RPC and Client Server Application

[Maurizio]

I'd like to ask some suggestion regarding a software that I'm
developping.
For develop the project I've to use VB.NET and Framework 3.5

This is a Client Server application.

I've some computer ( 1 server and 2 or 3 clients ) connected each
other in LAN.

This project is located in industial automation field.

On Server I've the automation routine, on client I've user interface.
On clients I've connected some serial devices such as card reader and
PLC.

This is a tipical situation:

User put the card into card reader.
Client where card reader is connected must inform the server that a
card has been inserted.
Server ask a client the CARD_ID, client have to read CARD_ID from card
reader and pass it to the server.
After that, the automation can continue exchanging other information
between client and server regarding user intercation. Every action
need to be notified from client to the server becouse if for exaple
PLC is in some particular state I've to disable the card reader.
Furthermore server can query the client for read the state of PLC or
for some other iteration

For develop this project I've two ideas:

1.
Deploy two service:

- server who listen on TCP port for incoming connection
- client connect to server

When communication is extablished data is exchange between two
machines using a protocol designed for this scope.
In case that a card has been inserted client send a message to server,
informing of this event.
So automation process can continue, after that other interaction will
take palce using the same exchange information.

2.
I've read some paper about RPC
I've think to deploy some class and compile it into DLL so for example
I've a DLL that manage card reader.
After that I'd like to know if it's possile using RPC to call from
server the DLL who read card numer on the client.
So I'd like to deploy a polling so every x second server ask to client
if a key has been inserted or other action have take place for example
PLC status is varied.

At this point I'm in doubt how to deploy this project if:

- implement network service design protocol communication
or
- use RPC

One important goal of this project is the stability and the absence of
error so if any error occur during network communication I should be
able to intercet.

I'd like to know your opinion about and if there is some book or
technical article where I can found more information about.

I'd like to thank you very much!!

Regards
Maurizio