Understanding bandwidth usage for softphones

Hey everyone. I’m toying with the idea of having my office physically close and having my 5 users all telework from home but I’m trying to determine bandwidth requirements. Right now we have a 12Mb down and 850k upload at the office and it works fine.

Now I know in general, calls are around 64k up and 64k down per call path, so when I speak it’s using 64k to upload my voice to my VoIP provider, and then 64k to download the other person.

Here’s where I want clarification. Let’s say I’m now at home and making a call. Would my office internet now be using 128k per call? Because from me at home to the office is 64k up then another 64k from the office to the VoIP provider. Then the same for download. Would that be using 128k per call now?

I’m just trying to figure out if my total number of available call paths gets cut in half.

My office connection would change, and I would pretty much be guaranteed 15Mbps download and 2Mbps upload. My actual connection would be 25 down and 7mb up but I’m saying 15/2 to be very conservative. If all users work remotely, how many concurrent calls could I realistically have?

Just an update with this, I connected my Sipura box from my home and tested it just now. FreePBX shows when I call voicemail or another extension that 66K is being used up and down. When I call an external number it goes to 133K up and down as well, so it definitely does use double the bandwidth. When I played with the codec on the Sipura device, one made calls to the PBX go to 33K instead of 64K. There’s G729 as well but I don’t have a licence for that one. Either way there’s definitely flexibility in that I can use 64K from VoIP provider to the PBX then 18-33K from PBX to the phones, or 18K both ways etc so thanks!

Would still be interested in finding out how VPN works though!

Thanks for your help. We’re actually a telecom reseller so definitely familiar with T1’s benefits or Ethernet etc, we just don’t sell VoIP that’s why I wasn’t sure. Just a few things:

  1. g.729 is a good idea, can definitely try that out if there seems to be any issues

  2. VPN always confuses me. We run windows small business server 2008 which has built in VPN for the users to connect from their laptops. I never understand though how it works with IP phones. Would the phone need to support VPN and somehow connect to the VPN or is it the router that does it?

3-5) Few things here. I’d most likely have the new office just in my home, where I can just do a home connection. I’d get an internet connection just for the phones and then one for servers etc. Right now on our office we have 12Mb down and 850k up and have no issues when physically there. At my home I can get Fiber to the node DSL 25Mb down and 7Mb up or Cable 50MB down and 2MB up. I’d probably go with the DSL since it’s cheaper and I have it right now as well and I get around 24-25 on down when I do speed tests and around 6.5 on the upload. They also guarantee the speed, which I know isn’t possible on DSL but they do it by actually giving you something like 28mb down and 8Mb up. I’m just thinking with speeds like that, if the connection is only used for the phones, I don’t think it makes sense to get a T1 since 25/7 even under the worst conditions should never drop slower than 1.5 or even 3.

Another thing, including myself we have 5 employees total. At any time, the max concurrent calls are maybe 2, or if very busy then it might push to 3 but that’s it. So I figure even if I assume 2Mb max download, doing 5 concurrent calls gives 400k to each of them which should be more than enough I’m guessing…

For your office connection you have two components the link to each agents house and the link to your provider.

Two suggestions:

1 - Use g.729 CODEC and budget 18k per call leg, make sure your carrier supports g. 729

2 - Use commercial VPN to agents houses so you can run QoS in the VPN tunnel

3 - Multiply your bandwidth estimates by a factor of 2 if using any type of oversubscribed connection (DSL or cable modem)

4 - Really consider a T1, available in most areas for under $400 it’s 1.54Mbps of guaranteed symmetric bandwidth.

5 - Ignore #4 if you can get fiber

I should add as well, not sure if it matters but when I say softphones, these would be actual SIP hardware phones like Polycom phones not softphones. Not sure if it makes a difference but I find right now using softphones sounds awful but if I use for example a Linksys Sipura device the calls sound fine.

I must be missing something…

If you’re going to close your office and have everyone work from home, how does the “office” internet connection come into play? How are your workers going to access the “office” internet connection?

The bottom line is that with 5 users, the maximum bandwidth is 64*5 up and down or about 320k per direction.

You mention a VoIP provider, does this mean you’re not running your own switch?


Sorry I’ll clarify. I’ll still have an office but it will be much smaller, only a few desks for teleworkers if they wanted to come into the office one day or for meetings. Not sure what you mean by running my own switch, I have a few VoIP providers that provide my SIP trunks for my phones right now.

The thing I’m not getting is I understand it’s 64 per user per direction. Let’s say I’m working remotely though and I’m making a call. Is it not 64k download at my office where it’s downloading the VoIP call, then 64k upload to upload it to my home, and then an additional 64k download from my office to download my voice from my home, and an additional 64k upload where it’s taking my voice and sending it to my VoIP provider?

Like if I’m in the office, sure it’s 64 k both ways since it’s going from my office to my VoIP providers servers, but when a user is at home, they’re not connecting to the VoIP provider directly, they’re connecting to my PBX at the office which is connecting to the VoIP provider so I’m just confused how it’s not 128k. Regardless of whether a call is 64k, it still has to use bandwidth to send the call from the office to the persons home?