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G.821 Measurement Definitions
Available Seconds (AS)
¾ The count of available seconds since the beginning of the test.
Available seconds equals the total test time minus any unavailable seconds.
Degraded Minutes (DGRM)
¾ The count of Degraded Minutes since the start of the test. A
Degraded Minute occurs when there is a 10-6 bit error rate during 60 available, non-se-
verely bit errored seconds.
Error Free Seconds (EFS)
¾ The count of error free seconds since the beginning of the test.
Error free seconds equals the total test time minus the number of errored seconds.
Errored Second (ES)
¾ The number of seconds with at least one error.
Severely Errored Seconds (SES)
¾ This is the count of Severely Errored Seconds since the
beginning of the test. A second with a bit error rate of 10-3 or higher is a severely errored
second. Severely errored seconds are not counted during unavailable time. Loss of signal
(LOS), loss of frame (LOF) and loss of pattern synchronization (LOP) are treated as se-
verely errored seconds
Unavailable Seconds (UAS)
¾ This is the count of UnAvailable Seconds that have occurred
since the beginning of the test. Unavailable time begins at the onset of 10 consecutive se-
verely errored seconds, and ends after 10 consecutive non-severely errored seconds. The
onset of unavailable seconds cause the SES count to be adjusted downward by 10. When
unavailable time ends, the UAS count is adjusted downward by 10.
Network Equipment
One possible network topology is shown in Figure 9-2.
The circuit between the MSC and BTS passes through the LEC central office, and in fact
may pass through multiple central offices. Within each office, it will in turn pass through
multiple pieces of transmission equipment. The Network Interface Unit (NIU) at the MSC
and the BTS may be a very simple device having only a remote loop back capability, or it
may provide very sophisticated performance monitoring capabilities. Its capabilities may or
may not be accessible to the wireless service provider technician. Some repeaters may exist
in the circuit when the signal is traveling long distances. Repeaters are full duplex devices
that regenerate or restore the pulse shape and amplitude.
9-2
Chapter 9 T1 Measurements
MSC
BTS
Figure 9-2. One Possible T1 Network Topology