Week Twelve Notes

Announcements

• We are doing 'self-service' roll call today. Please mark the appropriate box with an 'X'. Please tell me if your name is missing from the sheet.
• Monday: Second Magazine Article Review is due
• We are reading chapter eight this week.
• We study how to make a home page this week.
• Correction: freeware is not to be confused with free software

Chapter Eight -- Networking and Telecommunication

• The Sci Fi author Arthur C. Clarke 'prophesied' geostationary communications satellite technology in 1945.
• Samuel Morse invented the telegraph in 1844.
• Alexander Graham Bell invented the telephone in 1876.
• Computer networks facilitate sharing: hardware, software, and information.
• A Local Area Network (LAN) consists of networked devices (nodes) that are physically pretty close. For example, they could all be in the same building, or set of buildings.
• Many of the 'nodes' in a network are computers, but they can be other things, like networked printers and other peripherals.
• Nodes are connected through hubs and switches. Switches allow mulitple pairs of nodes to communicate simultaneously - hubs don't.
• LAN's employ wiring to make connections. Wireless links also play an increasingly important role.
• Metropolitan Area Networks (MAN's) - typically provides connectivity among in a metropolitan area.
• Wide Area Network (WAN) - extends over long distances - many miles - possibly thousands of miles.
• Nowadays different networks often interconnect using bridges and gateways. "The Internet" is the result of such interconnection.
• Routers are devices that make routing decisions in networks. A router is connected to more than one network link. When a message arrives at a router via one link, typically the router sends it out over a different link. The router routes by deciding which link to use. The goal is to conduct the message to its intended destination.
• Some specialized networks:
  • Global Positioning System (GPS)
  • ATM commercial banking network
• Bob Metcalfe's ethernet is a popular networking technology for LAN's
• Networks use various kinds of modems for long-range transmissions. Modems are modulator/demodulators. They convert digital information to analog for transmission. On the receiving end they convert from analog back to digital.
• Bandwidth is measured in bits per second. It refers to the amount of information that a node can receive in a fixed amount of time. If we think of network connections as pipes, bandwidth is the width of the pipe.
• DSL, Cable modems, satellite links, wireless broadband connections, and fiber optics (500 Mbps) all offer more bandwidth than 28.8 or 56.6 Kbps modem service.
• WiFi is the fastest-growing wireless LAN technology
• Bluetooth is a wireless technology for "personal area networks" consisting of computers, cell phones, PDA's, headsets, printers, and so forth.
• Current wireless network technology is susceptible to eavesdropping & hacking. The Wired Equivalent Privacy (WEP) encryption scheme provides security equivalent to that found on some wired networks. The use of Virtual Private Network (VPN) technology offers more security.
• In order to communicate nodes in a network have to understand and use the same communication protocol. A protocol is a set of rules about how communication is performed. Protocols determine things such as address and message formats. They also determine procedures for establishing connections and varying transmission speeds.
• Transmission Control Protocol/Internet Protocol (TCP/IP) refers to the family of communication protocols used by the Internet.
• Groupware allows two or more users on a network to work on the same document simultaneously.
• E-mail is a big part of network use. There are mail-reading programs that require clients to access mail spooled on a server. Other programs allow the client to download the e-mail. MIME extensions allow for viewing e-mail in various GUI formats. Attachments of various types are possible. Attachments can carry viruses. Certain formats of e-mail allow spammers to discover whether and when e-mail has been read.
• There are mailing lists for group discussions. Users can get digests of list messages. Some lists are moderated.
• Network newsgroups are electronic bulletin boards.
• E-mail and newsgroups are asynchronous.
• Instant Messaging and teleconferencing are synchronous.
• Computers can be used as telephones in a couple of different ways: They can be connected to the "plain old telephone service" and communicate through an internal modem. Also the networking capability allows voice to be be shunted between two computers. Voice over IP (VoIP) is a popular protocol.
• Various handheld computers blur the distinction between phone and portable computer.