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RE: VoIP QOS best practices

  • From: Ray Burkholder
  • Date: Mon Feb 10 14:20:56 2003

Ok, I've taken all the courses and done some stuff myself.

Here is roughly what to expect.

It IS important to do QoS at the CPE.  This ensures that during times of
congestion, voice traffic gets out to the real world in a timely

In networks supported by Nanog people, usually they have bandwdith to
spare, and so QoS isn't necessarily important.  The issue is when
traffic crosses ISP boundaries, because many times these links are
clogged.  It used to be you had to stay away from MAEWEST and such
because of big packet drops and delays (big no-no's for voice).  Things
are getting better in this regard because of a larger number of cross
connects between carriers.

General rule of thumb used by the big Voip guys is to send most of your
voip traffic through what could loosely be termed as Tier 1 providers
(please don't flame me on this remark).  They you can be pretty sure
that there is much excess bandwidth, fast switches, and fast transit
time with little drop out (all important criteria for good voice

The issues are always when crossing carriers, and at the network edge.
These are the troublesome spots.  Some solutions include peering with
multiple Tier 1 providers, and doing traffic engineering to ensure your
traffic goes through the best provider to the end destination, etc, ...

When you get into IP Telphony in a LAN environment I can get into a
whole other discussion of myth dispelling.  For example, just because
your LAN switch has underutilized GigE and FE ports, did you know that
you can still suffer horrible voice quality?  QoS fixes this in a LAN
enviroment which could be viewed as bursty system where as internet
switches tend to be more smooth flow in nature (if I'm wrong on this
one, I'd like to hear about it).

Ray Burkholder

> -----Original Message-----
> From: Charles Youse [] 
> Sent: February 10, 2003 14:03
> To: Bill Woodcock;
> Subject: RE: VoIP QOS best practices
> That doesn't seem to make a lot of sense - is it that QoS 
> doesn't work as advertised?
> As someone who is looking to deploy VoIP in the near future 
> this is of particular interest.
> C.
> -----Original Message-----
> From: Bill Woodcock []
> Sent: Monday, February 10, 2003 12:48 PM
> To:
> Subject: Re: VoIP QOS best practices
>     > > Looking for some links to case studies or other 
> documentation which
>     > > describe implementing VoIP between sites which do not 
> have point to
>     > > point links.  From what I understand, you can't 
> enforce end-to-end QoS
>     > > on a public network, nor over tunnels.  I'm wondering 
> if my basic
>     > > understanding of this is flawed and in the case that 
> it's not, how is
>     > > this dealt with if the ISPs of said sites don't have 
> any QoS policies?
> QoS is completely unnecessary for VoIP.  Doesn't appear to 
> make a bit of
> difference.  Any relationship between the two is just FUD from people
> who've never used VoIP.
>                                 -Bill

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