ESW 540-24 PoE

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Feb 19th, 2010
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I want to depoly 5 ESW 540-24 PoE switches in a network with depolyment of Polycom IP phones.

As you know these switches come with QoS preconfigured for deployment of IP phones.

Now I have general questions regarding advance QoS configuration done by Cisco as preconfigured.

The first question is that why in the "CoS to Queue" page settings the CoS value 0 and 1 is mapped to queue class 4 and CoS value 5 is mapped to queue calss of 1?

As we know the queue class 4 does have the highest priority than 1, and CoS value 5 is from the IP phone for the voice RTP traffic which in this settings is mapped to queue class 1 which it does have the lowest priority. In addition, the CoS value 3 is mapped to queue class 2 which this CoS is set by IP phones for the voice singaling traffic.

Cos     Queue

  0         4

  1         4

  2         3

  3         2

  4         3

  5         1

  6         2

  7         2

The second question is, in the QoS to queue page under general section the WRR queuing is set and not Strict Queuing which as we know Cisco has recommend in its CCNP ONT book that for deployment of IP phones in a giving network the LLQ queuing has to be used and not WRR.

The thrid question is, in the "DSCP to Queu" page why the DSCP 46 is set to queue 1 which this value is set by an IP phone for its RTP traffic. And why DSCP 26 is set to queue 2 which is the value set by an IP phone when sends its signaling traffic toward the switch.

The fourth question is, why in the "DSCP Mapping" page under Advance section the DSCP 26 & 46 mapped to 0 under "DSCP Out" section.

I have checked the Admin documents, but there is no general guide line for VOIP traffic configuration and there is no documents/configuration sample on the Cisco web page for deployment of IP phones.



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alissitz Fri, 02/19/2010 - 10:22
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These are some good questions and points. Let me ping our product management for this, as the defaults do not appear logical.

As you mention, this is set to weighted round robin (WRR) and not strict priority by default.  For voip, I agree that we should configure a strict priority queue and have the other 3 queues operate in WRR.

It looks like we have the queue mapping backwards according to the WRR bandwidth weights... however, let me check and make sure there is not something else going on here, or if this is a cosmetic error.

Once strict priority is enabled, then Queue 4 will be the priority.  At this point this mapping will be most important.  For now, it is based on ratios ... with all queues getting the amount of service based on their ratio.

As for the COS, if you have placed the phones in vlan 100, then these will have a COS value since the incoming packets should be tagged, the default vlan 1 will not be tagged and as such have no COS.  I agree, the default COS to queue mapping looks odd to me ...

Sorry I do not have more for now, hang tight please,

Andrew Lissitz

alissitz Fri, 02/19/2010 - 15:19
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Good evening,

Just a quick update - we have sent this to our QA teams and with the product management team we are investigating this more.

Thanks for your patience in the mean time.

Kindest regards and best wishes for a great weekend,

Andrew Lissitz

alissitz Mon, 02/22/2010 - 14:05
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Nothing as of yet ... this sparked quite a bit of emails internally and people checking on whether or not this is cosmetic or actually the wrong defaults being set.  For sure these settings are not what we recommend.

Please stay tuned.

BTW - how far out is the deployment? 

robert.michaelian Mon, 02/22/2010 - 14:19
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The deployment due date is mid March, but I need to start configuring the switches during this week.

alissitz Mon, 02/22/2010 - 19:32
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I have communicated this to them.  More to come.

In the mean time, have you upgraded the switches?  I would suggest to upgrade these to the latest version.  HTH,

Andrew Lissitz

robert.michaelian Tue, 02/23/2010 - 14:01
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Yes, I am upgrading all of them now to the latest firmware version which is 2.1.16

alissitz Wed, 02/24/2010 - 11:27
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Hello and good afternoon.

I have gotten a response, and in short the answer is to simply configure the smart ports appropriately. 

As for the defaults, we have previously done much stress testing and have found these configs to work well under voice and data load.  No voice quality issues.

Do you have any other questions or concerns with your install?  Do please ask them here.  HTH,

Andrew Lissitz

robert.michaelian Wed, 02/24/2010 - 15:04
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It's not clear whether what I'am seeing is what Cisco/Linksys thinks is the right config.

I'll upgrade the firmware, save the config, factory default, then apply the smartport macros to see what the results are.


alissitz Wed, 02/24/2010 - 15:07
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Ok, sounds good.


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