Bandwidth per call by codec
kbps in one direction with RTP, UDP, IPv4 and Ethernet headers, no VLAN or encryption:
| Codec | Codec, kbps | ptime 20 ms | ptime 30 ms |
|---|---|---|---|
| G.711 (PCMA/PCMU) | 64 | 87.2 | 79.5 |
| G.722 | 64 | 87.2 | 79.5 |
| G.729 | 8 | 31.2 | 23.5 |
| iLBC (20 ms) | 15.2 | 38.4 | 30.7 |
| GSM-FR | 13.2 | 36.4 | 28.8 |
| AMR-WB 12.65 | 12.65 | 36.0 | 28.3 |
Why a G.711 call takes 87 kbps, not 64
G.711 produces 64 kbps of voice, but every 20 ms the voice goes into its own packet, and the 160 bytes of voice get 12 bytes of RTP, 8 of UDP, 20 of IP and 18 of Ethernet on top. Fifty such packets a second come to 87.2 kbps. G.729 carries only 20 bytes of voice per packet, so headers are over two thirds of the traffic. A longer ptime of 30 or 40 ms cuts the header share but adds delay.
To work out how many lines or agents your call volume needs, use the Erlang calculator. To test your actual line, run the speed test.