Guidelines For Using Lre Profiles - Cisco Catalyst 2950 Software Configuration Manual

Configuring LRE Ports
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Guidelines for Using LRE Profiles

When assigning a profile to a switch LRE port, keep these considerations in mind:
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Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
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Age and type of wiring—You can estimate the type of wiring you have based on your site's age and
type.
Newer installations less than 15 years old often use Category 3 cable in bundles of 25 pairs.
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There is no significant difference between 25-pair bundles and larger bundles.
Older installations (hotel, school, hospital, commercial—North America) 15 to 30 years old
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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.
Older installations (residential—North America) 15 to 30 years old often use 26 AWG wiring
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with between 1 and 12 twists per foot (possibly type-2) in bundles of 100 or more.
Older installations (Europe) 15 to 30 years old often use 0.4 millimeter (similar to 26 AWG)
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wiring with between 1 and 12 twists per foot in bundles of 100 or more.
Older installations (Asia) 15 to 30 years old often use 0.4 millimeter (similar to 26 AWG)
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wiring with between 1 and 12 twists per foot in bundles of 100 or more.
Older installations over 30 years old often use heavy gauge wire (22 or 20 AWG) with no
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significant twist. In many cases, the cabling is set into the fabric of the building. The cables
might be tightly or loosely bundled. For this estimate, assume that they are tightly bundled in
groups of 25 or more.
Cross talk (noise) and interference—LRE operates with any number of wires in a cable binder
carrying the LRE signal. Anywhere from one wire pair to every wire pair in the cable can carry LRE
signals at the same time. LRE operates in full cable binders and adjusts power levels on each LRE
link to maximize the performance of all connections.
The greatest impact on LRE performance is from the frequency response of the cable at the higher
frequencies. LRE signals are more susceptible to interference at higher frequencies. The LRE
upstream signal operates at the high end of the frequency spectrum. Cables have higher attenuation
at higher frequencies and also interfere with other pairs in the bundle at higher frequencies. This
interference or cross talk can significantly impact the signal quality.
Phone lines typically operate at a frequency of up to 3.4 kHz. On the LRE link, the downstream
transmission runs in a low-frequency band from approximately 1 to 3.5 MHz. The upstream
transmission runs in a high-frequency band from approximately 4 to 8 MHz. Higher frequencies are
more susceptible to interference. Consequently, upstream signals are susceptible to cross-talk and
disruption on the link.
To maintain the quality of the LRE connection, use the asymmetric port profiles. These profiles use
a low upstream rate but provide a high downstream rate.
All POTS telephones not directly connected to the CPE device require microfilters with a
Note
300-ohm termination. Microfilters improve voice call quality when voice and data
equipment are using the same telephone line. They also prevent nonfiltered telephone rings
and nonfiltered telephone transitions (such as on-hook to off-hook) from interrupting the
LRE connection.
Chapter 12 Configuring LRE
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