To connect directly via the admin port without a modem you need an adapter. Avaya 355AF
You can make your own but be sure not to plug into an extension port by mistake. Sure fire way to blow out a serial port on the pc.
The pin out sequence is:
Mod Plug to 25 DB = To Avaya 355AF adapter
1 blue to 22
2 orange to 5, 6, 8
3 black to 20
4 red to 7
5 green to 3
6 yellow to 2
7 brown not used
8 white not used
Mod Plug to 9 DB = To Avaya 355AF adapter to DB 9
1 blue to 9
2 orange to 1, 6, 8
3 black to 4
4 red to 5
5 green to 2
6 yellow to 3
7 brown not used
8 white not used