Networking Options

Hell All…

I need help with a networking option.

I am installing a FreePBX/Asterisk system for a small company. They will be SIP based using a “flex” based T1. Actually it will be two (2) bonded T1’s with the SIP channels setup within the same data pipe. Bandwidth will allocate as needed.

Here is what I would like some feedback on, I can create a new VLAN on the router, setup a new switch off that specific port and put all the phones on that LAN segment. Basically using the Router to QoS my voice/SIP traffic at router level, OR I can put it all on the same LAN segment, get a new switch that can manage QoS internally at the switch and put all the systems on the same LAN segment (PC’s and phones).

The same LAN for all devices is of course easier, as I can use the ports to daisy chain the systems as needed, and its keeps it all “together” but I want to make sure Im getting the best quality I can.

Any feedback MUCH appreciated.



That’s Hello, not Hell… sorry about that!

That was probably the most thought out, nice and informative answer I have ever received on a forum!!! THANK YOU!

Looks like my best option for my deployment and the customers usage would be to replace the current switch with one that will prioritize voice traffic. The current one does not, and they pull all their files (documents are redirected) from the main server. This will make certain that the voice traffic has priority over all other traffic at the switch level. Once the “voice packet” hits outside of the LAN the provider who is also creating the SIP channels has verified that they will prioritize that data over all others.



People often get mixed up about QoS and where it’s needed. In almost all cases QoS deployments can be broken into two purposes: maintaining low latency, and prioritizing in limited bandwidth.

For your LAN all the way up to the T1, you really only need to worry about the latency. Presuming you’re running 100mbps or gig you should always have enough bandwidth for a phone call + whatever the PC is doing. In theory something could happen to use up all that bandwidth, but chances are pretty small (unless your users really like to copy large files from local servers). So the real point is, on the LAN, you need to make sure VoIP traffic gets forwarded in realtime, and doesn’t get stored or delayed at the switch. This is what most QoS enabled switches do for you… they handle the prioritization of VoIP packets vs anything else at layer 2.

Once you get to the internet connection, things change. This is because your internet connection typically has less bandwidth available than your LAN. Doesn’t sound like this is a big deal for you at the moment, but it all depends how much traffic you push… (even the biggest pipes can be filled). This is where the router comes into play. While most routers call this QoS, in reality they are often doing some form of traffic shaping. That is, they are making sure that out of the available bandwidth, there is always enough room to pass VoIP traffic without incurring a loss. The more VoIP traffic that occurs, the more the router delays or drops (throttles) the data traffic to ensure all the VoIP survives.

So with all that in mind… your question is do you need to physically separate the VoIP from the data (at the router using VLANs), or can you safely share them on the same wire. As long as you use QoS enabled switches, you can safely share the traffic. You should still of course make sure the router is doing QoS (traffic shaping) also, to ensure maximum quality throughout the system.

In reality even relatively cheap switches work fine for this kind of thing… just make sure they have QoS support. (If you were to try to use non-QoS switches you might still get away with it, but you increase the chances of a problem at some point).

That was a nice answer but don’t let it fill you with warm and fuzzies, it is an oversimplification.

First, it sounds like your T1 is managed, so any voice traffic arriving to it will be properly groomed. That puts you way ahead of most people in the QoS have.

However for the router and switch to be able to prioritize voice, it needs to be told what packets are priority! This is done with various marking schemes. However for your network that is too complex.

Using a VLAN allows you to segregate the voice, assign IP’s just for voice, a voice gateway to apply WAN priority and makes provisioning and management much easier. Almost all the new switches support auto VLAN assignment so with the endpoint manager you can “zero touch” config your phones from box to desk.

Lastly if you do have congestion on the LAN or a broadcast storm the VLAN provides some isolation.

No warm and fuzzies here! :slight_smile: I know this can get tricky, but I did like the detail he added.

That all said I think the best option is for a managed QoS switch, please correct me if I’m wrong here. This will allow me tag voice data and give it a LAN priority over normal file data. Once it its the outside route, give that the provider does the rest I should be good…

Seems like it should be good… though I have been wrong before…



Yes, you should be fine. If you have a managed switch just toss the phones and server in a VLAN. The phones will untag the data LAN and present it on the PC port.