3Com NBX 100 Administrator's Manual page 209

Configuring and Managing T1 Digital Line Cards 209
LB — Loopback (when lit, indicates that the card is in loop-back
testing mode; does not indicate any of the red, blue, or yellow alarms)
Nominal — T1 card is framed
The 3C10116D T1 card contains these status lights:
CO — Central Office:
Amber — Alarm condition at the remote end or the CO is not
connected or available.
Green — No alarm condition; the card is connected to the Central
office.
POST — Power On Self Test
Off — POST test is running. The test runs approximately 5-seconds
after you apply power to the board. After 5-seconds, Off indicates the
POST test failed.
Green — POST test completed successfully.
DCH — D channel status of an ISDN PRI connection
Off — No T1 or T1 PRI line is attached or that the card does not need
a D channel, such as when the card is running T1-robbed-bit (CAS).
Green — Card is configured for ISDN PRI operation and an active PRI
connection has been established.
Amber — The D channel has not yet been established. It can take
several seconds after the card has completed its power up tests for the
card to establish a connection with the PRI trunk. If the DCH light goes
to amber after the connection has been established, it can mean that
an active control channel connection through the PRI line has been
lost.
DNLD — Download
Flash — The card is downloading software from the NBX Network Call
Processor.
Green — The download is complete.
Amber — The download was interrupted before it completed.
On a LAN, the download process completes quickly. If the download
from NCP to digital line card must travel a routed network path, the
download may take a few minutes. If the DNLD light remains amber, it
can indicate a severely congested network or a hardware problem
with the T1 card.