G.729 is the legacy, default codec used for voice compression in most VoIP deployments. Organizations should look at an adaptive codec that can support quality audio under most conditions, but will adapt to poor network conditions such as jitter and packet loss. G.722.2, iSAC, and iLBC are examples of adaptive codecs, with the first two supporting wide-band audio. These codecs produce a higher quality MOS score per given bit rate than the legacy codecs, with little additional latency.As the cellular industry moves to 4G networks based on VoIP/SIP, we can expect this technology to continue to mature and gain market share. Cellular, VoIP/SIP Internet providers, Cable companies, and enterprises will peer with one another so that the codec choice that SIP negotiates is end to end and avoids the trans-coding that goes on in the middle of legacy IXC/LEC networks.
Enterprises will benefit by being able to reduce the size of their WAN pipes and offer a higher quality call experience. An enterprise WAN that is designed for VoIP typically has twice the bandwidth for voice that is required in order to have enough bandwidth in case one links fail. Call admission control is based on what one half of the network has been sized to carry. With an adaptive codec, the call admission control for P.01 of service could be based on the entire bandwidth of the WAN, and in the small fraction of time when one of the two WAN/MPLS links are down and there is a large call volume, then the codecs will adapt.
Anyone who buys VoIP gear should be requesting support for an adaptive codec and the ability to support future adaptive codecs via software upgrades. iLBC is the most mature with an open licensing model, but as wide-band audio moves into the mainstream, other codecs such as G.722.2 should be considered. Some vendors are hesitant to support these new codecs due to their licensing model. Skype developed their own called SILK to avoid licensing costs and to optimize call quality over public IP network connectivity.
It is time we move away from the lowest common denominator in voice compression. What the long term industry standard for adaptive codecs will be is still TBD, but this is the direction of the industry.
