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Jitter

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Jitter

I started playing with PlusTalk a bit last night, but was experiencing some jitter on the SIP->PSTN audio stream. My DSL connection was idle other than the SIP and RTP traffic for the call, but other SIP gateways (such as voipuser.org) seem to work fairly well even over a loaded DSL line since I do QoS queuing to prioritise low-latency traffic. The PSTN->SIP audio stream, on the other hand, seemed quite stable.

Has anyone else had this problem and does anyone know if PlusNet do QoS queuing on the DSL gateways to prioritise RTP traffic?

My setup is a machine running Ekiga as my soft phone, connected to Asterisk (on the same machine). Asterisk then dials out via PlusTalk.

On an unrelated note, are there any plans to provide geographic phone numbers for PlusTalk customers rather than just 0845's? At the moment I have a geographic number from SipGate but their service is crumby (their servers periodically stop replying to SIP traffic - I contacted them a few weeks ago and they said they were aware of the problem and it would be fixed "by the end of the week", which of course never happened).
2 REPLIES
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Jitter

I have also experienced this which is described by the person at the other end as sounding like a mobile phone getting out of range. I have had this happen on weekday evenings.

I suspect two possible causes:

- Contention on my local exchange. I have noticed my Speed Test result can drop from 1800 to 1200 on weekday evenings.

- Congestion at the Plustalk server which is overloaded with calls in the evenings.
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Jitter

After some lengthy investigation I think I've resolved this problem:

It was caused by upstream traffic on the DSL line. I am using the HTB queuing discipline on my Linux router, which should've ironed out the upstream traffic, but it was sending the traffic in bursts, creating jitter > 100ms. Reducing the size of the bursts seems to have resolved the problem.

If anyone wants my config, let me know and I'll post it here.