[App_rpt] ACID system adminostrators guide

App_rpt-users
1

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.

Steve
WA6ZFT

2

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

3

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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4

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

Ack. So the difference is EchoLink sends 80 millseconds of audio/GSM per
packet and Asterisk/app_prt only sends 20 milliseconds so there are 4
times as many packets with 3 times the header overhead. I excluded the
Ethernet header since it's stripped before going out the Wan port (at
least for dialup users which is where the calculation is most critical).

IRLP GSM sends 200 milliseconds of audio in each packet which is WAY WAY
too much IMHO. I have no opinion if 20 milliseconds or 80 milliseconds
per packet is "better", I'm just trying to understand the numbers.

Thanks for the math!

73's Skip WB6YMH

···

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
>
> _______________________________________________
> App_rpt mailing list
> App_rpt@lists.illiana.net
> http://lists.illiana.net/mailman/listinfo/app_rpt
>

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5

I'll take a look at it, as my Asterisk is close to an ACID system (I used the ACID install scripts on an existing CentOS box).

73 de VK3JED
http://vkradio.com

···

At 05:40 AM 8/3/2008, you 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.