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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

Introduction to Electronic GovernmentTelecommunicationsSunday, September 21, 2014

Hun Myoung Park, Ph.D.

Public Management & Policy Analysis ProgramGraduate School of International Relations

communication components
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)
analog vs digital signals
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)
frequency bandwidth
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).
transmission types 1
Transmission Types 1
  • Serial versus parallel transmission
  • Wired (faster and more secure) versus wireless network
transmission types 2
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.
circuit vs packet switching
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)
packet switching of internet 1
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.
packet switching of internet 2
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.
telecommunication media 1
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.
telecommunication media 2
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
telecommunication media 3
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.
telecommunication media 4
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
network physical topologies
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.
client server network
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)
peer to peer p2p network
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.
types of network 1
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.
types of network 2
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.