Cisco 678 Installation And Operation Manual page 140

Frequently Asked Questions about the WAN LNK LED
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Cisco 600 Series Installation and Operation Guide
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three PPP requests to be sent from the CPE, and if they are not answered by
the service provider's equipment, the CPE stops sending them and the WAN
LNK LED turns off.
There are a number of possibilities why this would happen:
VPI/VCI provisioning is not correct in the ATM cloud. This could signify
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that the service provider's equipment or the ATM switch along the path
does not have the correct provisioning.
VPI/VCI mapping in the service provider's equipment or the CPE is not
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configured properly.
ATM Cell scrambling is enabled on one end of the link but not the other.
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The show running command will display an entry with "ATM WAN Cell
Scrambling = disabled" if cell scrambling is disabled. No entry implies
the default behavior of ATM cell scrambling is enabled.
Service provider's equipment is powered off.
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CPE is configured for routing mode, but the equipment at the service
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provider's network that is terminating CPE traffic is configured for
bridging.
Use the show errors command to check the contents of the error log.
If the CPE trains up and the WAN LNK LED turns off, this is a sign of no
ATM cell delineation.Verify that you have the ATM link terminated at the
central office end. Without ATM cell delineation, the router will attempt to
retrain the line in 1 to 10 seconds.
If the CPE trains up and then immediately drops the connection, the near-end
DMT firmware might not be compatible with the far-end DMT firmware. For
example, an ITU G.Lite router might not train to an ANSI Issue 1 Central
Office. To see the DMT firmware version installed on your router, use the
show version command.
Chapter 6 Troubleshooting
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