Re: [LAD] 802.11n sound card

Hi,

On Thursday 24 December 2009 01:48:14 Patrick Shirkey wrote:
> On 12/24/2009 11:31 AM, Arnold Krille wrote:
> > On Wednesday 23 December 2009 23:52:46 Patrick Shirkey wrote:
> >> So the issue is with other streams being picked up by the receiver which
> >> affects latency by increasing collisions?
> >> Would this still be a problem on a secured connection? Surely the
> >> receiver would ignore all data that is not being transmitted over the
> >> secured access point?
> > No, the problem is one or two layers deeper in the stack. We are talking
> > wifi here. No matter if there is only two devices on that network or a
> > secure connection, its still wireless transmission over radio frequencies
> > in the 2GHz range. Which is per se much more affected by any disturbance
> > then a dedicated cable is. Every mobile phone, every blue-tooth device,
> > every neighbours network, every iron in your ceiling will influence this.
> > And not only with a constant background-noise in your frequency range,
> > but also with momentary scrambling and such stuff. So in the layers you
> > can not (easily) control by software there is already lots of resending
> > and rescheduling of packets. And all these introduce uncertainties and
> > latencies you don't want in your audio transmission. Unless you can do
> > with 100ms latency and more...
>
> This is good analysis. Thanks for taking the time.
>
> Is that number 100ms a real number or just an estimate?

I was once taught that a good estimate for an error is better then a bad
calculation. This number is a guess from my understanding and experience of
networks and the osi layers...

> > But getting the stream to be reliable is already complicated with things
> > like firewire (which has isochronous channels for exactly this purpose)
> > and its more complicated with usb (which has a master telling the clients
> > when to send bigger payloads to not disturb the other bus-members). Ask
> > the jack-over-udp guys how difficult it is to create such stream reliably
> > over tcp-ip network. And they take lost packets into account (which means
> > an xrun) and advise you to use it on dedicated networks if you want more
> > the the immediate experience...
> In this case are we comparing a network located over large distances
> with internet nodes in between or a couple of computers sitting within a
> couple of meters of each other?

Comparing local wired network and local wifi...

Have fun,

Arnold

_______________________________________________
Linux-audio-dev mailing list
Linux-audio-dev@email-addr-hidden
http://lists.linuxaudio.org/mailman/listinfo/linux-audio-dev