CHAPTER 5: Diagnostics
47
5.2 Description of Test Loops
Whenever a test loop is on, the TEST indicator will light and traffic will be disrupted.
5.2.1 L
OCAL
L
OOPS
1.
Local composite channel loop.
When the local composite channel loop is connected, the composite channel
data transmitted by the local stat mux is applied to the receive line of the local stat mux, and the
communication link is disconnected (this causes the remote stat mux to lose frame synchronization). All
the data arriving from the remote stat mux while this loop is connected is lost. This loop tests the complete
local stat mux.
As long as the loop is connected, the MAIN and SYNC indicators of the local stat mux must light
continuously. If they do not, this indicates a local stat mux problem.
Sub-channel activity indicators light according to traffic; the lighting of the OVF indicator means that stat
mux buffers are full because of flow-control problems caused by the equipment connected to one of the
local sub-channels.
2.
Local sub-channel loop.
When a local sub-channel loop is connected, the local transmit data is returned as
receive data on the same sub-channel. The local data is also multiplexed into the transmit data stream sent
to the remote stat mux. All the data arriving from the remote stat mux sub-channel while this loop is
connected is lost. As long as the loop is connected, the sub-channel activity indicator lights according to
traffic. The equipment connected to the sub-channel must receive its own transmit data without errors.
Failure to do so usually indicates problems with the sub-channel connection cable or with equipment
connected to that sub-channel.
5.2.2 R
EMOTE
L
OOPS
1.
Remote composite channel loop.
When the remote composite channel loop is connected, the composite
channel data transmitted by the local stat mux is returned from the remote stat mux after regeneration but
without any other processing. Any data transmitted from the remote stat mux sub-channels is lost during
loop connection.
This loop tests the complete transmission path, including the local stat mux and the communication link.
As long as the loop is connected, the MAIN and SYNC indicators of the local stat mux must light
continuously; failure to do so, after the local stat mux has performed satisfactory on the local composite
channel loop, indicates a problem in the communication link. For example, intermittent flashing of the
SYNC indicator indicates a high error rate on the link. Sub-channel activity indicators light according to
traffic; the lighting of the OVF indicator means that the stat mux buffers are full because of flow control
problems caused by the equipment connected to one of the local sub-channels.
2.
Remote sub-channel loop.
When a remote sub-channel loop is connected, the local transmit data is transmitted
to the remote stat mux. It’s returned to the local stat mux sub-channel instead of the transmit data
connected to the remote stat mux sub-channel. All the data arriving from the remote stat mux sub-channel
while this loop is connected is lost. As long as the loop is connected, sub-channel activity indicator lights
according to traffic. The equipment connected to the sub-channel must receive its own transmit data
without errors. Failure to do so, after the local stat mux performed satisfactory on the local sub-channel
loop, usually indicates a problem in the remote stat mux.
