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Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
OL-10101-02
Chapter 12 Configuring LRE
Configuring LRE Ports
• Rate selection is enabled on all interfaces, but a sequence with which to start rate selection is not
defined.
• LRE link persistence is enabled. The default is 3 seconds.
• LRE link monitoring is enabled.
• The interleave block size is 16 for non low-latency (LL) profiles and 0 for LL profiles.
• For the upstream power back-off mechanism, the default noise model is the ETSI-E model (available
only on the Catalyst 2950ST-24 LRE 997 switch).
• CPE toggle is enabled on a CPE Ethernet link.
• Syslog export is disabled.
Environmental Guidelines for LRE Links
The guidelines for your LRE environment are based on these factors:
• Maximum distance between the LRE switch and CPE devices—LRE runs on Category 1, 2, and 3
structured and unstructured cable. The maximum distance supported on the LRE link is from 3500
to 5000 feet (1524 meters), depending on the profile. The higher the rate, the shorter the distance.
In buildings where LRE traffic runs over bundled telco cabling, the maximum distance is
approximately 30 percent lower.
Each terminated bridge tap in a room can further reduce LRE link distances by 300 feet (91 meters).
The quality of the cable, the size of the cable bundles, and cross talk within the bundle also can affect
overall reach.
• Site type—If your site has either a private branch exchange (PBX) providing telephone service
throughout or has direct connections to the PSTN, you must identify the requirements of your local
public telephone service provider.
If your site is a single building (or is a connected set of buildings), consult a qualified electrician to
ensure that the wiring conforms to the appropriate regulations for indoor circuits.
If your site has separate buildings, you must determine how the buildings are cabled to each other.
Where the wiring between the LRE switch and CPE device leaves the building (or the armored
conduits certified for inside wiring standards), it must be protected against lightning and shorts to
high-voltage power. This protection might be provided by fuses or overvoltage protectors that
comply with local regulations for outside wiring protection. Consult an expert in local
telecommunications regulations for the details of this protection.
• Age and type of wiring—You can estimate the type of wiring you have based on your site’s age and
type.
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Newer installations less than 15 years old often use Category 3 cable in bundles of 25 pairs.
There is no significant difference between 25-pair bundles and larger bundles.
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Older installations (hotel, school, hospital, commercial—North America) 15 to 30 years old
often use 24 American Wire Gauge (AWG) wiring with between 1 and 12 twists per foot
(similar to Category 1) in bundles of 25 or more.
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Older installations (residential—North America) 15 to 30 years old often use 26 AWG wiring
with between 1 and 12 twists per foot (possibly type-2) in bundles of 100 or more.
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Older installations (Europe) 15 to 30 years old often use 0.4 millimeter (similar to 26 AWG)
wiring with between 1 and 12 twists per foot in bundles of 100 or more.
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Older installations (Asia) 15 to 30 years old often use 0.4 millimeter (similar to 26 AWG)
wiring with between 1 and 12 twists per foot in bundles of 100 or more.