VoIP problems

Posted on 2009-05-05
Last Modified: 2012-05-06
My network currently has 30 VoIP phones using 8x8. The network connection is Covad wireless 2MB up and down. Now I guess this is a dish on our roof. What the problem is clients in the office are getting dropped during calls and their phone will randomly display no service. I've checked the bandwidth and it looks like it's fine. Also the jitter looks fine. What should I look for when trying to diagnose this. Any tips?
Question by:thursdasy
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LVL 22

Expert Comment

by:Syed Mutahir Ali
ID: 24310468
What kind of routers are you using ? Have you tried any tools to monitor network traffic to see if their is a certain type of traffic which causes this ?
Also, consult with 8x8 to see if they have any newer firmware for their devices or any known issues like this ?

Author Comment

ID: 24310788
@mutahir, yes I've been talking with 8x8 support and they say everything is correct. I've also talked with Covad wireless and they say the connection looks fine. One thing I must note is that our phone network is half duplex. Is this bad? I'm attempting to switch it to full duplex.

And I haven't monitored the network traffic yet Ill be doing that tomorrow hopefully once I figure out how to do it with our new switch.

LVL 32

Expert Comment

ID: 24314631

Good quality VOICE over an internet connection is not impossible however it is best effort. In addition, you are using a wireless conenction to Covad to boot. Latency and jitter are both key components when doing VOIP as well as QOS. Without any meaningful way to prioritize your voice traffic end to end you are at the mercy of the networks best efforts.

The alternative of course is to get a dedicated service or use an ISP that has VOIP services directly, that way you are not potentially routing over the Internet.

harbor235 ;}
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LVL 22

Accepted Solution

Syed Mutahir Ali earned 250 total points
ID: 24317899
Half duplex isn't going to help much but as I mentioned, unless you have some kind of traffic analysis you can't come upto a conclusion
On the physical aspect of the topology as Harbor has mentioned a wired connection (dedicated) would definitely be of good quality then what you have at present.
Did you had these problems before? Was it running on wireless and was fine and just recently started to give problems? did the number of phones grew ? Many questions and aspects to look at

Author Comment

ID: 24319585
@mutahir This is mostly my point what can I use for  traffic analysis? And what am I looking for? Do you have any text that covers this? Currently Im using VisualRoute to get an idea of what the ping time is between us and the VoIP carrier.

I have experience some problems in the past but never this bad. Also we recently got 10 more users. Every time I do a speed test on the network though we don't have any bandwidth problems. What I am seeing though is QOS reports are coming back with a low percent.

LVL 32

Expert Comment

ID: 24321337

I did not see that , half duplex? Yes that is not good at all, i agree with mutahir.

harbor235 ;}

Assisted Solution

peter41 earned 250 total points
ID: 24324863
There are important two network parameters for good VoIP:
- low latency. Try to set ping from your network to your VoIP provider sever, for example "ping x.x.x.x -n 10000" and look at output. If responses are less than 70ms, it is fine, if times are more than 100ms, then it is commonly not suitable to use for VoIP. Maybe you will see some time intervals when ping responses will not be received at all... :-(

- sufficient bandwidth. It is depending on used voice codecs (type of compression), and this type determines needed bandwidth for voice streams. So check what codecs are used in your VoIP device. Personally I use in my VoIP router (Sipura) codec which needs about 180kbits (sum of both directions).
I am connected also through wireless connection from T-Mobile ISP, but there is used Flash-OFDM which has very good latency (comparable with cables) and thanks to this I can to use VoIP with their connection 1,8Mbit/512kbit. Sometimes (approx. once per month there is not good quality, but 99% calls it is OK and I can live with it. UMTS networks has not such good latency like Flash-OFDM technology, so investigate your wireless technology.  

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