Q&A: How many phones can be used on a VOIP Line?

Question by : How many phones can be used on a VOIP Line?
If someone has a business or office, how many VOIP lines on a single internet connection can they have? Considering that they don’t have their own PBX system?

Best answer:

Answer by VoIPtalk
Technically speaking, VoIP can accomodate as many lines (channels) and numbers (or DID’s) as you want.

You can have many different phone numbers (DID’s) that ring to one line.
And/Or, you can have one phone number that will ring to many lines. But, this scenario likely requires that you have an IP-PBX in the office.

With VoIP, simultaneous call are handled over separate “channels”. Some VoIP carriers will allow you as many channels as you want for as many simultaneous calls you need.

If you don’t have or want to install your own IP-PBX to handle many simultaneous calls, you can subscribe to a VoIP service that provides “Hosed Virtual PBX” service. In this case, the VoIP provider takes care of all the IP-PBX functions and forwards all the calls to your office “IP-Phones”.

You can have as many IP-Phones in your office as you like and limited only by the number of “Extension” or Lines that the Hosted Virtual PBX service provider can provide to your office via your Internet connection.

As far as how many simultaneous calls (or channels) your office can receive will depend primarily on your Internet bandwidth speed. Basically, high quality voice calls will be using G.711u or G.722 Codec for voice compression over Internet. On average, this means each channel of a call will consume between 90 – 110 Kbps bandwidth. So if your office needed to have a maximum of 5 lines or channels taking calls at the same time, then your Internet “upload” bandwidth will need to accomadate at least 5 x 110 Kbps = 550 Kbps. By the same token, 10 lines or channels will need at least 1.1 Mbps “Upload” speed.

I emphasize Upload speed because this is usually much less than the advertised Download speeds ISP’s advertise. For example, if your ISP is providing you with 10 Mbps download speed, they may only be giving your 1.0 Mbps Upload speed (maximum).

But don’t forget when you calculate your minimum Internet speed requirements, you have to include what your other computers in the office are using for web browsing, file transfers, email, etc, etc.
So, if all your VoIP phones need 1Mbps upload speed you should at least double or triple that number to account for all the other computers in the office using the Internet connections too.
This usually requires you to have Routers on your office network that implement QOS that give top priority to VoIP calls over all other local network traffic in your office.

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