The language of computer networks
- Computer network – an interconnection of computers and computing equipment using either wires or radio waves over small or large geographic areas
- Local area network – networks that are small in geographic size spanning a room, floor, building, or campus
- Metropolitan area network – networks that serve an area of 1 to 30 miles, approximately the size of a typical city
- Wide area network – a large network that encompasses parts of states, multiple states, countries, and the world
- Personal area network – a network of a few meters, between wireless devices such as PDAs, laptops, and similar devices
- Campus area network – a network that spans multiple buildings on a business or school campus
- Network cloud – a network (local or remote) that contains software, applications, and/or data
- Data communications – the transfer of digital or analog data using digital or analog signals
- Telecommunications – the study of telephones and the systems that transmit telephone signals (becoming simply data communications)
- Voice network – a network that transmits only telephone signals (essentially xtinct)
- Data network – a network that transmits voice and computer data (replacing voice networks)
- Network management – the design, installation, and support of a network, including its hardware and software
The Big Picture
of Networks
Networks are
composed of many devices including:
- Workstations (computers, tablets, wireless phones, etc)
- Servers: the computers that store network software and shared or private user files
- Network switches: the collection points for the wires that interconnect the workstations
- Routers (LAN to WAN and WAN to WAN): the connecting devices between local area networks and wide area networks such as the Internet
- Network nodes: the computing devices that allow workstations to connect to the network and that make the decisions about where to route a piece of data
- Subnetwork: the nodes and transmission lines, collected into a cohesive unit
Common Examples
of Communications Networks
1.
The
desktop computer and the internet
o
At
work or at school – connection is typically some form of Ethernet
o
At
home, for some, a dial-up modem is used to connect user’s microcomputer to an
Internet service provider
o
Technologies
such as DSL and cable modems are replacing dial-up modems
2.
A
laptop computer and a wireless connection
o
Connection
is typically some form of wireless Ethernet
o
Laptop
wirelessly communicates with a wireless router or wireless access point
o
Wireless
router is typically connected to a wired-network
3.
Cell
phone networks
o
One
of the most explosive area of growth in recent years
o
Large
number of cell phone towers are tied to some form of networks, allowing us to
send text messages or call around the world
o
When
a user talks into their cell phone or send text message, the data is
transmitted across the network to a telephone company building, the telephone
company then transfer the cell phone’s date over the public network or through
a connection onto the internet.
4.
Other
common network system
o
Industrial
sensor-based systems
- Not all local area networks deal with
microcomputer workstations
- Often found in industrial and
laboratory environments
- Assembly lines and robotic
controls depend heavily on sensor-based local area networks
o
Mainframe
systems
- Predominant form in the 1960s and 1970s
- Still used in many types of businesses
for data entry and data retrieval
- Few dumb terminals left
today – most are microcomputers with terminal emulation card, a web browser and
web interface, Telnet software, or a thin client
o
Satellite
and microwave networks
- Typically long distance
wireless connections
- Many types of applications including
long distance telephone, television, radio, long-haul data transfers, and
wireless data services
Network
Architectures
o
A
network architecture or communications model, places the appropriate layers and
pieces.
o
Each
layer in the model defines what services either the hardware or software
provides
o
There
are two network architectures or models: TCP/IP protocol suite and OSI model
1.
The
TCP/IP protocol suite
a.
Application
layer
i. Where the application using the network
resides
ii. Common network applications include web
browsing, e-mail, file transfers, and remote logins
b.
Transport
layer: Performs a series of miscellaneous functions (at the end-points
of the connection) necessary for presenting the data package properly to the
sender or receiver
c.
Network
(Internet or internetwork or IP) layer: Responsible for creating, maintaining
and ending network connections
i. Transfers data packet from node to node
(e.g. router to router) within network
d.
Network
access (data link) layer: Responsible for taking the data and transforming it
into a frame with header, control and address information, and error detection
code, then transmitting it between the workstation and the network
e.
Physical
layer:
i. Handles the transmission of bits over a
communications channel
ii. Includes voltage levels, connectors,
media choice, modulation techniques
2.
The
OSI Model
a.
Application
layer: Equivalent to TCP/IP’s application layer
b.
Presentation
layer: Responsible for “final presentation” of data (code conversions,
compression, encryption)
c.
Session
layer: Responsible for establishing “sessions” between users
d.
Transport
layer: Equivalent to TCP/IP’s transport layer
e.
Network
layer: Equivalent to TCP/IP’s network layer
f.
Data
link layer: Responsible for taking the data and transforming it into a frame
with header, control and address information, and error detection code
g.
Physical
layer: Handles the transmission of bits over a communications channel
i. Includes voltage levels, connectors,
media choice, modulation techniques
3.
Logical
and physical connections
a.
A
logical connection is one that exists only in the software, while a physical
connection is one that exists in the hardware
b.
In a
network architecture, only the lowest layer contains the physical connection,
while all higher layers contain logical connections
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