《计算机网络——自顶向下方法与internet特色》幻灯片lecture.ppt

Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History 1.4.1 Access networks Access networks can be loosely classified into three categories: residential access company access (university, company) wireless access Keep in mind: bandwidth (bits per second) of access network? shared or dedicated? 1. Residential access: 1) point to point access Dialup via modem up to 56Kbps direct access to router (often less) Can’t surf and phone at same time: can’t be “always on” 1. Residential access: 2) cable modems HFC: hybrid fiber-coaxial cable asymmetric: up to 30Mbps downstream, 2 Mbps upstream network of cable and fiber attaches homes to ISP router (by cable modem, thru 10base-T to PC) homes share access to router deployment: available via cable TV companies Service is always on 1. Residential access: 2) cable modems 3) Cable Network Architecture 3) Cable Network Architecture 3) Cable Network Architecture 3) Cable Network Architecture 2. Company access: local area networks company/univ local area network (LAN) connects end system to edge router Ethernet: shared or dedicated link connects end system and router 10 Mbs, 100Mbps, Gigabit Ethernet LANs: chapter 5 3. Wireless access networks shared wireless access network connects end system to router via base station also know as “access point” There are two broad types of wireless Internet access: wireless LANs (几十米半径范围): 802.11b/g (WiFi): 11 or 54 Mbps wide-area wireless access（上万米半径范围） provided by telco operator 3G ~ 384 kbps Will it happen?? WAP in Europe；3G in Japen 4. Home networks Typical home network components: ADSL or cable modem router/firewall/NAT Ethernet wireless access point 1.4.2 Physical Media what lies between transmitter receiver Brief life of a Bit: propagates between transmitter/rcvr pairs thru different physical m