Vorwort - SSS-Tools für Power System i Syntax System Services

4.3 A PPP Monitor Utility
By Michael Ryan
System i systems have communication capabilities as robust and feature-rich as any computing
system out there. We can communicate via TCP/IP and SNA, sockets or APPC, Ethernet
or dial-up–a host of possibilities. Many of the communication scenarios we employ are TCP/IP
based, whether over a private network or the Internet. Trading partners and financial institutions
often accept VPN connections or SSH connections to transfer data, or require encrypted files
they can then send over a public network such as the Internet.
Dial-up access is another method that’s been around as long as there have been systems
that needed to communicate. Though dial-up was once the only method of communication,
its use has decreased with the advent of the Internet and private networks. However, some
trading partners and financial institutions still require a dial-up connection. One of the most
popular protocols for dial-up is Point-to-Point Protocol (PPP). Another, less popular protocol is
Serial Line Internet Protocol (SLIP), Today, most System i dial-up connections that use TCP/IP
applications use PPP.
I won’t cover the configuration of PPP in this article–you can obtain good information about
setup and configuration from IBM’s Information Center. I’ll explain the operation of a program
I developed to programmatically obtain the status of a PPP connection.
Dial Blues
We get used to network communications. Whether across a WAN or a LAN, we’re used to
having the systems and resources available when we want them. We don’t need to establish a
connection to these servers and resources–we just access them (though we may need to login
first).
Alas, not so with dial-up. It’s just not as reliable as WAN or LAN communications. Also,
note that I’m specifically not talking about ISDN or DSL, both of which require a form of
dial-up. I’m talking specifically about PPP–the simple, widely used protocol to connect to a
system. Modems and POTS (plain old telephone system) lines are involved. Ever have a dropped
connection back in the days of dial-up service to AOL or Compuserve? The same issues apply
here. Ever had static on a phone line, whether it was a modem connection or just a voice call?
That’s the unreliability I’m talking about. And I’ve been experiencing that unreliability lately in
a mission-critical application. You know, one of those applications that’s run for years without
a hiccup, and all of a sudden we’re receiving errors that are near-impossible to troubleshoot.
Aging phone lines? Aging modems? Aging communication adapters? Aging programmers?
Whatever the case, we’ve been receiving PPP communication errors too regularly. That’s why I
developed this program.
So, if a PPP connection is inherently unreliable, how do we manage it? First, let’s review how
a connection is established. We use the Start TCP/IP Point-to-Point (STRTCPPTP) command to
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