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Internet Technologies Overview
Content
1. How do Computer Networks and Internets
Operate?
2. Explosive growth
3. Internet
4. Economic impact
5. Complexity
6. Abstractions and concepts7. Motivations and services
8. Protocol and layering
9. Internetworking and TCP/IP
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How do Computer Networks and
Internets Operate?
Network: system for connecting computers using a single
transmission technology
Internet: set of networks connected by routers that are
configured to pass traffic among any computers attached to
networks in the set
* Data transmission - transmission media, data encoding
* Packet transmission-
data exchange over a network* Internetworking - universal service over a collection of
networks (with different technologies)
* Network applications -programs that use an internet
(Eg. WWW)
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Explosive growth
New phenomenon - now, networks are an important part of
everyday activities
Business
Home
Government
Education
Global Internet growing exponentially
Initially a research project with a few dozen sites
Today, millions of computers and hundreds of networks
world-wide and ever-increasing
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Internet
Roots in military network called ARPANET (initiated byAdvancedResearch Projects Agency, USA)
Fundamental changes from centralized to distributed
computing
Incorporated features forreliability and robustness
Multiple links
Distributed routing
Ethernet made localnetworking feasible
TCP/IPprotocol made internetworking possible
a network protocolis a set of rules that specify the format and meaning of
messages exchanged between computers across a network
Exponential growth - doubling every 18 months and ever-
increasing
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Economic impact
Large industry has grown around:
Networking hardware
Computers
Software
Companies must integrate planning,
implementation, management and upgrade
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Complexity
Computer networking is complex
Many different hardware technologies
Many different software technologies
All can be interconnected in an internet
No underlying theory
Terminology can be confusing
Industry redefines or changes terminology from academia New terms invented all the time
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Abstractions and concepts
Will concentrate on abstractions and
concepts to unravel complexity
Examples:
Types of LAN and their basic structures and
operations, rather than details of LAN hardware
Definition and concept of routing, rather thanthe hardware routing mechanisms
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Motivation & Tools
1. Motivation of Networking &
Internetworking
2. Services
3. History and Growth
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Motivation
Cost effective
Early computers were expensive, scare and centralized
Couldn't afford to put computers everywhere
interconnect computers so that computing powers can
be shared by many sites
Resource sharing
access peripheral devices through the network
Eg. Many users sharing the same printer
sharing the same files on a disk Higher reliability
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Communication Services
Access to remote information
World-Wide-Web
File Transfer (FTP)
Exchange of information
News Group
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Military Network (ARPANET)
Advanced Research Projects Agency initiated
project to connect researchers with computers
Adopted new technology: Packet switching (accept & deliver individual
parcels of data called packets)
Internetworking
Resulted in system for remote access to
expensive resources
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Packet switching
Data transmitted in small, independent
pieces
Source divides outgoing messages into packets
Destination recovers original data
Each packet travels independently
Includes enough information for delivery
May follow different paths
Can be retransmitted if lost
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Internetworking
Many (mutually incompatible) network
technologies
No one technology appropriate for everysituation
Internetworkingglues together networks of
dissimilar technologies with routers
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History and growth
ARPANET began in late 1960s (not using
TCP/IP)
TCP/IP developed in late 1970s ARPANET switched to TCP/IP in early 80s
Start of Internet
Few hundred computers
Few tens of networks
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Growth since 1981
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Why Network Models ?
Network communication is an extremely complex task
Need co-operative effort
A standard model helps to describe the task of anetworking product or service
Also help in troubleshooting by providing a frame of
reference
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Who Define Network Model ?
ISO -International Standards Organization e.g. OSI,
MPEG-1,2,4, etc.
IEEE-Institute of Electrical & Electronic Engineers e.g.
IEEE 802, IEEE 754, etc.
ITU -International Telecommunication Union e.g. V.34,
H.323, H.324, etc.
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Protocols and Layering
1. Communication (network) protocol
2. Protocol family (suite)
3. Layered Protocol - OSI 7 layers
4. Layered Software & stack
5. Protocol Headers
6. Techniques for Reliable communication
Sequencing (Ordered delivery)
Retransmission
Flow control (stop-and-go & sliding window)
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Layering
y LAN/WAN hardware can't solve all computer
communication problems
y Why network software?
y Sending data through raw hardware is awkward and inconvenient-
doesn't match programming paradigms well
y Network softwareprovides high-level interface to applications
y Software for LAN and WAN systems is large and
complicatedy Layeringis a structuring technique to organize networking
software design and implementation
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Why protocols?
Name is derived from the Greekprotokollen, the index to a
scroll
Diplomats use rules, called protocols, as guides to formal
interactions A network protocolorcomputercommunication protocolis
a set of rules that specify the format and meaning of
messages exchanged between computers across a network
Format is sometimes calledsyntax
Meaning is sometimes calledsemantics
Protocols are implemented byprotocol software
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One or many protocols?
y Computer communication across a network
is a very hard problem
y Complexity requires multiple protocols,each of which manages a part of the problem
y May be simple or complex; must all work
together
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Protocol suites
A set of related protocols that are designed forcompatibility is called aprotocol suite (family)
Protocol suite designers:
Analyze communication problem
Divide problems into subproblems
Design a protocol for each subproblem
A well-designed protocol suite
Is efficient and effective-
solves the problem withoutredundancy and makes best use of network capacity
Allows replacement of individual protocols without
changes to other protocols
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Layered protocol design
Layering modelis a solution to the problem of complexity
in network protocols
Model suggests dividing the network protocol into
layers, each of which solves part of the networkcommunication problem
These layers address several constraints, which ease the
design problem
Network protocol designed to have a protocol or protocolsfor each layer
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The OSI 7-layer reference model
International Organization for Standards defined a 7-layer referencemodelas a guide to the design of a network protocol suite
Layers are named and numbered; reference to ` layern'' often means
the nth layer of the OSI 7-layer reference model
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The layers in the OSI model
Note-
many modern protocols do not exactly fit the OSI model, and
the OSI protocol suite is mostly of historic interest
Concepts are still largely useful and terminology persists
Layer 7: Application
Application-specific protocols such as FTP (file transfer) and SMTP
(electronic mail), directly support user applications
Example protocols: FTP, Telnet, HTTP
Layer 6: Presentation Common formats for representation of data, provide data encryption
Example application program: redirector (NT), SSL
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The layers in the OSI model
Layer 5: Session Management of sessions such as login to a remote computer, provide
dialog management
Example protocols: TCP, NamedPipes, NetBIOS
Layer 4: Transport
Reliable delivery of data between computers, translate between packets
and message
Example protocols: TCP, SPX, NWLink
Layer 3:Network
Address assignment and data delivery across a physical network,
determine route from source to destination
Example protocols: IP, IPX
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The layers in the OSI model
Layer 2: Data Link
Format of data in frames and delivery of frames through network interface,
translate data frame and bits
Example protocols: Ethernet, Token Ring
Layer 1: Physical
Basic network hardware - such as RS-232 or Ethernet, define how cable is
attached to Network card
Example protocols: Ethernet, Token Ring (Physical Part)
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Application Layer: e.g. File Transfer
The most traditional network task
Implemented by a simple Application Layer protocol
called FTP
FTP Client FTP Server
Network
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Layering principle
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Layered software and stacks
Software implemented from layered design has layered
organization
Related modules from previous figure are called a
protocol stackor simply a stack
Two constraints:
The software for each layer depends only on the services of the
software provided by lower layers
The software at layern at the destination receives exactly the same
protocol message sent by layern at the sender
These constraints mean that protocols can be tested
independently and can be replaced within a protocol stack
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Messages and protocol stacks
On the sender, each layer:
Accepts an outgoing message from the layer above
Adds a header and other processing
Passes resulting message to next lower layer
On the receiver, each layer:
Receives an incoming message from the layer below
Removes the header for that layer and performs other
processing
Passes the resulting message to the next higher layer
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Protocol headers
The software at each layer communicates with the correspond
inglayer through information stored in headers
Each layer adds its header to the front of the message from the next
higher layer
Headers are nested at the front of the message as the message traverses
the network
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Techniques for reliable network
communication
Model - reliable delivery of a block of data
from one computer to another
Data values unchanged
Data in order
No missing data
No duplicated data
Example -parity bit, checksum and CRC
used to ensure data is unchanged
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Interim Summary
Layering is a technique for guiding
protocol design and implementation
Protocols are grouped together into related
protocol suites
A collection of layered protocols is called a
protocol stack
Protocols use a variety oftechniques for
reliable delivery of data
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Internetworking
1. Internetworking concepts
2. Router
3. protocol for internetworking
4. TCP/ IP layering Model
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Motivation
There are many different LAN and WAN
technologies
In real world, computers are connected by
many different technologies
Any system that spans a large organization
must accommodate multiple technologies
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Universal service
y Telephones are useful because any
telephone can reach any other telephone
y Universal service among computers greatly
increases the usefulness of each computer
y Providing universal service requires
interconnecting networks employing
different technologies
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Internetworking
y Internetworkingis a scheme for
interconnecting multiple networks of
dissimilar technologies
y Uses both hardware and software
y Extra hardware positioned between networks
y Software on each attached computer provides
universal service
y System of interconnected networks is called
an internetworkor an internet
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Routers
y A routeris a hardware component used to interconnect networksy A router has separate interface for each network
Router forwards packets between networks of different technologies
(Eg, between a WAN and a LAN, between Token Ring and Ethernet)
Transforms packets as necessary to meet standards for each network
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Internet architecture
An internetwork is composed of arbitrarily many networks
interconnected by routers
Routers can have more than two interfaces
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Routers in an organization
Would be possible to interconnect all networks in an
organization with a single router
Most organizations use multiple routers
y
Each router has finite capacity; single router would have to handlealltraffic across entire organization
y Because internetworking technology can automatically route
around failed components, using multiple routers increases
reliability
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A protocol suite for internetworking
y The TCP/IP Internet Protocols or, simply, TCP/IPis the
mostly widely used internetworking protocol suite
y
First internetworking protocol suitey Initially funded through ARPA
y Becoming more popular after 1980
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Significance of
Internetworking protocols
TCP/IP is by far the most widely used
Vendor and platform independent
Used in theInternet- 36 million computers
in 107 countries
Others internetworking protocols includeVINES and, AppleTalk
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TCP/IP layering
OSI 7-layer model was developed before TCP/IP model. It
does not include Internet layer
TCP/IP layering model includes five layers
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TCP/IP layering
Layer 5: Application
Corresponds to OSI model layers 6 and 7; used for communication
among applications
Layer 4: Transport
Corresponds to layer 4 in the OSI model; provides reliable delivery
of data
Layer 3: Internet
Defines uniform format of packets forwarded across networks of
different technologies and rules for forwarding packets in routers
Layer 2:Network Access
Corresponds to layer 2 in the OSI model; defines formats forcarrying packets in hardware frames
Layer 1: Hardware
Corresponds to layer 1 in the OSI model; defines basic networking
hardware
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Hosts, routers and protocol layers
y A host computerorhostis any system attached to an
internet that runs applications
y Hosts may be supercomputers or personal computers
y TCP/IP allows any pairof hosts on an internetcommunicate directly
y Both hosts and routers have TCP/IP stacks
y Hosts typically have one interface and don't forward
packets
y Routers don't need layers 4 and 5 for packet forwarding
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Hosts, routers and protocol layers
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Summary
An internetis a collection of physical networks
interconnected into a single virtual network
Routersprovide the physical interconnection and forward
packets between networks Hosts communicate across multiple network through
packets forwarded by routers
TCP/IP is the most widely used internetworking protocol
suite
Reference:Data & Computer Communicationsby William Stallings, Prentice Hall
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