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A Brief Guide to AS/400 Networking for Thin-client Communications

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Author’s note: In this article, I use thin client to refer to both thin client and network computing technologies. For the purposes of AS/400 network configuration when using these technologies, this term will suffice for both configurations.

Thin-client technology is here to stay. It seems like there is some new thin-client success story published on the Internet every day. I know thin client works because I worked on a project that, to date, has deployed more than 1,500 thin-client bricks.

Do you want to move your AS/400 installation into the world of thin client? Are you aware of the networking requirements of this new technology? Remember all the changes you had to get used to when you converted from twinax to twisted pair? In this article, I will give you some ground rules for making sure your AS/400 and associated network are ready for the new paradigm of thin-client computing. It’s easier than you think!

Getting Started


First things first: twinax is dead. IBM just forgot to send you the letter! I know that IBM has a twinax-equipped network station that can be used in a thin-client network, but why would anyone want to use one? At a maximum speed of 2 MBps, you could get out and walk faster! So, I’ll assume that you’re going with the flow and eliminating the twinax in your AS/400 network.

What should you replace twinax with in the brave new world of thin-client computing? The short answer is CAT 5 unshielded twisted-pair (UTP) cabling. Thin-client technology does not require any special cabling. In fact, thin-client technology does not require any special network hardware or infrastructure changes. From a design perspective, think of a thin-client network as you would any other Ethernet-based network. Thin-client bricks have an integrated network interface card (NIC) in them and they connect to UTP nets via a standard RJ-45 jack. So, my best advice is to go with CAT 5 UTP and standard RJ-45 pinouts.


Although there are not any network infrastructure changes required to move into the thin client world, you cannot buy a pile of thin-client bricks and start merrily plugging them into your AS/400 network. “Why?” you ask. The answer is a key reason AS/400 Network Expert is published. In general, the bulk of AS/400 networks in operation today are poorly tuned. Largely designed for 1-16 MBps network traffic, these networks typically have not taken advantage of the latest in AS/400 networking technologies. So, take this opportunity to review your network.

As a rule of thumb, thin-client networks should be as flat as possible. Flat networks have the minimum number of network communication devices and software operating on it. Here are my guidelines for flattening an AS/400 network for (or in spite of) thin-client computing:

• Get rid of those old StarTek boxes, FiberMuxes, 5394s, 5494s, and other outdated or obsolete networking devices. You’ve been reading about the world of switched networks, right? Now is your chance to implement that technology in your AS/400 network. Outdated networking equipment is often more costly to maintain than its more contemporary counterparts, so here’s a chance to lower your cost of networking, too.

• Speaking of a new network infrastructure, let your Token-Ring equipment pass away quietly, too. After all, it is a dead networking technology. The same is true of 10 MBps half-duplex Ethernet. Let it go, too.

• Rearchitect your network using 100 MB full-duplex Ethernet, gigabit Ethernet, or Asynchronous Transfer Mode (ATM), which can act as the transport protocols for your new Independent Computing Architecture equipped (ICA-equipped) thin-client network.

• Doesn’t this seem like the right time to lose those directly attached printers in favor of network-attached printers? I think so.

• Read up on AS/400 TCP/IP. Not only is TCP/IP the preferred network model for all new AS/400 networks, it’s also the working model on which thin-client networking is based. The details of both AS/400 TCP/IP and Ethernet configuration are well- documented. See the OS/400 TCP/IP Configuration and Reference V4R3 (SC41-5420-02) and the TCP/IP Fastpath Setup V4R1 (SC41-5430-00) manuals for more information. Both manuals are available at IBM’s AS/400 online library at http://publib.boulder.ibm.com/pubs/html/ as400/online/homeeng1.htm.

Thin Traffic

Generally speaking, my designs for AS/400 thin-client networks try to leverage no more than three protocols used in combination: fast Ethernet carrying TCP/IP with encapsulated ICA. Although thin-client bricks can use a veritable laundry list of (primarily PC LAN-oriented) protocols, take my advice: leave your network configuration at ICA within TCP/IP over fast Ethernet. It’s a simpler, flatter network to diagnose when network problems occur, and it plays to the strengths of contemporary AS/400 networking. Moreover, there are countless books on TCP/IP and Ethernet connectivity from which you can learn.

Also, since TCP/IP will be the core protocol of your new AS/400 network connectivity, make sure you consider the AS/400 as your Domain Name System (DNS), Dynamic Host Control Protocol (DHCP) and perhaps—if your thin-client bricks require it—Bootstrap Protocol (BOOTP) server. I have used the AS/400 in this fashion and can say that the AS/400 not only makes a good DNS/DHCP server, but is much more reliable
(i.e., highly available) than an Intel-based server. Once you have your AS/400 network configured for fast Ethernet and TCP/IP, the next challenge is ICA. The good news (and the bad news, oddly enough) is that ICA is a very fast, very small, rather chatty protocol that, at this time, does not run natively on an AS/400. The word is that IBM is considering ICA for native implementation on the AS/400, but you didn’t hear that from me.

ICA is both good and bad news for your S/400 network because you can only tune ICA’s performance from a Wintel server, not from your AS/400. However, hands-on

experience has shown me that ICA is extremely efficient (most of the time). Just don’t attempt to use ICA for any graphics or multimedia-oriented sessions, especially on a WAN. ICA’s performance in those scenarios is dreadful.

What about Brick-to-AS/400 Connectivity?

Once you have a flat AS/400 network that is configured for fast Ethernet and TCP/IP (and, optionally, DNS/DHCP), and your Windows NT folks have configured ICA, it’s time to think about brick-to-AS/400 connectivity.

The good news is that thin-client technology offers several alternatives to this thorny issue. On the one hand, you could simply buy a brick that incorporates a 5250/3270 emulator. On the other hand, you could have your Windows NT folks configure a Microsoft Terminal Server/Citrix MetaFrame (or similarly software-equipped) server and then run Client Access/400 on top of that. I’ve tried both ways and, in an AS/400 TCP/IP network, either approach is a snap.

Getting There

It is fair to say that thin-client technology is here to stay. Now you know that configuring a network in a thin-client world is probably easier than you thought. There’s no magic or mystery. All you need is just a little basic AS/400 networking.

Linda Hirsch

Linda Hirsch started her career with IBM in 1984 in Rochester, Minnesota, and was raised in the midrange software lab, holding a variety of programming and technical marketing roles. She's still in the lab today, where one of her favorite activities is teaching customers and business partners about System i Access products. Linda can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it..



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