Agenda Last class: Digitization Today: Network Hardware Typing How do computers talk to each other? Needs? Same hardware Same rules (protocols) for encoding data Typing

Network Cable How to connect 2 computers? 4 computers? Hardware Network Cable How to connect 2 computers? 4 computers?

Client-Server Network One computer is the “server” - stores important files, data Other computers are “clients” - asks the server to use its files

Client-Server ANALOGY Server is like a waiter Clients are like customers - asks the server for food - not allowed into the kitchen

Peer to Peer Network All computers have equal access to others. Good for sharing.

Peer to Peer Network Another way to connect the computers

Hub or Repeater Just repeat signals to all computers Peer to Peer Network Hub or Repeater Just repeat signals to all computers Hello! Hello! Hello! Hello!

Bridge or Switch Send signal to whom you want Peer to Peer Network Bridge or Switch Send signal to whom you want Hello! Hello! Bye! Bye!

Router 3 computers 1 internet connection Peer to Peer Network Router 3 computers 1 internet connection Hello! Hello! Bye! To Internet Bye!

Peer to Peer vs Client-Server Pros and Cons Client-Server ++ Pros? -- Cons?

Peer to Peer vs Client-Server Pros and Cons P2P + More independent + File sharing + No wait time for server -- Low security -- Share internet connection (slow) Client-Server -- Broken server = Broken network -- Need a fast server + More security + Easier to configure many computers

LAN and WAN LAN = Local Area Network (eg: home, personal use) WAN = Wide Area Network (eg: school, apartment, for internet)

Internet Connection Router WIFI Internet Bluetooth Service Provider (ISP) Modem Cable DSL Satellite

Modem use phone line to send Slow: 56 kbps (56 kilo bits per second) “Bandwidth” Cheap Dial for connection Can’t use phone at the same time

Digital Subscriber Line DSL = Digital Subscriber Line Faster 10 Mbps Expensive ~900 rmb per month Uses phone lines too, but always online Can talk on phone at the same time Problem: need to be near the phone company

Cable Cable Faster! 50 Mbps Cheaper than DSL Use cable TV connection, always on Can be far from the cable company Problems: shared connection – slow during peak hours Low security

Other connections T1 line Satellite For government, university, big business $$$$$$$$$$$$$$$$$$$, but very fast Satellite For people living away from the city $$$ to set up

Internet Connection Modem – slow, $, phone DSL – fast, $$$, phone at same time Router Internet Service Provider (ISP) Cable – faster, $$, TV Satellite – away from city

Network History 1973: U of California and Stanford wanted to connect their networks. Made TCP/IP Military and Research use only 1989: Connect to the world. China connected in 1994 – why so slow?

Internet in China Government wants control Growth – not too fast Only give Internet to “good” people. Need license. Information – don’t let bad info spread Censorship Block websites (“Great Firewall of China”) News, politics, foreign sites. Some good, some bad. Internet police – delete messages of activism, criticism, controversy Money – government wants it, and they know Internet is good for business… so “Good” companies get the best opportunities

Internet in China Government wants control If you try to do something bad The Firewall will try to stop you first (Block site, delete email / messages) Go to Jail Die

Wednesday Quiz about networking