S-Access SA-REP-ETHERLINK_II-1DA-PL, Руководство пользователя

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ETHERLINK II - Repeater Manual
Page 93 of 106
6.2 Evaluation of the quality of the digital channel and operation parameters
The quality of the digital channel is evaluated by:

The ITU-T G.826 error performance monitoring of a DSL link is performed according to ITU-
T Rec. G.704. The evaluation of the G.826 error performance parameters is based on CRC
(Cyclic Redundancy Check) error detection. On the xDSL side, six CRC6 check bits are
generated per xDSL frame. CRC6 errors are used by the software to count the block errors
of the xDSL channel and to evaluate its error performance according to ITU-T Rec. G.826.
The
G826 command is used to display the G.826 statistics.

The Noise Margin performance monitoring.
The Noise Margin (NM) provides qualitative performance information of a specific link. The NM
command is used to activate this test. This parameter is calculated according to G.991.2 and is
an efficient tool for determining the qualitative performance of an xDSL link. The recommended
NM valus should be no less than 8 dB. This value provides the necessary reserve of the
signal/noise margin.
It is recommended to perform the ITU-T G.826 test regularly.
It is recommended to perform the Noise Margin performance monitoring during acceptance
tests and in case the system operates unstably. The test is used to locate the damaged cable
segment
.
In addition, it is also recommended to monitor regularly the quality of data transmission over E1
interfaces. On the E1 side, four CRC4 check bits are generated per sub-multiframe (SMF) and
compared with the corresponding bits of the next SMF. If they do not match, the CRC4 error
counter is incremented
.
The G826 command is used to display the G.826 statistics.
The correctness of configurations of network interfaces and operability can be checked by using
loopback tests (LOOP1) and G.826 statistics of E1 interfaces. If LOOP1 is activated on this
network interface and the G826 statistics displays errors, a conclusion can be made that the E1
network interface of the S-Access Etherlink_II system is configured improperly or malfunctions.