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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 10 Configuring LRE
Configuring LRE Ports
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.
Guidelines for Using LRE Profiles
When assigning a profile to a switch LRE port, keep these considerations in mind:
• 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.
Note All POTS telephones not directly connected to the CPE device require microfilters with a
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.
• When the link between the LRE switch and the CPE device must co-exist in the same cable bundle
as an asymmetric digital subscriber line (ADSL), we recommend that you use either the ANSI
profile (LRE-998-15-4) or the ETSI profile (LRE-997-10-4). For details on which profile to use
elsewhere, consult the regulations for connecting to the PSTN in your area.
• LRE signaling can coexist with ADSL signaling in one cable bundle. However, LRE signaling is not
compatible with T1 signals in the same cable bundle.
Use the show controllers lre status link privileged EXEC command to display the LRE link statistics
and profile information on the LRE ports. For information about these commands, refer to the switch
command reference.
CPE Ethernet Link Guidelines
Follow these guidelines when configuring CPE Ethernet links:
• Considerations for Connected Cisco 575 LRE CPEs, page 10-7
• Considerations for Connected Cisco 585 LRE CPEs, page 10-8
Considerations for Connected Cisco 575 LRE CPEs
You can configure the Cisco 575 LRE CPE Ethernet port to operate at 10 or 100 Mbps and at half- or
full-duplex mode, depending on the capability of the remote Ethernet device. Autonegotiation for port
speed and duplex mode is supported.
The default speed for the CPE Ethernet port is auto. The default duplex mode is half duplex with back
pressure.