IBM's WWW page <http://www.ibm.com/> can lead you to a helpful document
<http://www.austin.ibm.com/pub/www/services/aix_service/faxes/SLIP.DOC.zap>

From: marvin@tornado.oche.de (Christian Bode)

If you don't have problems with slattach you should have PTF 
bos.obj 3.2.0.0.U411505 installed.  I assume that you did the right
ifconfig commands to setup your slip-device (for example sl0).

1. Create a group called slip.

2. Create a user slip with smit like this:
                                                     [Entry Fields]
* User NAME                                          [slip]
  ADMINISTRATIVE User?                                true
  User ID                                            []
  LOGIN user?                                         true
  PRIMARY group                                      [slip]
  Group SET                                          [slip]
  ADMINISTRATIVE groups                              [system]
  SU groups                                          [slip]
  HOME directory                                     [/home/slip]
  Initial PROGRAM                                    [/bin/sh]
  User INFORMATION                                   [SLIP-Dialup]
  Another user can SU to user?                        false
  User can RLOGIN?                                    true
  TRUSTED PATH?                                       nosak
  Valid TTYs                                         [/dev/tty1]
  AUDIT classes                                      []
  PRIMARY authentication method                      [SYSTEM]
  SECONDARY authentication method                    [NONE]
  Max FILE size                                      [2097151]
  Max CPU time                                       [-1]
  Max DATA segment                                   [262144]
  Max STACK size                                     [65536]
  Max CORE file size                                 [2048]
  Max physical MEMORY                                [65536]
  File creation UMASK                                [022]
  EXPIRATION date (MMDDhhmmyy)                       [0]

3. Create a tty with getty on it:
                                   Add a TTY
                                               [Entry Fields]
  TTY type                                     tty
  TTY interface                                rs232
  Description                                  Asynchronous Terminal
  Parent adapter                               sa0
* PORT number                                  [s1]
  BAUD rate                                    [38400]
  PARITY                                       [none]
  BITS per character                           [8]
  Number of STOP BITS                          [1]
  TERMINAL type                                [dumb]
  STATE to be configured at boot time          [available]
  DMA                                          on
  Read Trigger                                 0,1,2,3
  Transmit buffer count                        [16]
  Name of initial program to run               [/etc/getty]

  Note: The following attributes are only applicable if /etc/getty is
        specified as the initial program to run.

  Enable program?                              respawn
  Run level                                    2
  Enable LOGIN                                 share
  TIME before advancing to next port setting   [0]
  STTY attributes for RUN TIME                 [hupcl,cread,brkint>
  STTY attributes for LOGIN                    [hupcl,cread,echoe,>
  RUN shell activity manager                   no
  Optional LOGGER name                         []

4. Change the hardware characteristics so that it uses NO XON/XOFF handshake
   section 1.613 also talks about tty flow control.

5. A (new) .profile template for slip accounts is provided in section
   8.07.  The author, David Migliavacca, writes, "I would also like to
   assert that, to my experience, it is NOT required that the SLIP user
   be made "administrative" or member of "system" as other parts of the
   FAQ (and the original script) say.  At least on my machine 8-).  I now
   create SLIP users as members of group slip, it being the ONLY group;
   allowed ttys are set to the available modem lines only; their home
   directory is owned by root and the .profile is only readable by group
   slip.

Here's another scenario:
From: oosten@angelo.ee.ualberta.ca (Brian Oostenbrink)

Operating System: IBM AIX 3.2.1 and 3.2.3

Configuring two RS6000s via a Serial Line Interface Protocol (SLIP) 
connection over two US Robotics Sportster 14,400 modems.

The AIX implementation of SLIP is slightly different from most others. 
The ifconfig command is used to bring up a serial interface, and the
slattach command is used to connect the interface to the serial port
used for the connection.  Dialer device commands can also be issued when
invoking the slattach command, using UUCP chat syntax.

The following describes a connection between two machines:

     local.j.k.l
         ethernet IP address 129.128.127.21
         slip interface IP address 129.1.2.1

     remote.a.b.c
         ethernet IP address 129.11.22.44
         slip interface address 129.11.22.1

1. Interface configuration

Each machine must have a separate IP address dedicated to the SLIP
interface. On remote.j.k.l, start the SLIP interface with:

         ifconfig sl0 129.11.22.1 129.128.127.1  up

and on local.a.b.c:

         ifconfig sl0 129.128.127.1 129.11.22.1  up

It is important in later versions of AIX 3.2.3+ to use the same SLIP
interface # as the ptty port #, ie. if you use tty12, use ifconfig sl12
instead of sl0.

At this point the interfaces are ready to be connected.

2. tty configuration
   The tty ports on both machines were configured in an identical manner
   using smit.
                                                 [Entry Fields]
 TTY type                                           tty
 TTY interface                                      rs232
 Description                                        Asynchronous Terminal
 Parent adapter                                     sa0
 PORT number                                        []                       +
 BAUD rate                                          [38400]                  +
 PARITY                                             [none]                   +
 BITS per character                                 [8]                      +
 Number of STOP BITS                                [1]                      +
 TERMINAL type                                      [dumb]
 STATE to be configured at boot time                [available]              +
 DMA                                                on                       +
 Read Trigger                                       0,1,2,3
 Transmit buffer count                              [16]                      #
 Name of initial program to run                     [etc/getty]

 Note: The following attributes are only applicable if /etc/getty is specified
 as the initial program to run.

 Enable program?                                    respawn
 Run level                                          2
 Enable LOGIN                                       disable                  +
 TIME before advancing to next port setting         [0]                      +#
 STTY attributes for RUN TIME                       [hupcl,cread,brkint,icr>
 STTY attributes for LOGIN                          [hupcl,cread,echoe,cs8,>
 RUN shell activity manager                         no                       +
 Optional LOGGER name                               []

On older versions of AIX, we encountered some problems disabling getty, and
resorted to changing the /etc/inittab file directly. For example, change

   tty0:2:respawn:/etc/getty /dev/tty0
to
   tty0:2:off:/etc/getty /dev/tty0

This will disable getty from running. After creating the SLIP tty device,
you will need to change its hardware configuration to disable Xon/Xoff
flow control. Software flow control should not be used for SLIP. Type
'smit chtty', and then select sub item 2: Hardware settings.

Most of the parameters in the tty configuration are the defaults.

3. Modem Configuration

   The modems were configured as follows:

   RTS/CTS flow control enabled.
   Xon/Xoff software flow control disabled. Usually this is automatic if
      RTS/CTS is enabled.
   Data rate, terminal to modem = fixed.
      This is the baud rate from the tty port to the modem. We used a
      fixed modem-port transfer rate, set to the fastest speed supported
      by both the tty port and the modem. Newer modems can use a higher
      transfer rate between the modem and serial port than the modem to
      modem rate, which is necessary to use data compression effectively.  
      In our setup, we used 14.4 kBaud modems with a port speed of 38.4
      kBaud. If your modem supports this feature, use it, otherwise set
      the port speed equal to the modem connection rate. On the USR
      Sportster at&b1 fixes the serial port rate to that of the last
      AT command. The speed parameter of the slattach command can be
      used to ensure that this rate is that set in the tty configuration.
   Error Correction enabled - not mandatory, but a good idea
   Data Compression - not required, but it helps, especially for text
      transfers.
   Auto Answer - If the SLIP connection is to be initiated from either
      machine, both modems should be set to auto answer, otherwise, just
      the answering modem.

   It is a good idea to configure the modem and then save the settings
   to NVRAM, so that the correct settings can always be restored by the
   slattach command.

4. UUCP configuration files

   /usr/lib/uucp/Devices
   /usr/lib/uucp/Dialers

   The Devices file must contain an entry with the tty and serial port
   speed used for the interface. In our example,
      Direct tty0 38400 slipdialer

   The keyword 'slipdialer' is merely an index into the Dialers file.
   For our purposes, the slipdialer entry in the Dialers file is simply:

      slipdialer

   This entry can also contain UUCP chat commands, or the chat commands
   can be included in the slattach command.

5. slattach invocation

   slattach connects the device on the tty port to the SLIP interface
   created by ifconfig, and sends any commands to the tty device if
   needed. For our example, remote.j.k.l would never initiate a call,
   only answer incoming calls. Therefore we execute:

         slattach tty0 38400 '"" ATZ OK ""'

   which connects the tty at 38400 baud. We could also simply run

         slattach tty0

   ie. without any modem commands, but the modem to port speed may not
   be correctly set this way. In addition, the ATZ command ensures the
   modem is set to the NVRAM settings.

   On local.a.b.c type:

         slattach tty0 38400 '"" ATZ OK \pATDT4925871 BIS ""' 4

   This establishes the link at 38400 baud, and executes the dial string
   as shown. The dial string is a UUCP chat string and are configured
   in an expect send expect send ... format. The string:

         '"" ATZ OK \pATDT4925871 BIS ""'

   is interpreted as:
   expect "" (null string) from modem
   send   ATZ              to modem
   expect OK               from modem
   send   \pATDT4925871    to modem
   expect BIS              from modem

   BIS is the end of the CONNECT STRING. You could use any portion of
   the string returned by the modem upon a connection as the expect
   string. It may be wiser to simply expect CONNECT since all
   connections should return this string.
   The null strings are necessary because the first parameter of the
   UUCP is an expected string from the modem, which can only be a null
   string until the modem has been given a command.

   The last parameter (4) of the slattach command is the debug level. 
   A debug level of 4 displays the UUCP chat strings, which is useful
   for checking the modem status.

6. Routing
   ifconfig is sufficient if all you want to do is talk between the
   two hosts.  If you are running SLIP so that you can talk to more
   than just that one other host you have to advertise your address.
   
   1) arp -s 802.5 iago 10:00:5a:b1:49:d8 pub
        where 802.5 is a token-ring network the hardware address can
        be obtained with `netstat -v` and iago was the SLIP client (My
        PC at home :)  pub is the important part it means "published"
        You may want to run this at boot time. 

   Routing through the SLIP link is similiar to routing of any gateway. 
   Invoking the ifconfig command automatically sets up a route between
   the two SLIP machines. An entry in /etc/hosts or the named database
   should be made, with the same machine name used for the SLIP address
   as the ethernet address on each machine. For example, in /etc/hosts
   on remote.a.b.c (and any other machine on remote.a.b.c ethernet):

     129.11.22.44 remote.a.b.c # ethernet address
     129.11.22.1  remote.a.b.c # slip address

   It is preferable to place the ethernet address in the hosts file
   before the SLIP address so remote.a.b.c will resolve to the
   ethernet address. When using named, it is important to have both
   addresses in the reverse file with the same name. We experienced
   difficulties with NFS mounting over the slip link, owing to some
   machine interpreting NFS requests from one of the two SLIP machines
   as coming from the SLIP address, while the SLIP machine believed it
   was sending the request from the ethernet address. This problem was
   eliminated by having both addresses reverse resolve to the same name.

7. Performance
   At a modem speed of 14.4 kBaud and a port speed of 38.4 kBaud, we
   realized a transfer rate through ftp of about 3.5 kB/s for text
   files, and 1.3 kB/s for compressed files.