Ted MacNEIL wrote:
Yes, IP drops packets. But also, yes, TCP keeps track of it all and requests retransmissions.
Not according to the traces.
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.
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!.
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.
IMHO it is *not* a proof that TCP/IP is bad and SNA is good. The only
thing it proves is you have a problem with some macro when switched from
SAN to TCP/IP. It can happen because of error in the script, emulator,
emulator settings, even network configuration (i.e. some packets could
be filtered).
I'm far from claiming that TCP/IP is the best solution, however single
case, especially not analyzed one is not a proof.
--
Radoslaw Skorupka
Lodz, Poland
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