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What are the differences among voice protocols, codecs and standards?

VoIP expert Jon Arnold explains the differences among voice codecs, voice protocols and voice standards.

Are voice codecs the same thing as voice protocols? And are voice protocols the same thing as voice standards? What are the differences among voice codecs, protocols and standards?

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When you start learning about Voice over Internet Protocol (VoIP), all three of these terms will be frequently used, and unless you know their meaning, it's easy to get confused or use them interchangeably. Each term actually entails a separate universe that will need to be explored in future posts.

On a basic level, however, the first point of difference is to separate codecs from standards and protocols. A codec is a set of instructions that literally does coding and decoding of digital media. Each type of media has different codecs, but when it comes to VoIP, voice codecs provide instructions to ensure that the originating call can be received at the other end in a usable manner.

Over the years, a variety of voice codecs have come into use, and since VoIP is not truly standardized, a basic challenge arises when each end of the call is using a different voice codec. This is quite common when VoIP calls traverse the public switched telephone network (PSTN) and they must pass through a media gateway. A core function of media gateways is transcoding, which performs the heavy lifting to address all the permutations that come when more than one codec is involved.

More on voice protocols, codecs and standards

A glossary of VoIP protocols and standards

Understanding the difference between the H.248 and H.323 protocols

What are media gateways, and how do support protocols work?

Voice over IP uses a number of codecs, some of which are free and some of which require a royalty payment for licensed use. Commonly used voice codecs are G.711, G.722 and G.729, and sooner or later you'll come across these and others. Moving on, voice standards and voice protocols are different, but also related, in that standards are really a subset of protocols. In both the legacy and IP worlds of telephony, well-defined standards exist that are devised by industry-based entities to allow vendors to develop products that work with everyone else's products. For the legacy telephony industry, standards are set by the International Telecommunications Union , or ITU, while VoIP falls under the standards body for the broader world of the Internet -- the Internet Engineering Task Force, or IETF.

Other standards bodies exist, and but not all standards are accepted and used by all vendors. In terms of the legacy equipment environment, telephony vendors built their competitive advantage around proprietary standards, but much of that has gone away with VoIP. Some vendors continue to support variations of standards that are still fairly proprietary and can do so based on their strong market position, however. While this runs contrary to the Internet's spirit of being open and standards-based, vendors will take any edge they can get. When you hear the term de facto standards, that's exactly what I'm talking about.

When standards are set, they are typically defined as industry protocols. These are basically the set of rules for how communications flow across networks. In the legacy world, H.323 is the major protocol for handling VoIP calls over the PSTN. It defines how most voice traffic is managed, since the PSTN is still the dominant telephony network. In time, however, it will be supplanted by IP networks, for which VoIP was designed from the bottom up. The major protocol for VoIP is Session Initiation Protocol, and while SIP is still evolving, it will eventually be the standard protocol for all voice traffic.

This was first published in February 2014

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