[Asterisk-Users] re: hardware requirement -asterisk

[Chris Albertson]

--- "dkwok at iware.com.au" <dkwok at iware.com.au> wrote:
> Referring to my previous post about degradation of voice quality when
> 
> having more than 2 connection.
> 
> The actual route is:
> 
> pc xlite -> local asterisk box -> iaxtel -> local asterisk
> 
> I have tried out a different situation:
> 
> pc xlite -> local asterisk box -> iaxtel
> 
> and the second connection
> pc xlite -> local asterisk box -> iaxtel -> local asterisk
> 
> The same degradation happens as soon as the second connection is
> connected.
> 
> I am suspecting the ADSL connection. The internet part is ADSL with
> 512k 
> down and 128k UP. The nic is a 3c905c 100baseTX and connected to a
> NEC 
> ADSL modem.
> 
> # ifconfig xl0 
> 
> xl0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
>                                       ^^^^^^^^
>          address: 00:01:02:78:11:e8
>          media: Ethernet autoselect (10baseT)
>          status: active
>          inet 203.219.167.126 netmask 0xfffffffc broadcast
> 203.219.167.127
>          inet6 fe80::201:2ff:fe78:11e8%xl0 prefixlen 64 scopeid 0x2
> 
> But ifconfig seems to suggest that it is running in simplex mode.
> 
> Is the degradation a result of the ADSL connection?

The fact that you 10BaseT is simplex will not matter as 10Mbps
is 20X faster than even the ADSL's downlink speed of 512kbps

You bottle neck is the 128kbps uplink speed.  You'd think that
is a lot but you can't got say "codec X uses Y bits per seciond,
so two calls are 2Y bps and keep adding calls untill your
128bps is "full".  It don't work that way.

Think in terms of _probibilities_.  Say your uplink is one
quarter full.  What does that mean?  It means it is running at
128kbps 25% of the time and zero 75% of the time.  So if
an audio packet is placed on that line there is a 25%
chance it will be delayed in an outbound queue.  It is
those delays that you hear.  Actually the amount of
delay is a distribution and what you hear are the "tails" of
the curve.  (i.e. there is a 25% change of a delay then
there is a 12% change that two packets back to back will
be delayed, 6% of three and so on.)
With one audio stream there is no competition
for the uplink.  Adjusting the packet size can have an
effect.  Very long packets are not good 


=====
Chris Albertson
  Home:   310-376-1029  chrisalbertson90278 at yahoo.com
  Cell:   310-990-7550
  Office: 310-336-5189  Christopher.J.Albertson at aero.org
  KG6OMK

__________________________________
Do you Yahoo!?
Yahoo! Hotjobs: Enter the "Signing Bonus" Sweepstakes
http://hotjobs.sweepstakes.yahoo.com/signingbonus