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Is there any point in enabling QoS on a dedicated VOIP network that only has VOIP traffic?

  • Are any links dropping packets? – Mike Pennington Dec 16 '13 at 11:33
  • Thanks Mike I will look into potentially dropped packets. We are just ocasionally getting some odd behaviour from the network, mainly sound from another endpoint being audible without a call completing. It doesn't happen often. – Brian Parker Dec 16 '13 at 16:02
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No, there is absolutely no reason why you would if you are on an isolated network. Quality of Service is simply a queueing mechanism that prioritize traffic based on predetermined requirements. If you enabled QoS on this network, you would effectively be saying "guarantee 100% of my already 100% available bandwidth is guaranteed for VoIP".

  • Fizzle, you are wrong! QOS, in most configurations it is not RESERVING of bandwidth, it is make "interesting" traffic more PRIORITY than other, for exaple: You have network interface with traffic in query: 99% simple traffic 1% voip traffic QOS will serve first of all voip, than other traffic, as usually it wont reserve anything en.wikipedia.org/wiki/… – pyatka Dec 16 '13 at 13:12
  • @pyatka You're right; I screwed up the last quote on my answer. Thanks. – Ryan Foley Dec 16 '13 at 13:53
  • Hi guys. It is a dedicated network, just for VOIP, no other traffic. I thought Fizzle had it nailed but Pyatka seemed to cast some doubt. I have to say my first thoughts were that QoS didn't seem to be necessary but I wanted to hear from those with more real-world network experience. – Brian Parker Dec 16 '13 at 15:58
  • @BrianParker My original answer was spot on. His challenge was correct with regard to my quoted "it would be like" example; which has since been modified. If you have a network dedicated to VoIP, you don't have any need for queueing mechanisms since they will never be used. – Ryan Foley Dec 16 '13 at 16:17
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Do you need QOS on a dedicated VoIP network?

Possibly not, but you probably want it in place.

It really will depend on the network layout/capacity, the complexity of your phone system, the volume of voice traffic, and your business needs.

Here is the most basic example I can think of:

If a link is so saturated with calls that call-control traffic can't get through, what happens? You should ideally still use QOS to give call-control traffic a guaranteed portion of each link. If you do not, you could potentially wind up with all sorts of unexpected call behavior. (Dropped calls, one way traffic, etc, etc)

Another consideration is, do you control the entire network? If this is multiple sites connected across some sort of MPLS service, you may need QOS to prioritize your traffic within the provider's network. (Which they'll gladly sell you at a cost.)

The bottom line is this:

Do you care about a specific portion of your network traffic reaching it's destination? Then QOS is your friend.

  • How about leaving some bandwidth for network protocols and using < 100% in priority queue for voip traffic? – generalnetworkerror Apr 20 '15 at 7:33
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If you have dedicated switches for VoIP, or your switches have no significant load, then there's no reason to use qos.

  • Please do not add an answer just to make a comment. – Mike Pennington Dec 16 '13 at 13:14
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If you have no voice quality problems, how will you notice, that QoS was really enabled and working? If you have some voice quality problems, you have to investigate them at first. Voip can exists with any other data in one network without QoS enabled in many cases.

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