Client: Sparekassernes Data Center, Copenhagen
Project: High Performance Transaction Message Switch
Dates: Jan 86 / Mar 87
for 15 months as a Team Leader on a large project at the Sparekassernes Data Center
near Copenhagen, building, integrating and testing a high
throughput OSI/SNA based banking transaction message switch on an IBM
3084 mainframe under MVS/XA. The message switch was one of the
components of a large network that included over 1300 Olivetti
mini-computers situated in savings banks throughout Denmark and
Greenland. These were connected, via the Danish PTT's X.21 switching
network, into 7 IBM 3725 communications processors at the data centre.
The switch being implemented, used standard SNA/VTAM sessions to
interface these 3725's to a host IBM 3084Q/3090 which ran the on-line
banking transactions system. The switch itself was based on modified OSI
Transport and Session protocols and running both high & low volume
data streams. Each
Local Computer opened a 'Path' to the Message Switch, over which it
would then establish ,p to 30 'Associations'.
These associations could run various type of data streams,
passing data as Letter Fragments. One
such data stream was for high volume, low. content, data consisting of
single fragment unacknowledged Letters (STP protocol).
An other data stream was for lower volume, high content data consisting
of multiple fragment acknowledged letters (SEP Protocol). This second
protocol implemented a pseudo OSI Class 4 Transport Layer and included
transmission/receive windowing, flow control, Letter fragmentation, and
re-assembly, re-sequencing, fragment retransmission and acknowledgement
The switch could
handle over 30,000 concurrent data streams with an averaged throughput
of 300 message pairs per second.