VOIP Recommended Speeds

Posted on 2012-03-12
Medium Priority
Last Modified: 2012-03-17
I'm converting my phones to Comcast VOIP, and they offer several different tiers of service. The base model is a 12 mbps up /2 mbps down (which is comparable to what I have now, and it seems to work well), but I'm wondering if it would be best to move up to the second tier, which is 22 mbps/5 mbps.

I have a Skype line that I use now on my current setup, and it seems to work fine for the most part. However, I'm concerned that if I have two VOIP lines, I'll end up with troubles. The cost is about $40/month more for the faster service so if I don't really need it I'd rather not pay it, but at the same time I don't want to shortchange myself. I can always go up after the install, but I'd have to pay a new fee of course.

I also use Netflix, Hulu Plus, and Vudu, along with standard internet usage (email, surfing, etc). I have 3 machines connected at the office, with no plans to add more at this time.

Any recommendations, especially from those with real-world experience? I don't need SpeedTest links or anything like that ...
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Accepted Solution

Brian earned 1000 total points
ID: 37711963
A single VoIP call actually takes up much less bandwidth than you might think. What you need to be sure is that it consistently gets its bandwidth. Most people use a large amount of bandwidth to avoid having a large file download bump in to the call.

We put in QoS units, and reserve the amount of bandwidth we expect the VoIP calls to use. You can calculate the bandwidth required based on the codec being used. The largest codecs used take up about 96 kbit/s. Double it to be safe. So for each call you should reserve 192 kbit/s, which is actually quite small. If that Netflixs movie takes the available bandwidth for the call down to 40 kbit/s, then you start to get choppy or dropped calls.

There are some inexpensive firewalls that include QoS, and all most all high end ones include it. Set QoS for VoIP and/or SIP and you should be good to go. So instead of spending more on the internet line, speed a little bit on a QoS firewall and it will pay for itself in 3-6 months.
LVL 85
ID: 37712655
Thanks for your input. I'm running a Cisco firewall that does allow me to manage QoS, so I'm good on that end.

I wasn't aware of the bandwidth requirements for voice calls, and it's kinda surprising - just thought there would be quite a bit more used for voice. The phone lines will be very busy for several months of the year (it's for my HVAC company here in the south, and we get heavy phone loads during the summer months, but not so much during the winter).
LVL 17

Assisted Solution

JRSCGI earned 1000 total points
ID: 37716763
The QoS settings on the firewall will not ensure quality.  Once the packets are on the Internet, it is strictly best effort.  The firewall QoS settings will help with egress (out) from your end, but it will not help with ingress packets.  QoS works great (when properly setup) over private network circuits, but it is not by itself enough when using the public Internet.  Many of our clients install two Internet drops, and direct voice traffic to one and all data traffic to the other.  As stated above, voice has a very low bandwidth profile -- it is not usually the size of the access that causes the quality problems but the contention for the bandwidth.  With only one circuit, an application download or heavy usage such as the video mentioned are the types of things that flood the circuit and introduce latency and jitter to the real time voice packets.  QoS can not prevent the inbound Internet traffic from using the entire pipe.
LVL 85
ID: 37732412
Thanks for your comments. I've been researching my router and the QoS features, and I think that is where I need to concentrate my efforts.

Your comments helped me to better understand the concepts of VOIP and such - thanks again.

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