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QoS on trunk ports ESW and SF models

How does the ESW 500 or SF300 line guarantee QoS of voice traffic when trunking switch to switch? I have (2) ESW 500 series switches in series. The phone on switch 1 have no audio issues, but the phones on switch 2 (the last in the series) have intermittent voice quality issues when dialing across a WAN circuit to another office. The phone on switch 1 do not have that issue though they traverse the same circuit. They are all using the same VLAN 100.

Any ideas??

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Re: QoS on trunk ports ESW and SF models

Hi Bill

Guarantee --- rough word when you talk in terms of QOS.

Firstly,  I would verify that the SF300 switch is using the most current firmware.

Bill, I can see from my SG300 GUI,  that I have basic QOS enabled with strict priority queuing and the switch will trust DSCP.  I am happy with that technique as my SPA phones do utilize DSCP as a marking that switch recognizes. as well as that smartports automatically apply QOS techniques to voice traffic.

So I know that these packets will egress from my SG300-10P before other data  packets.

But to improve the chances of certain traffic egressing out a switch port uplink  to a router, there are techniques that could be  used to achieve that objective.

They include the use of;

  • smartports - done automatically when connected to UC500 or Uc300, if you are using recent firmware.
  • specifying via CCA in the UC500 which vlan is a voice VLAN .
  • basic or advanced QOS
  • traffic shaping and marking  ...bla bla it goes on and on

Might i suggest you look at a excellent tech note by Ivor that tries to explain this complex topic;

https://supportforums.cisco.com/docs/DOC-16271

At the end of the tech note is a reference to the admin guide of the 300 series switch.

No where in that Admin guide is there a single reference to 'guarantee'.  But the Admin guide tries to explain the techniques that are and can be used to enhance the  QOS for your applications. 

You have the option if you want to setup a QOS policy that explicitly waits for high priority traffic to egress out of the switch to a router, before lower priority traffic.

Why the difference between the ESW and the SF300...

In fact a factory reset the configuration of a ESW switch , if you were to notice QOS section of the GUI,  a extensive QOS policy setup by default to make sure Voice has priority over data..

regards Dave

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