Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Attention: The Cisco Support Community site will be in read only mode on Dec14, 2017 from 12:01am PST to 11:30am for standard maintenance. Sorry for the inconvenience.

New Member

Frame-Relay DE - What FR devices can set DE

Hello all,

Not being a FR buff, I would assume that the only place that the DE bit in the FR header can be set, is by me, and by the FR carrier.

Now the question is, If a carrier has provided me with a 256k PVC from London to NY, I have this CIR. Is it only the first switch on the carriers network that can set the DE bit. Correct?

Can someone confirm this? Or is it any switch (although the CIR should not increase once past the first switch) in the FR network that can look at my CIR and set the DE bit.

One last point, is it any switch in the FR network that can discard my frame due to conjestion (if my traffic has DE set) or just the first switch?

Sorry if this sound stupid, but I can be sometimes :))

Kindest regards,


Hall of Fame Super Silver

Re: Frame-Relay DE - What FR devices can set DE


I agree that the logical place for DE to be set are your router and the ingress switch to the provider network, I believe that any switch that touches that frame is able to set the DE bit.

The answer to your second question is that any switch along the path can discard the frame if the switch is experiencing congestion.



New Member

Re: Frame-Relay DE - What FR devices can set DE

Thx Rick, thats great.

The reason I ask is that I am thinking of the following.

If I have one PVC from London to NY, both ends set to a CIR of 256k.

Then I order a second PVC from Manchester to the same site in NY.

The PVC should be end-to-end, ie, 2 x 256k PVC, but say I get the choice from the provider to not upgrade the NY PVC into their FR clould.

So potntially have 512 from the UK hitting (at some stage on ther FR network) an aggreagtion point that is not the last hop FR switch in the U.S. on the carrier clould.

This means that if the aggregation point is not the last hop FR switch there could be a potential bottleneck and potential congestion on the U.S portion of the PVCs from the start of the data aggregation point to the last hop switch and thus contention on the access portion of my circuit inbound on the U.S side.

Can and does this happen and this is why then and only then, it would make sense for an NNI FR connection to be able to set DE as you point out above. Do servie providers offer this type of service with these caveats?

Also, I assume for this to work, each node in the FR network needs to know about each customers CIR in relation to a PVC transiting the NNI switches, as to be able to compare CIR to actual TPUT, and does this not give more overhead on the carriers network as potentially each customers CIR for a PVC traversing the switch would have to be known or configured on the switch.

Many kind regards, and thx for the help,


CreatePlease to create content