Recommended Audio Codec
The preferred codec for use on our voice network is ALAW (G711A). When using this codec no transcoding occurs throughout the network and optimal voice quality is maintained. ALAW is also a very resilient codec that withstands network fluctuations better than most others, however, we strongly recommend the use of a Private IP connection to minimise exposure to variable network conditions. Bandwidth requirements for ALAW is around 64 Kbps synchronous per active phone call (this does not account for TCP/UDP overheads).
Low Bandwidth Audio Codec
If you have very limited bandwidth availability you may choose to use the G729 codec. This codec has low bandwidth requirements, at the cost of audio quality and resiliency to packet loss and latency fluctuation. There is a noticeable difference in the audio quality which is often described as being "more mobile-phone-like" which can be attributed to the codecs compression, as well as the fact that it needs to be transcoded back into ALAW within the VoIP network. This is a licensed codec and you may need to pay licensing fees to use it on your equipment.
Other Audio Codecs
- G722 provides very high audio quality but has high bandwidth requirements. The audio quality is only better when calling between 2 G722 capable VoIP handsets
- ULAW / G711U is the US version of the G711 codec. We do not recommend using this as it virtually the same as ALAW (G711A) aside from the fact that it needs to be transcoded into ALAW within the VoIP network, which can slightly degrade the audio quality compared to using ALAW.
- GSM should only be used where your handset or device only supports this codec. It is the audio codec used by 2G mobile phones.
The H.264 codec provides the highest video quality of the available options, however the best video codec to use depends on the available bandwidth and codec support of your video calling device or software. Please note that video transcoding is not supported on our network. This means that all devices that you intend to video call between must support the same codec that you intend to use. Experience has shown that there may be some variations between implementations of codecs and SIP negotiation between different vendors devices -- as a result it is typically advisable to use the same make and model of devices or software accross the board where possible.
These notes are intended as general information and do not constitute any guarantees or warranties.