeeting etc…)

* TCP port 1720 (H.225 call signalling for hosts)
* TCP ports 11000 to 65535 (H.245 capability exchange)
* UDP ports 16384 to 32767 RTP audio stream)

For H.323 (Callserve)

* UDP port 1719 (Callserve signalling)
* TCP port 1720 (Callserve signalling)
* UDP ports 5000 to 65535 (RTP audio stream)