Codecs (audio compressors) are used on VoIP hardware phones and softphones to squeeze more audio into your data connection. Support for codecs varies between hardware and softphone manufacturers so you can't always be certain what phone will have what support.
However, codecs automatically "negotiate" when you make a phone call and in most phones, you can define your codec priorities. So in a VoIP to VoIP call if the other party is using say GSM and you're using G.711, you will negotiate between you by working down the priorities to the best codec available for you both to have the best quality call you can. We currently support the following codecs as standard. In most devices you set an order of priority for codecs and we recommend the order below.
- G.711 a-law. This is also known as G711a or PCMA (European PSTN standard)
- G.711 u-law. This is also known as G711u, or PCMU (American PSTN standard)