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12-18
Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
OL-10101-02
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.
Beginning in privileged EXEC mode, follow these steps to assign a margin to a specific LRE port:
To return to the default values, use the no margin {downstream | upstream} interface configuration
command.
Note The margin command is effective with any profile, but only with rate selection and only when a link is
being activated.
Ta b l e 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-12-9 9.375 64 25 27 29 32
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-9-4 4.688 8 16 18 20 23
LRE-9-3 3.125 4 13 15 17 20
LRE-6 (default) 6.250 16 19 21 23 26
LRE-6-4 4.688 8 16 18 20 23
LRE-6-3 3.125 4 13 15 17 20
LRE-4 4.688 8 16 18 20 23
LRE-4-3 3.125 4 13 15 17 20
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
interface interface-id Enter the number of the LRE port to be configured, and enter
interface configuration mode.
Step 3
margin {downstream value | upstream value} Enter the downstream or upstream margin value (in dB). For the
values, see
Table 12-6 on page 12-16, Table 12-7 on page 12-17,
Table 12-8 on page 12-17, and Table 12-9 on page 12-18.
Step 4
end Return to privileged EXEC mode.
Step 5
show controllers lre profile details Verify the change.
Step 6
copy running-config startup-config (Optional) Save your entries in the configuration file.