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  Wandel & Goltermann's High-Speed Analyzers Tops in Tests continued February 8, 1999 Another deficiency of the high-speed analyzers is a lack of buffer memory for storing captured cells and packets. A typical buffer size was 64 MB or less. Theoretically at 155 Mbps, a buffer can fill up in less than four seconds. At 1 Gbps, a 64-MB buffer can fill in merely half a second. With these high data rates and limited buffering, good capture-filtering capability is a must. Like their ATM analyzer siblings, the buffer sizes in the current generation of Gigabit Ethernet analyzers are woefully inadequate. Having the potential to transmit more than 100 MB in less than one second means that a protocol analyzer needs to have high-speed capturing hardware and a large capture buffer. Setting capture filters and using frame slicing (capturing only the first hundred or so bytes of each packet) can help ease the strain on the capture buffer. A Gigabit Ethernet analyzer needs at least 256 MB of installed capture buffer memory with an expansion option to a minimum of 1 GB.
 Some ATM and gigabit switches don't have monitor ports, and fiber splitters are expensive, priced at $1,000 or more apiece. This leaves us with the pass-through option included with the analyzer. All the high-speed analyzers we tested came with an external pod or a built-in interface with a pass-through mechanism. Both let you tap into the full-duplex ATM or Gigabit Ethernet connection. The pods contain fiber ST receptacles and have four ports: one to capture the receive side, one to repeat the receive side, one to capture the transmit side and one to repeat the transmit side. No matter how you slice it, putting an analyzer in place is tricky and you have to disrupt the network to do it. Wandel & Goltermann Technologies DominoATM
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Despite some basic limitations in the technology, Wandel & Goltermann's DominoATM displayed a notable level of maturity in our tests and its decodes were generally impressive. Both it and GN Nettest's WinPharaoh ATM work with external pods. These pods contain the ATM module with a mechanism for pass-through monitoring or ATM end-device emulation, the ATM layer processing, capture memory and, of course, a connection to a host personal computer. As with Internet Advisor, the maximum capture buffer is only 16 MB, but DominoATM has the flexibility to allocate the memory in different amounts between the send and receive channels.Page 1 | 2 | Next Page |
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