Articles of Aaron's Worthless WordsFrame Relay Notes – DE, FECN, and BECN2011-06-23 14:06:31 Aaron Conaw ay

All are part of the frame relay congestion management suite.Frame relay switches monitor links for CIR or oversubscription congestion on links.

If the VC has a CIR of 256k, the switch knows there is congestion if the customer is sendingmore than 256k down that VC.

Discard Eligible

Flag in the LAPF headerMarks a frame as eligible to be dropped in case of congestionMarked via the MQC

Forward Explicit Congestion NotificationFlag in the LAPF headerSet by the switch when the frame is about to enter a link with congestion on a VC

Congestion in one directionFECNs are set when the frame is going into the congestion.

Receiving router can see that there was congestion on the way.FECNs can be used to activate adaptive shaping via FRTS.Plain English: If Router B receives a frame with the FECN flag set, that means that there iscongestion on the path from Router A to this Router B, and that Router B should expectdelays.

Backward Explicit Congestion NotificationFlag in the LAPF headerSet by the switch when a frame has just left the link with congestion

Congestion is the opposite direction.BECNs are set when the frame has just left a link that has congestion on it.

Notifies the original sending router that there is congestion along that VC.Plain English: If Router A receives a frame with the BECN flag set, that means that there iscongestion from Router A towards Router B and that the sending host should calm down alittle bit.

http://www.sinclair.org.au/keith/networking/frame_relay.html

–Corrections requested.

Aaron Conaway

I like to lean my head to the left, hit it with the palm of my right hand, and document what knowledge fallsout.

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