Transcript Networks & Telecommunications

Networks & telecommunications
October 9, 2014
LEARNING GOALS
• Identify the major hardware components in
networks.
• Identify and explain the various types of
computer networks.
• Identify the various types of transmission
media
• Describe the role of software used in
networks.
• Discuss telecommunications’ principles.
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Stand-alone computers v. Network?
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Why Networking ?
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Resource sharing
– Sharing hardware (printers, processors, etc.)
– Sharing software (programs, data files)
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High reliability
– Can set automatic backup of programs and data at different
locations
– Fault tolerance (if one server is down, others can provide
service. If a disk fails, data available through mirror or RAID-3
disks)
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Possible cost savings
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Communication tool
– Internal email service
– Remote Access service
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Computer Network
Once connected to the network,
the computer (or another device)
becomes a network node
• An interconnection of computers and
computing equipment using either wires or
wireless transmission media over small or
large geographical distances.
DEF
GHI
“Connect to GHI”
ABC
JKL
MNO
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Computer Network (cont.)
• Based on the definition from the previous
slide, what hardware elements are needed to
implement a computer network?
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Network scope
• Local area network (LAN): computer network where
the nodes are all in close proximity spanning a
room, building, or campus
• Metropolitan area network (MAN): network that
serves an area of 3 to 30 miles - approximately the
area of a typical city.
• Wide area network (WAN): a large network that
encompasses parts of states, multiple states,
countries, and the world
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Physical
Transmission Media
• Physical media
Wireless
– Transmission media used to physically connect nodes to
the network
– Transmits electrical or optical signals
– Could be copper wire or fiber optic cable
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Transmission Media (Continued)
• Twisted Pair
Category
Use
Signal
Data rate
Distance
Problem
Category 1
Telephone
Analog/Digital
<100Kbps
3-4 miles
Security, noise
Category 2
T1, ISDN
Digital
<2 Mbps
3-4 miles
Security, noise
Category 3
LANs
Digital
10 Mbps
100 m
Security, noise
Category 4
LANs
Digital
20 Mbps
100 m
Security, noise
Category 5
LANs
Digital
100 Mhz
100 m
Security, noise
Category 6
LANs
Digital
250 Mhz
100 m
Security, noise
Category 7
LANs
Digital
600 Mhz
100 m
Security, noise
• Fiber optic
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Source
Thin glass fibers surrounded by coating
Uses laser or light for data transmission
Very fast (10+ Gbps, 100 miles without any repeater)
Very secure
Photo diode
(LED or LD)
Photo receptor
Fiber optic cable (LED or LD)
Destination
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Wireless transmission media
• Infrared light
– Has many of the same characteristics as visible
light
– Travels in straight lines
– Cannot penetrate solid objects
• Radio waves
– Travel in straight lines
– Can penetrate through nonmetallic objects
– Can travel long distances
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Wireless Media issues
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Use electromagnetic waves or electromagnetic radiation for data
transmission
Propagation through space, and indirectly, through solid objects
Many problems:
Electromagnetic
Interference (EMI) from
Other stations,
Microwave ovens, etc
Radio waves tend to bounce
off objects. Receiver can
receive 2 or more signals.
Thick objects can block the direct
path. So, Receiver will be in a
Shadow zone where it cannot well
receive.
Shadow
Zone
Multipath
Interference
Laptop
Comm.
Tower
Insecure:
Easier to
“intercept”
messages
+ Much more attenuation: Inverse Square law
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Computing Equipment
• Network interface card (NIC): Device that
– provides a computer with unique address
– Converts data into signal for transmission
• Hub / Switch: Central collection point for transmission
media that interconnect computers
• Modem
– Converts digital data into analog signal and back again
• Router
– special hardware that determines optimal routing path for
data packets
– Usually used to connect a LAN to a WAN
• Bridge
– Forwards messages between LANs
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Small Network illustrated
Hub or Switch
Wide Area
Network
Router
Media
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Hub operation
1.
Station A transmits
to the Hub
2.
Hub broadcasts
to all stations
(Except sending station)
Station C must wait,
or its signal will
collide with Station A's
signal
Station
A
Station
B
Station
C
Station
A
Station
B
Station
C
Hubs split available bandwidth among computers, i.e. with a 100 Mbps hub, the network
speed will be 100 Mbps / n (where n is the number of computers)
Active hubs include repeater capabilities for regenerating signals.
Passive hubs don't regenerate signals. Limited to a 30meter distance apart from computers.
Switch operation
Switch
Switching table
MAC Address
A1-44-D55-1F-AA-4C
B2-CD-13-5B-E4-65
C3-2D-55-3B-A9-4F
;
1 2 3 4 5 6
Switch Sends
Signal out a
Single Port
Station A
Transmits
to Station C
Station
A
Port
1 (Station A)
2 (Station B)
5 (Station C)
;
Station B
Transmits
Simultaneously
Station to Station D
B
Station
C
Station
D
Switches send out a single port: destination port.
Most switches can efficiently handle simultaneous transmissions
Switches provide a full bandwidth to all connected computers.
Network Software
• Network operating system
– Used on servers
– Used for managing network resources
– Examples: Novell NetWare, Windows Server 2008
• Workstation operating system
– Used on client PCs
– Used to manage local resources & access network
resources
• Network monitoring software
– Packet sniffers – allow seeing data as it moves over
network
– Keystroke monitors – allow seeing what users are
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typing
Protocols
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An agreed upon set of rules that govern
communication in a network
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All computers on a network must use same protocol
for effective communication
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Example of protocols:
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Ethernet (for communication in a LAN)
Token Ring (for communication in a LAN)
TCP/IP suite (for communication in a LAN and the Internet)
Computer 1
Rules for Task 1
Rules for Task 2
Rules for Task 3
Rules for Task 4
Rules for Task 5
Computer 2
Rules for Task 1
Rules for Task 2
Rules for Task 3
Rules for Task 4
Rules for Task 5
Network Topologies
• The configurations of network components
– How physically the network looks like
– How logically data is transferred on the network
• Types of network topologies:
– Bus
– Star
– Ring
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Bus Network Topology
• Most simple network topology
• All devices connected to a common central
cable called a “bus”
• Inexpensive
• If cable fails, the entire network will shut down
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Star Network Topology
• Centered around
central device called a
hub or a switch
• All network nodes
connect to the
hub/switch
• Easy to install and
update
• If hub fails, network
fails
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Ring Topology
• Node connected to a
logical ring in a central
device called MAU
• More reliable than bus or
star
– Only one node sends at a
time (no collisions)
• Expensive and limited
speed
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Network Architectures/Models
• Defines how the
processing takes place
on the network
• Two primary models
– Client-server
– Peer-to-peer (P2P)
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Client-server model
• Nodes are either clients or servers
• Clients use services
• Servers provide services
– File service
– E-mail service
– Printing service
– Database service
• Client software on client node cooperates with
server software on server node
– The WWW is the largest client server application
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Client-server model
• Collaboration between Client and Server program
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Client-server model
• Division of Labor
– Client program handles lighter work, such as
user interface chores and light processing
chores
– Server program handles heavy work, such as
database retrieval
Client Program
Client Machine
Server
Program
Server 25
Peer-to-Peer model
• All nodes on the network are equal.
• Any node can be both a client and a server.
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Summary Questions
Book
Notes
1) Name categories of computer networks based on their scope;
i.e. their range of operation
2) Name one example of: (a) WAN, (b) LAN
3) Name physical and wireless media used in networking
4) What is the role of (a) a modem, (b) a router, (c) a bridge?
5) What is the difference between a Network operating system
and a workstation operating system?
6) What is a network topology?
7) Distinguish between network topologies
8) Distinguish between Client-server and P2P networks
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Summary Questions (cont.)
• What category of network is illustrated here?
Summary Questions (cont.)
• What category of network is illustrated here?
Problem
• Four students share a dorm. They would like to
set up a network in order to share programs
and data files. Three of the students own PCs
and the fourth student has a laptop computer.
Question: What computing equipments they need to
buy in order to set up the network with a star
topology?
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Telecommunications
Voice vs. Data Communication
• Originally, There was a Sharp Distinction:
– Voice Communication
– Data Communication, in which one or both
parties is a computer
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Database
Electronic mail
World Wide Web
• Distinction is fading because voice
communication is increasingly computer-based
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Circuit Switching and Reserved
Capacity
– Circuit switching is traditionally used in
telecommunications
– Circuit capacity is reserved during duration of
each call
– At each switch
– On each trunk line
Reserved
Capacity
Reserved
Capacity
Circuit
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Pros and cons of Reserved
Capacity
• Nothing like the congestion on the Internet
• Reserved Circuit Capacity is Expensive
– Have to pay for it whether you use it or not
– Good for voice, because conversations are
fairly constant
– Bad for data, because most data transmission
is bursty; e.g., in World Wide Web, download,
then stare at screen for a long time until next
download
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Packet-Switching Data Networks
• Packet Switching
– Large messages are broken into small pieces called
packets (or frames)
– Packets are short (averaging a few hundred bytes)
because networking devices handle short
messages more efficiently
Message
Packets
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Packet-Switching Data Networks
• Multiplexing
– Packets from many conversations are mixed
(multiplexed) over each trunk line
Packet Switching
Multiplexing on
Transmission Line
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