VoIP, QoS and metroethernet line

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Mar 20th, 2008
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Hi all. I have never had to configure VoIP and QoS before but now the need has arisen to do that.

We are connecting 2 locations(remote office and a central location) within the same city with a metroethernet link(several providers in play but they all offer L2 services) and we are planning to implement VoIP over the link to connect to the callmanager at central location.

For QoS I was intending to place it on my routers on both sides of the link. I was wondering does provider have to do any type of QoS on the L2 line because I had very different explanations told to me and I am at a loss which one is correct.

As for the configuration of QoS on the routers I was thinking of doing something like in attached file.

Of course priority will be changed as we are using g711 codec and there will be 23 IP phones on location(that's around 2 Mbits if all phones are in use if I calculated correctly). The line itself will be 6 Mbits large.

Should something else be done or should I ask the provider to do something?

Thanks in advance for any help.



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paolo bevilacqua Thu, 03/20/2008 - 12:49
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Hi, the config you sent is not very effective because:


1. there is no need to match by udp port. Phones send traffic marke DSCP EF and you can match directly by that.


2. because on the fasternet interface there is never congestion, a simple policy map applied there will never kick-in. See below for more on the matter.


So in summary I suggest you to do the following:


1. set you network without any QoS setting. Chances are, you will not need that.


2. If voice quality issues when large data traffic is set, ask your provider to give precedence to traffic marked DSCP EF. If they can do that, you're all set.


3. If they cannot do that, then yes you will need a policy map, but will be of the hierarchical kind, that shapes first to circuit speed, then applies voice priority. If you arrive to this third point, post back and I make you an example.


Hope this helps, please rate post if it does!

IgorHamzic Fri, 03/21/2008 - 05:56
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Thanks for the reply. It really helped and clarified some things that were a bit unclear.

The configuration I posted I took off one of the routers in the network that was configured for QoS for anther remote location that has fewer IP phones.

For one thing I always thought I had to apply QoS for voice on links that are of limited capacity whatever kind they are.

Anyway I'll take your advice and do some more research.


Happy Easter.


Joseph W. Doherty Fri, 03/21/2008 - 10:54
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If the 6 Mbps is fully dedicated to you, and assuming you intend to pass traffic other than voice, I would highly recommend QoS, unless you know you won't have any transient congestion.


Optionally, I would recommend running both Ethernet interfaces at 10 Mbps.


You could use your existing policy within a parent shaper policy.


E.g.


policy-map Shape6Mbps

class class-default

shape average 6000000

service-policy VoIP


Fastethernet 0

service-policy Shape6Mbps


PS:

In your existing VoIP policy, FQ within class-default doesn't perform as expected (other classes continue to obtain their minimum bandwidth) with other non-priority classes on most platforms . Recommend either elimination of voice-signaling class, or don't use FQ within class-default. Also, would try to see if there was a better method to identify the voice payload packets.

IgorHamzic Tue, 03/25/2008 - 08:06
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Thanks for the reply. After some research with the provider and the offers they made the CoS option for giving voice traffic priority over the link is rather steep(doubling the the price of the offer and the monthly costs) for a small office.

I will probably do QoS on our routers and shape the link first to 6Mbits and then dedicate 2Mbits for voice traffic.

The funny thing is that it surprised me how much of the link does VoIP traffic consume. 23 phones times 87,2 kbs for G.711 codec comes just under 2Mbits.

Anyway I'll post the QoS policy when I finish it so any advice then will be very welcome.

blackswans Fri, 08/28/2009 - 04:43
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Hi,


Did you do your policy if yes can you share it?


Thanks

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