Computer Network
Chapter 4
“I think there is a world of market for
maybe five computers”
Thomas J. Watson
Chairman IBM, 1943
Why Use Networks?
• Network
• Group of computers and devices
• Connected by transmission media
• Stand-alone computer
• Not connected to other computers
• Uses local software and data
• Advantages of networks over standalone computers
• Device sharing by multiple users
• Saves money and time
• Central network management
Types of Networks
• Network models
• Peer-to-Peer
• Client/server
Peer-to-Peer Network
Figure 1-1 Resource sharing on a simple peer-to-peer network
Client/Server Networks
Figure 1-2 Resource sharing on a client/server network
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Computers
Printer
Copier
Fax
Scanner
Personal Digital Assistants
Cell Phones
Radios
RFID (Radio Frequency ID)
Networks are everywhere
Introduction
• Today people are often linked by wires or air (wireless)
carrying voice and computer signals via the telephone system.
• Data communications dominate the world.
• Computer Network: The linkage of computer systems by
means of communication lines or channels (e.g., fiber optic,
microwave, satellite, telephone line, 802.11)
Computer Network
• At least two computers need to be connected
•Copper
•Fiber Optics
•Microwaves
•Infrared
•Satellites
Data Communications
Telecommunications + Data Processing
= Data Communications
Data Communication
• Electronic transfer of information from one computer to
another.
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Data
Text
Pictures
Graphics
Video
Voice
Network Components (Examples)
Interfaces
Fibers
Ethernet card
Switches/routers
Large router
Introduction
Links
Wireless card
Coaxial Cable
Switch
1-12
Why network?
• Resource sharing
– Files, Applications, Printer, Fax
• Communication Medium
– Email, Collaboration,
videoconferencing
• E-business
– Supply-chain, inventory, B2C
Business Applications of
Networks
• A network with two clients and one server.
Business Applications of
Networks (2)
• The client-server model involves requests and replies.
Home Network Applications
•Access to remote information
•Person-to-person communication
•Interactive entertainment
•Electronic commerce
Communication
Lines/Channels
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Fiber optic
Microwave
Satellite
Telephone Line etc.
Impact of Data
Communications
1.
It enables information to be accessed and transmitted
quickly.
– Automatic Data Collection or Polling (i.e. Chuck E. Cheese) –menu
update, get info from POS
2.
3.
It allows the storing of information in a centralized database
that may be shared by a few users in a small computer
network or by thousands of users in a large computer
network.
It facilitates centralized management and decentralized
operations (e.g., restaurant chain).
Impact of Data
Communications
• It links business processes performed by independent
computer systems to improve organizational efficiency and
effectiveness
• It links a business to its customers
• Communication devices, such as cell phones, personal digital
assistants, etc.
Local Area Network
• LAN is linkage of computers in a specific geographical area
(usually within an office or building) such as in hotels,
restaurants, or country clubs using transmission medium such
as twisted pair wire or coaxial cable.
Why Local Area Network
(LAN)?
• Increased processing and transfer requirements in many
graphics-intensive applications now require significantly
higher transfer rates (data, audio, image, video)
• Decreased cost of storage space leads to program and file
bloat, increased need for transfer capacity
• Watch this video
Basic LAN Hardware
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Computers/Server(s)
Resources
Cables
Connectors (Hubs)
Network Interface Cards (Ethernet)
ADVANCED
• Bridges
• Routers
Full versus half duplex
• Half duplex: communication can happen in both directions but
one at a time (like walkie-talkie)
• Full duplex: communication can happen in both directions at
the same time (like a phone)
Client
• Is any network entity that can request resources from the
network.
• Workstations can be clients but not all clients are workstations
• For example, a printer can request resources from the
network, it is a client, not a workstation.
Server
• A computer that provides resources to the clients on the
network.
• Servers are typically powerful computers
Switch
Hub vs. Switch
• Hub—sends signals to all computers connected
• Switch– sends signals to intended computer(s)
LANs share
• Files (databases)
• Resources (Printers, fax)
• Programs (Fidelio, MS Office)
• Working together
• Communication
WAN (Wide Area Network )
Communications Hardware
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WAN=Connection of at least two LANs
Down-line processor/ Multiplexer
Front-end Processor
PBX(Private Branch Exchange)
• Watch Video
WAN Connection Types
• Private Lines
– Frame Relay
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Dial-Up
Satellite
Down Line Processor or Multiplexer
Front-end Processor
PBX Switchboard
Shared Lines
– DSL
– Cable
WAN in Hospitality
• Global Reservation System
• Central Reservation System
• Property Management System
LA
Miami
NYC
Boston
Hotel Marriott NYC
Hotel Marriott Miami
• Dial-up (max 56Kbps)
•ISDN (128Kbps)
•DSL (1.5Mbps)
•Cable (3.5Mbps)
Hotel Marriott NYC
Hotel Marriott Miami
•T-1 (1.5Mbps)
•Frame Relay (1.5Mbps)
•T-3 (43Mbps)
•OC3 (155Mbps)
•ATM (622Mbps)
Hotel Marriott NYC
•802.11b (11Mbps)
•802.11g (54Mbps)
•802.11a (54Mbps)
•802.11n (<100Mbps)
A Small LAN
Wireless LAN
• Advantages
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Wireless LANs are simple to set up. It literally can take 10
minutes for a simple wireless network to be setup.
Wireless LANs are cheap to create.
When it is not possible to wire, Wireless LANs come into
rescue.
Disadvantages
1.
Security is the biggest down side of wireless LANs.
HP Server
IBM Server
Network Hardware: Repeaters
• Extend the length of transmission media
Server Types
• File Server: holds and distributes files
• Print Server: handles printing jobs from clients
• Proxy Server: performs a function on behalf of
other computers
• Application Server: hosts a network application
(i.e. Marriott’s central reservation system, Marsha)
• Web Server: handles web pages and other web
content (i.e. Marriott.com, Hilton.com,
Starwood.com)
• Mail Server: hosts and delivers electronic mail.
• Fax Server: sends and receives faxes electronically.
• Voice over IP Server: Handles calls on Internet
Protocol
Physical Media
• Coaxial Cable
• Thinnet (BNC Connector and RG-58)
• Twisted Pair Cable
• Category 1 – Category 6
• RJ-11 and RJ-45 Connectors
• Fiber Optic Cable
Coaxial Cable
• Contains a center conductor, made of copper, surrounded by a
plastic jacket
• Teflon type covering  plenum-rated coating does not burn
easily
• Coax is not used in LANs today but still used widely by TV
cable operators
Thin Ethernet
• Thinnet
• 10Base-2
• Thin coaxial cable– smaller than thick coaxial cable
A Stripped-back Thinnet
Thinnet
Connectors
• With thinnet, you use BNC (BayoNet Connector)
connectors to attach stations to the network.
• BNC Connector locks securely with a quartertwist motion
• A T-connector is used to connect backbone
devices
Male and Female
BNC Connectors
F type connector
Popular with TV Cable and Cable Modems
Twisted-pair cable
• Consists of multiple, individually insulated wires that are
twisted together in pairs
• Sometimes a metallic shield is placed around pairs shielded
twisted pair (STP)
• Unshielded twisted pair (UTP)
Why twisted?
• Electromagnetic signals create interference  crosstalk
• Twisting the cables in pairs reduce intereference
• Most common cable
Twisted-pair
• Cheaper
• Easy to work with
• Transmission rates are good
Fiber Optic Cable
• A glass or plastic fiber that carries light along its length. This
cable is the fastest and most expensive transmission medium
in the world today
Advantages of Fiber Optic
Cable
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Superior System Performance
Greatly increased bandwidth and capacity
Lower signal loss
Immunity to Electrical Noise
Immune to noise (electromagnetic interference [EMI] and
radio-frequency interference [RFI]
Lower bit error rates
Signal Security
Difficult to tap
Light weight
Topology
• Arrangement of workstations in a shared medium
environment
• Logical arrangement (data flow)
• Physical arrangement (cabling scheme)
Network Topologies
• The manner in which workstations are connected together
physically and logically is referred to as a NETWORK
TOPOLOGY.
• 4 Types:
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Bus (Video)
Ring (Video)
Star (Video)
Hybrid
BUS Topology
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Information transfer
Terminators
Setup is simple
Expansion
Repair
Cost
STAR Topology
• Central network
connector (switch)
• Less than 100m.
• Expansion—switchuplink
• Troubleshooting
• Cost—cable
Ring Topology
• Information flows one
way
• Close together
• Expansion
• Troubleshooting
• Cost
Hybrid Topology
Why Hybrid (Tiered)?
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Reliability—less service interruption
Capacity- not easily saturated
Cost – low cost networks can build up
Needs- not every department need the same equipment
(accounting vs. graphics)
Network Management
• Network management is a systematic approach to planning,
organizing, and controlling networks.
• The five basic functions of network management are:
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5.
Fault management
Configuration management
Performance management
Security Management
Accounting Management
Chapter 4