Remote loopback commands are intended to place compatible external equipment into a loopback state. The initiating unit will maintain normal data flows during these tests. (1) csu loop up - commands the node to send a standard in-band csu loop up pattern towards the WAN. This is a repetetive framed T1 signal consisting of four 'zeros' followed by one 'one' persisting for a few seconds in place of all T1 data. A device terminating the WAN's physical link is expected to enter a Line Loopback condition upon recognition of this pattern. The initating unit doesn't know if the command was accepted by the remote unit. (2) csu loop down - commands the node to send a standard in-band csu loop down pattern towards the WAN. This is a repetetive framed T1 signal consisting of two 'zeros' followed by one 'one' persisting for a few seconds in place of all T1 data. A device terminating the WAN's physical link is expected to clear any Line Loopback condition upon recognition of this pattern. The initating unit doesn't know if the commad was accepted by the remote unit. (3) dsu loop up - commands the node to send a proprietary in-band dsu loop up pattern towards the WAN. This is a repetetive framed T1 signal consisting of a pseudorandom pattern persisting for a few seconds in place of all T1 data. A compatible device terminating the WAN's physical link is expected to enter a Line Loopback condition upon recognition of this pattern. The initating unit doesn't know if the command was accepted by the remote unit. (4) dsu loop down - commands the node to send a proprietary in-band dsu loop down pattern towards the WAN. This is a repetetive framed T1 signal consisting of a pseudorandom pattern persisting for a few seconds in place of all T1 data. A compatible device terminating the WAN's physical link is expected to clear any Line Loopback condition upon recognition of this pattern. The initating unit doesn't know if the command was accepted by the remote unit.