[App_rpt] ACID system adminostrators guide

[Stephen Rodgers]

Skip

Each frame in Asterisk starts out as 20mS of audio or 160 words of
signed linear samples at a frame rate of 50 per second. Each 20mS 160
word sample is encoded in GSM which results in a compressed payload of
33 bytes.

Check.

Now, on to that 33 byte packet you have to add 4 bytes for the IAX
protocol header, 20 bytes for the IP header, 8 bytes for the UDP header,
and 18 bytes for the ethernet header. So now we have 33+4+20+8+18 or
83 bytes. At a frame rate of 50 per second, this means that we will have
83*50 or 4150 bytes per second which when multiplied by 8, is 33,200
bits per second. Throwing in 5% for IAX control frame overhead, and
occasional IAX control frame retries, we get 34860 bytes or about 35
KB/sec. I have verified this with ntop running on my firewall machine
and the numbers are very close to the calculations.

Steve
WA6ZFT













http://site.asteriskguide.com/bandcalc/bandcalc.php




Skip WB6YMH wrote:
>> all,
>>
>>
>> There is a 44 page document on dl.allstarlink.org which may answer a lot
>> of questions about how to configure app_rpt and Asterisk on an ACID
>> system. Hopefully, this will answer a lot of the same questions we keep
>> seeing on the list.
> 
> Excellent!
> 
> But ... this brings up a new question.  Where do your bandwidth numbers 
> come from for the chart on page 6?  Is that the total bandwidth in *both* 
> directions?  The numbers are about a double of the 17kbps I calculate for 
> EchoLink.
> 
> {  (8000 samples/second) / (160 samples/gsm frame) / (4 gsm 
> frames/packet) =  12.5 packets/second.  or 1 packet every .08 seconds.
> Each packet consists of an IP header and an UDP header so
> (12.5 packets/second) * (20+8+12+(33 * 4)) bytes/packet) * 8 bits/byte = 
> 17200 bits/second.}
> 
> 73's Skip WB6YMH
> 
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