All good points.
The FECN/BECN is not always a sign of
oversubscription. Oversubscription (and correct me if
I am wrong) causes delay. I've been involved in many
cases where delay was caused or increased as a result
of oversubscription. Most providers (and especially
if you have good support from them) do not recommend
oversubscription in Frame Relay.
FECNs and BECNs shouldn't be sent unless there's a
congestion point somewhere along the PVC path.
Traffic shaping is highly recommended when you are
interfacing a big pipe with a smaller pipe (example of
PVC from host site with DS3 to remote site with T1).
The site with the big pipe will try to burst to a
speed higher than CIR (sometimes the port speed from
the start) depending on the provider. In this case
you have a big data flow trying to be jammed in a
smaller pipe, the result the frame relay switch on the
provider side will invoque rate adaptation and
Congestion will occur causing you to see FECN/BECNs.
The solution as recommeded below: Traffic Shapping
Congestion can also be caused by the provider network,
however CIR is not a good traffic indicator. In this
case I would recommend you talk to your provider to
get more info on their network. By the way, do you
get utilization reports? the reports should give you
an idea.
I doubt that Oversubscription is measured based on
CIR. I know (from past experience) that Sprint does
not use CIR to measure oversubscription.
I would recommed that you implement Traffic Shapping
as a start, and get info from your provider on how
their rate adaptation works, some papers on the frame
relay switch they are using, and what their network
capacity looks like. This will give you a good idea
on where to focus on.
my $0.02 I hope it helps.
rb
--- Eric Hoffman wrote:
> If you feel that you maybe going over your CIR, I
> would suggest configuring
> traffic shaping on the router interface.
>
> The way I understand it, is that it will throttle
> the amount of traffic sent
> to the frame provider. If you see FECN and BECN's
> after configuring traffic
> shaping, you may have a case to contact the frame
> provider....
>
> Watch the wrap.
>
>
http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/qos_c
> /qcpart4/qcfrts.htm
>
> HTH,
> Eric
>
>
>
>
>
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED]]
> Sent: Wednesday, September 05, 2001 10:55 AM
> To: [EMAIL PROTECTED]
> Subject: Re: FECN/BECN below a CIR [7:18444]
>
>
> Don't forget as well that the time over which the
> CIR usage is calculated
> (I've forgotten the formal term and don't feel like
> searching for it right
> now) is generally of the order of a second (at least
> in this part of the
> world), while the load reported by the router is
> generally averaged over
> five minutes. If you have bursty traffic (routing
> updates, for example),
> you may be going above CIR for some periods, even
> though your five-minute
> average may be well under CIR.
>
> More relevant for DE rather than FECN/BECN, but
> something to keep in mind.
>
> JMcL
> ----- Forwarded by Jenny Mcleod/NSO/CSDA on
> 05/09/2001 09:48 am -----
>
>
> "Karen
> E
> Young" To:
> [EMAIL PROTECTED]
> Subject: Re:
> FECN/BECN below a CIR
> [7:18444]
> Sent
> by:
>
> nobody@groups
>
> tudy.com
>
>
>
>
>
> 05/09/2001
> 05:42
> am
>
> Please
> respond
> to
> "Karen
> E
>
> Young"
>
>
>
>
>
>
>
>
> If you're getting FECN/BECN traffic then its
> experiencing congestion.
> Congestion on the FR network prior to CIR being met
> is indeed a good sign
> of
> oversubscription. If its only occasional then it may
> simply have been a
> spike on the switch. However, if you're getting it
> fairly regularly, then
> you need to talk to your provider. There's NO reason
> to set FECN/BECN when
> there isn't congestion.
>
> Ask them how they determine subscription load. Some
> providers (such as
> Sprint last I heard) use the CIR to determine load
> on a switch, not the
> actual traffic. If they have alot of customers with
> 0 CIR then the switch
> can easily get oversubscribed to the point that the
> provider can no longer
> meet the CIR of their customers.
>
> HTH,
> Karen
>
> *********** REPLY SEPARATOR ***********
>
> On 9/4/2001 at 2:19 PM Paul Borghese wrote:
>
> >Does anyone know if a Frame Relay provider will
> send FECN/BECN messages
> even
> >if the CIR is not oversubscribed?
> >
> >Is looking at the FECN/BECN traffic a good
> determination of CIR
> >oversubscription?
> >
> >Paul
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