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Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 10 Configuring LRE Configuring LRE Ports
The g reate st imp act on LR E pe rf orm ance is from t he fr eq ue ncy respon se of th e c ab le at th e hi gher
freque ncies. LRE signal s are more susc eptibl e to interf erence at highe r freq uencies. The LRE
upstream signal operates at the high end of the frequency spectrum. Cables have higher attenuation
at high er freque ncies and al so interfe re with ot her pairs in the bundle at high er freque ncies. Thi s
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 lin es typic ally oper ate at a frequency of up t o 3.4 kHz. O n the LR E link, the downstream
transm issio n runs i n a l ow-freque ncy band f rom app rox ima tel y 1 t o 3.5 MH z. Th e ups trea m
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
disrupti on on the link.
To maintain th e quality of the LRE connection, use th e asymm etr ic por t p r of iles. These profiles use
a low u pstream 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 equ ipment
are using the sam e teleph one line. The y also p re v ent nonf ilte red telep hone rings and nonf iltere d
telepho ne t ransi tions (su ch as on-h ook to off-hook) f rom i nte rrupt ing the LRE c on nect ion.
•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 y ou use either the ANSI
profile (LR E-9 98-15- 4) or t he ET SI p ro file (LRE -997-1 0- 4). For det ails on wh ich profile to u se
elsewhere, co nsult the regul atio ns for connec ting to the PSTN in your ar ea.
•LRE signaling can coexist with ADSL signaling in one cable bundle. Howe ver , 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
comm an d ref e renc e.

CPE Ethe rnet L ink Guide line s

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 co nfigure the Ci sco 575 LR E CPE Ether net port to operat e at 10 or 100 M bps and at half - or
full-duplex mode, depend ing on the capability of the remote Ethernet device. Autonegotiation for port
speed and du plex mo de i s supp orted.
The defaul t speed fo r the CPE Eth ernet port is auto . The defaul t duplex mode is ha lf duplex with back
pressure.