Hello We are having problems with the internal cisco DSU/CSU cards on cisco 1721s as they are dying. I'm guessing this is due to energy surges, such as lighting and induced voltages. I cannot seem to find any optical isolation equipment, which would work. Opto isolation is the best, in my experience. Any recommendations on opto isolation are appreciated. What I have found, at [URL="http://www.edcosurge.com/products/telecom/lcpd.asp"]www.edcosurge.com/products/telecom/lcpd.asp[/URL] is RJ45 surge protection. It operates (clamps) at 8, 15 and 30 volts. Any recommendations on which volatage to select? Other circuits or devices for DSU/CSU protection? The circuits are Verizon 56kbps Frame Relay, if that matters.... Any discussion or recommendations are most welcome. James