User:PoC/Serial networking scenarios with-Cisco-routers

Sometimes, older, donated hardware comes without LAN I/O-adapters. Sometimes it has serial, synchronous capable communication I/O-adapters, though. This article shows several ways how to "network" AS/400 machines through these, with the help of (older) Cisco hard- and software, and points out pros and cons.

Note: This article is probably more about Cisco configuration than AS/400.

Cisco has provided a lot of configuration options to support different networking scenarios. Emphasis is to multiplex once separated IBM SNA and PC-/Workstation based traffic onto the same physical wiring. Expectably, huge cost savings for recurring bills resulted, because expensive leased lines could now be shared.

Decades later, the focus shifted from commercial applications to mainly hobbyist uses, with their own set of use cases.

Requirements

#6152 serial IOA (SPD), located in a P02

#2609 serial IOA (SPD), located in a P03

2609 Breakout-Brick — note that the Cisco cable is plugged directly which is wrong, and only shown for illustrational purposes.

IBM #2720 combined twinax- and serial IOA (PCI)

IBM #2721 dual serial IOA (PCI)

Physical Layer

On the physical layer, some kind of serial connection is required. In earlier times, AS/400's often had an external modem, providing remote diagnostics capabilities through ECS (Electronic Customer Support), connected to a serial port. For the sake of simplicity, the AS/400 in question is assumed to already have a serial port, RS-232 style.

Note: DE-9 or DB-25 connectors directly screwed to the chassis are meant for diagnostics and UPS connection. These are not normal serial ports!

Matching IBM V.24 Modem Cables for your particular hardware can be sourced e. g. through shops on the internet.

Cable designations:

Description	Length	Part Number	Feature Code
RS232 Cable DB-25F to DB-25M	6.1 m	22F0149	#9022
(Germany)		22F0150
(Japan)		22F0151
RS232 PCI Communications Cable Mini-Centronics to DB-25M		44H7480	#0348
(Germany)		44H7482
(Japan)		44H7484

There are other serial connectivity options but these are very rare.

On the Cisco-side of affairs, just two things are necessary:

• Cisco 16xx, 25xx, 26xx or similar router model with T-Type serial interface (card),
• Cisco CAB-232 FC.

Note! It is of utmost importance to keep in mind that the AS/400 serial ports have sense pins, to know which kind of cable is attached. If you plug in an ordinary PC serial cable, and vary on the line description, you’ll eventually find the succinct message in the QSYSOPR message queue, that a cable could not be found. Therefore the requirement of an IBM V.24 Modem Cable, or a self made cable, or adapter, providing the necessary sense pin connectivity. For this reason, you'll need to plug the DB-25F socket connector of the Cisco cable to the modem cable, and not directly to the AS/400’s port.

Configuration preparations

Obtain the resource names of the serial ports.

On the AS/400 systems, type wrkhdwrsc *cmn to get a list of communication hardware, and associated ports. Examples:

• V3/SPD:

Resource        Type  Text
CMB01           917B  Combined function IOP
  LIN01         2609  Comm Adapter
    LIN011      2609  V.24 Port
    LIN012      2609  V.24 Port

• V4/PCI:

Resource      Type  Status                Text
LIN01         2720  Operational           Comm Adapter
  CMN01       2720  Operational           V.24 Port   

Note! OS/400 V3 seems to not designate ports as CMN, but as LIN with three digits. Newer releases designate ports on an adapter as CMN.

On Cisco IOS, type show interfaces description to get a list of interfaces. Serial interfaces are designated by starting with Se.

See also

• Serial Cables IDs
• RS-232 Modem Cable Pinout
• Integrating LAN-less Machines into a local Token Ring
• Configuring X.25 link through Cisco IP network
• Configuring TCP/IP and SLIP with Cisco-Router and V3R2

Weblinks

• RS-232 timing signals, Wikipedia
• Serial Cable CAB-232FC, Cisco.com