I BECN you to help me with Frame Relay

mattsthe2

Hi Guys,

So ive read my frame relay chapter 2 times and im still not getting so i'm turning to my trusty forum for hep.

1) I'm not seeing the difference between FECN and BECN. I know it is used to relay congestion on the network and one goes one way and the other goes the other, but to me they sound like the same thing.

2) With inverse APR enabled do i still need the Frame-Relay Map command?

Bill Kaster

My understanding is that BECN says that traffic is congested on the pvc heading to the source router (DTE) while FECN does just the opposite, saying that traffic is congested heading toward the frame switch DCE. In other words they both measure congestion but in different directions - i.e. FECN means forward toward the frame switch and BECN means backward away from the frame switch.

mattsthe2

Bill Kaster wrote:

My understanding is that BECN says that traffic is congested on the pvc heading to the source router (DTE) while FECN does just the opposite, saying that traffic is congested heading toward the frame switch DCE. In other words they both measure congestion but in different directions - i.e. FECN means forward toward the frame switch and BECN means backward away from the frame switch.

Thanks Bill..you sound right.

I dont get FECN though.
If im on my router and i do a "sh frame-relay pvc"

i get the fact that BECN is congestion coming from the Frame-Relay cloud but FECN would be set by me and how the hell do i know if there is congestion from where i am (on the outskirt)??

mattsthe2

Any more help guys :
I'd appreciate it this is bugging me.

networker050184

You do not set the FECN bit manually.

mattsthe2

networker050184 wrote:

You do not set the FECN bit manually.

Thanks Networker.
Yes i wasn't talking literally. I meant what would be the point of my router setting the FECN bit going toward the Frame Relay switch.

Netstudent

http://www.sins.com.au/network/frame-relay-fecn-becn.html

http://www.networkworld.com/community/node/19958


Maybe these definitions will help. Basically FECN is set when a frame experiences congestion on it's way to the destination. This lets the destination know so that it can slow down it's requests for data. I read about a FECN being able to alert upper level protocols like TCP's window to slow down unacknowledged data and help with congestion. But I read that so I'm not quite sure how valid it is adnt hat may be something to look into further. Also a FECN bit alerts the destination, but it's the source that needs to slow down. Thats when a router hearing a FECN can set the BECN bit on the way back to the source to slow it down. I think frame-switches can also go ahead and set the BECN bit on frames traversing back towards the source. These are kinda difficult to learn when all you have is a homelab that will never experience congestion unless you have a traffic generator. I think FECN and BECN are usually set in the frame cloud.

mattsthe2

Netstudent wrote:

http://www.sins.com.au/network/frame-relay-fecn-becn.html

http://www.networkworld.com/community/node/19958


Maybe these definitions will help. Basically FECN is set when a frame experiences congestion on it's way to the destination. This lets the destination know so that it can slow down it's requests for data. I read about a FECN being able to alert upper level protocols like TCP's window to slow down unacknowledged data and help with congestion. But I read that so I'm not quite sure how valid it is adnt hat may be something to look into further. Also a FECN bit alerts the destination, but it's the source that needs to slow down. Thats when a router hearing a FECN can set the BECN bit on the way back to the source to slow it down. I think frame-switches can also go ahead and set the BECN bit on frames traversing back towards the source. These are kinda difficult to learn when all you have is a homelab that will never experience congestion unless you have a traffic generator. I think FECN and BECN are usually set in the frame cloud.

Dude, you managed to get through my thick skull to finally get me to understand it, those links really really helped.

also for those that issue the sh frame-relay PVC command OUT BECN and OUT FECN have no relevance for a DTE router.
We only need to concentrate on IN FECN and IN BECN.

Netstudent

Well thats good. Sometimes it's good to get different explanations because at least on of them has to make sense.

ronnie1009

that was a good one netstudent gave - the turrning bits on and off. Comprehensive.
I got the undestanding from "CCNA for Dummies" - bcos i jst needed a breakdown of that.

mattsthe2 wrote:

Hi Guys,

2) With inverse APR enabled do i still need the Frame-Relay Map command?

and Qn 2, Inverse ARP is not configurable but can be disabled and so once u use the "map" command, u have jst disabled IARP.