Introduction to electronic government telec ommunications sunday september 21 2014
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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.