Understanding Media Codecs

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An understanding of the media codec’s used within VoIP systems can help with diagnosing failed calls, issues with transfers and other seemingly resolvable issues.

We recommend and newly created devices should input this as their default that the codecs utilised are:

G722, G711a (also known as PCMA), G711u (also known as PCMU). This will ensure that you have no reach-ability issues internationally, we will try and trancode / convert on the fly from one codec to the next where required but this isn’t 100% guaranteed and as such we recommend a consistency in device codecs.

A codec in VoIP is a program able to code or decode a digital data stream. This program is implementing an algorithm capable of compressing and decompressing data to an audio format. The challenge for a codec is to be as light as possible (to reduce bandwitdh/storage space) while keeping the audio quality as good as possible. Each service, program, phone, gateway typically supports several different codecs, and when talking to each other, negotiate which codec they will use.

Here is the list of the available codecs in the SIPadmin Platform:

  • G729 – 8kbps (Requires License) – Un-preferred due to poor audio qualities due to the low bandwidth nature.
  • G711 / PCMU – 64kbps (North America) – The standard Choice
  • G711 / PCMA – 64kbps (Elsewhere) – The standard Choice
  • G722 (HD) – 16kHz – Prefered for incoming calls from our carriers, has significatly better qualities than G711
  • G722.1 (HD) – 32kHz
  • Siren (HD) – 48kHz
  • Siren (HD) – 64kHzcodecs

G711 are the one set by default in SIPadmin when you create a device. If you want to change the codecs that your device is using for example, go into Devices, select the device, and under the  Advanced Settings section select audio and drag your required codecs across.