How They Really Work
Osher Lifelong Learning
Institute
University of Illinois, Urbana-Champaign
Scott Badman, Instructor
The Internet
Two world wide public addressing systems: telephone numbers and Internet Protocol addresses
International Telephone System
Carries most world-wide communication traffic, including the Internet
Theoretically circuit-switched
A complete circuit is established at the beginning of the call, and then the call takes place over that same circuit for its entire duration.
Now almost completely packet-switched
The voice is digitized into a flow of binary numbers, which are then divided into packets, and sent individually to the other end, where they are reassembled and combined back to the original signal.
The packets do not have to travel the same route. There is no "circuit".
Internet
Packet-switched from the beginning over leased telephone lines
Now "interoperable" with the digital telephone system.
Internet and telephone interoperability achieved because the various pieces of equipment conform to the International Standards Organization's Open Systems Interface model.
Internet Connections with ISO / OSI Model (PowerPoint slides)
Typical Home Connections (PowerPoint slides).
ipconfig
Version 4: 32 bit dotted decimal notation
Version 6: 120 bit hexadecimal notation
Media Access Control (MAC) address, 48 bit hexadecimal number used in Ethernet and WiFi connections for one hop only.
Gateway Address: The "Router" that handles your computer -- the first piece of equipment that routes your datg to its destination.
ping www.cnn.com
Domain Name Service (DNS) finds the IP address of cnn.com
tracert www.abc.net.au (succeeds) and www.cnn.com (blocks in Atlanta)
www.speedtest.net actual speeds over the Internet from your connection
WWireshark (available at http://www.wireshark.org)
1. ipconfig /all - Keep this information visible.
If your IP address is 169.254.xxx.xxx, then your computer did not get a valid IP address from your home router, or from your Internet service provider. You will not be able to solve your connection problem until this problem is solved. Try rebooting the computer and seeing if you get a non-169.254.xxx.xxx address. If you don't get a different address, the problem is probably with the connection to the home router or Internet service provider.
2. ping 127.0.0.1 - If you get a reply, the PC hardware and TCP/IP software is O.K. You network connection is working to the connector on the back of the computer. If no reply, the problem is with your computer. Try rebooting. If the problem persists, get expert help to troubleshoot your computer.
3. ping your_ip_address from the ipconfig /all display above. If you get reply, the network is working to the nearest piece of equipment connected to you computer, probably your home router. If no reply, check the connection to the home router and make sure it is powered and running.
4. ping default_ip_address from the ipconfig /all display above. If you get reply, the network is working to the piece of equipment responsible for routing you to the Internet, which is probably owned by your Internet service provider. If no reply, make check all connections and associated equipment. If the problem persists, it is time to call your Internet service provider, but check the next step before you call.
5. ping dns_server_address from the ipconfig /all display above. If you do NOT get reply, your Internet service provider has probably disconnected you from the Internet. Cutting your access to the Domain Name Server (DNS) will prevent you from reaching the Internet. This is the usual way Internet Service providers cut you off, because it is very easy to do, and then to undo if they decide to provide you service again
6. ping www.google.com or www.nytimes.com, or some such web site. If you get a reply, your Internet connection is working properly. Any problems you have having are not caused by the connection to the Internet.