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About Link Noise Monitoring
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Configuration Tasks for Link Noise Monitoring
The LNM feature can be configured on theT1/E1 links of a line card or a SPA.
To configure T1/E1 links on a SPA (2-port Channelized OC12 SPA) refer chapter "Configuring a
Channelized SPA" in the Cisco 10000 Series Router SIP and SPA Software Configuration Guide.
To configure T1/E1 links on a line card (1-port Channelized OC12 or 4-port Channelized OC3/STM-1
line cards) refer chapters "1-Port Channelized OC-12/STM-4 Line Card Configuration" and "4-Port
Channelized OC-3/STM-1 Line Card Configuration" in the Cisco 10000 Series Router Line Card
Configuration Guide.
To configure the Link Noise Monitoring feature on a T1 link of a line card, perform the following
configuration tasks:
Cisco 10000 Series Router Software Configuration Guide
19-2
The LNM feature is supported only on T1/E1 links.
The use of a repeater removes errors at the physical layer (Layer 1) before passing the data, and
renders the LNM feature ineffective.
LNM provides the option of monitoring errors through LCV or PCV values, or both. If the LCV
value is specified, the router calculates the PCV value by a liner extrapolation of the Gaussian Curve.
Because of the extrapolation, the calculated PCV value can be the same for two close LCV values.
LNM can be enabled to issue a minor warning, a major warning or a removal. You cannot
simultaneously configure a major warning and a removal on the same T1/E1 link. The removal
functionality only works when the link is part of a multilink bundle.
We do not recommend link removals. The reason being, if two end points of a T1/E1 link
disagree about the status of the last T1 link, there exists the possibility of each end point
independently concluding that it is safe to remove the remaining links. This could result in the
last link being removed.
We do not recommend a low duration (set to a level as low as 4 seconds, when the default is set to
10). If the errors on the links fluctuate, the low duration value that is set triggers more events from
the line card (LC) to the route processor (RP). The flood of syslog messages (if enabled) generated
by the RP increases the load on the router CPU and the syslog server. A low duration value averages
out errors and leads to inaccurate results.
The Cisco 10000 series router only supports a maximum of 4000 TI links. An LC supports 336 T1 links
and a SPA supports 772 T1 links.
When many events are exchanged between the LC and RP, some events can get lost. The LNM
feature does not account for lost events sent from the LC or SPA to the RP.
If LNM is disabled on the T1/E1 link that is removed from the multilink bundle, the link can be
added to the bundle through the LNM feature.
If the ppp multilink links minimum num mandatory command is configured on an MLP bundle
with LNM enabled on a member T1/E1 link, all links get removed from the bundle through LNM.
If this command is configured, there is the danger of all links being removed from the bundle.
The 2-port Channelized OC12/DS0 SPA only monitors the PCV count for LNM.
Chapter 19
Configuring Link Noise Monitoring
OL-2226-23
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