Codec For GSM Gateway

Hi Guys I am using EuroStart GSM gateway for calling with asterisk 11 need help on below point.

I think this gsm gateway only support G723, G726,G727,G729,PCMA 8000 & PCMU 800
which codec i need to use for better voice quality here can i user G729 or G723 here

The last two, although there will be slight loss of quality if you don’t use them throughout the system.

Please note that GSM mobiles use vocoding codecs, and always have limited quality, particularly on anything other than speech.

If you are connecting to the PSTN directly, you should use PCM-A for the best possible quality (limited only by the PSTN), but access through a mobile network will significantly degrade, and certainly a lot more than the loss from converting from A to Mu law.

PCMA is actually alaw and PCMU is ulaw?

Almost PCMU is μ-Law (which is quite sloppy as, although it looks like a “u”, it is really an “m”.

ok thank so what should i use here do I need to go with G729 or G723/22/26?? with GSM Gateway

That depends on what codec variation the gateway uses. The best available GSM codec would probably require G.722 or G.711 to minimise degradation. Although, on its own, G.722 has a marginally better mean opinion score than G.711, I suspect that relates to its covering frequencies that GSM doesn’t cover, so the combination could be worse than G.711, and G.711 uses the same network bandwidth and less computing power to transcode it.

If your GSM network crams them in with the lowest bit rate option, it will make no differences as GSM will be the limiting factor.

Maybe you are failing to understand that GSM is always worse than G.711, not least because the internconnects will be in G.711, and therefore limited by that.

Remember that the MOS of a combination is likely to be worse than either in isolation, and won’t be better.