jochem

I have been sitting on this one all day now, maybe someone here can help me. I've got a Panasonic D816 here with the KX-TD286 ISDN Card. I'm using 4 of the ISDN ports for the external lines and i'm trying now to use the other 2 ports as internal ISDN ports.
I've connected a Teles Zephyr ISDN codec (audio device used at radio stations to transmit audio over ISDN) to a internal ISDN port.
The port is configured as folowing:
Line Setup
Line Type: Extension
L1 Mode: Call
L2 Mode: Call
Access Mode: P-MP
TEI Assign: Automatic
MSN Service: Disable
Extension Tone: Enable
Station Menu -> ISDN Internal 1
EXT: 195

Dialing out with de ISDN Device is no problem. Dialing in is a different story.
When i dial 195 from a internal phone (Panasonic KX-T7533) i can here the phone ringing (It sounds like i'm calling someone). When i look at the ISDN device it is not ringing.
When i dial in from an external line to the number is forwarded to extension 195 i can see a line comming in the PBX (a CO line is turning on) but i don't here anything on the phone i'm holding in my hand. After a couple of seconds the line is disconnected.

2 Questions now:
1: Is it posible what i want to do?
2: What am i doing wrong? (If it is even posible).

I hope someone here can help me.