CUSM, ISDN & Mac, questions

John Carey (
Wed, 15 Feb 1995 10:15:35 -0500


>I use cusm with an ISDN connection from my home at 56k/sec. This speed is
>the maximum limit my Mac IIcx port can handle, so even though my ISDN
>hardware can handle transmission rates of 128K/sec, the Mac IIcx cannot.
>However, there is a solution.

How about this solution. Don't use the serial port. If your Mac has an
ethernet capabilities, you can use an ISDN to ethernet bridge. The Combinet
160 is one such device. It hasn't any of the speed limitations of your serial

>But here is the dreadful catch: MacPPP, MacSLIP do not
>handle speeds over 56K/sec, there is no way to then, it seems, have a SLIP
>or PPP connection *and* 128K/sec ISDN! You have to slow down to the
>software's limitations, even though the hardware is primed to go at a
>faster speed! Yuck.

If you aren't using your serial port, you don't need to use MacPPP or Mac
SLIP. As far as your Mac is concerned, it is using Mac/TCP over an ethernet

>One other
>catch -- no ethernet, appletalk, and so on should be required -- this is a
>direct ISDN connection from a phone jack in my wall at home (AT&T 5eSS
>custom, I think).


>Any solutions, insights, brilliant hacks (like recoding MacPPP to handle
>128K/sec) would be hugely appreciated.

I don't see why you should prefer your Mac serial port to an ethernet
connection, and I really don't understand why you would want to use MacSLIP or
MacPPP which are both meant to be used over analog phone lines. The
limitations that you describe exist because of your hardware (Mac serial port)
and software (MacPPP and MacSLIP). Jettison them and you lose the problem.

I have an ISDN connection at my home. When I got it, Pac Bell told me that
mine was the first personal ISDN line installed in Northern California. This
is the hardware that I use, so I know that it works.

John (