【正文】 ? Net bandwidth – Actual speed information travels ? Symmetric connections – Provide same bandwidth in both directions 169。 Cengage Learning 2023 71 Connectivity Overview (cont’d.) ? Asymmetric connections – Provide different bandwidths for each direction ? Upstream bandwidth (upload bandwidth) – Amount of information from user to the Inter in a given amount of time ? Downstream bandwidth (download, downlink bandwidth) – Amount of information from the Inter to user in a given amount of time 169。 Cengage Learning 2023 72 VoiceGrade Telephone Connections ? Used in early days of Web ? Plain old telephone service (POTS) – Uses existing telephone lines, analog modem – Bandwidth between 28 and 56 Kbps ? Digital Subscriber Line (DSL) protocol – Higher grade of service – Use DSL modem (type of work switch) ? Integrated Services Digital Network (ISDN) – First technology developed using DSL protocol suite 169。 Cengage Learning 2023 73 Broadband Connections ? Broadband: connection speeds 200 Kbps – Asymmetric digital subscriber line (ADSL) ? DSL protocol providing broadband range service – Highspeed DSL (HDSL) ? More than 768 Kbps symmetric bandwidth – Cable modems ? Transmission speeds to server: 300 Kbps to 1 Mbps ? Connection bandwidths vary ? Subscribers pete for shared resource – DSL: Private line with no peting traffic 169。 Cengage Learning 2023 74 Broadband Connections (cont’d.) ? Rural connection option issues: voicegrade lines ? Datagrade lines in most urban and suburban locations 169。 Cengage Learning 2023 75 LeasedLine Connections ? More expensive technologies ? Classified by equivalent number of telephone lines included – DS0 (digital signal zero) ? Carries one digital signal (56 Kbps) – T1 line (DS1) ? Carries 24 DS0 lines ( Mbps) – T3 (DS3): Mbps 169。 Cengage Learning 2023 76 LeasedLine Connections (cont’d.) ? Large anizations require very high bandwidth ? NAPs and Inter backbone routing puters – Frame relay, asynchronous transfer mode (ATM) – Optical fiber (instead of copper wire) ? Bandwidth determined by fiberoptic cable class – OC3 (optical carrier 3): 156 Mbps – OC12: 622 Mbps – OC48: Gbps – OC192: 10 Gbps 169。 Cengage Learning 2023 77 Wireless Connections ? Previous satellite microwave transmissions – Download speeds of 500 Kbps – Upload handled by POTS modem connection ? Today: POTS modem connection not required – Use microwave transmitter for uploads (150 Kbps) ? Many wireless work types now available – Intercapable mobile phones, smart phones, game consoles, and notebook puters 169。 Cengage Learning 2023 78 Personal Area Networks ? Also called picos ? Bluetooth – Designed for use over short distances – Lowbandwidth technology (722 Kbps) – Advantages: ? Devices consume very little power ? Devices can discover one another and exchange information automatically 169。 Cengage Learning 2023 79 Personal Area Networks (cont’d.) ? Ultra Wideband (UWB) – Provides bandwidth up to 480 Mbps – Connections over short distances (30 to 100 feet) – Future personal area working applications ? ZigBee – Range: 30 to 300 feet – Applications in home energy management 169。 Cengage Learning 2023 80 Wireless Ether (WiFi) ? Also called ? Wireless access point (WAP) – Transmits packets between WiFiequipped puters and other devices within range – Bandwidth of 450 MBps – Range of 500 feet – Bandwidth and range affected by construction materials through which signal must pass 169。 Cengage Learning 2023 81 Wireless Ether (cont’d.) ? Capable of roaming – Shifting from one WAP to another – No user intervention ? Hot spots – WAPs open to public 169。 Cengage Learning 2023 82 FixedPoint Wireless ? Used in rural areas without cable service ? System of repeaters – Forward radio signal from ISP to customers ? Repeaters – Transmitterreceiver devices (transceivers) ? Uses mesh routing – Directly transmits WiFi packets through shortrange transceivers (hundreds or thousands) – Located close to each other 169。 Cengage Learning 2023 83 Mobile Telephone Networks ? Broadcast signals to/receive signals from antennas – Three miles apart in grid ? Short message service (SMS) protocol – Send and receive short text messages ? Thirdgeneration (3G) wireless technology – 2 Mbps download/800 Kbps upload speeds ? Fourthgeneration (4G) technology – Long Term Evolution (LTE) and Worldwide Interoperability for Microwave Access (WiMAX) ? Significance in mobile merce 169。 Cengage Learning 2023 84 169。 Cengage Learning 2023 85 FIGURE 215 Inter connection options 169。 Cengage Learning 2023 Inter2 and the Semantic Web ? Inter2 – Replacement for original ARPANET laboratory – Experimental working technologies test bed – High end of the bandwidth spectrum (10 Gbps) – Used by universities, medical schools, CERN – Focus: mainly technology development 169。 Cengage Learning 2023 86 Inter2 and the Semantic Web (cont’d.) ? Semantic Web – Goal: blending technologies and information into a nextgeneration Web ? Web pages tagged (using XML) with meanings – Uses software agents (intelligent programs) ? Read XML tags, determine meaning of words in their contexts – Resource description framework (RDF) ? Set of XML syntax standards – Development of Semantic Web will take many years ? Start with ontologies for specific subjects 169。 Cengage Learning 2023 87 演講完畢，謝謝觀看！