[asterisk-users] OSLEC vs HPEC vs Octasic

[Steve Underwood]

Kevin P. Fleming wrote:
> Gordon Henderson wrote:
>
>   
>> So at worst, it's saying it can handle 29 incarnations, and at best, 37 - 
>> that's assuming no other CPU load such as transcoding.
>>
>> So it's well capable of handing your requirements of 16 channels - more-so 
>> if you're using a "server" class box, and not the "embedded" type systems 
>> I'm using here.
>>
>> (On my dev box, an older 2GHz Celeron, 128KB cache, it's telling me it can 
>> do 120 incarnations, and on a 2.4GHz Xeon with 4MB cache, it said it could 
>> do 321)
>>     
>
> Those numbers are with a 16ms tail, which is very short, and unlikely to
> be an adequate echo tail for connection to the PSTN (although fine for
> analog phones). A more normal configuration would be 32, 64 or 128
> millisecond tails, which would cut those numbers down by a factor of 2,
> 4 or 8.
>   
If you try capturing echoes from real phone calls you will find very few 
exceeding 16ms, even for long distance calls. This is probably because 
the network has a canceller which you can't normally disable for a voice 
call. If you send a 2100Hz beep at the start of the call, you may then 
see much longer echoes appear. This is the echo canceller disable tone, 
which modems send to clear any networks cancellers from the line. The 
nature of modems means they need to do their own end to end 
cancellation, and that canceller certainly does need to cover a lot more 
than 16ms.

Regards,
Steve