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I have a ISDN phone that intermittently disconnects a call in progress. It is an 100 ohm device. Does anyone know what the terminating resistance of a TN-556B circuit pack is? Or any ideas? This happens at several locations and at different distances.  


Wich type of Isdn phone do you use? What is line distance from TN556 port (should be in 900 meters range)?
What type of calls is disconnecting- only off-premises or calls to extensions is disconnecting too?
I think that terminating resistor 100 ohm needs only in high theoretical discussions. ( Some Professors may be correct me now. In normal life IMHO you don't need this one.
As an idea for outgoing disconnect problem, try to check system-parameters features for
Off-premises Tone Detect Timeout Interval. It should be 20 seconds or a little more.
I had so kind of problem with BRI video calls wich were disconnected after
20-30 seconds of call in-progress(it was too short tone detect timeout).

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