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Beginner

QoS in a layer 2 network

Hello.

There is an issue into our environment, that cause bad performance into ip voice calls.

We have 5 switch (3750), managed by our own, while layer 3 (router and external communications) is managed by ISP.

We have ip phones (thomson) connected to some ports of the switches.

Users complain about bad voice quality.

I'd like to enable qos on layer 2 network.

If I configure qos globally (mls qos) and if I trust cos in every interfaces where there is a phone (mls qos trust cos), switches can obtimize ip voice packets transmission? I can't distinguish between phone and pc on the same port (with command "mls qos trust device cisco-phone"), due to the fact that phones aren't cisco devices.

Or do I need to do some other configurations?

Network is configured with only one vlan (mixed voice and data traffic).

Thanks

Daniele

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Advocate

Daniele,

Before adding any qos config you need to find the ansers to some questions.

1) What are the QOS values used by the ip phones ?

a) COS/DSCP for speach

b) COS/DSCP for signalling.

c) Is it specific UDP or TCP ports for speech & signalling

2) What QOS is being used by the WAN - DSCP values

Trusting device cisco phone only works with  ----- youve guessed cisco phones (uses CDP)

Regards,
Alex.
Please rate useful posts.

Regards, Alex. Please rate useful posts.
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Hello Alex and thanks for your reply.

I'm investigating with our partner that has installed the thomson phones.

2) What QOS is being used by the WAN - DSCP values

We don't control WAN, so this is not our problem; calls are degradated also between local phones, so, before, we want solve problem local.

Trusting device cisco phone only works with  ----- youve guessed cisco phones (uses CDP)

Yes I know that this feature works with cdp; so, my only alternative now is to trust COS on all interfaces connected to a thomson phone, regardless any other consideration.

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If you are seeing degredation between phones on the LAN, then I would consider segmenting your LAN into VLANs before looking into QoS although I appreciate that this is potentially a large piece of work.

What are the connections between your switches in terms of speed etc.?  It would be useful to see a LAN schematic showing how the switches are connected and showing which is the STP root.

If you have redundant uplinks back to the root switch  (which hopefully the router is connected to) you could use PVST spanning-tree costs to ensure that VOIP traffic went over a dedicated link which could also alleviate the problem if it is the uplinks that are congested.

Do you have anything on the LAN that is bandwidth intensive, or lots of local multicast traffic for which you have not configured igmp snooping queriers?  Any of these could lead to unnecessary traffic on the LAN.

I have a site with CCTV, IPTV, VOIP, Intercoms and all the usual client traffic all on separate VLANs and igmp queriers set up but with no QoS configurered whatsoever and it does not have any performance issues.  There is no L3 switch on the site, so I do inter-VLAN routing on a firewall of all places.  The site has ten L2 switches connected via 1Gb fibres. So based on my experience with this, I wouldnt have thought QoS was the issue.

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Hello again Alex.

1) What are the QOS values used by the ip phones ?

a) COS/DSCP for speach

b) COS/DSCP for signalling.

tos_sip=cs3

tos_audio=ef

cos_sip=3

cos_audio=5

c) Is it specific UDP or TCP ports for speech & signalling

SIP – UDP PORT 5060

RTP PORT PBX – RANGE (12000-13000)

Thanks for any suggesions.

Daniele

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Hello Alex.

Did you read my last message?

How can I configure catalyst to enable qos in our case?

Thanks

Daniele

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