Networks Flashcards
What is a network
A network is more than one computer system connected together allowing for communication and sharing of resources.
LAN
A local area network (LAN) has computer systems
situated geographically close together, usually
within the same building or small site, like a school
or office.
The network infrastructure of a LAN (such as servers
and routers) is usually owned and managed by the
network owner.
WAN
A wide area network (WAN) has computer systems
situated geographically distant to each other,
possibly across a country or even across the world.
WANs often use third party communication
channels, such as connections by internet services
providers like BT or Virgin Media.
Alternative network types
Other network types do exist, such as a Metropolitan Area Network (MAN) for computer systems connected across a town or city or a
Personal Area Network (PAN) for devices connected and used by an individual.
Client server network
Clients make requests to a server, the server manages that request and responds. For
example, if the user (client) makes a request to access www.bbc.co.uk to a web server.
Large services like Amazon and Google will need very powerful servers to handle millions
of requests a second.
The client is completely dependent on the server to provide and manage the
information. The server controls network security, backups and can be upgraded to
manage higher demand
Advantages of client-server networks
The network can be controlled centrally from the server to easily backup data and update software
Hardware, software and resources can be shared
across the network, such as printers, applications and data files.
The network allows for improved scalability, meaning more clients can be easily added to the central server.
Disadvantages of client-server networks
Large amounts of traffic congestion will cause the
network to slow down
If a fault occurs with the server then the whole
network will fail.
IT technicians may be required to manage and maintain the network.
Malware, such as viruses, can spread quickly across the network.
Peer-to-Peer Network
For peer-to-peer networks, data is shared directly between systems without
requiring a central server. Each computer is equally responsible for providing data.
Peer to peer is optimal for sharing files that can then be downloaded.
Advantages of Peer-to-Peer Network
This is a simpler network than client-server to set up as no server is required.
Clients are not dependent on a server.
Perfect for quickly sharing files between systems, such as downloading media files.
Disadvantages of Peer-to-Peer Network
Without a dedicated server there is no central device to manage security or backups.
Backups must be performed on each individual system.
Computer performance will decrease with more devices connected to the network, especially if other machines are slow.
Data Packets
When sending data across a network, files are broken down into smaller parts called data packets.
Whole files are too large to transfer as one unit so data packets allow data to be transferred across a
network quickly.
Each packet of data is redirected by routers across networks until it arrives at its destination. Data
packets may split up and use alternative routes to reach the destination address.
When all the packets have arrived at the destination address the data is reassembled back into the
original file.
Contents of a data packet
Header -
Source address
Destination address
Packet number
Protocol
Payload -
The data itself
Trailer -
A checksum - this is a calculation on the data to see if any errors or
corruption have occurred during transmission.
What is a network topology
Network topology refers to layout of computer systems on a local network.
Devices in a network topology diagram are often called ‘nodes’. Two types of typology are star and mesh
Star topology
Each computer system is connected to a central device, usually a hub or switch.
How it works:
Each computer system is connected to the central hub or switch and transfers its data packets there.
The hub or switch looks at the destination address and transfers the packets directly to the intended computer.
Advantages of the Star Topology
A star topology has improved security because data packets are sent directly to and from the hub / switch in the Centre and not necessarily all devices like in a bus or ring topology.
New systems can be attached directly to the central system so the network doesn’t need to be shut down. System failures of attached computers won’t usually cause complete network failure.
Transfer speeds are generally fast in a star topology as there are minimal network collisions
Disadvantages of the Star Topology
Extra hardware (the hub or switch) is required to be purchased, installed and maintained
If the central system (the hub or switch) fails then the whole network will be unusable until the error is fixed.
Mesh Topology
In a full mesh network, each computer system is connected to every other computer system.
There is also a partial mesh network where only some nodes (e.g. a printer) are connected to every other node
How it works:
Data packets are transferred to the destination address along the quickest path, travelling from node to node.
* If a pathway is broken, there are many alternative paths that the packets can take.
Advantages of Mesh Topology
If one cable or system fails then data packets can take an alternative route and still reach the destination address.
Because of the large possible number of systems and connections, a mesh topology can usually withstand large amounts of data traffic.
New systems can be added to the network without disrupting the entire topology.
Disadvantages of Mesh Topology
Because of the possibly large amount of cables required (especially in a full mesh topology) this network layout can be expensive to install and maintain.
Redundant cabling should be avoided - this is when cables are connected between systems that won’t ever need to communicate.
What are the factors that can affect the performance of a network
. Bandwidth availability
. Number of users at the same time
. Number of data collisions
. Interference
. Distance to signal
. Amount of data to transfer
. Applications being used
. Server / CPU performance
What is bandwidth
Bandwidth is the maximum
amount of data that can be sent
across a network at once.
Packet sending
When sending data across a network, files are broken down into smaller parts called data packets.
Whole files are too large to transfer as one unit so data packets allow data to be transferred across a network quickly.
Each packet of data is redirected by routers across networks until it arrives at its destination. Data packets may split up and use
alternative routes to reach the destination address.
When all the packets have arrived at the destination address the data is reassembled back into the original file.
Wireless Access Point
A Wireless Access Point provides a link between wireless and wired networks.
It creates a wireless local area network that allows WiFi-enabled devices to connect to a
wired network.
Examples of a wireless access point in a public space could be a WiFi or Bluetooth
hotspot, for example a WiFi hotspot in a coffee shop or airport to provide access to the
internet
A wireless access point may be a separate device or built into another device such as a
router.
Router
Routers are used to transfer data packets between networks.
Routers receive data packets and use the IP address in the packet header determine the best route to transmit the data.
Data is transferred from router to router across the internet towards the destination.
A router stores the IP address of each computer connected to it on the network and uses a list called a routing table to calculate the quickest and shortest route to transfer data.
