When a router connects to the internet it aquires an IP address, it then shares this ip's ports with any computers plugged into it. Each ip has about 65,000 ports.

Now Imagine a router is like a Telephone PBX system, 1 telephone number , lots of extentions and the secretary connects you to the right department. Now imagine the IP address is the telephone number, the extentions are 'ports' and the secretary is the router.

Streams/calls come from the internet to your IP address/telephone number but each piece of information/call has its own port/extention it needs to go to. Your computer needs to recieve this information, so the secretary/router needs to know where to forward the information/packets to.

Setting up these rules to control the flow of data is called 'Port Forwarding', you forward the external data to your 'Internal IP' address.

By default no forwarding is setup so the data is lost and you will get very slow speeds and bad video

There are 3 ways of port forwarding:

1. UPNP - Once this is setup on the router and your PC all ports are forwarded automatically, not all software supports this.

2. DMZ - This is a setting on the router where it will forward all external data to one internal IP address, This is very easy to setup. run 'CMD' from the run menu, type 'ipconfig /all', make a note of your internal IP address and enter it in to the UPNP settings page in the router, If you are using DHCP you will need to change the DMZ setting every time you restart your PC. If using a static this should only be required once.

3. Manual Port Forwarding - This is the hardest of the 3 but can be useful if you are having trouble with connections, There will be a page for port forwarding in your router, sometimes it is called something different. The idea here is you forward just the ports you need to your local IP address. Do not use this method if you are using DHCP, the default setting for networks.

Use this website for more informatino and guides on 'Port Forwarding'