Serial Port Modem is SLOW.. how can i fix?

[Calum]

my serial port modem is slow. it's on the desktop computer (it runs red hat 8.0). i have a laptop computer too (it runs mandrake 9.0), and it has a PC card modem. both connect to the same account at the same isp using the same telephone number. and both are 56k modems. the desktop serial port modem is connected normally on com1 or /dev/ttyS0. The PC card modem on the laptop i think is connected to an emulated com3, bt the mandrake installer put it automatically at /dev/modem and i have never checked to see where that points.

Now the serial port modem customarily seems to go at about 0.5kbps, peaking at 0.8kbps. This sucks compared to the PC card modem which goes at 4.2 kbps peaking at 5.2kbps.

I know this only from looking at the download speed while downloading rpm files while nothing else was using the connection, and also from the fact that webpages seem to load up a lot slower on the desktop than on the laptop.

Now what command line (or other) utilities can i use to determine some accurate speed ratings here, and then what can i do to make the serial port modem just as fast as the pc card modem. I really need to get a working modem on the desktop computer asap.

thanks in advance...

[voidmain]

There are no physical restrictions that should cause it to be slower, in fact it *should* be faster because it should not be using your processor for functions that win/linmodems use. You might what to check the modem log and see what connection speed your modem got with your provider's modem.

You also might want to check your serial port settings (Baud_base speed etc) with the "setserial -a /dev/ttyS0" command (or whatever port your modem is on, in fact you should be able to just use /dev/modem since it should be a symlink to the port your modem uses). See "man setserial" for a multitude of options.

Other things could be the initialization strings, or bad cables, or some other incompatibility between your modem and your ISP's modem.

[ January 10, 2003: Message edited by: void main ]

[Calum]

well, /dev/modem wasn't a symlink to start with, i installed red hat before i plugged the modem in, so i made the symlink myself with ln -s, also i am using redhat-control-network to connect and it has a built in GUI for baud rate, which is currently set to its highest setting (can't remember what that is), but i tried setting it down to 57000 or whatever the rate is for a 56k modem and it didn't help any... maybe i will try a different modem cable, although the one i am using is split new.

PS: what's an initialisation string and how do i find out more about it and how to set it. in particular, how would i go about fiddling with the initialisation strings to get the red hat one to be the same as the mandrake one?

and thanks for your speedy reply. you should get paid for the work you do on this site.

[ January 10, 2003: Message edited by: Calum ]

[voidmain]

You really should try to set it at 115200 if possible although this can cause problems on some modems. What make/model is the modem? Does it have dip switches and are they correctly set? Have you tried turning off some of the error correcting protocols in the init string?

After having cable for the last couple of years I had forgotten how much fun modems can be.  

[Calum]

it's a DYNALINK 56K V90 EXTERNAL MODEM (click for more info) and i don't think i would know a modem init string if it came and bit me on the ass! i'm not even 100% it has no dip switches. if they are physical objects then it has none. it has a smooth plastic case, weighs very little, and it only has a socket for the phone line (labelled 'data') and a socket for the power input and that's it. and it has all sorts of marvelous coloured lights on the front too.



here's a picture of the very modem in question...

[ January 10, 2003: Message edited by: Calum ]

[Calum]

well, a guy from my LUG list said:  

quote:  Calum,
The serial link between the modem and serial port probably won't work reliabliy above 115000.
Since you get connected everything else must be OK.
Have a look in /var/log/messages to see what chat messages are there after you get logged on.
Try tail /var/log/messages to see the last few lines. I think tail -n 100 /var/log/messages shows you the last 100 lines.

Reduce the serial port speed and see what happens.
Regards,

will try and will post results here, for others' reference.

[voidmain]

That's pretty much what I said in the last couple of messages other than you should try to get it to work at 115,200 if possible. With a 56k modem you will be limiting the troughput if you don't. But like I said you can't always get it to work at that high of a port speed. I have no experience with that brand of modem but it appears to have an AT command set. You might experiment with turning on/off error correcting protocols in your init string as I said before (I see Red Hat also has checkboxes in the modem properies for this).

On another note, most external modems I have used with great success are USR modems. But I have had a few Zoom modems that worked just as good. Look through your modem manual for a command set and modify your init string accordingly. Sorry I haven't been able to give you any more to go on...

[Calum]

i took your advice and now it seems my serial modem is working to full potential! thank you very much for your advice!

still, i am interested in these initialisation strings... maybe i will indeed read up on them.

[voidmain]

If it's working fine I wouldn't bother. Except for a couple of tricks I usually add to the init string for speeding up the dialing and turning off the sound:

M0 S11=50

The "M0" turns the speaker off and the "S11=50" sets the dialing speed up to 50 milliseconds between numbers (very fast, and about the fastest you can go ). If your modem has Hayes compatible AT command set these should work. Your manual should list all of the "AT" commands.

[Calum]

yup, i think it's hayes compatible, but i think i'll leave the speakers on since i like to be paranoid about having my modem owned and used to dial high price numbers in thailand without my knowledge!