Transcript chap02

Chapter 2
Networking Basics
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Objectives
In this chapter, you will learn to:
• Illustrate the different types of computer networks
• Describe LAN transmission media
• Discuss physical and logical LAN topologies
• Explain the network services provided by LANs
• Identify standards organizations and their role in
setting standards
• Describe the Seven-Layer OSI Model
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Valued Gateway
Client:
Types of Computer Networks
• A computer network consists of:
– Two or more computers, as well as
– Other devices such as printers or faxes connected by
some form of data transmission media such as a cable
• Network Operating Systems provide network services
including:
– File management
– Security
– Resource management
• Computers and network devices use a Network Interface
Card to connect with the network
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Local Area Networks (LANs)
LANs
• Are limited to a small geographic area, such as an office or
a building - will not use the public telephone system
• Have two basic architectures
– Peer-to-peer
– Client/server
what's the difference? and why do you care?
• Each computer has its own processing capabilities, but can
access files on other computers, network printers, and use
network services
• Each computer or destination device on the network is also
known as a node - nodes are 'self aware' of the network(s)
to which they belong
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Peer-to-Peer Networks
• Usually consist of six or fewer general-purpose
personal computers
• Computers communicate with each other and
share the same files and devices
• Every computer on a peer-to-peer network is
equal, that is, no one computer is in charge of the
other computers
• Does not require a special Network Operating
System - but note that microcomputer operating
systems since Windows 2000 and Windows XP
incorporate network capabilities
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Peer-to-Peer Network
• All computers are connected to one main cable
(also called the backbone)
• Simplest option when connecting two or three
devices
what happens if
the backbone
breaks?
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Peer-to-Peer Network with a Hub
• All computers are connected through a common
connection point (Hub)
• Can connect more computers and devices to a network
than a backbone
• can be 'daisy chained' but this is inefficient
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Peer-to-Peer Network with a Hub
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Peer-to Peer Network
Advantages/Disadvantages
• ADVANTAGES
– Simple and
inexpensive
network solution
– Does not require
special Network
Operating System
– Simplicity of
administration
• DISADVANTAGES
– Not practical for
more than five or
six computers
– Limited or no
security
– Business may
quickly outgrow
network
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Client/Server Network
• Consists of general-purpose personal computers which are
called clients and special high-performance computers
called servers - there is no special need for the 'server' to
have any more or less power than the clients
• Servers enable clients to:
– share data
– store data
– provide support for network services, such as e-mail
• Requires a special network operating system such as
Microsoft Windows 2000 Server, UNIX, or Novel NetWare
(Novel has a smaller part of today's market of network
operating systems)
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Client/Server Network
Architecture
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Client/Server Network
Advantages/Disadvantages
• ADVANTAGES
– Centralizes
management of
network services in
one location
– Increased security
– Support for greater
number of
computers, devices
• DISADVANTAGES
– Requires more
complex setup and
management
– Administration
requires higher
level of technical
expertise
– More expensive to
implement
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few people use the term "MAN" anymore, it is just a 'longer' LAN that does
note interface with the public telephone system
Metropolitan Area Network (MAN)
• A high-speed network connecting two or more
LANs
• A MAN is usually confined to a single
metropolitan area, such as a large city and its
suburbs
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Wide Area Network (WAN)
• Spans a larger area than a MAN and consists of two or
more connected LANs
• The Internet is a very complex and extensive WAN
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LAN Transmission Media
• Transmission media are the means for carrying
data from one node on a LAN to another node
• Transmission media is divided into two types:
– Cable
– Wireless
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Coaxial Cable (coax)
• High-capacity communications and video cable
• Has an insulated solid or stranded wire
surrounded by a solid or braided metallic shield,
wrapped in a plastic cover
• Carries heavy network traffic at high speeds
• Provides resistance to interference called “noise”
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Twisted-Pair Cable
• Consists of insulated copper wires twisted
around each other in pairs and then
enclosed in a plastic covering
• Two most common types are shielded and
unshielded
• By far the most prevalent medium today for
LANs
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Fiber-optic Cable
• Used to carry voice, video, and data signals
for very long distances without requiring
'repeaters'
• Contains one or more glass fibers at its core,
surrounded by a layer of glass cladding and a
protective outer jacket
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incorrect representation, should
be four groups of twisted pairs
for 8 total wires
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Infrared (IR) Transmission
• Relies on electromagnetic waves with a frequency
range above that of microwave but below the visible
spectrum
• solid objects block the transmission
• Infrared signals are transmitted through space in the
same way a TV remote control device sends signals
across a room
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Radio Frequency (RF)
Transmission
• Relies on signals sent over a specific frequency, like
radio broadcast
• not blocked by solid objects (but a solid object
lessens signal strength)
• RF transmissions are regulated by the Federal
Communications Commission (FCC) which licenses
frequencies by geographic location to ensure that
multiple transmitters do not interfere with each others’
transmissions
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Traveling at the Speed of Data
• Throughput – Amount of data that can be transmitted within
a specific time period
– Measured in units of bits per second (bps)
– 1 Kbps = 1,000 bits per second
– 1 Mbps = 1,000,000 bits per second = 1,000Kbps
– 1 Gbps = 1,000,000,000 bits per second = 1,000 Mbps
• Throughput for most (Ethernet) networks is between 10
Mbps and 100 Mbps
• Current media (category 7 twisted pair) runs 1Gbps (i.e.
1,000Mbps) with 10Gbps available but network interface
cards of 10/100Mbps are the most common
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Physical Topologies
of Local Area Networks
• Physical topology refers to a network’s physical
layout or the pattern in which its devices and
cabling are organized
• Three basic physical topologies:
– Bus
– Ring
– Star
• Modern LANs generally combine these topologies
into a hybrid topology
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Bus Topology
• Used on peer-to-peer
LANs
• Consists of a single
coaxial cable called a
trunk (or backbone)
to which all devices
are connected
• Because the cable is
shared, it carries only
one transmission at a
time
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Data Transmissions
• Data transmissions
involving one sending and
receiving node are called
point-to-point
transmissions
• Transmissions that involve
one sending node and
multiple receiving nodes
are called broadcast
transmissions
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Ring Topology
• Each node is connected to
the next node via a single
circle of twisted-pair or
fiber-optic cable
• Data transmissions travel
around the circle in a
clockwise direction,
passing through each
node
• When a node receives a
transmission, it accepts
the data addressed to it
and then forwards the
transmission on to the
next node
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Star Topology
• Each node is connected to
a central hub by a separate
twisted-pair or fiber-optic
cable
• Data is transmitted from
one node, through the
hub, and out again to the
destination node
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Hybrid Topology
• Contains elements of two
or more physical
topologies
• Star-wired ring topology is
the most common hybrid
• Data travels in a circle,
from one node to the next,
but each transmission
passes through the hub
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Logical Topologies
of Local Area Networks
• Logical topology defines the way in which the data is
transmitted between computers
• Specifies several network characteristics including:
– The access methods, or rules, the nodes follow to access the
transmission media
– The network’s physical topology
– The network’s transmission media
– The data throughput rate
• Logical topologies commonly used on LANs are Ethernet
and Token Ring (actually, token ring is much less common)
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Ethernet
• Uses Carrier Sense Multiple Access with Collision
Detection (CSMA/CD) access method, which directs
transmission traffic over the network
• All stations attached to the Ethernet are "listening" and the
station with the matching destination address accepts the
frame and checks for errors
• Collisions:
– If two nodes simultaneously check and then transmit,
their two transmissions collide
– In this case, both nodes immediately stop transmitting,
wait a random interval, recheck, and then rebroadcast
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Token Ring
• A network access method that uses a continuously
repeating 3-byte frame (the token) that is transmitted
onto the network by the controlling computer
• The token moves clockwise in a circle from node to
node
• When a node wants to send a message, it waits for an
empty token; then fills it with the address of the
destination node and some or all of its message
• Every node on the network constantly monitors
passing tokens to determine if it is the recipient of a
message, in which case it "grabs" the message and
resets the token status to empty
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Network Services
• Programs that manage data and operations on a
network, and provide services to multiple users
• Network services include:
– File services
– Print services
– Mail services
– Communications services
– Internet services
– Management services
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File Services
• Permit centralized storage of data files
• A high-speed computer in a network
stores the programs and data files shared
by users
• A file server acts like a remote disk drive
• Data stored on a file server can be
accessed by authorized users around the
network
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Print Services
• Enable employees to share printers across a
network
• Print services include storing print-image output
from all users of the system and feeding it to the
printer one job at a time
• A print server provides this service for one or
more printers in a network
• The print server function may be software that is
part of the network operating system or an addon utility
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Using Network
File and Print Services
1. Document is created and stored on the file server
2. Second user can retrieve document from file server
then edits and saves file on the file server
3. Remote user can retrieve document from file server
4. Sends document to network printer
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Mail Services
• Manages the sending, receiving, routing, and
storage of e-mail
• Controlled by a mail server, usually a computer in
a network that provides "post office" facilities
• Mail services include storing incoming mail for
distribution to users and forwarding outgoing
mail through the appropriate channel
• The software that performs this service may
reside on a computer providing other services
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Communications Services
• Enables traveling employees (remote
users) to connect to the network and
access their data files and e-mail
messages
• Company LAN is accessed using POTS
(plain, old telephone system) or ISDN
modem, or broadband connection through
a remote access server, or wireless, or any
other communications medium
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Using Network
Mail and Communications Services
1. User e-mails a document to a co-worker for
editing
2. Second user edits the document, then e-mails
copy to the remote user
3. Remote user connects to network, then
retrieves document from e-mail
4. Remote user edits document, then e-mails
document to the original user
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Internet Services
• Provides external Internet access, internal
intranet services, and management of Internetrelated technologies such as Web servers, Web
browsers, and Internet-based e-mail
• Used to establish and manage external business
Web sites to sell products and services, provide
customer support, and gather information about
potential customers and the marketspace
• Internet-based e-mail allows businesses to
maintain contact with customers and suppliers
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Network Management Services
• Enables administrator to monitor network activity,
manage user access and network resources
• Includes diagnostic and management tools for
troubleshooting problems and gathering
statistics for administration and fine tuning
• Centralized installation of software and backup of
stored data
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The Role of Standards Organizations
• A standard is a rule, description, or design
approved by an established organization or
accepted by an industry through common usage
• Networking standards that cover the formatting
and transmission of data are set by third-party
organizations that include government agencies,
scientists, research institutions, consumer
groups, engineers, manufacturers, vendors, and
other interested parties
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International Organization for
Standardization (ISO)
• A global alliance drawn from approximately 140
countries
• Establishes and publishes standards that help make
possible the international trade of goods and
services
• Standards govern areas such as: photographic
equipment and film speed, quality management,
environmental management, freight container, and
paper size
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International Electrotechnical Commission (IEC)
• Promote international standards in fields of electronics,
magnetics and electromagnetics, electroacoustics,
multimedia, and telecommunications
• Works with ISO to develop standards for the IT industry
ANSI - American National Standards Institute
• Non-profit organization that represents the U.S. to
international organizations such as ISO and IEC
• Promotes adoption of U.S. and international standards that
make U.S. businesses more competitive in global markets
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Additional Standards Organizations
• Electronic Industries Alliance (EIA)
– Develops standards for electronic components,
consumer electronics, and telecommunications
• Institute of Electrical and Electronics Engineers, Inc.
(IEEE)
– Internal authority on biomedical technology,
consumer electronics, computer engineering,
electric power, aerospace, and telecommunications
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Additional Standards
Organizations
• International Telecommunications Union (ITU)
– International forum for government agencies
and industry representatives
– Develops standards for telecommunications
• European Telecommunications Standards
Institute (ETSI)
– European standards organization in the areas
of telecommunications, broadcasting, and
information technology
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Open Systems Interconnection
(OSI) Model
• An ISO standard for worldwide communications
that defines a framework for implementing
protocols in seven layers
• Control is passed from one layer to the next,
starting at the application layer in one station,
proceeding to the bottom layer, over the channel
to the next station and back up the hierarchy
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Open Systems Interconnection
(OSI) Model
hubs are at level 1, routers
act at level 3, switches act
at levels 2 & 3
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Physical Layer (1)
• SENDING NODE
• RECEIVING NODE
– Passes bits onto the
connecting medium
– Receives bits from the
connecting medium
• Defines the physical and
electrical characteristics of a
system
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Data Link Layer (2)
• SENDING NODE
• RECEIVING NODE
– Subdivides data into
frames, and then
transfers without errors
– Retransmits frames if
acknowledgement is
not received
– Reassembles the
frames, performs error
checking, then
acknowledges receipt
of the data
• Ethernet technologies work at
the Data Link layer
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Network Layer (3)
• RECEIVING NODE
• SENDING NODE
– Determines best route
to receiving node
– Reassembles the
segmented frames
– Translates IP
addresses to MAC
addresses
– Segments frames into
smaller units
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Transport Layer (4)
• SENDING NODE
• RECEIVING NODE
– Breaks long frames
into smaller units
– Assigns sequence
numbers to each unit
– Uses the sequence
numbers to reassemble
units in correct order
– Acknowledges errorfree receipt of frames
• Ensures frames traveling
between nodes arrive without
error
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Session Layer (5)
• SENDING NODE
• RECEIVING NODE
– Sets up session with
the receiving node
– Decides which nodes
can communicate and
for how long
– Restarts terminated
sessions when
necessary
– Acknowledges session
request from sending
node
– Maintains
communications with
sending node
• Establishes and maintains
communications between the
sending and receiving node
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Presentation Layer (6)
• SENDING NODE
• RECEIVING NODE
– Formats data sent to
receiving node for
network use
– Compresses data into
the smallest number of
bits
– Can also encrypt data
– Formats data received
from the sending node
for application use
– Decompresses data
received from the
network
– Also decrypts
encrypted data
• Formats data for network and
application use
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Application Layer (7)
• SENDING NODE
• RECEIVING NODE
– Translates data
received from the
application into a
format recognized by
the Presentation layer
– Translates data
received from the
Presentation layer into
a format recognized by
the Application layer
• Enables the user applications
to access network services
such as: e-mail, file services
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