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Introduction to Electronic Government Telec ommunications Sunday, September 21, 2014

Introduction to Electronic Government Telec ommunications Sunday, September 21, 2014. Hun Myoung Park, Ph.D. Public Management & Policy Analysis Program Graduate School of International Relations. Communication Components. Sender encodes (converts) his message.

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Introduction to Electronic Government Telec ommunications Sunday, September 21, 2014

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  1. Introduction to Electronic GovernmentTelecommunicationsSunday, September 21, 2014 Hun Myoung Park, Ph.D. Public Management & Policy Analysis ProgramGraduate School of International Relations

  2. Communication Components • Sender encodes (converts) his message. • Receiver decodes (translates) the received message. • Message to be sent • Media or channel through which the message travels (air, radio, TV, phone, Internet, etc.) • Feedback (error checking)

  3. Analog vs. Digital Signals • Analog signals: continuous • Frequency • Amplitude • Digital signals: discrete • Modem (modulator/demodulator) • Dial-up connection • Bps (bit per second) • Baud (pulses per second) or modulation rate • Emulation software: check errors (parity bit)

  4. Frequency & Bandwidth • Frequency (Hz), the number of times a signal makes a complete cycle per second. KHz, MHz, GHz • Bandwidth (bps) is ranges of frequencies. The difference between the highest and lowest frequency transmitted (or amount of data transmitted) per second. Kbps, Mbps. • Wavelength: from long (low frequency) to short (high frequency—UHF, cell phone).

  5. Transmission Types 1 • Serial versus parallel transmission • Wired (faster and more secure) versus wireless network

  6. Transmission Types 2 • Direction of transmission: • Simplex: transmitted in a single direction only • Half-duplex: one direction at a time • Full-duplex: both directions at the same time • Timing of transmission • Synchronous: blocks of data are transferred • Asynchronous: start and stop bits to distinguish one byte from the others.

  7. Circuit vs. Packet Switching • Circuit switching establishes a connection (physical path and circuit) that cannot be use by others. PSTN (public switched telephone network) • Packet switching sends data in a series of packets and then assembles them in the destination. Paul Baran, Donald Davies, Leonard Kleinrock in the 1960s. PSDN (public switched data network)

  8. Packet Switching of Internet 1 • Data are split into small chunks, “packets” • Each packet has a header with information about its sequence number and the destination • Each packet may independently travel a different routes to get to the destination and be buffered and queued depending on network traffic. • No order in transmission.

  9. Packet Switching of Internet 2 • The packet header at the destination is stripped off and then packets are put together (assemble) in the proper order. • In case of failures of packets (e.g., damaged), they will be requested and sent again. • Safe way to communicate each other.

  10. Telecommunication Media 1 • Twisted-pair wire: RJ-45 (LAN) and RJ-11 • Coaxial cable (coax) in the cable TV industry. More expensive, faster, less susceptible to interference (by shield blocking electro-magnetic signals) • Optical fiber cable uses light pulse sent by a laser device thought the cable. Super-fast and in turn expensive. Used for backbone (telephone) network.

  11. Telecommunication Media 2 • Radio frequency (RF) transmission • Infrared (IR) transmission • Cellular radio: cell, cellular tower, mobile telephone switching office (MTSO). G3. • Microwave (“line-of-sight”): communication satellite use microwave stations (microwave antennas) and satellite dishes. • Global positioning systems (GPS), Wi-Fi, Bluetooth

  12. Telecommunication Media 3 • Telephone lines • Conventional dial-up connection • ISDN (Integrated Services Digital Network) ADSL (Asymmetric Digital Subscriber Line) and DSL use higher frequency than voce phone call on telephone lines. • Cable access (cable TV). • Satellite and fixed wireless access need modems and transceivers.

  13. Telecommunication Media 4 • Wired Ethernet (T1, T3) • Broadband over fiber (BoF) • Cellular broadband or mobile wireless (laptops, smart phones) • Wi-Fi (Wireless Fidelity) is wireless networking standards (wireless Ethernet) • IEEE 802.11 • 802.11g and 802.11n

  14. Network (Physical) Topologies • Star network has a central hub (router) connected by other devices. • Ring network: devices are connected from one node to the next. One-way direction of transmission. IBM’s Token Ring Network • Bus network has a central bus line to which devices (nodes) are attached. • Mesh network: each device is connected to multiple devices in a network. • Hybrid network combines above typologies.

  15. Client-server network • Servers process clients’ request and provide services to clients. Not particular machines but functions. • Depending on tasks, network, file, mail, Web, DNS, printer, license servers and others are available. • A single machine can run more than one servers. • Uploading and downloading (polling & addressing)

  16. Peer-to-peer (P2P) network • Direct access to other devices without central (in classical sense) servers. • P2P servers mange indexes, not contents. • Internet P2P computing for sharing resources online. • Suck down all available resources on the network, resulting in network congestion • Sharing contents through P2P oftentimes involves infringement of intellectual property rights.

  17. Types of Network 1 • Sharing programs, data, and devices • Access to databases and better security • LAN (Local Area Network) • Covers small geographical area • Bridge for same types of networks • Router for different networks (layer 3) • Gateway, bridge + router + etc.

  18. Types of Network 2 • WAN (Wide Area Network) • MAN (Metropolitan Area Network) • VPN (Virtual Private Network) allows remote and secure access to the network (intranet) through encrypted “tunneling” • Intranets versus extranets: private networks used for employees. Authorized outsiders can access extranets.

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