Workshop

Think about this for a moment. In a game of telephone, if the guy to my left is responsible for giving me
the correct message, and I’m responsible for giving the guy to my right the correct message, when I find
out that the message I have is not the correct one, I naturally suspect the guy to my left. If these messages
are packets and I’m a Token-Ring card, when I see an error, I naturally suspect the Token-Ring card
upstream of me.
Error Types
The types of errors discussed thus far are called isolating soft errors. They’re isolating because they’re
typically caused by a lone station rather than a generic ring problem, plus they’re reasonably easy to
track. They’re soft because getting a few of them is not terribly bad for the ring. Unless you’re going to
be a Token-Ring geek, it’s not worth dealing with the specifics of these errors; however, it’s good to
know which Token-Ring errors are isolating errors. If you look at an analyzer and it tells you that the
NAUN for an error is a certain MAC address, all you need to do is find that MAC address and turn the
machine off. No divide-and-conquer techniques required.
Here are the isolating errors:
• Abort delimiter
• A/C error
• Burst error
• Internal error
• Line error
All these errors pretty much mean the machine is ill and needs help. Because you’re not interested in
being a Token-Ring physician, the best thing to do is to remove the NAUN from the network and see if
the problems clear up. After all, you probably haven’t put a network analyzer on a segment unless you’re
experiencing problems—in other words, you probably have to take action after sizing up the situation. Be
aware, however, that if you put an analyzer on what is ostensibly a healthy Token-Ring, you’ll see a
limited number of errors, so don’t panic.
Any station that comes into the conversation or leaves the conversation breaks the ring momentarily.
This causes a burst error. A neighboring station notices this and reports it to the active monitor. This is
as normal to Token-Ring as collisions are to Ethernet. Having a couple burst errors on a healthy Token-
Ring is not a big deal; it’s just an indication that someone has turned his or her PC on or off. If you have
hundreds of these in a short period, then you have a problem. Don’t worry about a couple, though.
Receiver congestion errors are also okay in small amounts—they simply indicate that the workstation is
having a hard time keeping up. You’ll want to investigate large numbers of these, because they can slow
down your entire network. In general, though, a few of these just indicate that some workstation is
having trouble keeping pace with the ’90s.