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10-14
Catalyst 2950 Desktop Switch Software Configuration Guide
78-14982-01
Chapter10 Configuring LRE
Configuring LRE Ports
Note The margin command is effective with any profile, but only in conjunction with rate selection and only
when a link is being activated.
LRE Link Persistence
A brief LRE link down and up transition can cause the rest of the IOS modules to react immediately, for
example, the Dynamic MAC addresses are removed from that ports table. You can use the link
persistence feature to configure a delay duration on the Catalyst 2950 LRE of up to 20 seconds before
link failure is reported.
Refer to the lre persistence reference pages in the Catalyst 2950 Desktop Switch Command Reference
for further details.
LRE Link Monitor
You can use the link monitor feature to track undesirable or interesting conditions on a link and to take
system-defined actions after certain thresholds are reached. The link monitor can track these conditions:
• SNR, in decibels (db): The link must have a minimum SNR to function; a higher SNR value means
a better noise margin on the link. Links are not establish if the SNR is insufficient. (See the “Link
Qualification and SNR Margins” section on page 10-12 for more information.)
• Reed-Solomon (RS) errors: The RS Forward Error Correction circuit corrects small bursts of errors
so that noise events do not cause Ethernet FCS errors. This is implemented in the octal chip as a
32-bit counter. The count resets on read.
• Transmit (TX) Power, in dBm/Hz: This is fixed for the switch and adjusts automatically for the
CPE device. The local transmit power is always constant and the same for a given profile. The
remote transmit power varies according to distance from the switch to the CPE device, with a
minimum transmit power of 91.9 dBm/Hz (corresponding to short distances) and a maximum
transmit power of -55 dBm/Hz (corresponding to longer cable lengths or greater cable attenuation).
The CPE device’s power can reach its maximum at distances between 1500ft/450m and
3000ft/900m.
• Software controlled Automatic Gain Control (SW AGC Gain), in dBm: This gives an indirect
measure of the received power level. Higher values mean that the receive power is lower (and thus
in need of more boost).
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
interface LRE-interface Enter interface configuration mode, and enter the number of the
LRE port to be configured.
Step 3
persistence time Enter the length of time (in seconds) you wish to set for the
persistence. (The default is 3 seconds)
Step 4
end Return to privileged EXEC mode.
Step 5
show controllers lre status persistence Verify the change.