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Computer Science > 1. 3. 3 Networks > Flashcards

1. 3. 3 Networks Flashcards

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1
Q

Characteristics of a Network

A
  • Network, two or more computers are connected together allowing them to transmit data between each other and share peripherals
  • Two types, Local Area Networks (LAN) and Wide Area Network (WAN)
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2
Q

Advantages of Networks

A
  • Users can share files, peripherals, and connections to other networks (internet)
  • Users can access files from any computer on the network
  • Servers can control security, central updates and central backups
  • Allows communication with other people (emailing)
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3
Q

Disadvantages of Networks

A
  • Increased security risks to data
  • Malware and viruses spread easier on networks; one computer affected rest at risk
  • If server fails, computers connected may not work
  • Computers may run slower if large amounts of data is travelling across the network
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4
Q

LANs and WANs

A
  • LAN, small geographical area, Infrastructure/equipment owned (school or home)
  • WAN, large geographical area, Infrastructure/equipment hired from third parties (offices or the internet)
  • Largest WAN is the Internet, this is made up of a series of smaller networks
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5
Q

Protocols

A
  • Set of rules/instructions defining how two computers communicate over a network
  • They are a standard; all devices have designated method of communication with each other no matter the manufacturer
  • Standards are a set of hardware and software specifications that allow manufactures to produce products and services that are compatible with each other
  • Devices must share same protocol in order to exchange information (Same as languages)
  • HTTP (Hyper Text Transfer Protocol), used for web page rendering
  • HTTPS (Hyper Text Transfer Protocol Secure), same as HTTP but encrypted
  • TCP/IP (Transmission Control Protocol/Internet Protocol), networking protocol used in routing packets through networks (Used between two routers for error-free transmission)
  • POP3 (Post Office Protocol) & IMAP (Internet Message Access Protocol), mailing protocols, used for email access
  • FTP (File Transfer Protocol), used for transmission of files over a network
  • SMTP (Simple Mail Transfer Protocol), transfers outgoing emails between servers, also from email clients to servers
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6
Q

The Internet Structure

A
  • Internet is network of networks, allows communication of computers across the globe
  • Continents connected with international backbone cables (usually underwater)
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7
Q

TCP/IP Stack and Protocol Layering

A

Stack of networking protocols work together passing packets during communication, consists of 4 layers, Application Layer, Transport Layer, Network Layer and Link Layer

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8
Q

Application Layer

A
  • Top of stack, specifies protocol to be used, to relate the application being sent
  • For example, if app is browser, selects HTTP, POP3 or FTP
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9
Q

Transport Layer

A
  • Uses TCP to establish end to end communication between source and recipient computer
  • This layer splits data into packets, labelled with packet number, total num of packets and port number being used for communication
  • If packets get lost, this layer on recipient computer requests retransmissions of lost packets
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10
Q

Network Layer

A
  • Adds source and destination IP addresses (IP address + Port Number = Socket address)
  • Routers operate on this layer; it uses IP address to forward the packets
  • Sockets used to specify device the packets sent to, and application being used on device
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11
Q

Link Layer

A
  • Connection between network devices, adds MAC addresses identifying Network Interface Cards of source and destination computer
  • Device on same network, destination MAC address is address of recipient computer
  • Device on different network, destination MAC address is address of the router
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12
Q

Recipients Computer

A
  • The TCP/IP is a stack keep in mind, on recipient’s computer layers go from bottom to top
  • Once destination been reached following occurs
  • MAC addresses are removed by the Link Layer
  • IP Addresses are removed by the Network Layer
  • Port Number is removed, and packets are reassembled at the Transport layer
  • Data presented to recipient in form it was requested in at the Application Layer
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13
Q

MAC Address Vs IP Address

A
  • MAC address unique to every physical device
  • Your MAC address tells me who you are
  • Used in LAN to identify a computer system
  • IP address is an address used to identify a single computer or a network of computers
  • Your IP address tells me where you are
  • Used in WAN to identify “roughly” the location of the target computer system
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14
Q

DNS

A
  • Domain Name System, used to name and organise internet resources
  • Hierarchy, smaller domain separate larger domain with full stop (leeds.gov.uk)
  • TLD stands for Top Level Domain 2LD stands for 2nd Level Domain
  • Domain names easier to remember than IP addresses
  • Used to link servers across the world, domain name system server (DNS server) translates domain names into IP addresses when accessing a website
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15
Q

DNS process

A
  • User requests a URL via a browser (www.bbc.co.uk)
  • Browser sends domain name to DNS
  • DNS matches domain name to an IP address, returns this to browser
  • GET request for webpage sent to web server using IP address
  • Requested web page returned to client’s web browser
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16
Q

Network Communication- Data Packets

A
  • Packets are segments or data that are made up of a Header, Payload and Trailer
  • Header which contains IP addresses, Protocol, Order of packets and TTL
  • Sender and recipient IP addresses, allows packet to be delivered to correct destination as well as allowing recipient to trace where packet came from
  • Protocol being used, allows recipient computer to understand how to interpret data
  • Order of packets, packets reconstructed on arrival in appropriate order specified here
  • Time To Live (TTL) / Hop Limit, tells packet when to expire so does not travel forever
  • Payload is the raw data to be transmitted
  • Trailer contains a checksum to detect if any errors occurred during transmission
17
Q

Network Communication- Circuit Switching

A
  • Method of communication, direct link between two devices, maintained for duration of conversation between devices
  • Data arrives in logical order, quicker reconstruction of data
  • Two users hold a call without delay in speech
  • Bandwidth (Max capacity data can be transmitted, 40mbps for example) wasted in periods where data not being sent
  • Devices must transfer and receive data at same rate
  • Electrical interference, may produce corrupt or destroy data
  • Sections of network cannot be used till transmission complete
  • Telephone for example
18
Q

Network Communication- Packet Switching

A
  • Method of communication, packets sent across network through most efficient route (varies between packets)
  • Checksum ensures data arrives intact
  • Multiple routes, one breaks another used
  • Packets can be transferred over large network, global communication
  • Time spent constructing reconstructing packets (delay)
  • Must wait for all packets to arrive before data can be received
  • Sending an email for example
19
Q

Network Security and Threats

A
  • Network security we look at Firewalls, Proxies, Encryption and Other Preventions
  • Network threats we look at a variety looked at in another flashcard
20
Q

Firewalls

A
  • Application that uses packet filters (rules) to prevent unauthorised access to a network
  • Packet filtering limits access in accordance to administrator rules and policies
  • When access denied, packet dropped or rejected
  • Rejected packet sends alert to sender, notify them of error
  • Dropped packet does not send alert to sender
21
Q

Proxies

A
  • Application that acts as an intermediary, collects and send data on behalf of the user
  • Privacy of user is protected, remain anonymous
  • Can cache frequently visited websites, faster load times
  • Can reduce overall web traffic
  • Used by administrators to prevent access to sensitive or irrelevant info at school or work
22
Q

Encryption

A
  • Way of keeping data secure when it is being sent across a network
  • Makes data unreadable if intercepted, encrypted and decrypted with keys
  • Without keys, data is useless to hackers
23
Q

Other Preventions

A
  • Up to date security and anti-virus
  • Trained staff, levels of access, strong passwords created
  • Policies created that must be followed
24
Q

Threats

A
  • Malware such as Viruses, Worms, Keyloggers, Trojan, SQL injections
  • Spyware, adware
  • Social engineering such as Pharming, Phishing, Baiting, Weak passwords
  • Hackers, Denial of service, Data interception
25
Q

Network Hardware

A

Network Hardware we look at are NIC, Modem, Switch, WAP, Routers, Hub, Gateway and Cables.

26
Q

Network Interface Card (NIC)

A
  • Required to connect device to network, usually built into device, assigns MAC address to each device
  • 48-bit value coded into device, usually written as 12-digit hex number
  • Allows both wired and wireless communications between computers on a LAN or a large-scale network using the Internet Protocol (IP)
27
Q

Modem

A
  • Transforms digital info from computer into analogue signals (can be transmitted through wires)
  • Can also do vice versa (Analogue signals to digital data that computer understands)
  • Does this by modulating and demodulating electrical signals from phone lines, coaxial cables or other types of wiring
28
Q

Switch

A

Allows multiple devices to connect to a network, directs flow of data across a network, data received from sender device directly transmitted to target device. Switches typically faster than hubs.

29
Q

Wireless Access Point (WAP)

A

Allows device to connect to network, commonly combined with router/modem or hub to enable internet access

30
Q

Routers

A

Connect two or more networks together, allow private home networks to connect to the internet

31
Q

Hub

A

Allows multiple devices to connect to a network, broadcasts transmissions it receives to all devices connected, can make network susceptible to traffic, slower than switches.

32
Q

Gateway

A

Used when protocols not the same between networks, translates protocols so networks can communicate with each other, removes header from packets before adding data to packets using new protocol.

33
Q

Cables

A
  • Main methods of connectivity are wired and wireless
  • Choices of wired cable are twisted pair, coaxial and fibre optic
  • Twisted pair cable made up of pair of insulated copper wires
  • Affected by magnetic fields but more affordable than other two, low bandwidth (used for telephone networks)
  • Coaxial cables, made up of solid conductor wire, layer of insulation, grounding conduction and a layer of exterior insulation, affected by magnetic field but to lesser extent than twisted pair
  • Moderate bandwidth fair price, used for computer network connections, digital audio and cable television
  • Fibre optic, made up of optical fibres bundled together into single cable (either glass or plastic fibres)
  • Use light rays, high bandwidth, most expensive, used in long distance connections between cities and countries as well as organisations transmitting large volumes of data
34
Q

Client-server

A
  • Terminals (clients) connected to a server
  • Server is a powerful, central computer, stores all info and resources, better processing power than terminal
  • Client makes a request to a server for data, connections and other services
35
Q

Advantages and Disadvantages of Client-server

A
  • More secure, data only in one location
  • Central backups and updates, no need for individual backups and updates
  • Data and resources can be shared between clients (Files, Printer etc)
  • Relatively expensive to set up
  • Terminal’s server dependent (server is single point of failure if it fails users lose network access)
  • Trained staff required to maintain the server
  • Suited for organisations with large number of computers that may need access to same info
36
Q

Peer-to-peer

A
  • Computers (peers) connected to each other, can share files
  • Each device acts as a client and server, can request and provide resources
  • Peer is equal to all other peers
  • Used in piracy since it is almost impossible to trace the origins of the files
37
Q

Advantages and Disadvantages of Peer-to-peer

A
  • Cheaper to setup compared to client-server
  • Allows the sharing of resources, easy to maintain
  • Not dependent on central server (One terminal breaks rest fine)
  • Specialist staff not required
  • Impossible to trace origins of files
  • Backups must be done individually, poorer security
  • May be difficult to locate resources (Difficult to maintain well-ordered file store)

Computer Science (28 decks)

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