12-18
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
78-11380-12
Chapter 12 Configuring LRE
Configuring LRE Ports
The margin range for link qualification is from 1 to 10 dB. The recommended value in a low-noise
environment is 2 dB. The recommended value for medium noise environment is 4 dB. The recommended
value in a high noise environment is 6 dB.
If a profile has a theoretical minimum of 25 dB and you configure a margin of 3 dB, when the link is
established, the SNR should at the least be 28 dB to indicate a successful link. If a link is established
and if the SNR value at link time is 27 dB, the link is advertised as down, and the next profile in the
sequence is attempted. If you configure a margin of 0 (the default value), the software does not check
for the SNR value when the link is established.
Table 12-8 SNR Requirements for Downstream Rates for the Catalyst 2950ST-24 LRE 997 Switches
Profile
Gross Data
Rate QAM
Theoretical
Minimum SNR Low Noise SNR
Medium Noise
SNR
High Noise
SNR
LRE-12-9 12.500 256 31 33 35 38
LRE-12-3 12.500 256 31 33 35 38
LRE-9 9.3756425272932
LRE-9-6 9.3756425272932
LRE-9-4 9.3756425272932
LRE-9-3 9.3756425272932
LRE-6 (default) 6.250 16 19 21 23 25
LRE-6-4 6.250 16 19 21 23 25
LRE-6-3 6.250 16 19 21 23 25
LRE-4 4.6888 16182023
LRE-4-34.6888 16182023
Table 12-9 SNR Requirements for Upstream Rates for the Catalyst 2950ST-24 LRE 997 Switches
Profile
Gross Data
Rate QAM
Theoretical
Minimum SNR Low Noise SNR
Medium Noise
SNR
High Noise
SNR
LRE-12-99.3756425272932
LRE-12-3 3.125 4 13 15 17 20
LRE-9 9.375 64 25 27 29 32
LRE-9-6 6.250 16 19 21 23 25
LRE-9-44.6888 16182023
LRE-9-33.1254 13151720
LRE-6 (default) 6.250 16 19 21 23 26
LRE-6-44.6888 16182023
LRE-6-33.1254 13151720
LRE-44.6888 16182023
LRE-4-33.1254 13151720
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