Cisco 2950 - Catalyst Switch Configuration Manual page 284

Configuring LRE Ports
Table 13-8 SNR Requirements for Downstream Rates for the Catalyst 2950ST-24 LRE 997 Switches
Gross Data
Profile Rate
LRE-12-9 12.500
LRE-12-3 12.500
LRE-9 9.375
LRE-9-6 9.375
LRE-9-4 9.375
LRE-9-3 9.375
LRE-6 (default) 6.250
LRE-6-4 6.250
LRE-6-3 6.250
LRE-4 4.688
LRE-4-3 4.688
Table 13-9 SNR Requirements for Upstream Rates for the Catalyst 2950ST-24 LRE 997 Switches
Gross Data
Profile Rate
LRE-12-9 9.375
LRE-12-3 3.125
LRE-9 9.375
LRE-9-6 6.250
LRE-9-4 4.688
LRE-9-3 3.125
LRE-6 (default) 6.250
LRE-6-4 4.688
LRE-6-3 3.125
LRE-4 4.688
LRE-4-3 3.125
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.
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
13-18
Theoretical
QAM Minimum SNR
256 31
256 31
64 25
64 25
64 25
64 25
16 19
16 19
16 19
8 16
8 16
Theoretical
QAM Minimum SNR
64 25
4 13
64 25
16 19
8 16
4 13
16 19
8 16
4 13
8 16
4 13
Medium Noise
Low Noise SNR SNR
33 35
33 35
27 29
27 29
27 29
27 29
21 23
21 23
21 23
18 20
18 20
Medium Noise
Low Noise SNR SNR
27 29
15 17
27 29
21 23
18 20
15 17
21 23
18 20
15 17
18 20
15 17
Chapter 13 Configuring LRE
High Noise
SNR
38
38
32
32
32
32
25
25
25
23
23
High Noise
SNR
32
20
32
25
23
20
26
23
20
23
20
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