[cisco-voip] E1R2 getting clear backward state

[Jefflin Choi]

Hi,

Getting "clearbak" status on E1R2 line on 3845 router with 12.4(15)T7.
Working fine for a while and after sometime, call is not pushing
through.

Router#sh voice port summary
:
0/0/0:1        17  r2-digital  up    up   clearbak idle     y

0/0/0:1        18  r2-digital  up    up   clearbak idle     y

0/0/0:1        19  r2-digital  up    up   clearbak idle     y

configs:
controller E1 0/0/0
 framing NO-CRC4
 ds0-group 0 timeslots 1-15 type r2-digital r2-semi-compelled ani
 ds0-group 1 timeslots 17-31 type r2-digital r2-semi-compelled ani
 cas-custom 0
  country philippines use-defaults
 cas-custom 1
  country philippines use-defaults

Could someone give me insight on what causes "clearbak" state? How do
i troubleshoot this?

i can only find a caveat but on 12.2 ios version.

Thanks,
Jeff