wb 2 task 8.1 QOS Legacy Frame Relay Traffic shaping
Hi all,
it's not clear how bc it is fixed to 2560 without any given tc.
I mean ,if the cir is 256000 how I can calculate 2 variables like tc and bc?
Is perhaps missing tc=10ms in the task or is how we have to set like default with Voip packets?
Comments
The last point does say to ensure that all the shaping intervals are the smallest possible, which is 10ms.
Thanks so much Edmund for your fast help,now I found the doc!
http://www.cisco.com/en/US/tech/tk652/tk698/technologies_tech_note09186a00800d6788.shtml
Frame Relay Traffic Shaping For Voice
When configuring FRTS for voice, data performance may suffer at the
expense of good voice quality. Here are some guidelines to enhance voice
quality when configuring FRTS for voice:
Do not exceed the CIR of the PVC
Most users have difficulty following this recommendation because the
result is the router will no longer be able to burst to port speed.
Because voice quality cannot tolerate much delay, any queueing of voice
packets within the Frame Relay cloud must be minimized. When CIR is
exceeded (PVC CIR, not the router configured CIR), depending on the
provider and how congested the rest of the Frame Relay network is,
packets may begin queue in the Frame Relay network. By the time the
Frame Relay switch queues have backed up enough to trigger BECNs, the
voice quality is already diminished. Because customers have many
different Frame Relay providers and differing amounts of congestion
across their sites, it is difficult to forecast what configuration
works. Maintaining values at (or below) CIR on the PVCs that transport
voice has proven to work consistently.
Some providers sell a Frame Relay service of 0 CIR. Obviously, not
exceeding CIR in this case would prevent any voice from being sent
across the frame link. A service of 0 CIR may be used for voice but
there needs to be a Service Level Agreement (SLA) with the provider to
guarantee minimal delay and jitter for a certain bandwidth across the 0
CIR PVC.
Do not use frame relay adaptive shaping
If the configured CIR within the frame relay map class is the same as
the true CIR of the PVC, there is no need to throttle down traffic due
to BECNs. If CIR is not exceeded, BECNs are not generated.
Make Bc small so that Tc (shaping interval) is small (Tc = Bc/CIR)
The minimum Tc value is 10 ms, which is ideal for voice. With a small
Tc value, there is no risk of large packets using all the shaping
credits. Large Tc values can lead to large gaps between packets sent
because the traffic shaper waits an entire Tc period to build up
additional credits to send the next frame. Making Bc = 1000 bits is
usually a low enough value to force the router to use the minimum Tc of
10ms. This setting should not affect data throughput.
Set Be = zero
To ensure the CIR value is not exceeded, Be is set to zero so there is no excess burst within the first shaping interval.
Note: A good solution employed by some customers is to use
separate PVCs for data and voice. This solution enables the customer to
transmit up to port speeds in the data only PVC while maintaining a load
at or below CIR on the voice PVC. Some frame providers may not find the
solution appropriate depending on the frame switch and its queuing
structure. If possible, have the Frame Relay provider prioritize the
voice PVC over the data one so that there is not any queuing delay
because of the data packets.
Hello All,
My question is about the use of fragment size. From my understanding, the IOS calculates this for you automatically. If so, is this required as part of the answer. If I leave it out from the soultion, will I get the marks for it?
Just in case you need assistance with the calculation
How to obtain the Fragment Size:
Serialization Delay : Fragment Size(bit) /link bw (bps)
So in this case we are given the Serialization Delay which is 10 ms and the link bw (256kbp)
So the formula will be :
Fragment Size = Serialization Delay * Link BW
X= 0,01 * 256000
X= 2560
That's the fragment Size that we can send over that link in 10 ms.
Now, on the Frame-Relay configuration we MUST set it in bytes so we must turn the 2560 bits into Bytes:
2560/8 = 320.
That's how you get the value
Regards,
Jcarvaja
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