# Task 10.50 - Using MQC CBWFQ with Legacy FRTS

in QoS

Can someone explain how did we get Bc of 25600 ??? Tc is 10ms .... i came up with Bc of 5120 based on Bc=CIR * Tc/1000 ....

map-class frame-relay LEGACY_FRTS
frame-relay cir 512000
frame-relay bc 25600
frame-relay mincir 256000

• That's a great question.

The requirements stated "shape average of 512Kbps, Tc 10ms, BECN adaptive down to 256Kbs. Then the MQC requirements of 64Kbps and 192Kbps.

With the figures in the solution guide we never send above 256Kbps as the Bc is 25600 and Be is 0. This also breaks the Tc interval requirement of 10ms.

Shouldn't the solution be:

map-class frame-relay FRTS_TO_R5

frame-relay cir 512000

frame-relay bc 2560

frame-relay be 2560

frame-relay mincir 256000

The logic being that "Bc" should not be above minCIR, and"Be" brings us to the CIR rate of 512Kbps. When you received BECN's you back off to "Bc" to get minCIR.

Or am I looking at this all wrong?

Pete

• Or maybe there is just a mistake in exercise content. There is no VoIP traffic so 10ms Tc has no sense. If you pay attention to show output you will see that there is 50ms interval time. I think there should be 50 ms instead of 10ms.

• You right ... i missed that interval of 50 in their output ... Looks like either the task has wrong Tc 10 instead of 50 or 50 was used during calculation isntead of 10 (may be left over from some other config) ...

I think there should be 50 ms instead of 10ms
• Agreed ... either Tc = 50ms or Bc = 5120 bits

• Agreed ... either Tc = 50ms or Bc = 5120 bits

I agree. It's either the task requirement or the solution needs to be amended.
We can cross check with task 10.21 Legacy Adaptive FRTS for the calculation.
On page 1607 SG v5.019, it mentions:
CIR = 384Kbps
minCIR=256Kbps
Tc=10ms
Bc=CIR * Tc/1000 = 384000 * 10/1000 = 3840 bits

• +1

• I agree. It's either the task requirement or the solution needs to be amended.
We can cross check with task 10.21 Legacy Adaptive FRTS for the calculation.
On page 1607 SG v5.019, it mentions:
CIR = 384Kbps
minCIR=256Kbps
Tc=10ms
Bc=CIR * Tc/1000 = 384000 * 10/1000 = 3840 bits

I also agree that Tc should be 50ms but then why SG has choosen Be to be 0 instead of leaving it as default ?

•

I also agree that Tc should be 50ms but then why SG has choosen Be to be 0 instead of leaving it as default ?

it's zero by default.. isn't ?

Rack1R2(config)#map-class frame TEST
Rack1R2(config-map-class)#frame-relay cir 512000
Rack1R2(config-map-class)#frame-relay bc 25600
DIDN'T CONFIGURED HERE
Rack1R2(config-map-class)#frame-relay mincir 256000
Rack1R2(config-map-class)#exit
Rack1R2(config)#int se0/0
Rack1R2(config-if)#frame-relay interface- 205
Rack1R2(config-fr-dlci)#class TEST

Rack1R2#sh run | be map-
map-class frame-relay SHAPE
frame-relay cir 512000
frame-relay bc 5120
frame-relay be 0
frame-relay mincir 256000
service-policy output CBWFQ

• This is now task 10.32.  the burst interval requirement given is not met in the SG as per the discussion here so this is still an error.

Just leaving this for the next person to do the task to find.

-h