Communications and Computer Network Hun Myoung Park, Ph.D., Public Management and Policy Analysis Program Graduate School of International Relations International University of Japan

Outline Communication Basics Analog versus Digital Frequency and Bandwidth Transmission Types Telecommunication Media Network Typologies Type of Network Network Data Security

Communication Basics 1 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)

Communication Basics 2

Analog vs. Digital Signals Analog signals: continuous Frequency Amplitude Digital signals: discrete

Modem 1 Modem (modulator/demodulator) Converts analog signals to digital ones (modulation) and vice versa Dial-up connection Bps (bit per second) Baud (pulses per second) or modulation rate Emulation software: check errors (parity bit)

Modem 2

Frequency Frequency (Hz), the number of times a signal makes a complete cycle per second. KHz, MHz, GHz Wavelength: from long (low frequency) to short (high frequency—UHF, cell phone).

Bandwidth Bandwidth (bps) is ranges of frequencies. The difference between the highest and lowest frequency transmitted (or amount of data transmitted) per second. Bps, Kbps, Mbps. Baud (pulses per second) or modulation rate Broadband has a rate of greater than 1.5 Mbps (telephone).

Transmission Types

Transmission Types 1 Serial versus parallel transmission Wired (faster and more secure) versus wireless (electromagnetic radiation) network

Transmission Types 2 Direction of transmission: Timing 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 (e.g., email).

Telecommunication Media

Media 1 Twisted-pair wire: pairs of copper wire. IEEE 802 standards of RJ-45 (LAN) and RJ-11 (Telephone) Coaxial cable (coax) in the cable TV industry. Inner conductor. More expensive, faster, less susceptible to interference (by shield blocking electro-magnetic signals)

Media 2 Optical fiber cable uses light pulse sent by a laser device thought the strands of glass. Thin coating “cladding” prevents the light from leaking out of the fiber. Super-fast and in turn expensive. Used for backbone network.

Media 4 Use of wireless media is often regulated Radio frequency (RF) transmission: 3kHz- 300MHz Microwave (“line-of-sight”): communication satellite use microwave stations (microwave antennas) and satellite dishes. 300MHz- 300GHz Infrared (IR) transmission: 300GHz-400THz

Media 5 Cellular radio: cell, cellular tower, mobile telephone switching office (MTSO). G3. Global positioning systems (GPS), Bluetooth, near field communication (NFC) : short range

Network Channel 1 Telephone lines Conventional dial-up connection ISDN (Integrated Services Digital Network) DSL (Digital Subscriber Line) uses higher frequency than voce phone call on telephone lines. DSL splitter separates digital and analog signals ADSL (Asymmetric DSL)

Network Channel 2 Cable access (cable TV). Satellite and fixed wireless access need modems and transceivers. Wired Ethernet Bell Lab’s T1 (1.5Mbps), T3 (44.7Mbps) Broadband over fiber (BoF)

Network Channel 3 Cellular broadband or mobile wireless (laptops, smart phones) Wi-Fi (Wireless Fidelity) is wireless networking standards (wireless Ethernet) IEEE 802.11 802.11a, …802.11g, 802.11n 802.11ac (2.4 GHz or 5.0 GHz) 3G, 4G, 5G, LTE (Long Term Evolution)

Network Typology

Network Topology 1 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.

Network Topology 2 Mesh network: each device is connected to multiple devices in a network. Hybrid network combines above typologies.

Type of Network

Types of Network 1 Sharing programs, data, and devices Access to databases and better security

Types of Network 2 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 3 WAN (Wide Area Network) MAN (Metropolitan Area Network) VPN (Virtual Private Network) allows remote and secure access to the network (intranet) through encrypted “tunneling”

Types of Network 4 Intranets versus extranets private networks used for employees. Authorized outsiders can access extranets.

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 Network Direct access to other devices without central (in classical sense) servers. P2P servers mange indexes, not contents to bridge users. Internet P2P computing for sharing resources online. But it often infringes intellectual property rights. Suck down all available resources on the network, resulting in network congestion

Network Hardware 1 Modem and cable modem Gateway is an entrance to another network Wireless access point and hot-spot Private Branch Exchange (PBX)

Network Hardware 2 Router forwards data packets between computer network (layer 3-network). IP address is used. Network switch (switching hub, bridging hub) contains ports to which all the devices (nodes) on the network can connect (layer 2-data link). Only one broadcast domain. MAC is used. http://www.diffen.com/difference/Router_vs _Switch

Network Data Security Encryption converts an original message into a form that can be understood only by the intended receiver Encryption key is applied to a set of unencrypted text to produce encrypted text Encryption algorithm: symmetric versus asymmetric algorithm. RSA is a symmetric algorithm for public-key cryptosystems Wireless Protected Access 2 (WPA2)

Virtual Private Network “Extends a private network across a public network” (Internet) to allow remote users to send and receive data as if they are directly connected to private network. Establish a virtual point-to-point connection through tunneling protocols. Support secure, encrypted connections between a company’s employees and remote users

References Stair and Reynolds. 2016. Principles of information systems, 12th ed. Cengage Learning. Stair and Reynolds. 2012. Information systems, 10th ed. Cengage Learning. Morley and Parker. 2015. Understanding computers, 15th ed. Cengage Learning. Hutchinson and Sawyer. 2000. Computers, Communications, and Information, 7th ed. Irwin/McGraw-Hill