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Getting rid of / reducing Jitter

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by levi_l

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I have a remote location that is on Time Warner Cable's Business Class Road Runner product. I have a VPN setup between their location and my location via our Adtran NetVanta routers.
We are running VOIP over the VPN to provide that location with voice services.
We seem to be experiencing a lot of Jitter over the VPN. I have setup QOS in the router to give voice traffic priority, but that didn't seem to help.

Anyone have any ideas on how to remedy or improve the situation?

8 replies

by levi_l

bandwidth to suffice the connection. At the main site we have a 3mbps up and down fiber connection, and at the remote site we have a 10x1mbps cable connection.
We have adtran routers in place at both locations and are using traffic shaping to limit the outgoing traffic to 1mbps at the remote location and 3mbps at the main location (so we don't overwhelm the pipes).

Not sure what you mean by media.

by robo_dev

but seriously....

http://www.voiptroubleshooter.com/indepth/jittersources.html

In terms of testing things, I would first measure how the ISP is doing from cable-modem to cable-modem end to end.

If it's the ISP who is at fault, then they're the only one who can fix that.

Not to answer a question with a question but, I would assume that those cable companies who offer VOIP must do QOS with their own voice traffic?

Several years ago I was running Vonage on a Cable Modem and I swear that the ISP was purposely borking the Vonage traffic while trying to sell you on their VOIP service.

by levi_l

First off, I have been doing some testing. I have been noticing some packet loss over the VPN.
I was looking into it all day yesterday to try and figure out what is causing it.
I finally spoke with our main site's ISP, and have discovered that we are maxing out our down pipe, so the VPN would not be able to be sustained. So i am currently working on limiting the bandwidth that each user at this site can use, to hopefully reduce our pipe-usage and fix that issue.

As for your question on QOS:
I am running a VPN, so my guess would be that the ISPs would not even see the VOIP traffic (although I could be wrong), but even if they did, it doesn't seem like they would offer me the service (at least Time Warner wouldn't).

by robo_dev

You can do QOS over VPN, but you are only managing your own traffic. Effectively it is QOS within the VPN...as the ISP cannot identify/tag different packets within the VPN, as that would defeat the security
of the VPN. But it would help to make sure your less important traffic over the VPN does not affect the VOIP.

http://www.ciscoblog.com/archives/2007/04/qos_over_vpn_tu.html

by levi_l

What I was trying to convey, was that the ISP wouldn't be able to setup COS, as the packets would be encased in the VPN. I have QOS setup on each of the routers, giving voice traffic priority.

by petike222

VPN is very bad and ugly solution for voip unless used on a LAN.
If you need security, try to use some encryption solution which can encrypt the media packets (over UDP) one by one. For example SRTP or proprietary solutions. Search for "voip tunneling" to see some resolutions for this problem.

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