This animal spent most of its life in a studio rack, receiving remote broadcasts from near and far. Yes, ISDN technology is obsolete and the ISDN codec functions of this unit are only beneficial if you have an existing ISDN line. Although many are still operating around the world. The value in this unit lies in the included four channel mixer. Four mic or line level signals switchable to either left or right channels or both, with multiple headphone feeds. Phantom power switchable as well. All functions work as designed.

Working but does not come with power cable. It was tested using a different units power cord