ABSTRACT
The ultimate Ethernet troubleshooting tool is the protocol analyzer (see "Lesson 131: Protocol Analyzers:' June 1999, page 26). At the high end of the market, there are specially designed network interfaces on some protocol analyzers that can isolate and identify Physical-layer problems that might not be picked up by an ordinary NIC in a laptop computer running protocol analysis software. For 100BaseT networks, most protocol analyzers have add-on buffers that permit full wire-speed captures-comprehensive decoding software can't keep up with continuous levels of 100Mbits/sec, much less full-duplex traffic. Of course, like the handheld tools, protocol analyzers can look at all seven layers, not just Ethernet's Data-link and Physical layers. Cable testing functions, generally built into handheld testers, are not an option with protocol analyzers.
