Carrier hold-down timer/interval - What is it used for?

Modified on Thu, 20 Jul 2023 at 01:12 PM

CENTAURI operates in free space and weather conditions such as rain & scintillation which can reduce receive power levels momentarily (milliseconds power drops). 

These microdrops are unavoidable. 

The SFPs in L2 switches/routers are sensitive to RX power and they trigger a physical 'link down' alarm whenever they detect any drop in power.

By default, a physical port 'link down' event triggers an immediate notification and a cascade of alerts and alarms in upper layer protocols (OSPF, BFD, MPLS, etc).

Configuring a “down-hold interval” allows the system to wait for the specified time interval to expire before checking the link status again, and only then notifying the upper layer protocols if the drop is still observed.

Microdrops with durations less than the configured “down-hold interval” will be suppressed, reducing longer downtimes triggered when upper-layer protocols would otherwise react to the microdrop as a full-blown outage.

Refer to the diagram below.

The recommended carrier hold-down interval when using CENTAURI is 300ms.

If this feature is not available in a carrier’s existing router, adding a layer 2 switch between CENTAURI and the router is recommended. 

This adds buffer time before providing feedback on the link status to the router.

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