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Re: [HLL] Frame-Layout



Status: RO
Content-Length: 2410
Lines: 68

At 21:10 04.01.1998 +0100, you wrote:
>-----BEGIN PGP SIGNED MESSAGE-----
>
>Hi,
>
>
>some thoughts about frame-layout:
>
>* Old format supported 8 logical channels,
>  I would like to reduce that to 4:
>  * 1 Channel for control  (additional control-bandwidth in frame data-zone)
>  * 1 Channel for audio    (gsm voice-data)
>  * 1 Channel for sio-data (transparent user-channel via serial port)
>  * 1 Channel <reserved>   (might be multiplexed to support a higher
>                            number of logical channels than standard=4)
>  This looks ok, or what do you think ?

Yes. But think about an implentation where only Voicedata is exchanged.
This is more easy to implement and gives more throughput. Any Form of
Controllchannels will drop Bandwith 5-10%.

>
>* Do we operate the modem in "raw" mode (without error correction,
>  but in "real time" operation) ?  Sure about that ???

Yes Sir!

>  Does this mean that we can be *absolutely sure* to be able to
>  transmit data at 1800 Byte/Sec (14400 Baud Modem) all the time ?

No Sir!

>  So also no "retraining sequence" (600mSec++ no data) ?
>  Should we add little redundancy to the frames (loosing some bandwidth) ?

Too much CPU wasted. Let us retransmit the Packets or drop them.

>  Decryption trashes several sequencial bytes for one bad input-bit !
>
>* Old frame-layout supported loosing only parts of a frame.
>  This meant that a one-bit-error could only trash one logical channel,
>  not causing you to loose a whole frame.
>  Is this a feature worth to be kept ?

No. Due to the Nature of V.3x more than one Bit is transmitted in a coding
/decoding scheme (4-8Bits at a single Time) so if there is going something wrong
the other 3-7Bits are invalid most of the Time. If we have a V.34 Channel its
better to transmit all Data twice.

That is to much tought about the modempart. If we are going to transmit
things over TCP/IP we will loose whole Packets and not only bits.
We could design diffrend Comunication Layers but make this Sense?

>
>Thats enough for today ;-)
>
>
>Volker
>


Hacko

Hartmut Schroeder             Email:hacko@mail.hh.provi.de
http://www.mms.de/~hacko      32U0564185 5937869 (WGS84)

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