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Introduction
Aleksandra Smiljanić
[email protected]
Uses of Computer Networks
• Business Applications
• Home Applications
Business Applications
• Sharing resources
• Common databases for customer
records, inventory, accounts
• E-commerce
• Video-conferencing
• Disseminating the information, and
coordination
Home Applications
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Getting the remote information
Person-to-person information
E-commerce
Entertainment
E-flea
Network Types
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Local Area Networks
Metropolitan Area Networks
Wide Area Networks
Wireless Networks
Home Networks
Network Types
Classification of interconnected processors by scale.
Local Area Networks
Two LANs
(a) Bus-broadcast
(b) Ring
Metropoliten Area Networks
Switch
Two MANs
(a) Star-switched
(b) Ring
Metropolitan Area Networks
A metropolitan area network based on cable TV.
Wide Area Networks
Circuit switch
Relation between hosts on LANs and the subnet.
Wide Area Networks
A stream of packets from sender to receiver.
Wireless Networks
Categories of wireless networks:
• System interconnection
• Wireless LANs
• Wireless WANs
Wireless Networks
(a) Bluetooth configuration
(b) Wireless LAN
Home Network Categories
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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).
Network Hardware
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Transmission medium
Transceivers: transmitters and receivers on the
point-to-point connections
Multiplexers, demultiplexers
Packet and circuit switches
Bridges
Routers
Servers, gateways, management units
Transmission Medium
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Air: different frequency bands
Wires: twisted pairs
Coaxial cables
Optical fibers
Transceivers
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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.
Multiplexers and Demultiplexers
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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.
Circuit and Packet Switches
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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.
Servers, Gateways, etc.
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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.
Layered Structure of Networks
Layers, protocols, and interfaces.
Protocol Hierarchies
Example information flow supporting virtual communication in layer 5.
Design Issues for the Layers
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Addressing
Error Control
Flow Control
Multiplexing
Routing
Services to Protocols Relationship
The relationship between a service and a protocol.
Reference Models with Layers
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A layer should have well defined function
Function of a layer should be
internatinationally standardized
The information flow between interfaces
should be minimized
Reference Models
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The OSI reference model
The TCP/IP reference model
Hybrid reference model
Reference Models
The OSI
reference
model.
Reference Models
The TCP/IP reference model.
Reference Models
Protocols and networks in the TCP/IP model initially.
Comparing OSI and TCP/IP Models
Concepts central to the OSI model
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Services
Interfaces
Protocols
Concept of TCP/IP
• Implementation of the required
functionality with three layers
A Critique of the OSI Model and Protocols
Why OSI did not take over the world
• Bad timing
• Bad technology
• Bad implementations
• Bad politics
Bad Timing
The apocalypse of the two elephants.
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
Hybrid Model
The hybrid reference model to be used in this book.
Example Networks
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The Internet
Ethernet
Wireless LANs: 802.11
Example Networks
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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, hosthost
1969 experimental network, UCLA, UCSB, Stanford
University, Yuta University
The ARPANET
(a) Structure of the telephone system.
(b) Baran’s proposed distributed switching system.
The ARPANET
The original ARPANET design.
The ARPANET
Growth of the ARPANET (a) December 1969. (b) July 1970.
(c) March 1971. (d) April 1972. (e) September 1972.
TCP/IP Development
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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.
NSFNET
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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.
NSFNET
The NSFNET backbone in 1988.
Further Development
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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
Internet Usage
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Traditional applications (1970 – 1990)
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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
Architecture of the Internet
Overview of the Internet.
Ethernet
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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
Ethernet
Architecture of the original Ethernet.
Wireless LANs
(a) Wireless networking with a base station.
(b) Ad hoc networking.
Wireless LANs
The range of a single radio may not cover the entire system.
Wireless LANs
A multicell 802.11 network.
WLAN Issues
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CSMA/CD may not be applicable
Multipath fading
Mobility
Network Standardization
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Who’s Who in the Telecommunications World
Who’s Who in the International Standards World
Who’s Who in the Internet Standards World
ITU
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Main sectors
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Radiocommunications
Telecommunications Standardization
Development
Classes of Members
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National governments
Sector members (AT&T, Cisco, Intel, AOL Time
Warner…)
Associate members
Regulatory agencies (FCC)
ISO
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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
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.
Internet Standards
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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