Data Comes To An Abrupt FINish By Bill Alderson and J. Scott Haugdahl   Q: We are responsible for maintaining a mission-critical network at a major hospital and outpatient clinic. A number of times throughout the day, users--anyone requiring access to patient data--are unexpectedly kicked out of a terminal-to-host application that communicates patient information to and from a minicomputer. Needless to say, users are becoming irritated. The problem occurs on both our Windows for Workgroups and Windows95 workstations. Bill: How about a diagnosis and a prescription to help with their problem? Scott: Perhaps the problem is in the ether, since Ethernet is servicing all the users with problems. Bill: In that case, let's just switch them to a T oken-Ring configuration. Scott: Yeah. Then we could have them take two tokens and call us in the morning. Bill: On the other hand, maybe ATM is the solution. Scott: Are you kidding? And have those cells running all over the clinic? Bill: OK...we started by looking at the network path between the client and the host. Scott: Basically, we were looking at 10BASE-T Ethernet hubs in the clinic that attached to FDDI via translational bridging. The hos t, a Digital Alpha, connected directly to the FDDI. Bill: The user's application relied on the old standby, telnet, a remote login protocol that operates over TCP. Scott: The telnet packet was sent through a router on the FDDI, which, in turn, performed protocol translation between telnet and Local Area Transport (LAT), a proprietary Digital terminal protocol. Bill: The router functioned as a gateway, communicating with users using TCP/IP and communicating with the Alpha using LAT. Scott: Users reported random application kick-outs with no apparent rhyme or reason. Bill: As we noted in one of our very first columns (see "A Whole Lot of LAT..." at techweb.cmp. com/nc/513/513colalderson.html), the LAT protocol is susceptible to network delays. Scott: We set up a second analyzer on the FDDI Ring to see if delays through the bridge, then the gateway, could be causing a problem. Bill: Analysis of traffic on both sides of the gateway showed minimal delay, so we didn't feel that LAT time-outs would be an issue. Scott: By analyzing packets on the clinic's Ethernet segment containing the most users of the ap plication in question, and having them notify us immediately upon a disconnection, we were able to catch a few disconnects--a process that took nearly two hours.

On The Edge by Art WIttmann FreeWire by Bill Frezza Corporate VIew by Brian Walsh In The Middle by Bruce Robertson Updated May 23, 1997