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Re: [HLL] Sync 14.4-Data



Status: RO
Content-Length: 2383
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>> [Synchonous mode 14.400 modems]
> 
> Big advantage is avaiable technology (gsm-coder, 14.4-modems/lines).
> So i'm stuck to on this idea a bit...
> 
> Standard hayes-kompatible 14.4-modems have a sync operation mode.
> Looks as if they could operate with VP1-sync-standard etc.
> The problem is only the pc-comm-port, which can't operate synchron.
> There would be not problem with HLB, because we design i/f ourselfs.
> 
> So for a compatible implementaion (pc/hlb/vp1) we would need a way
> to encode/decode this sync-data on standard com-ports.
> No problem with standard i/f-hardware (but probably unwanted),
> but would require tricky programming if done in software.
> Software-Solution might be ok for DOS, but impossible when
> using WIN or LINUX etc., because of timing issues.

This would make the PC version very difficult. I pretty much see
hand-working the UART as an impossibility right now. (Doesn't that involve
extra wires such as 'clock' ?) I would suggest using the half speed codec
for now, and waiting to see if Lucky gets his hands on a better codec.

If that doesn't work out, why not build a device that can use the full speed
codec at 28.800 or between two boxes in sync 14.400. The problem is that you
have to know what mode you're going to use before the connect, and this
would involve knowing to press diffent buttons depending on whether the
other side can use sync.

This sync mode would have to be an 'extra option' though, because
software-only implementations may not be able to use it, and _everything_
should interoperate, at least to me that's the whole plan.

I wonder if this is worth it considering the minimal price difference
between 14.400 and 28.800 modems since 33.600 came out. I see no real
prolems in building something that sounds shitty at 14.400 yet perfect at
28.800. If you use this device a lot, you get a cheapo 28.800, and if you
use if over Int'l circuits you're not going to be on the phone forever
anyway.


Here is an alternative, possible solution, but I don't like it myself:

If in the negotiation, two boxes find out that they both support sync and
that at least one has only 14.400 modem capability, they terminate their
async link without hangin up (the link to the phone is still there, so it
won't hang up ?) and reconnect sync. Ugly, takes long, sucks.



Rop