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I am developing an application using remote (internet) clients which each need a permanently open incoming TCP/IP connection.

Each client will coonect to one unique incoming port (the actual numbers being configurable).

I need up to 80 clients online at any one time. Is this OK? (or will I hit some limit in either VRPC or WinXP?)

You will need to ensure that all the ports in the range you are using are:

Free for use (ie. not claimed by another other application)
Not blocked by any Firewalls

I presume that there is a good reason for using more than 1 port? I ask because it may prove more reliable to use one single port and to preface each data block with a unique identifier for the particular client machine (for example in the range 1 to 80). In my opinion using lots of user configurable ports is going to make debugging very difficult, plus gives users on each client machine a good way to mess everything up.

The ports will be free.

There are no 'users' - the clients are unmanned.

And the current design says that the clients will remain permanently connected - sending 'keep alive' requests every minute to keep the sockets open.

It all works with just two clients - which is all I have at the moment.

Fair enough. If you know the ports will be available and also know that there won't be a Firewall blocking access I can't see any particular problems - provided there is enough bandwidth for all the clients to communicate correctly.

That's good.

I just wanted to check that the number of open sockets would not be a problem.

Whilst I have written some networking stuff (years ago) I've never needed to open lots of sockets at once. However I can't forsee any other obvious problems with opening and monitoring large numbers of sockets at once.

OK - Thanks.

I nearly have some test software ready, so I will give it a whirl.