bit rate is 13333bps, giving 1667 bytes/sec
packetization is 20ms, giving 34 bytes per packet

Actually, iLBC in asterisk uses 30ms frames..

Everything asterisk does is in 20ms frames. In IAX and RTP this is hardcoded, so whatever iLBC think it's doing, asterisk does 20ms.


IAX header is 4 bytes
UDP header is 8 bytes
IP header is 20 bytes

you're also forgetting the ethernet, PPP, or other low-level overhead..

not forgetting. we're talking about WAN bandwidth consumption, which, in all cases except dial-up, is reported in bandwidth available to IP.


this means one packet is 34+4+8+20=66 bytes
50 packets per second gives 3300 bytes/per second, meaning 26400bps

Is there a way to bring it down?


yes
hack asterisk to use a lower packetization value

Or use trunk mode, which can do this for single calls (try setting trunkfreq to 60), and also significantly reduces overhead for multiple calls..

does this pack multiple frames?

roy

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