Mojo describes what concerns me more than distance/shielding issues. When looking at a product description online, it's often difficult to tell if the RJ's are 4/6/8 way, and it's a good bet that the manufacturer has never heard of ISDN. Hopefully I'll never have to use ISDN again, but it's still unclear if it's safe to run 100/1000 ethernet -- not to mention DS1/T1 -- through one of these things.