Transcript 02-computer_networks

Networking BASICS
Introduction to Networking
Objectives
Define a computer network.
List the four purposes of a network.
Explain the elements of
communication.
List and describe the two types of
networks.
What Is a Computer Network?
A computer network is computers and
devices connected together.
A single computer is limited to its own
hardware and software.
The capabilities of a computer are
increased when connected with other
devices to form a computer network.
Purpose of a Computer Network
Summarized in a single word: sharing.
Individual computers are isolated.
Networked computers can share
resources.
Three types of resources can be shared.
Networks also make computer
management easier.
Share Software and Data
Application and utility software can be
shared by all users across the network.
This requires only a single software copy
to be purchased and maintained.
Data files can also be shared.
This makes data more accessible and
maintains integrity.
Share Hardware
Sharing is an essential feature of a
computer network.
This reduces costs and the work of
support staff.
Printers, fax modems, scanners, hard
drives, CD-ROMs, and DVDs can all
be shared.
Improve Communications
Communication is essential in today’s
businesses.
Computer networks can help in improved
communications through groupware.
E-mail, electronic calendars, collaborative
writing, and video conferencing are
available.
Centralize Management
Support staffs are stretched to the limits.
Computer networks allow computers to be
managed from one central location.
Software updates can be “pushed” to users’
computers.
Problems can be diagnosed over the network.
Training can be done over the network.
Types of Networks
Two types of network
classifications
Classified by device that
controls network
Classified by distance between
devices
Peer-to-Peer Network
No single computer controls
the network.
Each computer is the same (a
peer) to all others.
It is suitable for small offices.
Types of Networks
Server-Based Network
The network is controlled by a special
high-powered server.
The server is dedicated to running the
network.
Print and file servers, application servers,
communication servers, and directory
service servers are common.
Server-Based Network
Local Area Network
Network computers are located relatively
close to each other.
They are generally limited to buildings
owned by one organization.
They operate at high speeds.
They are low-cost networks.
Local Area Network
Wide Area Network
Network computers are spread out over a
larger area.
They generally cross public thoroughfares.
They are often managed by public
carriers.
They operate at lower speeds.
They are a higher-cost network.
Wide Area Network
Summary
A computer network is defined as multiple computers
and devices that are all connected together. By
connecting the computers together, the capabilities of
each computer are increased so the users can
accomplish more.
The purpose of a computer network is to share.
Application software, utility software, and the data that
serves as input into the software can all be shared
across a network. Computer hardware can also be
shared on a computer network. Printers, fax machines,
scanners, modems, hard disk drives, CD-ROM drives,
and DVD drives are just a few of the hardware devices
that can be shared across a computer network.
Summary (continued)
Computer networks can be important tools that help
improve communication between users. A special
category of software that assists with communication
over a computer network is known as groupware.
Groupware refers to programs that help people work
together collectively even if they are located remotely
from each other. One of the most common groupware
applications used across computer networks is electronic
mail, or e-mail. Groupware services also include
electronic calendars, collaborative writing software, and
video conferencing.
The communication that takes place between devices on
a computer network is known as telecommunications.
Telecom-munications is defined as transmitting
information over a distance and is generally considered
to be a two-way transmission of voice, video, or data.
Summary (continued)
Computer networks allow the computers connected to
the network to be managed from one central location.
Software updates can be “pushed” across the network to
all computers, thus eliminating the need for support staff
to visit every office and perform the new installation.
Problem diagnosis can be performed across the
network. Centralized management can be used for
training as well.
Computer networks are generally classified two different
ways. The first classification of networks involves the
device that actu-ally controls the network. In a peer-topeer network, no single high-powered computer controls
and manages the network. The computers collectively
run the network instead of a special dedicated computer
doing it. These networks are suitable for small offices
that need to share a printer or computer data.
Summary (continued)
The second type of network classified by the device that
con-trols the network is known as a server-based
network. Unlike a peer-to-peer network, a server-based
computer network is con-trolled by at least one special
high-powered computer. These special computers are
called servers, while the individual com-puters on the
network are called clients. Servers are usually dedicated
to running the network and do not function as clients.
Instead, their sole job is to service requests quickly from
the network clients and ensure the security of the
software and hardware. There are many different types
of specialized servers.
Summary (continued)
Networks can also be classified by geography or how
close the devices are to each other. There are two
categories of networks based on geography. The first is
a local area network (LAN). A LAN is a computer
network that has all the computers relatively close to
each other. They operate at high speeds for a low cost.
A wide area network (WAN) transmits over a public
thorough-fare, such as a road, highway, railroad, or body
of water. A WAN service must be purchased from a
carrier. WANs are managed by the carrier instead of by
the user. Compared to LANs, the cost of WANs is high
and they operate at a low speed.
Networking BASICS
Network Media
Objectives
Explain how data transmissions
are sent and received.
List and describe the types of
transmission media.
Describe the functions of a
network interface card.
Types of Networks
There are two types of
networks by which
information is transmitted:
– circuit switched networks
– packet switched networks
Circuit Switched Network
There is a dedicated and direct physical
connection between sender and receiver.
No other transmissions can take place while the
connection is active.
Once the transmission is ended, other
connections can be made with other devices.
It is ideal for voice communications because
there are no interruptions from other devices or
delays.
Packet Switched Network
This network requires data transmission be broken into
smaller units called packets.
Each packet is sent independently through the network.
It is used for data transmission because data is not as
time-sensitive as voice communication.
It allows multiple devices to share one line or frequency.
It facilitates error correction.
Transmission Media
Copper cables
Fiber optic cables
Wireless
Copper Cables
Thin coaxial
Shielded twisted pair (STP)
Unshielded twisted pair (UTP)
UTP rated by Category 1 - 6
Copper Cables
Copper Cables
Fiber Optic
This cable uses a thin cylinder of glass to send
light impulses.
The cable consists of a strand of glass (core)
surrounded by a glass tube (cladding).
Single mode - one light source flashes a light
down the cable.
Multimode - supports many simultaneous light
transmissions.
Fiber Optic
Wireless
Transmission is sent and received through
invisible waves
Less expensive than copper or fiber optic lines.
Allows the user to move freely around the office
or campus and still remain connected to the
network
Fastest-growing segment of network media
today
Wireless Transmissions
Infrared transmits data using infrared (IR) light.
IR shares many of the same properties as visible
light .
Radio frequency signals can be transmitted over
radio waves similar to local radio station
transmissions.
The signal comes in at a lower power level and
does not reach as far.
Network Interface Card
The NIC serves as the connection between the
personal computer and the network media.
It connects to the computer on its base by
plugging into an expansion slot of the computer.
Another connection is accessible from the
outside of the computer and has connections for
the cables to plug into the network.
Network Interface Card
Changes from parallel to serial
transmission
Creates packets
Determines when to send
Transmits packet
Network Interface Card
Summary
Switching involves moving (switching) the signal from
one wire or frequency to another. A circuit switched
network creates a dedicated and direct physical
connection between the sender and receiver. No other
transmissions can take place while the connection is
active, but once the transmission is ended, other
connections can be made with other devices. Circuit
switching is ideal for voice communications. Computer
networks sending data use packet switched networks.
Packet switching requires that the data transmission be
broken into smaller units called packets. Each packet is
then sent independently through the network to reach
the destination.
Summary (continued)
There are many different types of network media, yet they
all can be classified into three major categories: copper,
fiber optic, and wireless. Thin coaxial cable is
approximately one-quarter of an inch in diameter, has a
single copper wire at its center, and is surrounded by a
layer of insulation. Around the insulation is a braided
copper mesh channel, and everything is covered by a thick
outer shield of insulation. Twisted pair cable has become
the standard today for copper cabling used in computer
net-works, replacing thin coaxial cable. Twisted pair cable
is two insulated copper wires that are twisted around each
other. Each pair is then bundled together with other pairs in
a jacket. There are two types of twisted pair cables.
Shielded twisted pair (STP) cables have a foil shielding on
the inside of the jacket, which reduces interference.
Unshielded twisted pair (UTP) cables do not have any
shielding.
Summary (continued)
A fiber optic cable uses a very thin cylinder of glass,
instead of copper, at its center. Fiber optic cables send
light impulses instead of transmitting electrical signals.
Wireless communica-tion uses no visible connection,
such as a copper cable or fiber optic line, between the
network devices. Instead, the transmis-sion is sent and
received through invisible waves. Transmission signals
can be sent by infrared light waves or radio frequency
waves.
Summary (continued)
When connecting a personal computer to the
transmission media on a LAN, hardware known as a
network interface card (NIC) is used. A NIC serves as
the connection between the personal computer and the
network media. The NIC connects to the computer on its
base by plugging into one of the expansion slots of the
computer. The other connection, found on the side of the
NIC, is accessible from the outside of the computer and
has connections for the cables to plug into the network
(or an antenna for wireless transmissions). These
connections depend on the type of network media being
used.
Networking BASICS
Network Design
Objectives
List and describe the
characteristics of the mesh, bus,
ring, star, and hybrid topologies.
Tell what items should be
considered when selecting a
network topology.
Objectives (continued)
Define channel access method.
Give the advantages and
disadvantages of contention,
polling, token passing, and
demand priority channel access
methods.
Topologies
Physical layout of network
devices
Four types: mesh, bus, ring,
and star
Mesh Topology
It is also called a point-to-point
topology.
Each device is connected directly to
all other network devices.
It provides fault tolerance.
It is only found in wide area networks.
Mesh Topology
Bus Topology
It is a multipoint topology.
Each device shares the connection.
The bus has one starting and one
ending point.
Packets stop at each device on the
network.
Only one device at a time can send.
Bus Topology
Ring Topology
It is a circle with no ends.
Packets are sent from one
device to the next.
It does not slow down as
more devices are added.
Ring Topology
Star Topology
All devices are connected to a central
device (hub).
The hub receives and forwards
packets.
It is the easiest topology to
troubleshoot and manage.
It has a single point of failure.
Star Topology
Hybrid Topologies
They are variations of two or more
topologies.
Star bus – used to connect multiple
hubs in a star topology with a bus.
Star ring – wired like star, but
functions like a ring.
Design Considerations
The best topology involves
matching with the environment it is to be used in.
The physical arrangement of
computers do not dictate the
necessary topology.
Summary
Topology refers to the physical layout of the network
devices and cabling and how all the components
communicate with each other. Computer network
topology refers to how the computer network is
arranged. There are four basic types of computer
network topologies: mesh, bus, ring, and star.
A mesh topology is also called a point-to-point topology.
Each device is connected directly to all other devices on
the network. A mesh topology is sometimes used in a
wide area network (WAN) setting to ensure that all the
sites continue to transmit in the event of a cable failure
or another similar problem. Mesh topologies are rarely
used in a LAN.
Summary (continued)
LANs typically use a multipoint topology in which each computer on
the network has just one connection. This connection is attached to
a single cable that is shared by all other devices on the network. The
most common type of multipoint topology is a bus topology. A
computer network bus topology is characterized by one starting
point and one ending point. A bus network topology works well for
smaller networks and is inexpensive to install. However, it can
become slow when more devices are added to the network.
A star topology describes a network in which all the devices are
connected to a central device known as a hub, which is respon-sible
for receiving and forwarding packets to other devices on the
network. Because everything is centralized in a star topology, it is
the easiest topology to manage and troubleshoot.
Summary (continued)
A multipoint ring topology is the opposite of a bus. A bus has two
end points, but a ring is a circle with no ends. All the devices on the
network are connected to the ring. Unlike a bus topology, in which
the network devices do not play an active role in the network, each
device has additional network functions in a ring topology. A ring
topology works well for a computer network with many devices
attached to it.
Not all topologies are strictly mesh, bus, star, or ring. Some
variations of these topologies, known as hybrid topologies, are also
used. These variations are actually combinations of two or more
topologies.
Summary (continued)
A star bus topology is typically used to connect multiple
hubs in star topologies with a bus topology and provides
additional fault tolerance. A star ring topology is wired
like a star, but functions like a ring. The packets in a star
ring do not go directly to the next device on the ring, but
instead go to a central hub.
Networking BASICS
Network Architectures
Objectives
Explain why standards were
developed for LANs.
Give several examples of Ethernet
architectures.
List the features of a token ring
network.
Tell how a wireless LAN functions.
Provide guidelines for designing a
network.
Standards
Different architectures could restrict
the growth of networking.
The Institute of Electrical and
Electronic Engineers (IEEE)
developed computer network
architecture standards.
There are three dominant standards:
Ethernet (802.3), token ring (802.5),
and wireless (802.11).
Ethernet
Ethernet is the most popular LAN architecture
today.
It is easy to install and inexpensive.
Data transmission is broken into packets.
The standard method of labeling different
versions is Maximum Speed-Transmission
Mode-Segment Length or Media Type.
10Base2
It is a bus topology that uses contention
(CSMA/CD) and thin coax.
Segments are connected together through
a repeater.
It can connect up to five 200-meter
segments using four repeaters (5-4-3
rule).
10Base2
10Base-T
It runs 10 Mbps and uses
CSMA/CD.
It is a star-wired bus topology.
It is still used today due to its
reliability and ease of use.
10Base-T
100Base-T
It uses CMSA/CD as a star-wired bus.
There are three subcategories of
100Base-T networks with different
cable requirements.
The most common is 100Base-TX
(Category 5 or higher UTP).
Switched Ethernet
A switch knows which segment
belongs to which device.
It uses a table stored in memory
to send a packet.
It increases bandwidth by
decreasing traffic and collisions.
Switched Ethernet
Gigabit Ethernet
1000Base-T is a star topology
that uses Category 5 or higher
cabling.
It increases speed by sending
more bits and using 4 pairs of
wires simultaneously.
WLAN
Wireless local area network
It is used when mobility is needed,
but it still must remain connected to
the network.
802.11b or Wi-Fi (11 Mbps)
802.11a or Wi-Fi5 (108 Mbps)
802.11g (54 Mbps)
WLAN
Only wireless network interface cards and
access points are needed.
An access point acts as a link between
wireless and wired networks.
802.11b uses Carrier Sense Multiple
Access with Collision Avoidance
(CSMA/CA).
WLAN
Network Design
Basic rules should be followed for a good
network design.
The switches in an Ethernet network must
be configured in a hierarchy.
Smaller network segments are better than
larger network segments.
Summary
In the early 1980s, the Institute of Electrical and
Electronic Engineers (IEEE) began work on developing
computer network architecture standards. Known as
Project 802, this work estab-lished the foundation for
three network architecture standards that make up over
95 percent of the LANs in use today. These three
dominant standards are Ethernet (802.3), token ring
(802.5), and wireless (802.11).
IEEE Project 802.3 set specifications for a type of local
area network known as Ethernet. Several versions of
Ethernet trans-mit at 10 Mbps, but these are rarely used
today. 10Base5, also called Standard Ethernet, required
the use of thick coaxial cable. Other versions of 10 Mbps
Ethernet were designed to run over fiber optic cable in
specific settings.
Summary (continued)
10Base2 is a version of Ethernet that used to be very
popular and is still used today, although not as
extensively. 10Base2 is a bus topology that uses
contention (CSMA/CD) and requires thin coax cable as
the transmission media. 10Base-T also runs at 10 Mbps,
uses CSMA/CD, and can support a total of 1,024
devices on the network. 10Base-T is a star-wired bus
topology, which means it functions like a bus (in that
each packet makes a stop at every device), but is wired
like a star (with one central controlling device).
Summary (continued)
As faster network architectures were needed beyond 10
Mbps, the IEEE subcommittee began work on creating a
new Ethernet standard called 100Base-T (or Fast
Ethernet). 100Base-T has many of the same basic
characteristics as 10Base-T. It uses CSMA/CD as its
channel access method, the topology is a star-wired bus,
and it continues to use the same basic equipment (such
as hubs in distribution racks with patch panels). The only
new items for 100Base-T networks were 100-Mbps NICs
and 100-Mbps hubs. To increase the speed even more,
a switch (or a switching hub) is used. A switch knows
which segment goes to which network device. This
dramatically increases the band-width on the network
because it decreases the traffic and the number of
collisions. Ethernet networks that use switching hubs are
often called Switched Ethernet.
Summary (continued)
Gigabit Ethernet (or 1000Base-T) is the standard that
most closely resembles 100Base-TX. 1000Base-T is a
star topology that uses Category 5 or higher cabling.
1000Base-T achieves its higher speed by increasing the
number of bits sent and sending data in over all four
pairs of wires simultaneously. 10G Ethernet transmits at
10 billion bits per second.
Summary (continued)
IEEE Project 802.5 set specifications for a type of local
area network known as token ring. Token ring runs at 16
Mbps and uses twisted pair cable in a hybrid star ring
topology. The packets in a star ring do not go directly to
the next device on the ring; instead, they go to a central
hub, which then sends the packet to the next device on
the ring. At the center of a token ring network is a hub,
called the Multistation Access Unit (MAU). Token ring
also has the ability to diagnose and avoid network
problems.
Summary (continued)
Wireless local area networks (WLANs) are found
anywhere a user needs mobility but still must remain
connected to a net-work. The list of components
necessary for a WLAN is short. Only wireless network
interface cards and access points are needed for
communication to take place. A wireless NIC per-forms
the same functions as a wired NIC except an antenna is
used to send and receive radio frequency signals. An
access point (AP) is a device that contains a radio
transceiver (to send and receive signals) along with an
RJ-45 wired network inter-face, which allows it to
connect by cable to a standard wired network.
Networking BASICS
Protocols and Network
Software
Objectives
Explain the OSI reference model.
Define protocol.
List and describe the functions of
TCP/IP.
Explain the functions of client and
server network software.
OSI Reference Model
It was created by the International
Standards Organization (ISO).
It breaks network functions into seven
layers.
It illustrates how each layer provides
specific services and shares with the
layers above and below.
OSI Reference Model
The “flow” between layers goes
down when data is sent and up
when data is received.
The function that each layer
performs is to add or remove
network information on a packet.
OSI Reference Model
Protocols
Protocols are rules for communication.
A combination of protocols is called a
protocol stack or protocol suite.
A connectionless protocol assumes that
packets will arrive.
A connection-oriented protocol establishes
a link between devices.
TCP/IP
Transmission Control
Protocol/Internet Protocol (TCP/IP)
It is the most common protocol suite
used today for LANs as well as the
Internet.
It is composed of several different
protocols.
TCP/IP
Internet Protocol (IP)
The hosts on a TCP/IP network use a
logical address.
This logical address, called the IP
address, is assigned to each host.
IP is responsible for the addressing of
packets.
IP Addressing
An IP address is four bytes (octets).
Each contains eight bits (total of 32
bits in length).
Each octet is a number from 1 to 254.
IP addresses are usually given as
dotted decimal notation.
IP Addressing
Subnet Mask
A subnet mask is used to separate a
network number from the host
number in an IP address.
1 represents a network and 0
represents a host.
Subnet masks are also used to
subdivide networks.
Transmission Control Protocol
(TCP)
TCP is responsible for the reliable
transmission of data from one host to
another.
It is based on port numbers.
The combination of an IP address
and a port number is called a socket.
IPv6
The current version of the IP protocol is
IPv4.
The next generation of the IP protocol is
called IPv6.
340 trillion, trillion, trillion addresses
It uses a fixed packet header size of 24
bytes so that information always appears
in the same place.
Network Software
Software that runs on
the client
Software that runs on
the server
Client Software
Network Driver Interfaces - “Middleman”
between NIC and client’s operating system
software.
Redirector - Sends request to network.
Designator - Keeps track of which drive
letter is associated with which network
device.
Server Software
Network operating system Manages and coordinates users and
requests across the network.
Directory service - Database stored
on the network containing information
about users and privileges to
resources.
Summary
The International Standards Organization (ISO) released
a set of specifications that was intended to describe how
dissimilar computers could be connected together on a
network. Called the Open Systems Interconnections
(OSI) reference model, it illustrates how a network
device prepares data for delivery over the network to
another device and how data is handled when it is
received. The key to the OSI reference model is layers.
The model breaks networking steps down into a series of
seven dif-ferent layers. Each layer cooperates with the
layer immediately above and below it by sending and
receiving information.
Summary (continued)
The rules for communication between network devices
are known as protocols. These protocols are essential
for proper communication to take place between the OSI
reference models on the network devices. Instead of
having just one single proto-col, computer networks
typically employ several different proto-cols that function
together. This combination of protocols is known as a
protocol stack or a protocol suite. Protocols use one of
two different methods for delivering data through a
network: connectionless protocols, which place the
packets on the net-work and then assume that they will
arrive at the destination, and connection-oriented
protocols, which establish a connection between the two
devices before sending any packets. As each packet is
received, an acknowledgment is sent back to the sender.
Summary (continued)
The most common protocol suite used today for LANs as
well as the Internet is Transmission Control
Protocol/Internet Protocol (TCP/IP). Because it is a suite,
TCP/IP is composed of several different protocols that all
function together. Although the TCP/IP suite is
composed of several different protocols, the two major
protocols are those that make up its name, TCP and IP.
The IP is responsible for addressing the packets and
sending them on the correct route to the destination.
Each device on a TCP/IP computer network must have a
unique number. Com-puters on a TCP/IP network use a
logical address instead. This logical address, called an
IP address, is assigned to each host computer.
Summary (continued)
Server software plays a critical role on a computer
network. A network server uses network operating
system (NOS) software. NOS software manages and
coordinates all users and their requests across the
network. A directory service is a database stored on the
network. It contains information about users and network
devices. A directory service also keeps track of the
resources on the network and a user’s privileges to
those resources.