From: Joe Chang (changjoe@earthlink.net)
Date: Fri Mar 28 2003 - 15:59:42 GMT-3
Whether or not you need traffic shaping at the R1 and R13 will depend on the
service contract to those sites. If the provider says there is no bursting
allowed and no BECN signalling during congestion, you might as well utilize
configure some sort of queueing to stay strictly below the guaranteed CIR.
On R5, the design seems to rely on BECNs to throttle down the two PVCs if
their total traffic exceeds the physical port speed of 64 Kbps. I don't
think this would work, please take a look at the following scenario:
1) Outgoing traffic to R1 and R13 experiences a spiked increase.
Simultaneously both traffic shapers allow bursting up to 64 Kbps because
previous traffic has been low and the token buckets are full.
2) The IOS sends these bursted backets to the interface driver-level queue
(the FIFO transmit ring). Since the physical port speed is 64 Kbps and the
combined PVC traffic is 128 Kbps, the transmit ring will become full.
Packets are dropped and the driver notifies the IOS to queue up subsequent
packets at the IOS level, until the transmit ring empties.
3) The frame switch network currently has plenty of bandwidth. It forwards
the 64 Kbps traffic from the two PVCs without having to send BECNs. The end
result is that congestion within R5 will lead to packet drops that FRTS will
not be able to avoid.
----- Original Message -----
From: "CCIE FUN" <ccieexam2002@yahoo.com>
To: <ccielab@groupstudy.com>
Sent: Friday, March 28, 2003 11:53 AM
Subject: Traffic-shaping question
> Hello all,
> I have traffic-shaping question and i have also
> mentioned the solution i used.
>
> please help me out to identify if it's correct and
> what commands are useful to determine that the traffic
> shaping is going to work as configured.
>
> Here is the question:
> 1.The router R5 has two PVC's going R1 and R13 each
> has CIR of 48Kbps and burst size of 64Kbps.
>
> 2. The circuit from R5 to the frame-relay switch is
> provisioned at a speed of 64Kbps.
>
> 3. If BECN's are recieved, R5 needs to throttle back
> back the PVC's to 32Kbps.
>
> 4. Using CIR, Bc and Be configure traffic-shaping on
> R5.
>
> Now here is my config for Router R5 relevant to
> Traffic-shaping. I have not shown any frame-maps or IP
> information for clarity purposes.
>
> !
> interface s0
> encap fram
> no arp fram
> no fram inv
> frame-relay traffic-shaping
> frame-relay class Shape
> !
> map-class frame-relay Shape
> frame-relay cir 48000
> frame-relay bc 6000
> frame-relay be 16000
> frame-relay mincir 32000
> frame-relay adaptive-shaping becn
>
>
>
> Now my question is do i need to configure R1 and R13
> for shaping even if it is not mentioned in the
> Question.
>
> Also is my solution correct.
>
>
> Thanks for your help.
>
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