User`s guide

Performing Loopback Modes and Pattern Tests
6-8
7800-A2-GB26-80
May 1999
Data Channel Loopback
The Data Channel Loopback (DCLB) loops the data for a particular synchronous
data port back to the network interface after the information has passed all the
way through the DSU/CSU (i.e., just before it is sent to the customer’s
equipment, either through the Network T1 interface or the DTE T1 interface, see
the figure below). It is useful for verifying the end-to-end integrity of a circuit for a
particular interface.
Network T1
Interface
DTE T1
Interface
CSU
DSU
DCE
Port 1
DCE
Port 2
496-15102
DCLBDCLB
Data Channel Loopback (DCLB) – V.54, Loop 2
Data Terminal Loopback
The Data Terminal Loopback (DTLB) loops the data for a particular synchronous
data port back to the interface just before it is combined with the rest of the T1
data stream (see the figure below). It is useful for both isolating errors to the DTE
equipment connected to the DSU/CSU and ensuring that the data for the
interface is being received/transmitted correctly by the DSU/CSU.
Network T1
Interface
DTE T1
Interface
CSU
DSU
DCE
Port 1
DCE
Port 2
496-15103
Data Terminal Loopback (DTLB) – V.54, Loop 3