Hi, Olga!

Sunday July 13 2003 02:12, you wrote to me:

 IK>>  Only zip archives ? ;-))

 OZ> MNP5 uses some kind of zip compression before transfer any data.

 Yes. And when MNP5 tries to compress already compressed data, the speed
only decreases. And V42bis can automatically detect if data is compressed
and turn the compression off. That's why modern modems rarely use MNP5,
although, AFAIK, all of them support it.

 IK>> transferring the uncompressed data (plain text etc.)

 OZ> I've read specifications of V42. It transfer only compressed data. You
 OZ> mean V90 doesn't compresse data?

V42 - is error correction protocol. Data compression protocol is V42bis, by
the way. ;-)
I mean that if a modem with V42bis transfers the uncompressed data, it
compresses it "on the fly", and then the other modem decompresses
it. So, between two modems data is compressed and CPS, surely, will be
higher.
That's why the port speed should be approximately two or three times higher
than modem speed (9600 is enough for a 2400 modem, 38400 for a 14400 modem,
57600 for a 33600 modem, 115200 for a 56000 modem).

 IK>> V90 it's easy to achieve very high CPS (theoretically, 56000 bits
 IK>> per second = 7000 bytes per second;

 OZ> It's a theoretical high limit of a digital line. Usual speed can't be
 OZ> more than 90% of it.

Surely. The highest connection speed I've seen was, AFAIK, 51333 .

 IK>> using V42bis at uncompressed data -
 IK>> apporx. 14000 CPS).

 OZ> Character is 8 byte. 14000*8=112000 - limit of usual ;-) COM port

Yes, and this speed is quite enough for a usual analog modem. ;-)


Igor "Magic"


  np: silence (Winamp is not active ;-)

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