Transcript Unit 3

Basic Computer Application
Unit3: Network Basic
Bo Li (李波)
[email protected]
Xi’an Jiaotong University
Basic Computer Application
Network Basics

Network Classifications

Communication Systems

Communication Channels

Network Topology

Network Nodes

Communication Protocols

LAN-Ethernet
Basic Computer Application
Networking
Basic Computer Application
Network Classifications

Personal
Area
interconnection
devices
Network
(PAN)
–
of
personal
digital

Neighborhood
connectivity
buildings

Local
Area
Network
(LAN)
–
usually
connects computers in a single building

Metropolitan Area Network (MAN) – public
high-speed network with range of about 50
4
miles
Area
Network
spread
over
(NAN)
–
several
Basic Computer Application
Communication Systems

Networks can be classified in many
ways; as a network user, you’ll want
to keep in mind the idea of control
and how it affects your privacy and
security

A network links things together

A communication network (or
communication system) links devices
together to data and information can
be shared among them
Basic Computer Application
Communication Systems

In 1948, Claude Shannon, and engineer at Bell
Labs, published and article describing a
communication system model applicable to networks
of all types

His diagram illustrates the essence of a network:
Basic Computer Application
Communication Channels

A communication channel is the medium
used to transport information from one
network device to another

Wired channels


transport data through wires and
cables
Wireless channels

transport data from one device to
another without the use of cable or
wires
Basic Computer Application
Communication Channels
twisted
pair
wires
telephone
land
lines,
coaxial
cables
cable
television
networks,
Category
6
cables
LANs
fiber-optic
Basic Computer Application
Communication Channels

When you set up a wired connection,
you don’t have to worry about hackers
intercepting your data from outside
your house

There are ways to tap into a wired
network, but they require physical
access to the cable or fairly
sophisticated snooping equipment
Basic Computer Application
Communication Channels
Basic Computer Application
Communication Channels
Basic Computer Application
Communication Channels

The most widespread wireless channels for communication
networks are radio signals and microwaves

Most wireless channels transport data as RF signals
commonly called radio waves

RF signals are sent and received by a transceiver (a
combination of a transmitter and a receiver) that is
equipped with an antenna
Basic Computer Application
Communication Channels

Microwaves (the waves themselves, not
your oven!) provide another option for
transporting data wirelessly

Microwaves are electromagnetic signals
that can be aimed in a single
direction and have more carrying
capacity than radio waves

Microwave installations usually
provide data transport for large
corporate networks
Basic Computer Application
Communication Channels


Advantages of wireless

Mobility

No unsightly cables

Less susceptible to power spikes
Disadvantages of wireless

Speed

Range

Security

Licensing
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Basic Computer Application
Communication Channels

Bandwidth is the transmission capacity
of a communication channel

Network channels that are capable of
moving at least two megabits of data
per second (2 Mbps) are classified as
broadband

Channels slower than 2 Mbps are
classified as narrowband
Basic Computer Application
Network Topology

In the context of communication networks, topology refers to
the structure and layout of network components, such as
computers, connecting cables, and wireless signal paths

Point-to-point topology refers to the process of peripheral
devices connecting to a host device using expansion ports,
USB cables, or Bluetooth

Star topology connects multiple devices
either as a full mesh or a partial mesh

The less popular bus topology connects devices in a linear
sequence
to
each
other,
Basic Computer Application
Network Topology
Basic Computer Application
Network Nodes

Any device on a network is called a
node

Devices on a network are classified as
DTEs or DCEs

DTE stands for data terminal equipment and
can be any device that stores or generates
data

DCE stands for data communication
equipment; these devices control the speed
of data over networks, convert signals from
cables to wireless, check for corrupted
Basic Computer Application
Network Nodes

A router is a device
that controls the flow
of data within a
network and also acts
as a gateway to pass
data from one network
to another

A modem contains
circuitry that
converts the datacarrying signals from
a digital device to
signals that can
travel over various
communications
Basic Computer Application
Network Devices
Chapter 5: LANs and WLANs
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Basic Computer Application
Network Nodes

DCEs such as
repeaters,
switches, and
hubs can
extend the
range of your
home network
Basic Computer Application
Can various network be
interconnected?

Same networks can be connected by a
device called repeater

Two similar networks can be connected
by a device called a bridge (or switch)

Gateway is a generic term for any
device or software code used to join
two networks

Router(to connect your home LAN to the
Internet)
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Basic Computer Application
Clients, Servers, and Peers

Chapter 5: LANs and WLANs
Network
devices
servers
can

Application server

File server

Print server
function

Networks that include one or
operate in client/server mode

Peer to Peer(without server)
as
clients
more
or
servers
23
as
can
Basic Computer Application
Communication Protocols

In the context of
networks, a
communication protocol
refers to a set of
rules for efficiently
transmitting data from
one network node to
another

This process is called
handshaking

Networks use more than
one protocol, and the
collection of protocols
for a network is
referred to as a
Basic Computer Application
Protocol Stack
Basic Computer Application
Basic Computer Application
LAN

LAN technologies are standardized by the
Institute of Electrical and Electronics
Engineers (IEEE) Project 802 – Local
Network Standards

IEEE 802.3 specifies the standards for
Ethernet wired local area networks


How devices physically signal each other, how
devices “share the wire in the wall”, etc.
Ethernet is the de facto standard for
wired LAN in use today
27
Basic Computer Application
Communications Protocols

Rules (Standards) for efficiently and
effectively transmitting data from one
network node to another. They define
how to:

Divide messages into packets

Affix addresses (of the nodes) to packets

Initiate transmission (arbitrate access)

Regulate flow of data

Check for transmission errors

Acknowledge receipt of transmitted data (in
Basic Computer Application
Why not just send an entire
file?

Circuit-switching
technology vs.

Packet switching
technology


The Internet

Voice over IP (VoIP)
Advantages of one
vs. the other?
Chapter 5: LANs and WLANs
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Basic Computer Application
Packet
Chapter 5: LANs and WLANs

When you send a file ,you might suppose
that it is transmitted as an entire unit
to its destination?

File is
pieces

A packet is a “parcel” of data that is
sent across a computer network

Each packet contains the address of its
sender,
the
destination
address,
a
30
sequence number, and some data(payload)
actually
choppd
up
into
small
Basic Computer Application
Ethernet Frame Structure
Type
IEEE 802.3 Ethernet frame
64 – 1518 bytes in length




Preamble: 8 bytes
 7 bytes with pattern 10101010, followed by one
byte with pattern 10101011 (frame delimiter)
 used to synchronize receiver, sender clock
rates
Addresses: 6 bytes, frame is received by all
adapters on a LAN and dropped if address does not
match
Type (Length): 2 bytes, length of data segment
(min. 46 bytes)
CRC (Cyclic Redundancy Check): 4 bytes, created by
sender, checked by receiver, if error
detected,
the frame is simply dropped
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Basic Computer Application
Address

Every packet that travels over a packetswitched network includes the address of
its destination device

Most physical devices have more than one
address

A MAC address is a unique number assigned
to a network interface card when it is
manufactured

An IP address is a series of numbers used
to identify a network device in an
internet
Basic Computer Application
HomePNA and
Powerline Networks

Chapter 5: LANs and WLANs
HomePNA
(HPNA)
networks
existing telephone wiring to
network devices


utilize
connect
Special NICs and cables are required
Powerline networks transmit data over
power lines as low-frequency radio
waves
33
Basic Computer Application
Ethernet


Chapter 5: LANs and WLANs
Simultaneously broadcasts data packets
to
all
network
devices
(a
star
topology)

IEEE 802.3 defines the Ethernet protocol

CSMA/CD protocol used to share the channel
Vary in speed from 10Mbps to 10Gbps
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Basic Computer Application
Ethernet-CSMA/CD
On an Ethernet, data
travels on a first
come, first served
basis. If two
workstations attempt
to send data at the
same time, a
collision occurs.
That data must be
resent.
CSMA-Carrier Sense Multiple Access with Collision Detection
Chapter 5: LANs and WLANs
35
Basic Computer Application
Summary

Network Classifications

Communication Systems

Communication Channels

Network Topology

Network Nodes

Communication Protocols

LAN-Ethernet
Basic Computer Application
Thank YOU
Bo Li (李波)
[email protected]
Xi’an Jiaotong University