User`s guide

Performing Loopback Modes and Pattern Tests
6-10
7800-A2-GB26-80
May 1999
CSU or External Network Loopback
CSU loopback is an external loopback that is located as close as possible to the
network interface (see figure below).
DSU CSU
DTE
Interface
Aggregate
DTE
Port
DDS
Network
Port
496-14929
DDS Leased-Line Access Unit
DSU or Internal Network Loopback
DSU loopback is an Internal loopback that is located as close as possible to the
customer interface serving the DTE (see figure below).
DSU CSU
DTE
Interface
Aggregate
DTE
Port
DDS
Network
Port
496-14933
DDS Leased-Line Access Unit