First off, I am not a network engineer so apologies if I get terminology messed up, i realize accuracy is important here.

Currently, we have a small(ish) network with around 40 devices and 20 IP phones all connected over the same LAN. For some reason the call quality on the VoIP system has tanked and we are getting a ton of "Jitter" and very occasionally a dropped call. That's the problem in essence, so after some research I have discovered.

  1. Ideally, the VoIP system should be on its own VLAN - to minimise broadcast traffic
  2. Some QoS should be setup on the switches

I have checked my switch (Netgear GS724T) and it supports VLAN. I am pretty sure I could get this working if I plug the VoIP server into the VoIP VLAN but I don't see how this is achievable while also keeping it on the default VLAN so it can talk to the Domain controller.

Whats the best setup for this, remembering the overall goal that is removing the jitter and improving call quality

Should the VOIP server be off the domain and on the VLAN with the phones and just totally segregate it that way? Then, would they be better of on their own IP subnet also?

Whats more likely to be the issue, the fact that they share the LAN, or the lack of QoS. Should I do both? I have no idea in my switch how to prioritize VoIP traffic. Do the "interfaces/ports" get prioritized? Do I need to care about QoS if the VoIP system eventually gets its own private network.

Are there any other options I can look into to help reduce the jitter?

Phew, thanks for any advice, I didn't set this network up, I have inherited so I realise there are probably other glaring issues here also....


I should note that currently the VOIP server is virtualised, so, do I have to move it to a physical box to plug it into the VoIP VLAN?


I would move VOIP server to separate box as the first step. This is a small environment, and my guess is that either VM Host network interface or too tiny VOIP VM is the culprit.

  • ok, I will try that first. Then at least I will be able to move that machine onto the VLAN if it doesn't help and increases mobility. Bring on Monday. Maybe its time to upgrade the voip software while im at it! – Keeno Oct 11 '13 at 18:49
  • more info on the VMs, its MS Hyper-V. This particular VM has 1 core and 2GB memory, its only function is VOIP. I can add more memory and/or cores, but I dont think its that. No idea about its interface :) – Keeno Oct 11 '13 at 18:54
  • Your MRTG/Cacti/Whatever graphs will give you some info... :) – Dusan Bajic Oct 11 '13 at 19:03

Putting the VOIP phones and server in their own VLAN (layer 2) will necessitate putting them in their own subnet as well (layer 3). If you have a way to route traffic between the VOIP VLAN and the main VLAN then the VOIP server won't be isolated from the DC. I've never worked with VOIP before but isolating the VOIP traffic from the rest of the network sounds like the best first step.

As far as QOS is concerned I would hold off until you see if things improve after implementing the VOIP VLAN. I've never worked with QOS either but my understanding is that it only comes into play when there is bandwidth contention (based on your QOS rules), so if there's no bandwidth contention then it may have no affect at all.


As to how to connect your VOIP server to the VOIP VLAN, it's dependent on what virtualization platform you're running and what hardware the hypervisor has available.

The simplest and most straightforward solution would be to install an additional NIC in the hypervisor (if it doesn't already have one), connect this physical NIC to the VOIP VLAN, create a new virtual switch bound to this NIC, and connect your VOIP server to this new virtual switch.

  • thanks, i will give that a go, my next issue is that currently my VoIP server is virtualised, so how the hell do I plug it into the VoIP VLAN...some more research needed :) – Keeno Oct 11 '13 at 16:29
  • QOS - not totally. This is layer 2 QOS and you could just put the VOIP vlan on higher priority than the regular one, so that this traffic always has priority, based on required speed and same time guaranteed slow bandwidth... as VOIP wont fill up the pipe. This is standard setup and your Netgears may have - mine have - autovoip to move voip phones to their own vlan automatically. – TomTom Oct 11 '13 at 16:35

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