Chapter 4
Test Results
G.821 results
Data Communications and Diphase Testing Manual
January 2016
21148872, Rev. 002
Page 37
Interpreting available and unavailable seconds
CCITT Recommendation G.821 defines unavailable and available time as follows:
“A period of unavailable time begins when the bit error rate (BER) in each second is
worse than
10
-3
for a period of 10 consecutive seconds. These 10 seconds are consid-
ered to be unavailable time. The period of unavailable time terminates when the BER
in each second is better than
10
-3
for a period of 10 consecutive seconds. These 10
seconds are considered to be available time.”
The instrument measures available and unavailable time in seconds. After initial pattern
synchronization, the unit counts each second as
available
until 10 consecutive
seconds, each with a BER worse than
10
-3
occurs. At that point, the unit counts each
second (including the 10 that triggered the unavailable seconds count) as
unavailable
.
Example
If a test runs for 25 seconds after initial pattern synchronization, and each of the 25
seconds has a BER better than or equal to
10
-3
, the instrument counts the 25 seconds
as available, and the
Avail Secs
count in the G.821 Result Category is 25.
In the 26th second, the BER becomes worse than
10
-3
. The 27th and 28th seconds also
have a BER worse than
10
-3
. However, in the 29th second, the BER improves to
10
-3
or
better. Because only three seconds occurred with a BER worse than
10
-3
, and 10
consecutive seconds are required to initiate the unavailable seconds count, the instru-
ment includes them in the
AS
count (29 seconds are available). The
UAS
count would be 0.
The three seconds with a BER worse than
10
-3
in the example are also counted as
severely errored seconds; therefore, the
SES
count would be 3.
UAS
Number of seconds judged unavailable due to 10 or more
SES (see
). Count includes the 10 SES. See
ing available and unavailable seconds” on page 37
.
Table 14
G.821 results (Continued)
Test Result
Description
