B.2. A Serial NULL Modem Cable

A serial null modem cable will work for both SLIP and PPP. Again, you will need two DB-25 connectors. This time your cable requires only eight conductors.

You may have seen other NULL modem cable designs, but this one allows you to use hardware flow control—which is far superior to XON/XOFF flow control—or none at all. The conductor configuration is shown in Figure B-2:

Again, if you have a shield, you should connect it to the first pin at one end only.

Figure B-1. Parallel PLIP cable


Figure B-2. Serial NULL-Modem cable