[Asterisk-Users] ilbc high bandwidth

[Roy Sigurd Karlsbakk]

>> 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