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QoS over the Internet..HA!

Does anyone have any history with trying to implement VoIP and getting a decent call quality by using lower level Internet connections like SDSL, ADSL or Cable modem? I want to try a setup with Callmanger and the remote users coming in through our VPN with IP Phones on their end. I have all the parts ready to go(router, 3005 software etc) but this will take away time from other projects. I can get all my users 128k SDSL at a minimum. Most already have cable modems that are pretty fast but I am concerned about available bandwith at certain times of the day. Using the SDSL is it worth a shot?

6 REPLIES
New Member

Re: QoS over the Internet..HA!

I've used IP Phones with a Cable Modem and a VPN to work. They work pretty well, but occationally they can get a little funky. Bandwidth is not really the issue when you are using g729 compression; it's the latency and jitter. You can only delay so many packets before the voice quality will suffer.

Try to get the fewest hops (ie less latency) possible between the CCM and the user. Try using the same ISP for both sides if possible. Lower the encryption level on your VPN if security for voice is not that important. That just a couple of ideas. Others may have more.

Cisco Employee

Re: QoS over the Internet..HA!

I have used a 7960 over a VPN tunnel between VPN3002 client and VPN3k concentrator... over a cable modem connection that is 2Mbps down and 384kbps up. Using G.711 the quality is great. The only time any jitter or other loss of quality is when uploading a file in the slow direction.

Cisco Employee

Re: QoS over the Internet..HA!

I have had the same success that Dave has had. But like you said it is the Internet. I think it can be a success as long as your users understand what is going on. I have had sometimes where I get the robotic voice or not the best quality with cable modem. But 95% of the time it is great. The point I am making is just educate your users that they are going over the Internet and should not expect the best quality 100% of the time.

Just my $.02,

-Mckee

New Member

Re: QoS over the Internet..HA!

Mine works great over my DSL. It is difficult to control quality when different people are using different ISP's. However, one of our ISP's that we use is Internap (www.internap.com). I'm sure there are other ISP's that do what they do, but we get very good quality and low latency from all of our DSL/Cable modem users due to the way Internap handles routing.

New Member

Re: QoS over the Internet..HA!

The main concern is that The Internet is unpredictable. You never know what service will be like.

Another more common problem is that most, if not all DSLAMs are oversubscribed. When traffic picks up, packets are dropped. Again, it is unpredictable.

Delay can be a nuisance as well. If the one way delay exceeds 250ms, folks will start to talk at the same time. Keep in mind that the delay includes packetization, transport, encryption, etc.

The voice codec makes a big difference. G.711 is much more tolerant of loss than G.729a. Sounds better too, but takes alot more bandwidth.

If you are using the DSL link for both voice and data, data will interfere with voice. You should prioritize voice traffic onto the DSL link, but have no control over the downstream direction.

New Member

Re: QoS over the Internet..HA!

I've tested the SoftPhone over ADSL and VPN via the concentrator, and it works fine most of the time.

One thing to remember; when your users want to call externally, fine. But when they call each other and both is on similar connections, the delay and jitter might be just too poor, since the traffic has to run via the concentrator both ways (if you're not using split tunneling, which is not recommended).

Depending on what sort of business it is, it might be a solution. For business-class, it's a no-go.

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