1.3 Computer Networks Flashcards
OCR GCSE Computer Science J277
Network
a group of devices connected together, either using cables or wirelessly, so that they can communicate with each other and share resources.
Topology
the physical or logical arrangement of connections and devices in a network.
Networks can be structured in different ways called topologies.
Network standards and protocols
allow a wide range of devices from different manufacturers to communicate with each other.
Network performance
The speed at which a network operates at it is most important to users.
Network performance is affected by:
Bit rate
Bandwidth
Number of devices
Latency
Benefits of networks
Shared files
Multi-user access
share devices
central backup
central deployment
NIC
Network interface card. Hardware built into the device
A network interface controller (NIC) is a component that allows a device to connect to a network.
Wired and wireless versions are available.
Nearly all new computers have an NIC built directly into the motherboard.
Network manager
in larger organisations, makes decisions about the network and run its day to day in the IT team
LAN
Local Area Network is a single network that is located in a small geographical area such as someone’s home, an office, or to cover a school site. Uses its own infrastructure, cabling and equipment.
WAN
A Wide Area Network (WAN) is a network that connects two or more networks over a wider geographical area. WANs connect LANs together to form larger networks. Uses third party infrastructure such as telephone lines, satellites.
Public telecoms companies
Many Wide Area Networks (WANs) will make use of public telecommunications infrastructure. These are links managed by other companies.
Organisations that run their own WANs will often lease (loan) bandwidth from these companies, who in turn maintain telephone cables, ducts, cabinets and exchanges on a national network.
Examples of these companies:
Openreach (owned by BT)
Virgin Media
Data collisions
In a LAN, if two or more devices are attempting to transmit at the same time along the same channel, data collisions occur, and the data has to be retransmitted.
This is like two people talking on the telephone at the same time.
Bit rate
the measure of the amount of data (in bits) that is being transferred per second. The abbreviation bps is commonly used in place of bits/s, which is the standard unit of measurement.
Because communication channels carry millions or billions of bits per second, the unit is usually prefixed.
Bandwidth
is the theoretical maximum amount of data that a communications channel can carry at one time.
Latency
the delay between the time a signal is transmitted and the time a signal is received.
Client-server
allow you to access your files and emails from any authorised device.
- A client sends a request to a server
- The server processes the request
- The server sends a response back to the client
a networking architecture where devices are designated as clients or servers. Clients make requests for services from servers that respond to these requests.
These classifications explain the role that devices have within a network, and are not related to whether the network is a LAN or a WAN.
Peer-to-peer
(P2P) is a networking architecture where all devices have equal status and can share resources directly with each other
In a peer-to-peer network, there are no central servers. Every computer can be configured to shares its resources.
Peers communicate directly with each other. Computers must be switched on to share resources.
The owner of each device gives permission to access some or all of the device’s resources.
These classifications explain the role that devices have within a network, and are not related to whether the network is a LAN or a WAN.
server
a powerful computer which provides services or resources required by its clients
A server is a program on a computer that shares resources with or provides services to any authorised client.
Most servers will run 24 hours a day, 7 days a week, so that the client can send a request for resources at any time.
In large organisations servers will usually run on high-powered, dedicated, computers that are able to handle a lot of requests at any one time.
In smaller organisations, multiple servers may run on a single computer system.
client
a computer that requests services or resources provided by the server (such as your desktop computer, phone, laptop or tablet)
A client is a program that typically runs on a device used by an end-user, such as a laptop or a mobile phone.
Email server
Store and forward emails. Some services filter out spam
Print server
Provide printing services across the network and manage print queues
Database server
Store databases, run queries and allow data to be manipulated
File server
Store and provide files
Web server
Store and provide web pages
WAP
Wireless Access Point or Wireless AP enables wireless devices to connect to a LAN.
It creates a wireless network using radio waves. A Wi-Fi enabled device can connect to it to communicate with the network or Internet.
Router
A router is a networking device with two or more interfaces, each in a different network.
You will find routers where communication happens between two separate networks, that are required to connect.
A router examines the destination IP address of incoming packets (data) to decide which interface to use to forward the packet.
Network Access Device
In your home network, the network access device (sometimes called the home hub) that is typically provided by your Internet Service Provider (ISP) will incorporate a router to connect your home network to that of the ISP (WAN).
Network access devices typically contain:
A wireless access point (WAP)
A switch to allow all the wired devices to be networked
A router to act as the network gateway and direct external requests out of the LAN
Media to transmit data
such as an ADSL (telephone) cable or even fibre-optic. If there is no cable, the external connection may be 3G/4G/5G or even satellite.
Core Routers
On the wider internet, core routers are used to forward packets to their destination along the backbone of the internet.
These routers examine the destination of each packet and consult a routing table of known networks.
The table indicates which connection is best to use to send the packet towards it intended destination.
Hub
A hub will simply repeat messages to all connected devices.
This is inefficient because it sends data to places other than its intended destination.
a hub is a network device that is used to connect devices on a LAN. It is used to simplify cabling systems and acts as a repeater.
When data arrives at a port, it is broadcast to the devices connected to every other port.
Switch
a network component that is used to connect devices on a LAN. A switch learns which device is connected to each of its ports to that it can switch traffic directly to the correct recipient.
A switch only sends messages to its intended destination device.
The switch builds up a table with the MAC address of every device that its connected to each of its ports.
When a signal is received, the data is analysed to determine the destination MAC address. The data is then sent to the port connected to the device with the MAC address.
MAC Address
Each NIC has a unique identifier called a Media Access Control (MAC) address.
is a unique hexadecimal identification number assigned to every network interface card used in networked devices.
It is 48 bits long, and it usually referred to in hexadecimal notation, for example:
cd:f1:24:e4:89:a1
The MAC address is allocated by the manufacturer and cannot be changed.
UTP
Unshielded Twisted Pair cable. A type of cable where two conductors are twisted together to reduce interference. Also known as Ethernet cable.
Ethernet Cable
An unshielded twisted pair (UTP) cable is a common type of cable for connecting computers. It is often referred to as an ‘Ethernet cable’ thought it is not technically an Ethernet cable, it can support Ethernet.
Fibre-Optic Cable
a cable that can be used to transport electromagnetic waves in the infrared region. These waves are modulated to carry digital data at high speeds over long distances.
Fibre-optic cables transmit data as pulses of light through a single strand of glass fibre which can transmit large amount of data over long distances and without interference.
Fibre-optic cables support data transfer speeds of up to 10 gigabits per second and can transmit data for up to 2km.
Coaxial Cable
a cable made up of an inner conductor and an outer conducting shield, separated by an insulator.
Coaxial cables have numerous issues with poor connections, and these issues, combined with the development of cheaper alternatives and improved electronics, has led to this type of cable falling out of use.
The internet
The internet is a global system of interconnected computer networks
The internet facilitates a wide range of services, including:
The World Wide Web
Email
Internet telephony (VOIP)
File sharing (FTP)
Communication backbone
At the heart of the internet is the communication backbone - fibre-optic cables and industrial routers that move data at superfast speeds.
Most of the backbone is provided by giant telecommunication companies.