Facility Data Link (FDL)
The ESF Facility Data Link is a 4 kbps channel carrying maintenance
requests and responses, plus other maintenance messages.
FDL Register
The term FDL register refers to telco register contents obtained from
a far-end Access-T (or other interface device) via the FDL.
Fractional T1
Fractional T1 refers to the leasing of portions of T1 bandwidth (a
specific number of DS0s) by carriers. FT1 allows for more economical
networking in some applications.
In-Band Codes
Specific bit patterns which are transmitted in the information band-
width to control loopbacks or other functions.
Line Availability
The percentage of monitored seconds which are not Unavailable
Seconds (UAS).
Line Build-Out
Line build-out is an impedance compensator used to compensate for
various cable lengths and conditions between CSUs and the first telco
line repeater.
Line Coding
The method of encoding data for transmission over a particular
facility. Line coding schemes for T1 include AMI and B8ZS. It is
critical that all equipment on the line be configured for the same line
coding, or transmission will not be reliable.
Loopback
Loopback is the returning of received data toward the sender.
Loss of Frame
Access-T declares Loss of Frame (also called Loss of Sync) from the
line when an Out of Frame condition continues for 2.5 seconds.
Access-T responds to Loss of Frame by declaring Red Alarm. While
Access-T is in Red Alarm, it transmits Yellow Signal (if enabled) to
the line as an indication of the alarm condition. Loss of Frame is
cleared within one second after the receipt of a correctly-framed
signal.
Loss of Frame Count (LOFC)
A tally of the number of times Loss of Frame has been declared.
Appendix B
ACST-0351-005
Glossary
June 1996
B-6