From an old Post regarding DMS switches, and yes a DMS 500 supports all, or most all protocols, like the 250
1 U459PRI - 5ESS custom protocol. This will work for a basic PRI interface, but does not have the fancy features a 5ESS central office has for the 5ESS custom.
2 N449PRI - System 85 protocol
3 U449PRI - 4ESS custom protocol
5 NTNAPRI - DMS custom protocol. This is not a true NI-1 protocol since the maintenance messages use an older protocol discriminator information element.
6 NIPRI - This is Nortel's NI-2 protocol.
The DMS 100 switch can use all of the above. The DMS-250 can use all except the NIPRI protocol.
If you require the delivery of a calling name, then the the NI-2 (NIPRI) protocol must be used. As long as the PBX is fully NI-2 compliant, then there should not be any problems with NI-2. Fully NI-2 compliant means the protocol discriminator information element in the maintenance (service) message is set to 0000 0011. This can be tested at turnup by having the LEC person do a PMDEBUG to watch the messages. Then have the LEC busy then return to service one b channel. The LEC person can tell if the PBX is responding properly with the PMDEBUG tool....asuuming they know how to read it.
Adn yes the field L1FLAG in table TRKSGRP must be set to yes (Y). L1FLAG is a layer 1 flag.