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I have experienced this frequently on a SX2000 with analog (ground start) trunks in several per cabinets. I have heard that it also occurs on the 3300, with analog trunks (likely loop start) as well as with PRIs.
The problem likely occurs more often when a customer transfers a call outside the switch (using a 2nd trunk) and for some reason the trunks do not get release. The CO is DMS.
Besides checking for COD (Central Office Disconnect) / Disconnect Supervision at the CO (on the DMS), are there other things to check?
Normally we discourage customers from making outbound transfers. however, some times they insist (or have been told it will work by sales) so we have to put up with it.
In my experience, with the analog trunks, I would just put the butt set on each trunk, and if I heard dead air, pull the jumpers off, and you would always see two trunk lights go out. This is why I assume that it happens during outside transfers.
Any thoughts??