VOIP over Comcast causing problems

voip

We're running a VOIP system over Comcast. The problems are:

Some calls don't complete (both incoming and outgoing)
Some phone calls get terminated in the middle of the call.

I want to run some kind of throughput test on the Comcast service (which could test the throughput several times per second) to ensure that there is enough bandwidth available for the phonecalls. Which free or trial software or applications would you recommend?

Best Answer

For the most part, VoIP is not bandwidth-intensive. It is, however, quite sensitive to variable latency. In your testing, you need to test both aspects. I'd recommend you look at setting up an iperf server on one end of your connection. You'll then connect to that from a client on the other end. Iperf will be able to not only report on the bandwidth available, but also on the jitter of the connection, which is quite useful when troubleshooting VoIP issues.

Additionally, you may want to look at doing some real SIP tests using SIPp. You'll be able to send incrementally increasing numbers of calls through and find where things start breaking.

Related Solutions

VoIP: converged or not

A lot of this depends on the bandwidth that your phone system is going to use - if it's a call center with hundreds of people on the phone simultaneously you'll have a higher need for a separate network than an office of hundreds who just want phones on their desks but aren't heavy users. A conservative (as in, "way more than is really used") estimate is 128kbps per simultaneous call, or 8 calls per megabit, so gigE can do approximately 8000 simultaneous calls (okay, a little less due to overhead, but that's the right order of magnitude). So it's unlikely to be a bottleneck. And as long as you have QoS so that big downloads won't affect your phone traffic you should be fine.

Something you don't address is the Power Over Ethernet (PoE) angle - PoE switches are a significantly more expensive (both to buy and to run) than their non-PoE counterparts. One nice feature of PoE is that a single UPS on the switch keeps all the phones running during a power outage.

What I've done in the past is: run a PoE and a non-PoE port to everyone's desk. The PoE is labeled 'Phone', the non-PoE is 'data'. This preserves data speeds for the user's computer, gets the aforementioned power redundancy for the phone, and allows me to (eventually, if needed) separate out the networks more.

So I guess what I'm saying is: don't bother with 'software' non-convergence, but do bother with separate networks where the hardware matters. If the hardware's going to be the same though (ie. you're running all PoE or all-non-PoE switches) then a converged network should be fine.

Voip external extension behind nat

Road Runner tends to block high ports. However, I was able to get my remote phone working by using Port Address Translating (similar to NAT, and frankly it's the same thing)...

On your remote network in your router settings, map each one of the ports Talkswitch specifies...

ports 5060 / UDP, 6000 - 6006 / UDP, 69 / UDP, 8484 / TCP, 9393 / TCP

...to an unused outbound port below 1024 (UDP 69 does not need translating), then on your company router map those incoming ports back to the Talkswitch device on the correct port.

The phone system has no problem with this because to it, it's sending and receiving on the right port.

Horrible text graph below. If it doesn't make sense let me know and I'll do a graphical in the morning.

Remote Phone <> (Port 5060 UDP) <> Remote Router <> Internet (Port 1011 UDP) <> Local Router <> (Port 5060 UDP) <> TalkSwitch box.

Best Answer

Related Solutions

VoIP: converged or not

Voip external extension behind nat

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