chapter 3 internet architecture. awad –electronic commerce 2/e © 2004 pearson prentice hall2...
TRANSCRIPT
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WWWWWW
Chapter 3
Internet Architecture
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2WWWWWW Awad –Electronic Commerce 2/e© 2004 Pearson Prentice Hall
Overview
• What is a Network?• IP Addresses• Networks• Information Transfer• Cable Types• Key Components of a Network• Factors in Designing a Network• Network Management System
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What is a Network?
• A connection between at least two computers for the purpose of sharing resources
• Types:– Local Area Networks (LANs)– Wide Area Networks (WANs)– Metropolitan Area Networks (MANs)
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Peer-to-Peer Network
• Computers linked together as equals
• No centralized control
• Share resources on the same network in any way and any time
• Promotes institutionalized chaos
• < 10 computers
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Peer-to-Peer Network (Cont’d)• Benefits
– Easy to install/configure
– Inexpensive
– User is able to control their own resources
– Independent from a dedicated server
– No need for a network administrator
• Drawbacks– Security problems
– Performance suffers when a computer is accessed
– Difficult to have backup
– Decentralized logon passwords
– No centralized data management
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Client/Server Network
• Server – designed to address a client’s request• Client – any computer connected to a server
within a network• A cluster of computers (called clients) connected
to one or more servers to form a network• Allow authorized user to access any
programs/application resided on the server
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Client/Server Network (Cont’d)• Benefits
– Centralized security control
– Simpler network administration than peer-to-peer network
– Centralized password
– More scalable
– Ideal for computers are apart
• Drawbacks– Network failure - clients
are helpless
– Specialized staff are needed
– Higher costs
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IP Address
• A host number that identifies itself to other hosts• Consists of strings of 32 bits• E.g. 10111111010101010100000000001100 =
191.170.64.12 • Host Name
– Human-friendly internet addresses
– E.g. ema3z.mcintire.virginia.edu
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Networks
• Network vs. Local
• Networks are classified by three sizes
Class Beginning Bit
Bits in remainder of network part
# of bits in local part
Max. # of networks
Max. # of hosts in network
A 0 7 24 136 16 million
B 10 14 16 16,000 65,000
C 110 21 8 2 million 254
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Networks (Cont’d)
• Zone– Three-letter kind (com, gov, edu)– Two-letter kind (ca, uk, jp)– New general-purpose zones (firm, store)– Last (rightmost) part of a domain name
preceded by a dot
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Information Transfer
• Packet– Grouping of data for transmission on a network– Large messages are split into a series of packets for
transmission
• Protocol– A rule governing how communication should be
conducted between two parties, two computers, or a sources and a destination
– Internet Protocol• Set of rules used to pass packets
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Information Transfer (Cont’d)
• Open Systems Interconnection (OSI)– A layered approach to networking– Each layer handles a different portion of the
communication process
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OSI Reference Model
Layer Info Transacted TCP/IP Protocols
Application Application messages HTTP, FTP, SNMP
Presentation Compressed data
Session Session messages
Transport Multiple packets TCP
Network Packets IP
Data Link Frames Ethernet, PPP
Physical Bits Wiring, cables
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OSI Reference Model (Cont’d)
• Application Layer– Defines requests and response formats
– Standard: HTTP• Governs requests and response between browser and Web
server application program
• Other standards: SMTP, POP
• HTML-compatible
– File Transfer Protocol (FTP), Simple Network Management Protocol (SNMP), Domain Name Service (DNS)
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OSI Reference Model (Cont’d)
• Presentation Layer– Converts data into a format the receiving application
can understand
• Session Layer– Exchanges data for the duration of session
– Keeps track of the status of exchange
– Ensures only designated parties are allowed to participate in the session
– Enforces security protocols for controlling access
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OSI Reference Model (Cont’d)
• Transport Layer– Manages the transmission of data across a
network– Transmission Control Protocol (TCP)
• Specifies how two host computers will work together
• Flow control• Sequence assurance• Reliability and integrity
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OSI Reference Model (Cont’d)
• Internet Layer– Routes messages across multiple nodes for
delivery– Handles network congestion to minimize
performance problems– Internet Protocol (IP)
• Standard for routing packets
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OSI Reference Model (Cont’d)
• Data Link Layer– Packages data into frames for delivery
– Point-to-point (PPP)• Framing – mark boundary between packets
• Error detection
– Ethernet
• Physical Layer– Converts bits into signals for outgoing messages and
signals into bits for incoming messages
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Cable Types
• Twisted-Pair Cable
• Unshielded Twisted Pair (UTP)
• Shielded Twisted Pair (STP)
• Optical Fiber
• Coaxial Cable
• Wireless Technology
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Twisted-Pair Cable• Consists of two pairs of insulated copper wires twisted
around each other• Advantages
– Protect against cross talk and interference– Easy to add computers to network– Well understood technology– Less expensive
• Disadvantages– Susceptibility to noise– Least secure– Distance limitations– Requires more expensive hubs
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Unshielded Twisted Pair (UTP)
• Pair of wires do not have the shielding against electrical interference
• Advantages– Less expensive
– Easy to install
• Disadvantages– Vulnerable to electromagnetic interference and
crosstalk
– Subject to attenuation
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Shielded Twisted Pair (STP)
• An electrically grounded woven copper mesh wrapped around each twisted pair
• Advantage– Reduces electromagnetic interference (EMI)
• Disadvantage– Makes the wiring thick and is difficult to
maintain
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Optical Fiber• Uses light rather than voltage to indicate one and zeros• Advantages
– High speed transmission– High security– Smallest in size– Supports voice and video data
• Disadvantages– Expensive– Difficult to install– Require two cables to transmit & receive data– Require special connections
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Coaxial Cable
• Copper center shielded by a plastic insulating material• Advantages
– Transmits up to 10Mbps over 500m– Easy to install– Low maintenance– Good resistance to noise over long distances
• Disadvantages– Inflexible– Low security– Limited distance
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Wireless Technology
• Microwave– Connect LANs in separate buildings
• Radio waves– No distance limitations
– Susceptible to atmospheric and electronic interference
– Subject to government regulations
• Infrared transmissions– Interference from bright light
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Key Components of A Network
• Network Interface Card (NIC)
• Hubs and Switches
• Routers
• Gateways
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Network Interface Card
• Installed in a slot with a cable plugged into the back
• Plugged into a wall jack connection or into the hub/switch directly
• Modem – Converts digital signals into analog form for
transmission and incoming analog signals into digital signal across the telephone line
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Hubs and Switches
• Hub– Operates at Physical Layer– Acts as a connecting point– Passive, active, and intelligent hubs
• Switch– Offers direct connection to a particular PC– Available for almost every OSI level
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Routers
• Operate at Internet Layer
• Evaluate network traffic and stop local traffic from causing congestion
• Filter out packets that need not be received
• Expensive and difficult to operate
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Gateways
• Special-purpose computer allowing communications between dissimilar systems on the network
• Operate at Application Layer primarily
• Difficult to install and configure
• Expensive
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Factors in Designing a Network
• Location
• Capacity
• Distance limitations
• Cost
• Potential growth
• Security
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Factors in Selecting Network Architecture
• Hardware requirements
• Software requirements
• Disaster recovery and fault-tolerance requirements
• Corporate culture and organizational factors
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Network Management System
• Manager
• Managed Nodes
• Objects
• Management Information Base (MIB)
• Requests and responses
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Large-Scale E-commerce Issues
• Financial exposure
• IP exposure
• Legal security
• Packet sniffing
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Ensuring Corporate and Information Security
• Firewalls
• IP Security
• Intrusion detection systems
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WWWWWW
Chapter 3
Internet Architecture