EXFO FTB-8510B Guia Del Usuario página 975

For STM-256: The MS-REI error is declared when the combination of
the M0 and M1 bytes indicates that one or more BIP violations have
been detected.
channel 2 (timeslot #4)
SONET/SDH Application
M0
Located in STM-1
0000 0000
0000 0000
0000 0000
:
0001 1000
0001 1000
:
1111 1111
M1
Located in STM-1
channel 3 (timeslot #7)
0000 0000
0000 0001
0000 0010
:
0000 0000
0000 0001
1111 1111
SDH Tabs
Multiplex Section RX (SDH)
Indicates
0 BIP violation
1 BIP violation
2 BIP violations
6144 BIP violations
0 BIP violation
:
0 BIP violation
325