An integer corresponding to the Errored Symbol Window
field in the most recently transmitted Errored Symbol
Period Event TLV in an Event Notification OAMPDU (see
57.4.3.2).
This integer is updated when a OAM:MA_DATA.request
service primitive is generated within the OAM sublayer
with an OAMPDU Code field value equal to the Event
Notification code as specified in Table 57-4 and Event TLV
Type field equal to the Errored Symbol Period Event value
as specified in Table 57-10.