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7/30/2019 DSI 07 DataCommNet
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Data Communications and
Networking
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IntroductionData Communication
NetworksProtocols and Standards
Standard Organizations
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Why study data
communicationsICT is the fastest growing technologies in our
culture today
Data communications and networking are
important elements that enable information to be
shared
It is important to understand the concepts and
mechanisms of these technologies - what they do
and when to use
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Data Communication
Data communication is the exchange of data
between two devices via some form of
transmission medium
The communicating devices are part of the
communication system made up of hardware and
software
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Data Communication
Characteristics of effective Data Comm Systems
Delivery
The system must deliver data to the correct destination
Accuracy The system must deliver data accurately
Timeliness
The system must deliver data in a timely manner
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Data Communication
Components
1
2 3
4
5 5
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Data Communication
Components
Message the information (data) to be communicated; text,numbers, pictures, sound, video, etc or combination
(data refers to facts, concepts and instructions presented in
whatever form agreed upon by the parties creating and using thedata)
Sender the device that sends the message; computer,workstation, telephone handset, video camera, etc
Receiverthe device that receives the message; computer,workstation, telephone handset, video camera, etc
Medium the physical path for the transmission; copper wire,fiber-optic cable, laser, radio waves, etc
Protocol the set of rules that govern data communications;agreement between the communicating devices
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Networks
Definition
A network is a set of devices (often referred to as
nodes) connected by media links
A node can be a computer, printer, or any otherdevices capable of sending and/or receiving data
generated by other nodes on the network.
The links connecting the devices are called
communication channels.
Networks promotes distributed processing a task is divided among multiple computers
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Networks
Advantages of distributed processing
Security/encapsulation a system designer can limit the kinds ofinteraction that a given user can have with the entire system
Distributed databases
storage capacity can be at differentlocations
Faster problem solving concurrent processing by manycomputers in solving a problem is faster than a single computer
Security through redundancy multiple computers running the
same program improve security Collaborative processing multiple computers/users can interact
on a single task
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Networks
Network Criteria
To be considered effective and efficient
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Networks
Network Criteria
Performance
number of users, type of transmission medium, hardware and
software Reliability
frequency of failure, recovery time of a network after a failure,
contingency plan on catastrophe
Security
unauthorized access, viruses
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Protocols and Standards
A protocol is a set of rules (conventions) that
govern all aspects of data communication
Defines whatis communicated, howit is communicated
and when it is communicated The key elements syntax(structure/format); semantics
(meaning of the structure); timing(when to send and how fast)
A standard provides a model for development
that makes it possible for a product to workregardless of manufacturers
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Protocols and Standards
De jure
legislated by official bodies
De facto industry standard, proprietary & non-proprietary
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Standard Organizations
ISO dedicated to a worldwide agreement on internationalstandards
ITU-T related to the UN for telecommunications
ANSI
US non-profit org, representing US to ISO and ITU-T
IEEE largest professional society developing standards forcomputing, communication, electrical engineering, electronics
EIA - non-profit org, promoting standards for electronics
manufacturing
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Standard Organizations
Forums
Frame Relay Forum
(DEC, Nortel, Cisco, etc)
ATM Forum and ATM Consortium
(PBX exchange manufacturers, telecom providers, etc)
ISOC/IETF
deals with the progress of the Internet
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Basic Concepts
Line Configuration
Topology
Transmission Mode
Categories of Networks
Internetworks
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Line Configuration
defines the attachment of communication devices to a link
a linkis a physical communication pathway that transfers data
from one device to another
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Line Configuration
Point-to-point A dedicated link between two devices, i.e. the entire capacity of
the channel is reserved for transmission
e.g. wire
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Line Configuration
Point-to-point A dedicated link between two devices, i.e. the entire capacity of
the channel is reserved for transmission
e.g. wire
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Line Configuration
Point-to-point A dedicated link between two devices, i.e. the entire capacity of
the channel is reserved for transmission
e.g. microwave and satellite links, etc.
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Line Configuration
Multipoint (aka multidrop) more than two devices share a single link
spatially shared several devices can share the link simultaneously
time-shared devices take turn to use the link
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Topology
defines the physical or logical arrangement of links in a
network
geometric representation of the relationship of all links and nodes
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Topology - Mesh
each node has a dedicated point-to-point link to every
other node
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Topology Mesh
Advantages each connection can carry its own data load eliminating traffic
problems
if one link becomes unusable, it does not incapacitate the entire
system robust
a dedicated line guarantees security
easy fault identification and fault isolation - reroutable
Disadvantages the amount of cabling and number of i/o ports required
expensive
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Topology Star
Each device has a dedicated point-to-point link only to a
central controller (or hub).
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Topology Star
Advantages only one link and one I/O port required per device
less expensive than mesh topology
if one link fails, only that link is affected robust
easy fault identification and fault isolation (as long as the hub is working)
Disadvantages if the hub fails, the network is down
requires more cabling than tree, ring and bus topologies
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Topology Tree
A variation of a star
majority of devices are connected tosecondary hubs (active/passive) than a central hub (active).
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Topology Tree
Advantages generally similar to star
secondary hubs allow more devices to be connected increase
the distance
allows the network to isolate and prioritize communications from
different computers
Disadvantages generally similar to star
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Topology Bus
One long cable (the backbone) link all the devices in the
network multipoint
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Topology Bus
Advantages easy installation
use less cabling than mesh, star or tree
Disadvantages difficult reconfiguration and fault isolation
a fault or break in the bus cable stops all transmission
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Topology Ring
Each device is linked only to its immediate neighbors
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Topology Ring
Advantages each device incorporates a repeater
easy to install and reconfigure
Disadvantages in unidirectional traffic, a break in the ring can disable the entire
network (some implementations use a dual ring or a switch)
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Topology Hybrid
combination of several topologies as subnetworks linked
together in a larger topology.
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Transmission Modes
the direction of signal flow between two linked
devices.
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Transmission Mode
simplex the communication is unidirectional only of the twodevices on a link can transmit, the other receive
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Transmission Mode
half-duplex each device can both transmit and receive, but notat the same time.
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Transmission Mode
full-duplex (or duplex) both devices can transmit andreceive simultaneously
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Categories of Networks
Determined by its size, ownership, distance covered and
physical architecture
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Networking
Point to point communication not usually practical
Devices are too far apart
Large set of devices would need impractical number of
connectionsSolution is a communications network
Wide Area Network (WAN)
Local Area Network (LAN)
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Local Area Network (LAN)
Usually privately owned and links the devices in a single
office,
building or
campus
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Local Area Networks
Smaller scope
Building or small campus
Usually owned by same organization as attached
devicesData rates much higher
Usually broadcast systems
Now some switched systems and ATM are being
introduced
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Local Area Network (LAN)
Size limited to a few
kilometers
Common topologies
are bus, ring and
star
High data rate
4/10/16 Mbps to
100 Mbps or
gigabits
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LAN Configurations
Switched
Switched Ethernet
May be single or multiple switches
ATM LAN Fibre Channel
Wireless
Mobility
Ease of installation
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Wide Area Networks
Large geographical area
Crossing public rights of way
Rely in part on common carrier circuits
Alternative technologies
Circuit switching
Packet switching
Frame relay
Asynchronous Transfer Mode (ATM)
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Wide Area Network (WAN)
long-distance transmission over large geographical areas(continent/world)
utilize public,
leased or private
communication incombinations
An enterprise
network is a WAN
owned by one
company
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Circuit Switching
Dedicated communications path established for
the duration of the conversation
e.g. telephone network
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Packet Switching
Data sent out of sequence
Small chunks (packets) of data at a time
Packets passed from node to node between
source and destinationUsed for terminal to computer and computer to
computer communications
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Frame Relay
Packet switching systems have large overheads
to compensate for errors
Modern systems are more reliable
Errors can be caught in end systemMost overhead for error control is stripped out
Asynchronous Transfer
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Asynchronous Transfer
Mode
ATM
Evolution of frame relay
Little overhead for error control
Fixed packet (called cell) length
Anything from 10Mbps to Gbps
Constant data rate using packet switching
technique
Metropolitan Area
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Metropolitan Area
Networks
MAN
Middle ground between LAN and WAN
Private or public network
High speed
Large area
Metropolitan Area
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Metropolitan Area
Network (MAN)Extend over entire city, may be wholly owned by a private
company, popular service SMDS
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Internetworks
internet network of networks