Cisco 2950 Software Configuration Guide - Page 273

Chapter 13 Configuring LRE Understanding LRE Features • Certain CPEs do not work with certain switches. For details, see the LRE switch and CPE compatibility matrix (see Table 1-2 on page 1-2). You can connect Cisco 575 LRE CPEs and Cisco 585 LRE CPEs to the Catalyst 2950ST-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 enabled by default. CPE toggle cannot be disabled on a Cisco 575 LRE or Cisco 576 LRE 997 CPE link but can 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 command to display the internal 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 undesirable or interesting conditions 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 more information, see the "Link Qualification and SNR Margins" section on page 13-16. • Reed-Solomon (RS) errors: The RS Forward Error Correction circuit corrects small bursts of errors so that noise events do not cause Ethernet frame check sequence (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 power can reach its maximum at distances between 1500 feet (450 meters) and 3000 feet (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 the link monitor to log events, set traps, change to a lower rate profile, and disable the automatic power back-off feature. 78-11380-10 Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide 13-7