dialup modem switchbox not working

[aleX]

I started another switchbox project today, and I'm starting to wish I
hadn't bothered.
I bought a 4-way DB-9M Manual Data Switch so I could connect my three
computers to one modem. Constantly pulling the modem cable out of one
computer and putting it into another was becoming a chore as I have
limited space to move the cases for access to the rear. The switchbox is
listed as being suitable for this purpose:
http://www.maplin.co.uk/Module.aspx?ModuleNo=36484&TabID=1&source=14&doy=15m4

The switch has 5 DB-9M ports (Male) listed as 'COMM' and 'A', 'B', 'C', 'D'.
I had the cable for the 'COMM' port to 56k Modem (I presume the 'COMM'
goes to the modem, and not to one computer with the modem on another
serial port - still to test), so I also bought 3 '9 Way Null
Female-Female' cables to go from the switch to my computers:
http://www.maplin.co.uk/Module.aspx?ModuleNo=13509&TabID=1&source=15&WorldID=&doy=15m4

The problem is that no matter which way I set the switch, the modem is
not accessible.

I'm thinking maybe these 'null' cables are not what I needed, even
though I need a Female connection on each end. Should I have bought
male-female cables plus a male-female convertor for each?
Is there a difference in the pin-outs, which is why the cables don't
seem to work? Could be a faulty switchbox but I doubt it.

I can exchange the cables if required, but hope I don't need to buy 3
convertors - I'd have been cheaper buying another 2 modems!

Any advice welcomed, thanks. Will report back if I do get it working.

 

[aleX]

I've been doing a bit of reading up and it seems to me that 'Null Modem
Cables' have nothing to do with modems at all, they're just for
connecting computers where there is no modem available. A bit like a
network crossover cable? Damn, looks like I'll have to exchange the
cables and buy the m-f convertors - or just get a refund. Please correct
me if I'm wrong and can still get it working with what I have.

 

[Grinder]

I've been doing a bit of reading up and it seems
to me that 'Null Modem Cables' have nothing to do
with modems at all, they're just for connecting
computers where there is no modem available. A bit
like a network crossover cable?

It's true -- null modem connectors are analagous to ethernet crossover
cables.

 

[aleX]

It's true -- null modem connectors are analagous to ethernet crossover
cables.

I need 3 serial cables to extend my 3 computer's serial ports to the
switchbox. I won't need to get any male-female convertors either. Don't
know why I never realised this before - I just saw the word 'modem' on
the null modem cable packaging and bought them without thinking. Well,
at least I've learned what a 'Null Modem' cable is today

 

[JANA]

You need standard serial extension cables with the proper connectors on each
end, as I believe you figured out.

Putting your modem through all that cable, and switch box must slow it down
a bit? Also, you increase the chance of having more noise in the data
signal.

Have you considered using a router, and getting a modem that can be shared
on the router?

Have you considered going high speed, using a router, and a high speed
modem? You can set everything up in a network type operation, and have a
much more efficient system.

--

JANA
_____

It's true -- null modem connectors are analagous to ethernet crossover
cables.

I need 3 serial cables to extend my 3 computer's serial ports to the
switchbox. I won't need to get any male-female convertors either. Don't
know why I never realised this before - I just saw the word 'modem' on
the null modem cable packaging and bought them without thinking. Well,
at least I've learned what a 'Null Modem' cable is today

 

[Paul Murphy]

You need standard serial extension cables with the proper connectors on
each
end, as I believe you figured out.

Putting your modem through all that cable, and switch box must slow it
down
a bit? Also, you increase the chance of having more noise in the data
signal.

Have you considered using a router, and getting a modem that can be shared
on the router?

Have you considered going high speed, using a router, and a high speed
modem? You can set everything up in a network type operation, and have a
much more efficient system.

--

JANA
_____




I need 3 serial cables to extend my 3 computer's serial ports to the
switchbox. I won't need to get any male-female convertors either. Don't
know why I never realised this before - I just saw the word 'modem' on
the null modem cable packaging and bought them without thinking. Well,
at least I've learned what a 'Null Modem' cable is today

The other option is just to connect all the PCs together with network cards
(wirelessly if need be) and use Windows own built in internet connection
sharing (assuming they're all windows machines). This means the modem can
permanently be left connected to the main PC that's most often used and when
one of the other PCs wants to go online, Internet connection sharing will do
what's required to get the other machine with the modem to dial up and then
transfer the required data through a normal network connection. The only
downside with this setup is that the machine with the modem must be up and
running when any of the PCs need to go online. The suggestion of a router
with built in modem port would get around this though - a similar setup to
using an external print server.

Paul

 

[aleX]

The other option is just to connect all the PCs together with network cards
(wirelessly if need be) and use Windows own built in internet connection
sharing (assuming they're all windows machines). This means the modem can
permanently be left connected to the main PC that's most often used and when
one of the other PCs wants to go online, Internet connection sharing will do
what's required to get the other machine with the modem to dial up and then
transfer the required data through a normal network connection. The only
downside with this setup is that the machine with the modem must be up and
running when any of the PCs need to go online. The suggestion of a router
with built in modem port would get around this though - a similar setup to
using an external print server.

Paul

Thanks for the replies Paul and JANA, I exchanged my cables for serial
cables today and it's working fine now. Luckily my modem speed doesn't
seem to have suffered going through the extra cable and switchbox.
Broadband will have to wait for now as I may be moving in the near future.

I do have the computers networked, 2 W2k and 1 Debian, but I hit a
problem with using the modem on the linux computer when the network card
was installed. I've tried many reinstalls but I just can't create a new
'defaultroute' despite trying everything (this is probably best left to
another thread).

I use the computers for testing various things out, I'm learning linux &
plan to install it in another computer too, so my current modem option
is easier for me for getting straight on the net when I require during
any installs - there's no guarantee I will always have an existing PC up
& running to use as the main Internet Connection Sharing PC. Maybe Linux
to Windows Internet Connection Sharing is possible, I don't know -
I'll get to that eventually if it is.

For the future, a router sounds good. I have looked for one before, but
routers with a 56k modem port are increasingly rare. There is only one I
can recall (a Sitecom I think) but I could only find it online. I could
order one, but I'll probably just wait for broadband then get a router.

Thanks again.