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I sometimes face voice break when calling through a VOIP application. Since all VOIP applications uses UDP for data transmission, is there any tool in Linux to measure the amount of packet loss and measure the performance of the network.

What could be the general reason for UDP packet loss and what measures I need to take when there is lot of packet loss ?

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iperf works good for testing UDP. It reports back loss and jitter. –  Zoredache Dec 20 '10 at 21:23
I used iperf and it is reporting high data loss and jitter. What steps should I take to fix this problem ? –  Supratik Dec 21 '10 at 12:20

2 Answers 2

What could be the general reason for UDP packet loss

Congestion (too many packets) with lack of QOS (random packets dropped, VOIP not handled with priority) and / or faulty equipment (line quality etc.) For the first, get QOS capable equipment, for the later check the lines (hardware, switches, whatever) for being bad.

Note that you need for an internet conenction QOS routers on both ends - which you wont have (unless voip is offered by your provide, then he likely has the infrastructurei n place). That said, as your down channel typically is a lot bigger than the up channel, a local router prioritizing only the out channel is normally "good enough", as: it already brings hugh improovements.

Bad line quality is a general hard to handle problems, though.

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If you're suffering UDP packet loss, you're almost certainly suffering TCP packet loss as well. The difference is TCP will re-transmit lost packets and UDP does not. VoIP applications cannot re-transmit because if they did, the information would no longer be any good.

I'm going to assume your VoIP calls are going over the Internet. QoS may be necessary, but it won't do any good, if your Internet connection is not working properly. Use this packet loss test to check it out. It will tell you were packet loss is happening, i.e in the ISP or at your local site.

If it finds trouble at your local site, then it's time to check out your cable or DSL modem for good signal noise ratio, output power and attenuation (DSL).

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