The Fluke Networks offers TruView and Visual Performance Manager X.21 LinkSafe inline probe ASE. This is deployed inline on an access line that is typically between a CSU DSU and customer premises equipment. The ASE Supports X.21 through DTE interface and DCE on the user side. The ASE operates data rates up to 2.048 MBps delivering timing from the network side and sourcing timing on the user side.