We have a PBX server (also connected to the internet) and all VoIP devices currently (early stages of deployment) set up on a network that is phsyically separate from the main computer network.

As very soon the network is going to get reorganized, I'm thinking about the "consequences" of merging the VoIP network it into the computer network as the telephony and computer services are getting more and more "interconnected" - while it works well currently, I worry that by leaving it this way will lead to headaches when trying to add services in the future.

It seems there are both configurations "in the wild" - mostly depeding on if the VoIP network was build upon the previous telephony network or if it was added to the computer network before phasing out the telephony network.

The pros of leaving the networks separate I can think of are security and not having problems with network congestions etc., while the cons are obvious - difficulty in interconnecting to/from other services and devices.

Is there anything else I'm missing here? Considering the people connected to the computer network are not heavy network users, I don't really expect any problems regarding that, but just to be on the safe side, should I?

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    If you do merge the two networks together, look into QoS packet prioritization for the phones. The last thing you want is your computer traffic getting higher or equal priority than your voice packets, and having the pipe get so busy that you loose call quality. You'll need to configure your router(s) properly for the QoS, and you'll also need to make sure that your ISP and your SIP service provider honors the flagging of your voice packets for higher prioritization. – David W Dec 18 '11 at 5:53

VoIP servers (particularly Asterisk) are pretty notorious for having security holes - the degree of risk they pose being dependent on what they have access to (This guy has made a hobby of finding issues with VoIP servers, with Asterisk taking the bulk of the heat). Accordingly having a separate VoIP network (or at least a separate vLAN) with limited access to the rest of the company's network is pretty much the de facto Best Practice, and it would be my recommendation were I designing the network.

Separate hardware has other advantages (as you noted one advantage can be protecting voice traffic from network saturation), though I wouldn't consider it critical for most environments - vLANs are sufficient in most cases.


I recently experienced a Ethernet packet storm on our network. The Asterisk server was in the network and the result was, that no phone calls were possible anymore. This was a major problem. So you should place the server at least in its own VLAN.

  • But wouldn't having the server in its own VLAN basically be the same as if the networks are physically separated, ie. I would have to route the traffic between the VLANs? – Carko Dec 19 '11 at 2:35
  • Yws, except you dont need separate ahrdware and are more flexible in setting things up. Good VOIP hardware supports both VLAN sa well as ethernet pass through - so one cable goes to teh phone, which then has another cable to the computer. Result: One port only used. – TomTom Dec 19 '11 at 5:45

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