- Network : System of interconnected computers, telephones, and/or other communications devices that can communicate with one another and share applications data.
-Share peripheral devices, such as printers, scanners, disk drives
-Share software
-Share data and information
-Better communications
-Accessing databases
-Centralized communications
-Security of information, because of improved backup systems
Types of networks : WANs, MANs, & Others
- Wide area network (WAN) : Communications network that covers a wide geographic area, such as a country or the world. Most long-distance and regional telephone companies are WANs. WANs are used to connect local area networks. The best example of a WAN is the internet.
- Metropolitan area network (MAN) : Communications network covering a city or a suburb. Many cellphone systems are MANs.
- Local area network (LAN) : Connects computers and devices in a limited geographic area, such as one office, one building, or a group of buildings close together. LANs are the basis for most office networks, and the organization that runs the LAN owns it. WANs and MANs generally use a common carrier--a telecommunications company that hires itself out to the public to provide communications transmission services--for at least part of its connections. (A home area netwok is a LAN).
Network architecture : How Networks Are Structured
- Client/Server
- Consists of clients, which are computers that request data, and servers, which are computers that supply data.
-File servers act like a network-based shared disk drive.
-Database servers store data but do not store programs.
-Print servers connect one or more and schedule and control print jobs.
-Mail servers manage email.
2. Peer-to-Peer (P2P)
- All computers on the network are "equal" and communicate directly with one another, without relying on servers.
Intranets, Extranets, & VPNs : Use the Internet as their base
- Intranets - use infrastructure and standards of the internet and the web, but for an organization's internal use only.
- Extranets - similar to intranets but allows use by selected outside entities, such as suppliers.
- VPNs (virtual private networks) - use a public network (usually the internet) plus intranets and extranets to connect an organization's various sites but on a private basis, via encryption and authentication; regular internet users do not have access to the VPNs data and information
All use firewalls for security, a system of hardware and/or software that protects the system from intruders.
Network
Components
— all networks have several things in common:
•Wired : twisted-pair, coaxial cable,
fiber-optic cable
•Wireless : infrared, microwave, radio, Wi-Fi, satellite
•Hosts and
Nodes : Client/server network has a host
computer, which controls the network; a node is any device attached to the
network.
•Packets : fixed-length blocks of data for transmission, reassembled after transmission.
Protocols - set
of conventions, or rules, governing the exchange of data between hardware
and/or software components in the network; built into the hardware or software
you are using.
The
protocol
in your
communications software specifies how receiver devices will acknowledge sending devices, a matter called handshaking.
Handshaking
establishes the fact that
the circuit
is available and operational. It also establishes the level of device compatibility and the speed of transmission.
• In
addition,
protocols specify the type of electronic connections used, the timing of message exchanges,
and error-detection techniques.
• Each
packet, or electronic message, carries four types of information that will help
it
get to
its destination;
1.the
sender’s address (IP)
2.the
intended receiver’s address
3.how
many packets the complete message
has been broken into
4.the
number of this particular
packet. The packets carry the data in the protocols that the Internet uses—that is,
TCP/IP
Network
linking
devices:
•Switch—Device that
connects computers to a network; sends only to intended recipients; operates back and forth at
the same time.
•Bridge—Interface device that connects same type of networks.
•Gateway—Interface device
that connects dissimilar networks.
•Router—Device
that directs messages among several
networks, wired or and/or wireless.
•Backbone—Main
Internet highway that connects all
networks in an organization; includes switches,
gateways, routers, etc.
•NIC (Network
interface card)—inserted
in a slot on the motherboard, enables computer to operate as part of a network.
•NOS (network
operating system)—the
system software that manages network activity.
Network
topology: The layout (shape) of a network
•Star – all nodes are connected through a
central network switch
•Ring – all nodes are connected in a
continuous loop
•Bus –
all nodes are connected to a single wire or cable
•Tree –
a bus network of star networks
•Mesh –
messages sent to the destination can take any possible shortest, easiest route
to reach its destination. There must be at least two paths to any
individual computer to create a mesh network. (Wireless networks are often implemented as a mesh, and the Internet is a mesh.)
Star Network
Ring Network
Bus Network
Tree Network
Mesh Network
Ethernet
•Network standard for linking all devices in
a local area network that
describes how
data can be sent between computers and other networked devices usually in close proximity.
•Ethernet
deals with LAN collisions;
Ethernet is
a LAN technology that can be used with almost any kind of computer and that describes how data can be sent
between computers and other networked devices usually in close
proximity.
•The Ethernet communications
protocol is embedded in software and
hardware devices intended for
building a local area network (LAN), and it
is commonly used in star topologies.
