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sensor works (4) ? Sensor works spread small devices over an area – Multihop work: devices send sensed data to collector via wireless hops Problems: 24, 25 RFID amp。 Sensor Networks (2) ? The Category of RFID Tags – Passive RFID tags have neither an electric plug nor a battery. – Active RFID has a power source in the tag. ? The Category Frequency of RFID – UHF RFID (UltraHigh Frequency RFID) tags municate at distance of several meters. It is used on shipping pallets and some drivers licenses. – HF RFID (High Frequency RFID) is likely to be in the passports, credit cards, books, and noncontact payment systems. – LF RFID (low Frequency RFID) is used for animal tracking. RFID amp。 each cell provides wireless service to mobiles within it via a base station 3G mobile phone works (2) ? Base stations connect to the core work to find other mobiles and send data to the phone work and Inter Architecture of UMTS 3G work 3G mobile phone works (3) ? As mobiles move, base stations hand them off from one cell to the next, and the work tracks their location – Soft handover vs. hard handover Handover 3G mobile phone works (4) ? Security – SIM (Subscriber Identity Module) card ? Authentication ? Cryptographic keys on the chip are used to encrypt transmissions ? Encryption cell phone ? 4G and WiMAX Wireless LANs (1) ? Two different munication modes in – Infrastructure wireless LAN: Clients municate via an AP (Access Point) that is wired to the rest of the work. – Ad hoc works: clients can municate directly in same radio rang. Wireless LANs (2) ? Signals in the ISM band vary in strength due to many effects, such as multipath fading due to reflections – requires plex transmission schemes, ., OFDM Wireless LANs (3) ? Radio broadcasts interfere with each other, and radio ranges may inpletely overlap – CSMA (Carrier Sense Multiple Access) designs are used Wireless LANs (4) ? Mobility – Over a single work – Across different works (IEEE ) ? Security () – WEP (Wireless Equivalent Privacy) was flawed and broken – WPA2 (WiFi Protected Access) – WAPI (Wireless Authentication Privacy Infrastructure): China standard (GB 15629) RFID amp。 ROSS, Computer Networking: A TopDown Approach, 5th Edition Inter (3) ? The modern Inter is more plex (1) – ISP works serve as the Inter backbone – ISPs connect or peer to exchange traffic at IXPs – Within each work routers switch packets – Between works, traffic exchange is set by business agreements Inter (4) ? The modern Inter is more plex (2) – Customers connect at the edge by many means ? Cable, DSL, FibertotheHome, 3G/4G wireless, dialup – Data centers concentrate many servers (“the cloud”) – Most traffic is content from data centers (esp. video) – The architecture continues to evolve Inter (5) ? ICANN (The Inter Corporation for Assigned Names and Numbers) announced ?Available Pool of unallocated IPv4 Inter Addresses Now Completely Emptied? in Feb. 3, 2022 ? US, EU (European Union), and Japan have scheduled for IPv4 to convert into IPv6 Inter (6) Source: 鄔賀銓 , 《 中國下一代互聯(lián)網(wǎng)的研究和 CNGI項目 》 , Inter (7) ? China39。 omits some OSI layers and uses the IP as the work layer. IP is the “narrow waist” of the Inter Protocols are shown in their respective layers Model used for this Course ? It is based on the TCP/IP model but we call out the physical layer and look beyond Inter protocols. Critique of OSI amp。 ) Web security (167。 ) Congestion control (167。 ) Protocol layering (167。 ) Network growth and evolution Addressing (167。si, “The physics of the Web”, Physics World 14, (202