Mailinglist Archive: opensuse (4547 mails)

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Re: [SLE] Still cant connect to my ISP
  • From: Basil Chupin <blchupin@xxxxxxxxxx>
  • Date: Sun, 02 May 2004 16:36:37 +1000
  • Message-id: <409496F5.6020108@xxxxxxxxxx>
Carlos E. R. wrote:
The Friday 2004-04-30 at 18:15 +1000, Basil Chupin wrote:


pppd: CONNECT 115200 <===================================XX
pppd: --> Carrier detected. Waiting for prompt.

Here's your problem - the connect at 115200.


Not really.

There are two speeds to note, and they can be different. One is the speed
from the computer to the modem, and it is quite correct to set it a 115200
- I'll explain later.

Then there is the speed at which the local modem connects to the remote
modem, and this is negotiated while the connection is established - it is
not set by the user directly (not normally). The maximum for a V90 modem
is 57600: speeds between 45000..52000 are normal.

However, V90 can use compression; this will not work if you limit the
speed at which the computer feeds data to the modem. That's the reason why
the computer can (and should) connect with the modem at 115200 cps.


It is physically not possible to connect on a dial-up connection above 57600 baud - nor can data flow faster than the theoretical 57600 baud simply because this is the upper limit of the beast.

A connect speed of 115200 simply indicates that the settings are wrong and the modem is reporting the DCE speed and not the actual connect speed of the 2 modems. (Depending on the modem, one can control the connect speed using the S37 register together with the (AT)N parameter - and have the connect speed reported using the (AT)W paramteter; however, one cannot go above the prescribed 57600 connect speed although, of course, one can deliberately connect at a lower rate (essential if the phone line(s) are bad). But I don't think it is necessary to go into all this in Keith's case :-) ,)

I admit that in my reply to Keith I was just a bit sloppy - but I was tryng to get the message across that the settings (computer to modem at 115200 [provided that the modem can actually accept this speed] baud and modem-to-ISP at 57600) have to be checked to solve his problem.

The compression you mention above can only apply to data which can actually be compressed, but even if it is compressed it can still only get transmitted at the theoretical upper limit of 57600 bps; and being compressed it *appears* that it is being transmitted quicker. An example of data which can be compressed is a text document (an ASCII document); an example of something which cannot be compressed is a zip-ped file or, in Linux terms, a *.gz file because these are already compressed. Something else which cannot be compressed is a *.jpg file - which one sees all the time on websites - because, again, it is already compressed.

(The MNP5 protocol, the data compression protocol, can actually be a pain in the behind because it will compress/uncompress data whether or not the data requires it and therefore can slow down the flow of data. I normally switch it off (it's normally ON by default in modems) with the AT%C0 command).)


The modem should really report the real speed at which it is connecting to
the remote, but this is usually configurable - somehow, but I can't
remember how..

Again depending on the modem, the S95 register together with the (AT)W parameter will do this

Cheers.

--
I am not young enough to know everything.



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