The Care and Feeding of ISDN4BSD
7 The isdntrace Utility	7 The isdntrace Utility	7.2 Analyzing an S0

7.1 Normal Usage

The isdntrace utility is used to decode, display and log what goes out to your S0 bus and what comes in. It may be started without isdnd or in addition to isdnd for debugging and logging purposes.

Isdntrace is able to decode the D-channel Q.921 and Q.931 protocols, report the state of the Layer 1 according to I.430 and produce a hex dump of the B-channel activity.