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Catalyst2950 and Catalyst2955 Switch Software Configuration Guide
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Chapter13 Configuring LRE Understanding LRE Features
•Certain CPEs do not work with certain switches. For details, see the LRE switch and CPE
compatibility matrix (see Table1-2 on page 1-2). You can connect Cisco 575 LRE CPEs and
Cisco 585LRE CPEs to the Cataly st 2950 ST-8 LRE or 2950ST-24 LRE switch. You can connect a
Cisco 576 LRE 997 CPE only to a Catalyst 2950ST-24 LRE 997 switch.
•You can hot-swap the CPE devices without powering down the switch or disrupting the other switch
ports.
•The CPE toggle feature automatically changes a CPE Ethernet link from down to up if the LRE link
comes up in less than 30 seconds. This feature is enable d by d efaul t.
CPE toggle cannot be disabled on a Cisco 575 LRE or Cisco 57 6 L RE 9 97 CPE li nk but c an be
disabled on a Cisco 585 LRE CPE. For more information, see the “Configuring CPE Toggle” section
on page 13-22.
Use the show controllers ethernet-controller privileged EXEC comm and to display the inter nal switch
statistics, the statistics collected by the LRE switch interface, and the statistics collected by the LRE CPE
interface. For information about this command, refer to the command reference for this release.
LRE Link Monitor
When the link monitor feature is enabled, an LRE switch tracks undes irab le or inter esting cond ition s on
a link and takes system-defined actions after certain thresholds are reached. The link monitor can track
these conditions:
•SNR, in 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 established if the SNR is insufficient. For mor e information,
see the “Link Qualification and SNR Margins��� section on page13-16.
•Reed-Solomon (RS) errors: The RS Forward Error Correction circuit corrects sma ll bursts of errors
so that noise events do not cause Ethernet frame check sequence ( FCS) er r or s. T hi s i s i mpl em en ted
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 ad justs automatica lly 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 ma xi m um transmit power
of –55 dBm/Hz (corresponding to longer cable lengths or greater cable attenuation). The CPE device
power can reach its maximum at distances between 1500 feet (450 m ete rs) a nd 300 0 fe et
(900 meters).
•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).
•Link Fail Counts: The number of times the link failed. A failed link interrupts operation of the
Ethernet link for a small number of milliseconds. During this interruption, some packets might be
dropped (depending on traffic levels).
•PMD Freeze Event Counter: This counts the occurrence of micro-interruption or saturation events.
Micro-interruptions and Analog to Digital Converter (ADC) saturations are caused by impulse noise
for a short duration. This is implemented in the octal chip as a 8-bit counter.
The link parameters need to be monitored both for the upstream and downstream directions.
You can use the information that you get from th e link monitor to log events, set traps, change to a lower
rate profile, and disable the automatic power back-off feature.