On Thu, 15 Jun 2006 00:00:00 GMT, Ted MacNEIL <[EMAIL PROTECTED]> wrote:
>>Yes, IP drops packets. But also, yes, TCP keeps track of it all and requests retransmissions. > >Not according to the traces. I obviously can't comment on traces I haven't seen. I can say that TCP provides guaranteed delivery ... if you (and your software) are willing to cope with some very ugly timings. > >If TCP/IP is so robust, why has it NEVER happened in 7 years under SNA (how long we've had the TN3270 client we use), and it always happens under TCP/IP. I don't understand that statement. If you've been using Tn3270 for 7 years you've been using TCP/IP. By definition, Tn3270 is 3270 over TCP/IP. >We have MACROS (scripts) coded for call centres to screen scrape an old CICS application and answer customers' questions. >They have never failed under SNA. >The only change we make (and I know it's the only change because I am co- ordinating it and controlling it), is we make the TN3270 client talk to TCP/IP. >Invoke the MACRO and BOOM!. First, in my VERY unhumble opinion, anybody using screen scraping gets what he or she deserves. (BOOM!) That was as true under pure SNA as under TCP/IP. (If you went for 7 years without screen reformatting you lived in a very static world, indeed. >Corrupted (incomplete) data sent to the host, the application session gets terminated and the user is blown to a blank sign-on screen. > >Doesn't even have the logo and sign-on crap we display when the PC first connects to the mainframe. > >Every time. Not intermittent. No re-transmission requests. No session. No data. That sounds like a problem with the Tn3270 client, or some kind of incompatability between the Tn3270 client and server, or some such. If this is not an intermittant problem it is absurd to blame it on dropped IP packets. Dropped packets are not a repeatable issue ... unless you are violating the protocol or have something misconfigured. (Sending packets too large for a level-2 switch will be dropped every time. And trying to set up an SNA connection between mismatched ends will fail, too. Remember NRZI vs non-NRZI?) I happen to be an SNA bigot and have no love for TCP/IP, but don't like seeing bogus arguments against TCP/IP. Crying "wolf" helps nobody. Find more specifics about your failure; there is something more specific than just "TCP/IP" here. Pat O'Keefe ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
