What is a SSDP protocol request with notify http/1.1 ? How can I find out what this network traffic is?
It's the protocol used to control the WiFi access-point that sits between your cable-modem/DLS and your home.
It does a number of things for you. First of all, it tells you that the device exists, with a URL. You should then see an icon appear in various places on Windows that you can click on in order to open up a web browser to access to pages on the device to manage it. That's especially important for the multipurpose devices that support disk drives, music players, printers, and so on.
It's also used by applications in order to open up ports on the firewall. For example, if you run P2P applications like BitTorrent, you'll use this system to open up the port to receive incoming connections.
It's a Windows things, btw. Macintosh uses a competing standard based on MDNS.
The Wikipedia article is pretty scarce on this: http://en.wikipedia.org/wiki/Simple_Service_Discovery_Protocol