Download - Aleksandra Smiljani ć aleks@ieee
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Uses of Computer Networks
• Business Applications
• Home Applications
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Business Applications
• Sharing resources
• Common databases for customer records, inventory, accounts
• E-commerce
• Video-conferencing
• Disseminating the information, and coordination
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Home Applications
• Getting the remote information
• Person-to-person information
• E-commerce
• Entertainment
• E-flea
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Network Types
• Local Area Networks
• Metropolitan Area Networks
• Wide Area Networks
• Wireless Networks
• Home Networks
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Network Types
Classification of interconnected processors by scale.
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Local Area Networks
Two LANs(a) Bus-broadcast(b) Ring
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Metropoliten Area Networks
Two MANs(a) Star-switched(b) Ring
Switch
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Metropolitan Area Networks
A metropolitan area network based on cable TV.
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Wide Area Networks
Relation between hosts on LANs and the subnet.
Circuit switch
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Wide Area Networks
A stream of packets from sender to receiver.
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Wireless Networks
Categories of wireless networks:
• System interconnection
• Wireless LANs
• Wireless WANs
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Wireless Networks
(a) Bluetooth configuration(b) Wireless LAN
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Home Network Categories
• Computers (desktop PC, PDA, shared peripherals)• Entertainment (TV, DVD, VCR, camera, stereo, MP3)• Telecomm (telephone, cell phone, intercom, fax)• Appliances (microwave, fridge, clock, furnace, airco)• Telemetry (utility meter, burglar alarm, babycam).
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Network Hardware
• Transmission medium
• Transceivers: transmitters and receivers on the point-to-point connections
• Multiplexers, demultiplexers
• Packet and circuit switches
• Bridges
• Routers
• Servers, gateways, management units
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Transmission Medium
• Air: different frequency bands
• Wires: twisted pairs
• Coaxial cables
• Optical fibers
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Transceivers
• Transmitters perform modulation and coding to provide efficient and reliable communication.
• Receivers perform the reverse operations.
• Depending on the medium transceivers are electronic devices, antenas, or lasers and photodiodes.
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Multiplexers and Demultiplexers
• Multiplexers receive multiple lower bit-rate streams of data and according to some rule transmit the higher bit-rate stream of data.
• Demultiplexers do the opposite.
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Circuit and Packet Switches
• It does not make sense to connect every user with every other user in the network.
• Circuit and packet switches connect multiple inputs to multiple outputs.
• In circuit switches, the configuration pattern changes on a slow time scale.
• In packet switches, the configuration changes on a packet-per-packet basis.
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Servers, Gateways, etc.
• Servers store various kinds of information for users, for example DNS databases, e-mails, web pages and provide it to the users.
• Gateways convert data format, and negotiate QoS with the network.
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Layered Structure of Networks
Layers, protocols, and interfaces.
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Protocol Hierarchies
Example information flow supporting virtual communication in layer 5.
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Design Issues for the Layers
• Addressing• Error Control• Flow Control• Multiplexing• Routing
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Services to Protocols Relationship
The relationship between a service and a protocol.
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Reference Models with Layers
• A layer should have well defined function
• Function of a layer should be internatinationally standardized
• The information flow between interfaces should be minimized
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Reference Models
• The OSI reference model
• The TCP/IP reference model
• Hybrid reference model
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Reference Models
The OSI reference model.
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Reference Models
The TCP/IP reference model.
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Reference Models
Protocols and networks in the TCP/IP model initially.
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Comparing OSI and TCP/IP Models
Concepts central to the OSI model• Services• Interfaces• Protocols
Concept of TCP/IP
• Implementation of the required functionality with three layers
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A Critique of the OSI Model and Protocols
Why OSI did not take over the world
• Bad timing
• Bad technology
• Bad implementations
• Bad politics
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Bad Timing
The apocalypse of the two elephants.
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A Critique of the TCP/IP Reference Model
Problems:• Service, interface, and protocol not distinguished• Not a general model• Host-to-network “layer” not really a layer• No mention of physical and data link layers• Minor protocols deeply entrenched, hard to replace
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Hybrid Model
The hybrid reference model to be used in this book.
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Example Networks• The Internet
• Ethernet
• Wireless LANs: 802.11
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Example Networks• 1960. Barn from RAND co. first proposal• 1957 Advanced Research Project Agency (ARPA)• 1967 Larry Roberts proposes ARPANET, that was
implemented by BBN co.• Interface Message Processors (IMP) were connected
by 54kbps links. Protocols: host-IMP, IMP-IMP, host-host
• 1969 experimental network, UCLA, UCSB, Stanford University, Yuta University
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The ARPANET
(a) Structure of the telephone system.(b) Baran’s proposed distributed switching system.
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The ARPANET
The original ARPANET design.
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The ARPANET
Growth of the ARPANET (a) December 1969. (b) July 1970.(c) March 1971. (d) April 1972. (e) September 1972.
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TCP/IP Development
• In 1974, TCP/IP model has been established by Cerf and Kahn, and incorporated into Berkeley UNIX.
• Because of the large number of hosts, domain name system (DNS) was created in 1980s.
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NSFNET
• NSF (National Science Foundation) invested into the network for all universities.
• Backbone included supercomputers at several universities, it is connected to ARPANET at Carnegie-Mellon university.
• MCI rented cables at 448kbps, and IBM provided computers as routers.
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NSFNET
The NSFNET backbone in 1988.
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Further Development
• 1990 non-profit organization Advanced Networks and Services (ANS) started comercialization, and improved speed to 45Mbps, ANSNET started. In 1995 sold to AOL
• In nineties EuropaNET and EBONE are developed
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Internet Usage
• Traditional applications (1970 – 1990) – E-mail– News– Remote login– File transfer
• World Wide Web developed by CERN physicist Tim Bernars-Lee, and Mark Andressen at National Center for Supercomputer applications
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Architecture of the Internet
Overview of the Internet.
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Ethernet
• Bob Metacalfe graduated MIT and Harvard, and worked on Hawaii on ALOHANET.
• He designed first computer LAN at Xerox Parc in Palo Alto.
• DEC, Intel, Xerox make DIX standard that becomes IEEE802.3
• Metcalfe founds 3Com
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Ethernet
Architecture of the original Ethernet.
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Wireless LANs
(a) Wireless networking with a base station.(b) Ad hoc networking.
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Wireless LANs
The range of a single radio may not cover the entire system.
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Wireless LANs
A multicell 802.11 network.
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WLAN Issues
• CSMA/CD may not be applicable
• Multipath fading
• Mobility
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Network Standardization
• Who’s Who in the Telecommunications World• Who’s Who in the International Standards World• Who’s Who in the Internet Standards World
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ITU• Main sectors
• Radiocommunications• Telecommunications Standardization• Development
• Classes of Members• National governments• Sector members (AT&T, Cisco, Intel, AOL Time
Warner…)• Associate members• Regulatory agencies (FCC)
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ISO• 200 Technical Committees, divided into
subcommittees, and working groups involving 100000 voluneers.
• TC97 in charge for computers and information processing.
• American National Standards Institute (ANSI) is US representative in ISO.
• National standards organization -> committee draft ->draft international standard -> standard
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IEEE 802 Standards
The 802 working groups. The important ones are marked with *. The ones marked with are hibernating. The one marked with † gave up.
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Internet Standards• In 1983, Internet Activities Board (IAB) was
established.
• Communication was done through “request for comments” (RFC) documents.
• IAB is moved to Internet Research Task Force (IRTF) and Internet Engineering Task Force.
• Proposed standard -> draft standard -> standard