As previously described your address 192.168.x.x is an RFC 1918 address and as such, is not routable.

Your public IP address assigned to you by your ISP is likley being translated into the RFC1918 address via a broadband gateway performing a function known as Network Address Translation or NAT. The gateway is probably configured for one-to-many NAT in that many private addresses are sharing the same public address.

The net-sum result of this is that you cannot established an unrequested session into any host on your private lan without doing one of two things.

The first would be to either get another IP address from your ISP and map this directly to the private address of your server. Alternatively, if your gateway supports it you could do port mapping if you only need to map a certain port like port 80. This would allow you to use one IP but have all http requests go to the private host as an example.

The other, and IMHO the best alternative would be to use IPSEC to establish a VPN session into your private network.

At any rate, you have some reading to do...good luck