Transcript Information Systems

Introduction to the Technology of
Data Communications
• Consider computer networks as a structure for the
transmission of integrated data of all types voice/video/telephony, etc.
• What are different types of computer networks?
• What are the uses of computer networks?
• What hardware do computer networks use?
• What software do computer networks use?
• Other factors (ethical, legal, performance,
security)
Chapt 1 Introduction
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Defining Computer Networks
• Autonomous computers
– Hosts/ stations /devices
– Interconnected by communication subsystem
• Links – fiber, copper, microwave, radiowave, infrared
• Nodes - Routers/ bridges/ gateways
– Distributed control
– Built over layers of hardware and software
– Distributed system is coherent to users
Chapt 1 Introduction
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Usage of computer networks
• Communications
– Email, instant messaging, telephony
– Social networking
– E-commerce
– E-education
– Games
• Resource Sharing
– Data (search engines assist in finding the data)
– Printers and other peripherals
– Load sharing
– Storage
• Home Networks
• Data Input (e.g., sensorChapt
networks)
1 Introduction
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More uses of computer networks
• RFID (Radio Frequency Identification)
– Product identification
– Pet and child identification
– No battery or activity required
• GPS
• Cloud computing
• Convergence of telephony, radio and television
networks, computer usage and storage
Chapt 1 Introduction
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Some advantages of computer
networks
• Reliability/ Availability
– Redundancy provides advantages over centralized
systems
• Scalability
• Opportunities for geographically challenged
people
• Time and effort simplified by working from home
• Discrimination is harder
– Age, race, sex are not evident
Chapt 1 Introduction
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Some disadvantages of computer
networks
• Security
– Privacy is more easily compromised
– Intrusion is easier
– Authentication is more easily compromised
• Decentralized control is harder
– Ex: Child pornography and bomb making information
can be found on the World Wide Web
• Other social issues
– Infringement of patents and copyrights for songs and
movies is easier through networks and the web
– Easy access to gambling, pornography
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Classifications of networks
• By Geography (i.e., distance covered)
– WAN – Wide Area Network
– MAN – Metropolitan Area Network
– LAN – Local Area Network
– PAN – Personal Area Network
– (also SAN- Storage Area Network )
• By Media
– Guided/ wired – copper, fiber
– Wireless
• By Technology
– Circuit Switching
– Packet Switching (computer networks)
• By Control
– Client-server
– Peer-to-Peer
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Storage Area Networks
– High speed, short distance, large amount of data
• Includes disks, tape libraries, and CD arrays
• Fibre Channel (updated from HIPPI); parallel interface
– Large databases have special transmission & storage
needs; SANs integrate all storage devices on network
• High data speed
• Reliability/ redundancy
– Storage devices are directly available on the network;
they do not require access through servers; do not use
Internet protocols
• Example: direct storage-to-storage communication used for
backup and replication
Chapt 1 Introduction
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Some issues in Network
Hardware
• Broadcast or point-to-point media:
– Broadcast – signal sent to all stations within range
• Wireless LANs
• Coaxial cable with multiple taps
• Typical bus or hub based LANS
– Point to point
• Connection between pairs of machines using switches, routers
• Broadcast/multicast/unicast addressing for
hardware
• Simplex/Duplex/Half-Duplex channels
Chapt 1 Introduction
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Network Topology
• Graph – redundant, irregular links – WANs
• Star – hub or switch based LANs, local loop
in WANs
• Bus – multiple taps on copper
• Ring – circular bus
• Tree – attached bus or star segments
Chapt 1 Introduction
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History of Local Area Networks
• 1970s – Alohanet (random access packet
radio)
• 1970s - Ethernet – Metcalfe and Boggs
– DEC, Intel, Xerox standardized and made nonproprietary (public domain)
– Random access (carrier sense) with collision detection
• 1980s -IEEE802 standards: 802.3, 802.5, 802.11
• 1990s, 2000s -Fast, Gigabit Ethernet
• 2000s, 2010s -Wireless LANs & PANs
Chapt 1 Introduction
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NIC (adapter) functioning in a LAN
Chapt 1 Introduction
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Wired LANs, MANs, WANs
• Fiber networks are mainly:
– Internet infrastructure using graph topology
– MAN infrastructure, the local loop with FIOS
• Cable networks
– Typically MANs using coaxial for local loop
• Copper twisted pair networks
– Ethernet LANs over 90% of wired LAN market
– Switch or bus or tree topology
Chapt 1 Introduction
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Sample LAN topology
Chapt 1 Introduction
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Wireless Networks
• Developed mainly for mobile users
• Types
– Wireless LANs, PANs, MANs, WANs
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Microwave links for satellite, MANs
Cellular phones
Access Points – 802.11 LANs in infrastructure mode
Peer-to-peer – Bluetooth; 802.11 in ad hoc mode
• Switching between cells for mobile users
– Frequency reuse
• Different technical needs than wired LANS
(reliability, security are more vulnerable)
• Ease of installation, mobility
Chapt 1 Introduction
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Network Software
• Architecture & Modularity
– Layers and hierarchies
• Protocol – what is it?
– Peer protocols (fig. 1-13)
• Layer interface
• Services provided to the next higher layer
– Services available at SAPs (Service Access Point)
• Cost of calls between layers
• IDUs and ICIs, SDUs and PDUs
– Interface Data Unit; Interface Control Information
– Protocol Data Unit= Service Data Unit + Control Info
Chapt 1 Introduction
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Circuit switching
• Traditional telephone system
• Connection is established/released
• Bandwidth is pre-allocated for entire
connection
• Same path is used for entire connection
Chapt 1 Introduction
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Packet switching
• Bandwidth is allocated on demand
• Requires storing of data units during bursts of traffic
• May be connection-oriented or connectionless
• Message is broken into some maximum size unit called a
packet (cell) at the network layer
• Requires identification on each data unit
• May have same path (virtual circuit) or different path
(datagram switching) for each packet
• Packet is switched at each router
• Store and forward network
• Utilizes speed and code conversion
Chapt 1 Introduction
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Connection-oriented Service
• Model was telephone system
• Connection is established, released
– Overhead in time, transmission
• Each PDU needs smaller connection ID rather
than entire source and destination address
• Quality of Service (options), authentication may
be negotiated for entire connection
• PDUs are delivered in sequence
• Sample protocol: ATM
• PDUs are sent on same route in network layer
Chapt 1 Introduction
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Connectionless Service
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Model was smail, telegraph systems
Each PDU is sent on its own
Full address on each data unit
PDUs may arrive out of order
May or may not be acknowledged
May or may not provide error correction
PDUs may use different routes in network layer
Sample protocol: IPv4
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Basic network Services
• Send /receive/ reply
• Reliable or unreliable
– Reliable (acknowledged & corrected, sequenced)
– Unreliable (no ack, no sequencing)
• Connection–oriented or connectionless
– Connection-oriented : Connect/disconnect/send/receive
– Connectionless: Send/receive
• Service to higher layer is implemented by protocol
Chapt 1 Introduction
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OSI Reference Model of ISO
• Top (7th) Layer -Application Layer
– Provides interface to users; does user “work”
• 5th & 6th – Presentation & Session Layers
– Services are not differentiated by TCP/IP
• 4th Transport layer
– Forwards user PDUs (segment) to network
• These protocols are in software at hosts
Chapt 1 Introduction
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OSI Reference Model
• 3rd Network Layer (PDU is packet)
– Functions include Routing, Network
administration, network addressing
• 2nd Data Link Layer (PDU is frame)
– Framing, Media access for broadcast media
• 1st Physical Layer (bit)
• Media dependent and media independent sublayers
• Determines what is a bit (timing, coding, clock
synchronization)
• Implemented in firmware on NIC in host and on routers
Chapt 1 Introduction
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OSI model concepts
• Services
• Interfaces
• Protocols
Each layer defines what services it offers to
higher layer (such as send) and the interface – how
and where to reach service (such as SAP). Protocols
– rules for communication - are interchangeable.
Virtual communication via peer protocols
• Why study OSI model?
Chapt 1 Introduction
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TCP/IP Reference Model
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Application Layer
Transport Layer
Internet Layer
Link layer/ network interface layer
(physical + data link layer)
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Development of Internet
• Why the Arpanet developed (cold war)
• How the Arpanet developed (RFCs)
• Protocols developed by students
– TCP/IP Reference Model
• TCP, UDP, IPv4, IPv6
• Telnet, FTP, SMTP, DNS
• ICMP and other control protocols
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Comparison
• SNA (IBM)
– Proprietary system
– Homogeneous system
– Central control
• Arpanet
– DARPA wanted distributed control (cold war)
– 4 node network of University sites Dec. 1969
• Digital packet switching
– IP designed to connect different types of computers
– DNS (Domain Name System) added as system grew
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NSFNET & ANSNET
• Expansion of the Arpanet
• NSF built backbone networks by the 1980s
(NSFNET)
• Gave it to ANSNET as the first step
towards commercialization
• NSPs & ISPs in the 1990s for home &
business use
– WWW with graphical browser (Mosaic,
Netscape, Explorer, Firefox, Bing, Chrome)
Chapt 1 Introduction
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Other Protocols
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SNA – IBM WAN
ATM, SONET – wired WAN
X.25 – wired WAN
Novell NetWare, Windows NT
Ethernet, Token Rings – wired LANS
802.11(b, a, g, n)ac, ad, etc. – wireless LAN
Bluetooth – wireless PAN
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Standards and Standards
Organizations
• Advantages of standards
– Allows manufacture of interchangeable
components
• Disadvantages of standards
– Standards are frequently obsolete by the time
they are issued
• IEEE, EIA, ISO, IETF, etc., etc., etc., etc.
Chapt 1 Introduction
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