Agreed, inter-pbx trunks, E&M for example provide answer and disconnect supervision, Consta on the other hand is piggy-backing Nortel (analogue extension lines) to Mitel 3300 LS (loop start) trunks. Not ideal, but we’ve all done it.
Trunk lock-up is occurring because the Mitel LS trunk is expecting a line break to indicate the (Nortel) far-end has hung-up. Outside of North America the Central Office (public telephone exchange) typically sends a disconnect “busy tone” as the clear down signal rather than a line break. Line reversal is a CO Descriptor option.
You may have noticed a Class of Service option to provide this on ONS ports introduced recently. Guessing this was introduced for European based applications. Google busy tone disconnect, take a look at the Max Terminator, used this way back with the SX2K.
Since about Release 8/9 LS trunks on the CX/CXi/MXe/ASU support tone disconnect, you will find CO Tone Disconnection in ESM and a bunch of tone/frequency settings (primarily for Latin America) hidden away in the Product Support (software) directory. In practice, unless you have a friendly service provider or handy data sheet you need to record the tone, analyse it, configure CO Tone Disconnect and reboot. It does work!
