VeEX MPA User Manual page 326

MPA_e_manual_D07-00-129P_RevA00
repeats indefinitely and does not contain CRC-7.
The J0 trace is part of the Section Overhead and is known
as the Section trace or J0 byte.
When TIM Alarm Reporting is Enabled, a TIM-S alarm
occurs if the incoming J0 trace does not match the Expected
J0 Trace.
SONET Tab
326