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RTP Payload Formats

There are plenty different RTP payload formats around

Known Formats

GSM-FR as per IETF RFC 3551

GSM-FR as per ETSI TS 101 318

GSM-EFR as per IETF RFC 3551

GSM-EFR as per ETSI TS 101 318

GSM-HR as per IETF RFC 5993

GSM-HR as per ETSI TS 101 318

AMR as per IETF RFC 4867

AMR-WB as per IETF RFC 4867

Audio at various Interfaces

SIP-I based CS

This is closest to what osmo-sip-connector offers to the outside world, and hence what we'd have to support from the msc-colocated MGW.

See 3GPP TS 26.103 Section 7 3GPP Codecs for OoBTC in a SIP-I -based Circuit Switched Core Network

  • AMR as per RFC 4867
    • The bandwidth efficient mode of RFC 4867 shall be used. CRC and robust sorting shall not be applied.
  • EFR as per RFC 3551
  • FR as per RFC 3551
  • HR as per RFC 5993
  • PCMA as per RFC 5993
  • PCMU as per RFC 3551
  • audio/telephone-event as per RFC 4733

3GPP AoIP

It's surprisingly hard to find where the RTP payload details for AoIP are specified... It's in 3GPP TS 48.103 Section 5.4.2.2

Codec RTP PT Spec Clock Freq
uLaw 0 RFC 3551 8 kHz
aLaw 8 RFC 3551 8 kHz
GSM FR 3 RFC 3551 8 kHz
GSM EFR 110 RFC 3551 8 kHz
GSM HR 111 RFC 5993 8 kHz
AMR-NB 113 RFC 4867 8 kHz
AMR-WB 120 RFC 4867 16 kHz
CSD 121 RFC 4040 + RFC 2198 8 kHz

AMR: According to TS 26.102 Section 9.2: "The bandwidth efficient mode of RFC 4867 shall be used. CRC and robust sorting shall not be applied. "

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