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

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

3. 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)

4. Communication Basics 2

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

6. 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)

7. Modem 2

8. 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).

9. 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).

10. Transmission Types

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

12. 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., ).

13. Telecommunication Media

14. 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)

15. 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.

17. 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

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

20. 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)

21. 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)

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

24. Network Typology

25. 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.

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

28. Type of Network

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

30. 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.

31. 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”

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

33. 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)

34. 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

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

36. 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.
_Switch

37. 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)

38. 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

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