Practical Industrial Data Networks:Design, Installation and ...

Industrial Ethernet overview 243An interesting feature of the PsiberNet probe is that it is non-intrusive, i.e. it is a clampstylemeter that simply clamps on to the wire and does not have to be attached to a hubport.Figure 15.10Psibernet gigabit Ethernet probe15.6.3.7 Software protocol analyzersSoftware protocol analyzers are software packages running on PCs and using either ageneral purpose or a specialized NIC to capture frames from the network. The NIC iscontrolled by a so-called promiscuous driver, which enables the NIC to capture allpackets on the medium and not only those addressed to it in broadcast or unicast mode.On the lower end of the scale, simple analyzers are available for download from theInternet as freeware or shareware. Middle of the range packages such as NDG Software’sNetBoy Suite offer good value for money but rely heavily on the user for interpreting thecaptured information. Top of the range software products such as Network Associates’Sniffer or WaveTek Wandel Goltemann’s Domino Suite have sophisticated expertsystems that can aid in the analysis of the captured software. Unfortunately, this comes ata price.15.6.3.8 Hardware-based protocol analyzersSeveral manufacturers such as Hewlett Packard, Network Associates and WaveTekWandel Goltemann also supply hardware-based protocol analyzers using their protocolanalysis software running on a proprietary hardware infrastructure. This makes them veryexpensive but dramatically increases the power of the analyzer. For fast and gigabitEthernet, this is probably the better approach.15.6.4 Problems and solutions15.6.4.1 NoiseIf excessive noise is suspected on a coax or UTP cable, an oscilloscope can be connectedbetween the signal conductor(s) and ground. This method will show up noise on theconductor, but will not necessarily give a true indication of the amount of power in thenoise. A simple and cheap method to pick up noise on the wire is to connect a smallloudspeaker between the conductor and ground. A small operational amplifier can beused as an input buffer, so as not to ‘load’ the wire under observation. The noise will beheard as an audible signal.