Chapter 9A
Network Definition
• Set of technologies (hardware, software,
media) that connects computers
• Allows communication and collaboration
between users
• Data Communications:
– The electronic transfer of information between computers.
– Information can be text, voice, audio and video traffic.
Network Definition
• When most people think of a network,
• they imagine several computers in a
single location
• sharing documents and devices such as
printers.
• But a Network can include all the
computers and devices in a department,
a building , or multiple buildings,
The Uses of a Network
• Network allows many users to access
shared data and programs instantly.
• Data and programs are stored on a
network and are shared.
• Individual users can reduce the need for
programs on their computers.
The Uses of a Network
• Simultaneous access to data
– Data files are shared
• Access can be limited
– Shared files stored on a server – Software can be shared
• Site licenses
• Network versions • Application servers
The Uses of a Network
• Simultaneous access to data:
– There are moments in business when
several workers may need to use the same data at the same time
– A good example is a company’s quarterly sales report which needs to be viewed an updated by several managers.
– Without a network, workers must keep separate copies of data store on their computers.
The Uses of a Network
• Simultaneous access to data:
– When data is modified on one computer, others become outdated.
– It becomes difficult to determine which copy of the data is most current.
• Solution:
– Companies can solve this problem by storing commonly used data at central location called Network server.
The Uses of a Network
• Network Server:
– A central computer with a large storage device and other resources that all users can share.
– If the server stores data files for users to access, It is also called a file Server.
– The business can store a single copy of data file on the server that employees can access
– If one user makes a change to the file,
Sharing Data
File server contains documents used by other computers.
The Uses of a Network
• Application Server: Most office
workers also use the software or
programs from servers.
• If an environment where PCs are not
networked, a separate copy of each
program must be installed on every
computer.
• This can be costly for two reasons:
– Software can be expensive ( buy many copies) – Installing and configuring a program on different
The Uses of a Network
• Site Licenses: purchase site license for
application:
• A business buy a single copy of an application and then pays the developer for a license to
copy the application onto a specified number of computers.
• Under a site license each user has complete, individual copy of the program running on his PC
• Thus business generally pays less money then it would by purchasing a complete copy of the
The Uses of a Network
• Network versions:
– Only one copy of the application is stored on the server.
– Connect user’s computers to a central server
– And enable users to share a network version of a program.
– Workers need to load program from server into the RAM of their on desktop.
The Uses of a Network
• Shared peripheral device
– Printers and faxes are common shares – Reduces the cost per user
– Devices can be connected to the network – Print servers control network printing
The Uses of a Network
• Personal communication
– Email • Instantaneous communication – Conferencing • Tele conferencing • Video conferencing • Audio conferencing• Data-conferencing (shared white boards, application sharing)
– Voice over IP
The Uses of a Network
• VOIP: System’s bypass the need for the
cost of regular telephone service by
using the company’s internal network to
send and receive phone calls.
• It transmits the sound of your voice over
a computer network
• Uses Internet protocol (IP) rather than
sending the signals over traditional
The Uses of a Network
• Easier data backup
– Backup copies data to removable media – Server data backed up in one step
– Employees can access storage device through a network.
Common Network Types
• Local Area Network (LAN)
– Data communication system
– Contains printers, servers and computers – Systems are close to each other
– Contained in one office or building – Physically connected using cables
Common Network Types
• Wide Area Networks (WAN)
– Two or more LANs connected – Over a large geographic area
– Typically use public or leased lines
• Optic fibers • Satellite
– The Internet is a WAN
– For example a company may have head office in one city and marketing offices in different citites.
Hybrid Network Types
• Campus Area Networks (CAN)
– A LAN in one large geographic area
– Resources related to the same organization – Each department shares the LAN
Hybrid Network Types
• Metropolitan Area Network (MAN)
– Large network that connects different organizations
Hybrid Network Types
• Home Area Network (HAN)
– Small scale network (Home network)
– Connects computers and entertainment appliances: • Printers • Telephone • VCR’s • DVDs • Televisions • Video games
Hybrid Network Types
• Personal Area Network (PAN)
– Very small scale network
– Range is less than 2 meters
How Networks Are Structured
• Server based network
– Node is any network device
– Servers control what the node accesses – Users gain access by logging in
– Server is the most important computer – Users gain access to files, printers and
other network based objects
– Users must log-on to the network to access resources.
How Networks Are Structured
• Client/Server network
– Nodes and servers share data roles – Nodes are called clients
– Individual computers share the processing and storage workload with central server. – Servers are used to control access
– The network requires special software for the nodes and server.
How Networks Are Structured
• Client/Server network
– Example: Database software
• Accessed by many computers on the network. • Database is stored on the network server
• DBMS: allows the users to work with the database on server
• Clients machine have DBMS to access DB
How Networks Are Structured
• Peer to peer networks (P2PN)
– All nodes are equal
– Nodes access resources on other nodes – Each node controls its own resources
– Most modern OS allow P2PN i.e.
• Windows 9x, Windows 2000 professional • Windows Me, Windows XP, MAC OS
– Enables the users to set a simple peer-to-peer network using no other
Network Topologies
• Topology: Important feature of LAN
– Logical layout of wires and equipment – Network designs considers:
• Distance b/w computers
• The type of computers and cabling • The speed at which data must travel • Cost of setting up network
– Choice affects
• Network performance • Network size
Network Topologies
• Packets
– Pieces of data transmitted over a network
• Packets are created by sending node • Data is reassembled by receiving node
– Packet header
• Sending and receiving address
• Network reads each packet’s header to determine where to send it.
– Packet payload
Network Topologies
• Topology:
• In the Internet environment Packets are called data grams.
Network Topologies
• Bus topology
– Also called linear bus
– One wire connects all nodes – Terminator ends the wires – Advantages
• Easy to setup
• Small amount of wire
– Disadvantages
Bus Topology
Network Topologies
• Star topology
– All nodes connect to a hub
• Packets sent to hub
• Hub sends packet to destination
– Advantages
• Easy to setup
• One cable can not crash network
– Disadvantages
• One hub crashing downs entire network • Uses lots of cable
Network Topologies
• Ring topology
– Nodes connected in a circle – Tokens used to transmit data
– Last node connects to first node – Advantages
• Time to send data is known • No data collisions
– Disadvantages
Network Topologies
• Mesh topology
– All computers connected together
– A cable runs from every computer to every other computer.
– Internet is a mesh network
– Advantage
• Data will always be delivered
• If one connection goes down , there are other ways to route the data
– Disadvantages
Network Media
• Links that connect nodes
• Choice impacts
– Speed – Security – Size
Wire Based Media
• Twisted-pair cabling
– Most common LAN cable
– Called Cat5 or 100BaseT
– Four pairs of copper cable twisted
– May be shielded from interference
– Speeds range from 1 Mbps to 1,000 Mbps
Wire Based Media
• Coaxial cable
– Similar to cable TV wire
– One wire runs through cable – Shielded from interference – Speeds up to 10 Mbps
Wire Based Media
• Fiber-optic cable
– Data is transmitted with light pulses
– Glass strand instead of cable
– Immune to interference – Very secure
– Hard to work with – Speeds up to
Wireless Media
• Data transmitted through the air
• LANs use radio waves
• WANs use microwave signals
• Easy to setup
Network Hardware
• Network interface cards
– Network adapter
– Connects node to the media
Network Hardware
• Network linking devices
– Connect nodes in the network – Cable runs from node to device
Network Hardware
• Hubs
– Center of a star network
– All nodes receive transmitted packets – Slow and insecure
Network Hardware
• Switches
– Replacement for hubs
– Only intended node receives transmission – Fast and secure
Network Hardware
• Bridge
Network Hardware
• Router
– Connects two or more LANs together – Determine best route for the packet
Network Cabling
• Cabling specifications
– Bandwidth measures cable speed
• Typically measured in Mbps
– Maximum cable length
Network Cabling
• Ethernet
– Very popular cabling technology – Maximum bandwidth 10 Mbps
Network Protocols
• Language of the network
– Rules of communication – Error resolution
– Defines collision and collision recovery – Size of packet
