DS3 byte counter counts the DS3 AIS/Idle code bytes and generating an AIS/Idle bytecount enable control signal if {TAIL ~ the number} of DS3 AIS/Idle code bytes is less than a predetermined number of DS3 bytes to be mapped in a given row of {HEAD ~ the STS 1 frame} 
DS3 byte counter counts the DS3 AIS / Idle code bytes and generating an AIS / Idle bytecount enable control signal if { TAIL ~ the number } of DS3 AIS / Idle code bytes is less than a predetermined number of DS3 bytes to be mapped in a given row of { HEAD ~ the STS 1 frame }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD