WCF Session, number of clients?

I'm developing as system with a WCF service back end, and thinking about implementing sessions. But I'm worried about the number of client that can be connected at the same time. I will have up to 500 clients connected, and each client will constantly make calls every 5-10 seconds. How expensive w开发者_开发百科ill it be for the service to have one instance per client?

Thanks

Jon

The Enterprise Library caching and authentication blocks may be used in this scenario. Your infrastructure servers will need high specification SQL and Application machines.