Thursday, November 27, 2008

pathchar

I just had one of those serendipitous google experience where you learn something-- the snippits bar about gmail had a link to a company called Packet Design, which has developed a tool to improve visibility into IP routing protocols; sounds like BGP, IS-IS, EIGRP, and OSPF mostly. Anyways, I always look at the people first, and in this case it looks like both Van Jacobsen and Judy Estrin are on the board; okay, this seems serious. However, in Van Jacobsen's bio it lists several tools he's developed like traceroute, and one I had never heard of: pathchar. Maybe this is well known, but no one brought it up in class the other day when we were all talking about estimating hop-by-hop latency. Several [very old] binaries are available at ftp://ftp.ee.lbl.gov/pathchar/; the linux one sort of seemed to work for me. What's very interesting are the presentation slides explaining the challenges of estimating link latencies; he notes (obviously, I suppose) that queuing delay is what makes this hard, although you can easily filter it on a single hop.

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