VOIP Questions

With the recent phone issues we have been having I've been doing some thinking. I don't know much if anything about VOIP so I'm hoping someone might be able to help me work through some issues.

Does one VOIP call take up 40 Kilobits or Kilobytes of bandwidth?

I ask because we've made changes to the network (new core switches, new router, vlans) and we're still having issues with the phones. Now I was thinking about what my boss said (he said the VOIP calls are only taking up 40k worth of bandwidth each. So I started to work through the math (I suck at it, but I try) and looked at our bandwidth. We have two T1's dedicated to VOIP (I believe). So we are looking at 3 megabits per second, which is 384 kilobytes. Thus if it's 40 kilobits then if we have 20 outside calls going on we are using a third of our bandwidth. If it's kilobytes then we are smashing our bandwidth....

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Comments

Ashenwelt

As a general rule, network badwidth is always in bits. Now, I don't know what VOIP solution you are using, but most I have used ranged fom 24kbps to 60kbps. Remember though, that you need to leave some headroom in your planning, or use some layer four controlls to protect your voice bandwidth (unless you want your users screaming).

binarysoul

It would kilobits/second.

The amount of bandwdith used by VoIP depends on the codec, e.g. G.729, G.711 and etc. G.729 is compressed codec that uses 24kbits/session (plus a bit overhead). From my experience, sometimes VoIP call issues are not due to lack of bandwidth, but due to packet loss, congestion between two ends of the call, i.e. between caller and receiver.

My advice would be to collect some data and see where the fault is.

malcybood

the_Grinch wrote: »

With the recent phone issues we have been having I've been doing some thinking. I don't know much if anything about VOIP so I'm hoping someone might be able to help me work through some issues.

What issues are you having? What are the symptoms?

the_Grinch

Dropped calls (mainly to receptionists where all outside calls come in), echoes, and quality issues.

Ashenwelt

the_Grinch wrote: »

Dropped calls (mainly to receptionists where all outside calls come in), echoes, and quality issues.

What system are you using?

the_Grinch

We are using a hosted VOIP solution. They are using two codecs: G.729 G.711u(8k). I really think it is a bandwidth issue because the calls seem to drop during the busy periods of the day, 11-2 and then 3-5. It seems to me if we are zapping our pipe then calls would be dropped and quality issue arrive because there is no more room for them. Our T1 provider says we are only using about 50% of our bandwidth, but if they are looking at a 24 hour period and for 12 of those hours we aren't there then you get 50%. I'd like to see a bandwidth chart during the working hours of 9 to 5. Any ideas, am I wrong in my thinking here?

darkerosxx

Monitor your bandwidth for a bit and see for yourself:

MRTG - Tobi Oetiker's MRTG - The Multi Router Traffic Grapher

Ashenwelt

the_Grinch wrote: »

We are using a hosted VOIP solution. They are using two codecs: G.729 G.711u(8k). I really think it is a bandwidth issue because the calls seem to drop during the busy periods of the day, 11-2 and then 3-5. It seems to me if we are zapping our pipe then calls would be dropped and quality issue arrive because there is no more room for them. Our T1 provider says we are only using about 50% of our bandwidth, but if they are looking at a 24 hour period and for 12 of those hours we aren't there then you get 50%. I'd like to see a bandwidth chart during the working hours of 9 to 5. Any ideas, am I wrong in my thinking here?

I agree with darkerosxx, do check your bandwidth. More than that though, keep an eye on your latency. You could easily be having problems, depending on how your ISP is setup (and how badly over subscribbed) with high latency killing your calls.

the_Grinch

Had the phone company do a check on the bandwidth for the week, during peak hours, and they said we aren't hitting more then 50%. Now I had the network company check and they are seeing undersized packets being sent from the two receptionists phones. I even switched the port and the issue continued. Any ideas?

networker050184

What kind of undersized packets are they talking about? If its only two phones having issues I'd check the obvious like cabling and the actual phones. Might have to just get a some new users that don't complain so much too

the_Grinch

I would love new users who don't complain as much. Networker I think you're right, as our network company believes it to be the cables. Lets just say that none of this cables are certified. The good news is it will be a none issue once we switch buildings, as all the wiring is cat6, certified, and brand spanking new. Now to figure out what to do!