VoIP Bandwidth 101
Bandwidth is very common and important concern when considering the move to VoIP. There is a direct relationship between available bandwidth and QOS (Quality of Service = The voice quality of phone calls utilizing VoIP) Just how much bandwidth does an IP Phone require in order to make high quality telephone calls?
Wikipedia.com defines bandwidth as follows:
“In a digital communication system, bandwidth has a dual meaning. In the technical sense, it is a synonym for baud rate, the rate at which symbols may be transmitted through the system. It is also used in the colloquial sense to describe channel capacity, the rate at which bits may be transmitted through the system. Hence, a 66 MHz digital data bus with 32 separate data lines may properly be said to have a bandwidth of 66 MHz and a capacity of 2.1 Gbit/s — but it would not be surprising to hear such a bus described as having a “bandwidth of 2.1 Gbit/s.”
A more simple definition? Bandwidth describes the capacity of an internet connection (56K Modem, Cable, ADSL, ISDN, T1, etc) to transfer data from one point to another in a given time. We learned earlier that in a VoIP system, voice signals are converted from an analog format, to a digital format, and are treated much like traditional data in terms of how they are transmitted and received over the internet. Voip is ideally a broadband application, and if you are limited to a 56K “dial up� connection you may not be able to use VoIP.
There are two distinct elements that comprise bandwidth, upload and download. Upload bandwidth describes the amount of data you are capable of sending out to the internet. Download bandwidth describes the amount of data you can receive from the internet. Users with a DSL internet connection typically have an upload bandwidth up to 640 Kbps, and a download bandwidth of up to 1.5 Mbps. Cable internet users typically enjoy bandwidth of around 10Mbps for both upload and download. A T1 connection contains 24 channels, and send and receives data at 1.544 Mbps. There are other types of broadband connectivity, including ISDN and satellite, but these are the most common broadband connections used in the US market. Cable and DSL are both comparable in price, but if given the choice, cable is likely your best option if you intend to utilize VoIP in a residential or small business setting. A PRI / T1 line also makes sense if you have sufficient users to justify the monthly cost, and can be utilized for both voice and data traffic. As your business approaches 10 employees, you may want to start looking at PRI/T1 as an option for carrying your voice/data.
A typical VoIP phone call will utilize 90Kbps (kilobits per second) of bandwidth. Many VoIP service providers can accommodate service with less available bandwidth, as low as 30Kbps, without a noticeable reduction in quality of service (QOS). However, the amount of bandwidth required by a VoIP provider to deliver quality Voice Over IP is an important consideration when choosing a service provider.
