Client/Server Applications - what to use?

We are also moving from remote DQ via VB and CA to sockets.  Some
applications call the validation programs while other send to a DQ for
transaction processing.

Our main business is retail point of sale transaction processing and 
based on a DQ.  This allows us to run multiple interfaces, communication 
programs, into one queue with multiple server processing from the queue.

Our dedicated transaction processing systems can process 100 or more 
queue entries per second.  They are keyed FIFO where the interface program 
send to the DQ with a key value of zero, and waits for a response with the key 
value equal to its job number, which is passed in the original queue entry.  
This give us the flexibility to change the application and re-set it with out
disrupting/resetting any communication jobs.  The servers read the next
entry with a key value of zero, FIFO.  If an entry was on the queue for 
more than 3 seconds, we start another occurrence of the server.  If a server
times out, we start ending them.  We have a control data area that hold 
the value of the minimum and maximum number of occurrences to be running.

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