Back to Basics: Codecs and Bandwidth Calculations for VoIP

Brett Harney Bandwidth management, VoIP

Considering Voice over IP for your business?  In our Back to Basics blog series, we discuss terminology that you will come across when looking to move to VoIP.  In the past, we looked at SIP Trunking, Quality of Service, and Erlang Studies. The following is an explanation of the term codec, courtesy of TechTarget When we talk about VoIP call quality, think of the term codec, which stands for coder-decoder. Here's the basic explanation of how VoIP works: A codec converts an audio signal (voice) into compressed digital form for transmission, then converts it back into an uncompressed audio signal for replay. The most popular and frequently supported codecs are:
  • G.711: The standard that digitizes analog voice signals and requires 64 Kbps of bandwidth
  • G.729: The standard that digitizes analog voice signals using an algorithm for an 8:1
  • G.722: The standard that provides higher-fidelity speech and uses 48 to 64 Kbps
  • G.726: The standard that requires 16 to 40 Kbps of bandwidth and is primarily used in international trunks in the phone network.

Using Codecs to determine bandwidth requirements

Most service providers work with G.711 to ensure good voice quality when the VoIP connection is riding over a dedicated data line. However, the bandwidth requirements above do not include IP overhead, which should be factored in as an additional 23 Kbps. This means a G.711 codec requires 87 Kbps of bandwidth per call. G.711 provides the same quality as a landline-to-landline telephone call, while G.729, using 8:1 compression, provides quality similar to that of a mobile call. If the connection is via the Internet, call quality can be seriously affected when there is heavy Internet traffic, causing VoIP packets to be delayed, dropped or lost during a call. Adding additional bandwidth doesn't always correct this quality, and using a dedicated Internet connection so VoIP calls are routed through it with minimal delay is usually recommended. There are other factors besides simultaneous calls that will impact the bandwidth you need, but codecs are just one aspect of the conversation that you should have with an expert on voice over IP. Corporate Technologies Group specializes in helping companies convert their voice traffic, and determine what bandwidth is necessary for the quality you need and expect.