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VoIP over DSL - what is the reality?

Was wondering about VoIP for a small office of around 8 to 10 people. Is VoIP using a DSL connection a viable voice carrier? Would two DSL lines and a load balanced router suffice? What is the real world solution?
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bcampbell74
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bcampbell74
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jimtechCommented:
VoIP Phone service is my profession for the last year with a cable company making homes/MTA's VoIP Serviceable.  Currently offering only residential service but getting ready to launch commercial VoIP service.  As far as voice carrier, just depends on the charges for the package.  I have seen where local phone carrier service is cheaper for some and Vonage cheaper for others.  So definately check out your options and prices for each.  As far as the router, the VoIP Phone service is carried by a seperate IP from your computer IP so a router for it will not work.  If you have any questions, please let me know and I will try to help you.  Thanks!

Here is a link to a forum to check this out: http://www.vonage-forum.com/ftopic10493.html  Be sure to keep in mind what I have said here while reading the posts to the bottom.

And this one talks about "How to Choose Open-Source Telephony" for a business if you are interested: http://www.eweek.com/c/a/Knowledge-Center/How-to-Choose-OpenSource-Telephony/ 
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bcampbell74Author Commented:
Apologies - I think I have confused things through my terminology. I was talking about actually using the DSL for incoming and outgoing calls. I have a test setup here using 3CX (software IP PBX), sipgate service, Linksys SPA962 and QoS configured for sip which is working fine however I do not have enough other people here to give it a good test. Is using DSL viable for incoming and outgoing calls in a small office?
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bfasonCommented:
If you have good call quality now then the line is probably acceptable in terms of jitter and latency. The problem you will run into is bandwidth and qos. Most dsl's are limited to 384K up which is plenty if you are using g729 for the call but if you have other applications such as email, web and file transfer using the same line then you may run into some issues.
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bcampbell74Author Commented:
Yeah - was thinking that 2 DSL lines witha s high an upload speed as available (Be Unlimited can be up to 1.2Mbps upload) on a load balanced router may be adequate plus provide a fall over capability too!
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bfasonCommented:
I wouldn't recommend the load balancing for voice. Packets may arrive out of order depending on the hardware.
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Reid PalmeiraTelecom EngineerCommented:
On DSL the limit is generally going to be the upload out. Unfortunately there's no clear "reality" in terms of VoIP. If you're getting VoIP service from the same provider that gives you the DSL service there may be QoS on the WAN link. If you get the DSL service from Provider A and the VoIP service from some other provider all bets are off for QoS. At bfason already noted, load balancing probably won't help you much. Particularly for VoIP, most load balancing will just push the first packet out the first circuit, the second packet out the second circuit and round-robin the outbound traffic. This is fine for data but not for voice. You'll increase jitter.

The other thing to look at beyond end to end QoS is the codec being used. For calls using a G.711 codec, you can expect to use 80 Kbps of bandwidth, for a G.729 call you can expect to use in the area of 20 Kbps after the overhead is applied. This is a big difference. if you're running an ADSL link with no QoS its much harder to push 6 quality G.711 calls then it is to push 6 quality G.729 calls. So you need to look at the codec as well as the QoS

What can reduce a lot of the bandwidth needed is running the RTP internally. For example, if you're using the 3CX system on your LAN and two statiosn are calling each other, the only thing you really need to have travese the WAN link is the signalling (SIP, H.323, whatever) and the real heavy part of the traffic, the RTP, stays only on your LAN so it won't bottleneck at your DSL link, in which case it shouldn't make much difference.
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bcampbell74Author Commented:
Excellent and informative answer.
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