Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements
Users might experience few discrepancies in Search results. We are working on this on our side. We apologize for the inconvenience it may have caused.
New Member

Telepresence QoS questions

I'm configuring QoS settings on the uplinks of some 6500 chassis. The QoS is mainly to prioritize telepresence, VoIP, and call signaling traffic through the uplinks. The uplink ports are on a WS-X6724-SFP module. Here are the queue sizes:

Q1 - bulk data/scavenger - 5%

Q2 - best effort - 60%

Q3T1 - call signaling - 5%

Q4 - priority - 30%

In the Telepresence Campus QoS Designs guide there is an example that shows:

wrr-queue queue-limit 5 35 30

wrr-queue bandwidth 5 35 30

I've changed the numbers to be:

wrr-queue queue-limit 5 60 5

wrr-queue bandwidth 5 60 5

My question is, is the 'wrr-queue bandwidth' I've configured above set correctly?  I've read two conflicting statements, one that shows the above config, and one that says that the larger the queue-limit, the smaller the queue-bandwidth.  What is the relationship between queue-limit and bandwidth.

A second question has to do with how the queues are serviced.  Consider the following config lines as presented in the Telepresence design quide for the same example above:

wrr-queue random-detect min-threshold 1 80 100 100 100 100 100 100 100

wrr-queue random-detect max-threshold 1 100 100 100 100 100 100 100 100

wrr-queue random-detect min-threshold 2 80 100 100 100 100 100 100 100

wrr-queue random-detect max-threshold 2 100 100 100 100 100 100 100 100

With the above lines, during congestion, what distinguishes Q1 from Q2 so that packets in Q1 are dropped before packets in Q2 since the min and max values are the same?

1 ACCEPTED SOLUTION

Accepted Solutions
Super Bronze

Telepresence QoS questions

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

But, now I'm really confused about the min/max queue question. Are you saying that if Q1 and Q2 min/max are the same, then there is no difference between Q1 and Q2?

Alone, no.  I also wrote you have to account for the bandwidth allocations between queues.  Only if the bandwidth ratios were the same, then there would be no difference.

3 REPLIES
Super Bronze

Telepresence QoS questions

Disclaimer

The      Author of this posting offers the information contained within this      posting without consideration and with the reader's understanding   that    there's no implied or expressed suitability or fitness for any    purpose.   Information provided is for informational purposes only  and   should not   be construed as rendering professional advice of any  kind.   Usage of  this  posting's information is solely at reader's own  risk.

Liability Disclaimer

In      no event shall Author be liable for any damages whatsoever    (including,   without limitation, damages for loss of use, data or    profit) arising  out  of the use or inability to use the posting's    information even if  Author  has been advised of the possibility of   such  damage.

Posting

I've read two conflicting statements, one that shows the above config, and one that says that the larger the queue-limit, the smaller the queue-bandwidth.  What is the relationship between queue-limit and bandwidth.

They're not conflicting as much as they have different objectives.

One approach is, if traffic is such low importance it gets little guaranteed bandwidth, then it also is of such low importance it can be dropped.  So, little bandwidth, little queuing.

The other approach is, if traffic is given little bandwidth guarantee, it's more likely to queue and queue deeper, so you need to increase such traffic's queue limit.

One approach then is to size queue limits in proportion to bandwidth guarantees the the other to size queue limits in inverse proportion to bandwidth guarantees.

Which to use depends on how you want to manage likely drops and what that means to the application, for instance, if bulk file transfer transfer we might want to drop as the application will both resend the lost packet(s) and slow its send rate.  If the traffic was video, we want to avoid drops especially if some delay is tolerable (e.g. streaming video).

A second question has to do with how the queues are serviced.  Consider the following config lines as presented in the Telepresence design quide for the same example above:

wrr-queue random-detect min-threshold 1 80 100 100 100 100 100 100 100

wrr-queue random-detect max-threshold 1 100 100 100 100 100 100 100 100

wrr-queue random-detect min-threshold 2 80 100 100 100 100 100 100 100

wrr-queue random-detect max-threshold 2 100 100 100 100 100 100 100 100

With the above lines, during congestion, what distinguishes Q1 from Q2 so that packets in Q1 are dropped before packets in Q2 since the min and max values are the same?

You need to consider bandwidth ratios for the queues too.  If bandwidth ratios were the same, then they would be treated the same (with above).  If bandwidth ratios were different, queue with lower bandwidth guarantee (everything else being equal) will queue first and queue deeper and hence its packets are more likely to be dropped (with the above).

New Member

Telepresence QoS questions

Your explaination of queue-limt vs bandwidth is good - thanks.

But, now I'm really confused about the min/max queue question. Are you saying that if Q1 and Q2 min/max are the same, then there is no difference between Q1 and Q2? The examples on pgs 5-24 to 5-27 of the Telepresence Campus QoS Designs Guide, and pgs 2-159 to 2-164 of Medianet Campus QoS Design 4.0 show min/max of all queues, except the last queue before the priority queue, as having the same values - the examples are for both 1P3Q8T and 1P7Q8T. In other words the example for 1P7Q8T has min=80 max=100 for Q1,2,3,4,5,6. If I understand you correctly, that means that packets from any of those queues will be treated the same, regardless there COS values and regardless of whether they are best-effort packets or call signaling packets or multimedia streaming packets?

Are the examples I point to in the QoS guides incorrect? Should I in fact have lower min/max values in Q1 than Q2, Q2 lower than Q3, Q3 lower than Q4 etc.?

And the last queue, Q3, of the 1P3Q8T example, has min = 60,70,80,90.... max=70,80,90,100...  Does that mean the packets in Q3 will drop before any packets int Q1 or Q2?

Super Bronze

Telepresence QoS questions

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

But, now I'm really confused about the min/max queue question. Are you saying that if Q1 and Q2 min/max are the same, then there is no difference between Q1 and Q2?

Alone, no.  I also wrote you have to account for the bandwidth allocations between queues.  Only if the bandwidth ratios were the same, then there would be no difference.

495
Views
5
Helpful
3
Replies
CreatePlease to create content