OsmoDevCall - GSM networks that require transcoding to G.711: the problem and possible solutions

Transcoding to G.711 is necessary when interfacing GSM networks with external networks and VoIP providers, as most only support G.711 codec

Network codec selection typically follows a fallback chain: AMR as first choice, then EFR (Enhanced Full Rate), and FR1 (Full Rate) as last resort for legacy phones

DTX (Discontinuous Transmission) support is important for power efficiency, particularly DTX uplink which saves mobile station battery life

Codec libraries face licensing challenges - particularly for EFR codec which is derived from ETSI/3GPP code with restrictive licenses

Current solutions require building custom transcoding components due to limitations in existing open source implementations

Plugin-based architecture proposed for flexible codec support without hard dependencies

Bit-exact transcoding capability is important for matching commercial network quality

Legacy phone support requires implementing older codecs (FR1, EFR) in addition to AMR

DTMF handling presents challenges when interfacing between GSM and SIP/VoIP systems

Current Osmocom architecture makes transcoding integration complex due to separation between MSC and MGW components