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Computing A level > Networks > Flashcards

Networks Flashcards

1
Q

Mail server*

A

Acts as a virtual post office, for all incoming and outgoing mail. They route mail according to their database of local network user’s email address’. They also STORE MAIL UNTIL IT CAN BE RETRIEVED

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2
Q

TCP/IP

A

A set of protocols acting together as four layers connected, passing incoming and outgoing data up and down the layers during network communication. It enables communication with any other computer connected to the internet, regardless of its location

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3
Q

Each layer in TCP IP…

A

Only communicates with adjacent layers.
Envelopes/ unwraps with more packet data.
Has different roles, with various protocols

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4
Q

Application layer

A

Uses protocols relating to the application being used to transfer data over a network (e.g. Internet)
E.g. Browser may use ftp, or http or POP3 as the high level protocol

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5
Q

Transport layer

A

TCP protocol used to establish end to end connection with recipient computer.
Splits data into packets, labels with packet sequence number, total packet number and port number (ensuring correct application handles packets.)
If packets go astray, retransmission requested .
Receipt of packets acknowledged

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6
Q

Network layer is aka

A

IP layer/internet layer

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7
Q

Network layer*

A

Adds source and destination IP addresses (port number + IP address = socket)
Router operates on this layer, forwarding packet onto correct destination according to IP addresses
More ERROR checking
router is hardware that operates at this layer

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8
Q

Link layer

A

LINK LAYER PROTOCOL used e.g. Ethernet
Physical connection between network nodes
Mac addresses are added, identifying NICs of the source and destination computer (where the packets are to be sent to next)- initially of the first router being sent to, unless same network
So once correct network found, correct hardware then can be found
Sent down CABLE
Cable and NIC are hardware that operate at this layer

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9
Q

Receiving end of TCP IP

A

MAC addresses stripped by link layer
IP addresses stripped by network layer
Port numbers removed and packets reassembled at transport layer
Then passed to application and data presented to user

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10
Q

Routers in IP TCP

A

Operate at network layers, and so MAC addresses or source and destination change at each network node
Packets move up and down lower layers at each switch/ router between client and server

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11
Q

File transfer protocol definition

A

An efficient method used to transfer data across a network, often the internet

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12
Q

Describe FTP*

A

Works as a HIGH LEVEL PROTOCOL IN THE APPLIC LAYER USING APPROP SOFTWARE
User is presented with a file management screen with file and folder structure in remote website and local computer
Files transferred via drag and dropping
Often need username and password but can use anonymously

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13
Q

Uses of FTP

A

Uploading images to remote newspaper headquarters by photographers
Companies offering large updates

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14
Q

POP3, post office protocol*

A

Protocol used to retrieve mail from a mail server TEMPORARILY STORING INCOMING MAIL
It is transferred to local computer then deleted from server so can’t synchronise across devices
Developed before WWW when mail stored on hard drive

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15
Q

IMAP internet message access protocol

A

Email protocol designed to keep emails on mail server, ensuring mail is synchronised (synchronicity) across devices
Used in PUSH email (sending email without request)

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16
Q

SMTP

A

Used to transfer mail from one server to another and from a client to a server
Bit after @, domain, shows which mail server to direct mail to. First own mail server then recipient’s

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17
Q

Client server network*

A

1 or more computers: clients are connected to a (or many performing different tasks) powerful central computer called servers
Each client may hold its own files and resources e.g. software and can also access resources held centrally by server
Server also DEALS WITH REQUESTs
EG in schools, businesses, hospitals

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18
Q

Why have many servers in a client server network

A

For many different tasks

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19
Q

File server*

A

Holds and manages DATA for all the clients

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20
Q

Print server

A

Manages print requests

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21
Q

Web server

A

Manages requests to access the web

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22
Q

Database server

A

Manages database applications

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23
Q

Requests in client server network

A

Client sends request to the server which then processes the request and responds with the requested data providing the device has permission to access the data

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24
Q

Adv client server network

A
  • better since all files stored in a central location and access rights are managed by the server centrally, as well as authentication
  • no need for individual backups of data because done centrally. If breakdown and data is lost- recovery procedures enable restoration
  • data and other resources can be shared eg network printers and other peripheral devices
  • can access server from any workstation in network and even at home with VPN
  • downloading software and patching done centrally, saving time and bandwidth when keeping up to date
  • one license rather than individual licenses for clients
  • security and antivirus handled centrally
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25
Q

Disadvantages client server network

A

Expensive to install and manage OS and servers
Need professional IT staff to maintain servers and run network
Server failure = massive disruption to whole network

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26
Q

Peer to peer network*

A

No CENTRAL SERVER. Individual computers are connected to each other and share FILES which are stored on the hard disk. Can be over LANs or WANs. Particularly good if in one site e.g. Small office or home. All computers are 1) of equal importance 2) act as both a client and a host. Hosts can decide access rights for resources

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27
Q

Advantages peer to peer

A

Cheap to set up
Not difficult to maintain
Enables users to share resources e.g. Printer or router

can be more reliable, not dependent on companies server to distribute all requests from all users

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28
Q

Uses of peer to peer*

A

Video on demand and downloading videos.
Different computers in different LOCATIONS hold parts of the video so share the load so faster- main principle behind torrent websites: enabling sharing of files, often containing copyright material

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29
Q

internet*

A

a worldwide network of networks set up to allow computers to communicate with each other globally, regardless of their location, by using the same protocol

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30
Q

how was internet developed

A

via ARPANET created in 60s for US defence military project enabling distant departments working together to communicate without physical travel

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31
Q

WWW*

A

world wide web: a collection of webpages (i.e. LINKED HYPERTEXT) that reside on computers connected to the internet. the internet is the service used to communicate information on these pages

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32
Q

intranet

A

a private network using internet protocols

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33
Q

who developed WWW

A

Tim Berners-Lee, developed concept of WWW and browsing for information

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34
Q

physical structure of the internet

A

each continent has backbone cables connected by transcontinental leased lines fed across SEA BEDS and ISPs connect directly to this backbone and distribute and sell internet connection to smaller providers which distribute to individual homes and businesses

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35
Q

URL*

A

uniform resource locator: FULL address of a location of an internet resource inc file type and resource name. BROWSER REQUESTS FROM WEBSITE SERVER

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36
Q

http://www.domainname.com/folder/subfolder.html#element

A

http is the protocol being used, www is the hostID, folder is the pathname, and #element is the resource

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37
Q

URN

A

uniform resource name, unique resource name allowing you to find a resource even if moved to a new site/new page on the same site e.g. isbn (namespace identifier) 02498459 (namespace specific string)

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38
Q

URI

A

uniform resource identifier made up of URN and URL used to identify the target of a hyperlink

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39
Q

Internet registrar*

A

private companies which must be accredited by governing registries, it hold LISTS and RECORDS of all existing website names and details of domains available to purchase currently

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40
Q

internet registries*

A

5 global organisations governed by ICANN (internet corporation for assigned names and numbers) with WORLDWIDE DATABASES holding records of all domain names currently ISSUED to individuals and companies, and their DETAILS e.g. name, type, registered mailing address, registrar that sold and data of registry
They allocate IP address’ and keep track of corresponding domain name as part of the DNS

41
Q

what does a domain name do* and how its set up

A

identifies the area/domain a webpage resides in. Theres a HIERARCHY of smaller domains, written as a string with full stops, dictated by RULES of DNS

42
Q

first level domains

A

generic top level: .com, .edu, .gov

country top level: .uk, .fr

43
Q

second level domains

A

.sch, .co, .gov

44
Q

third level domains

A

.bbc, .lidl, .ebay

45
Q

root domain

A

www.ROOTDOMAIN.com

46
Q

subdomain

A

WWW.domain.com

www is the subdomain

47
Q

DNS*

A

CATALOGUES all domain names and IP addresses in a series of GLOBAL DIRECTORIES, which domain name servers access in order to find the correct IP address location for a resource

48
Q

without DNS

A

have to type in IP address in URL bar instead of domain name

49
Q

process of DNS*

A

webpage requested by URL entered by user, browser requests for IP address from a local DNS (firstly ISP with preprogrammed database of IP related to domains), if not found, search extended up hierarchy to larger DNS database and when found, user’s computer sends data request to that IP address location to find webpage data VIA IP/TCP PROTOCOL

50
Q

FQDN

A

fully qualified domain name containing host server name e.g. mail.google or www.google, depending on server resource is hosted on

51
Q

IP address*

A

internet protocol address, a unique address assigned to a NETWORK DEVICE indicating where a packet of data is to be sent/has been sent from. routers use this to direct packets

52
Q

IP addresses of domain names*

A

the address is of the server the site is residing on

53
Q

IP addresses are made of

A

four numbers IPv4 with number between 0-255 and now IPv6 has 6 numbers because so many IP address being used

54
Q

272.15.63.144

A

272 is the geographical location
272.15.63 is the network ID identifying a network
144 is the hostID identifying hosts (individual devices) on a network

55
Q

computer network

A

a number of computers linked together to allow the sharing of resources e.g. software, hardware, data

56
Q

server

A

a powerful central computer able to provide one or more services to a network and its users e.g. file storage

57
Q

WAN

A

wide area network, a network of interconnecting networks inc LANs that spread over a large geographical locations (e.g. continents) can be connected using internet, satellite links and leased lines (rely on third party carriers eg british telecom) e.g. internet, bank cash dispensers.
LANs use routes to connect to these other networks

58
Q

LAN*

A

local area network, a number of a COMPUTING DEVICES single site/building consisting of computers, printers and a central server for example. Users SHARE hardware and data and can COMMUNICATE to each other. data travels quickly over these short distances

59
Q

physical bus topology

A

all computers connected to a single cable and the end of cable is connected to a terminator

60
Q

adv of physical bus

A

inexpensive to install as less cable and no additional hardware
effective for small networks

61
Q

disadv of physical bus

A

low security, all other computers can see data transmissions
traffic means degraded performance
if main cable fails then network data can’t be transmitted to any of the nodes
troubleshooting individual devices issues is hard
collisions

62
Q

physical star topology

A

has a central node, a switch or computer which acts as a router to transmit messages.
switch has a record of MAC addresses of each device on a network and can identify particular computers on networks to send data to

63
Q

adv of physical star*

A
  • one cable FAILS, only one station affected
  • consistent performance even if heavily used
  • COLLISIONS aren’t a problem: each station has own cable to server
  • higher transmission speeds: better performance
  • more SECURE: messages sent directly to central node and harder to intercept
  • easier to add new stations without disrupting networks
64
Q

disadv of physical star

A
  • costly installation e.g. cost of cable
  • if central switch goes down, network data can’t be transmitted to any more nodes
  • number of nodes restricted by capacity of central device
65
Q

physical topology

A

the physical design layout of a network, important for when deciding wiring layout

66
Q

logical topology

A

shape path of data travels in and describes how components communicate

67
Q

topologies are…

A

independent of each other so a physical star topology can act logically like a bus topology using appropriate PROTOCOLS and physical SWITCHING

68
Q

ethernet topology

A

logical bus topology regardless of physical layout

69
Q

wifi*

A

local area wireless technology allowing devices to connect a device to a network resource or internet via a wireless network access point (usually 20m indoors but more outdoors)

70
Q

1999 WiFi alliance

A

group of 100s of worldwide companies formed to establish international standards for interoperability and backward compatibility
enforces use of standards for device connectivity and network connections

71
Q

mesh network topology

A

each nodes is connected to all other nodes by transmitting data over intermediate nodes
only one node requires internet access, others share connection

72
Q

use of mesh network topology

A

more common with widespread use of wireless technology. can spread over whole cities

73
Q

adv of mesh network topologies*

A
  • no cabling COSTS
  • self healing- if one connection breaks it can be circumvented by another route so more nodes = faster and more RELIABLE
  • new nodes automatically incorporated into network
  • FASTER communication as data packets don’t pass through central switch
74
Q

disadv of mesh network topologies

A
  • harder to manage: continuous supervision

- many devices needed = expensive

75
Q

circuit switching

A

creates a direct link between two devices for the duration of the communication e.g. public telephone system. so you have all the bandwidth between two points and no other messages can use the connection

76
Q

adv circuit switching

A
  • you have all the bandwidth between two points and no other messages can use the connection
  • exclusive connection means packets arrive in the same order that they are sent, simplifying the reconstruction process
77
Q

disadv circuit switching

A
  • bandwidth is being wasted when no data is being sent
  • data has to be transmitted at the same RATE by both devices so only devices operating at same transfer rate can be connected
  • switches connecting and disconnecting circuits cause electrical interference so data is lost and corrupt if path is used to transmit data: so leased line can be used instead if problem
78
Q

packet switching*

A

method of communicating packets of data across a network whilst other network communications are happening simultaneously e.g. website data and emails are sent and RECEIVED as a series of PACKETS. relies on packets to travel via entirely different ROUTES (fastest and least congested)

79
Q

what are data packets*

A

manageable chunks/packets of data BROKEN DOWN from data to be sent across a network. the size can be FIXED or VARIABLE: usually between 500-1500 bytes

80
Q

payload of data packet

A

body of data being sent

81
Q

trailer of data packet

A

cyclic redundancy check/checksum: a hash total is created and attached, calculated from packet data to detect transmission errors. calculated by number of 1s in transmission. CRC is RECALCULATED and MATCHED at end of transmission to verify data is unchanged- if totals differ packets refused with suspected data corruption and a NEW COPY requested from sender

82
Q

header*

A

IP address of sender and recipient, PROTOCOL used for this packet type, packet sequence number, time to live/hop limit when packet expires and discarded

83
Q

packets at other end

A

reassembled in correct order and packets requested for again if didn’t make it.
data extracted

84
Q

advantages of packet switching

A
  • network failures don’t stop messages
  • easy to add more nodes
  • secure, unpredictable route and packet split
  • takes advantage of unused connections
  • cheap as efficient use of bandwidth (only charged per unit of data rather than connection time)
85
Q

disadvantages

A
  • can be corrupted in transmission

- must be reassembled at end of transmission

86
Q

end to end principle

A

endpoints control communication and security, midpoints just pass on packets

87
Q

open architecture principle

A

anyone can design a network just through creating a linking computer called a gateway

88
Q

MAC address*

A

media access control address. each device capable of connecting to a network has a wired or wireless NIC with a unique MAC address ASSIGNED to and hardcoded by a manufacturer uniquely identifying a device (48bits long, 12 hex digits)

89
Q

protocol*

A

a set of rules defining common methods of DATA communication- standard rules allow devices to COMMUNICATE with each other

90
Q

HTTP

A

standard protocol for browsers to render webpages

91
Q

telnet*

A
  • allows communication between one computer and another

- allowing a user on one computer to log into another computer on the SAME NETWORK

92
Q

sending mail from one place A to another B

A 
A uses SMTP to send message; this goes via her LOCAL EMAIL SERVER which checks the DOMAIN to which the email is addressed e.g.@domain.com; and forwards
the message (often via other mail servers); to B webmail server.
B logs in via his local ISP; and downloads his message using POP3/IMAP.
93
Q

switches and router are used for?

A

handling traffic and ensuring requests and files get to the correct location

94
Q

wifi workstations

A

when you connect to a network using a wireless access point

95
Q

router

A

connects at least two networks: 2 LANs/WANs or LAN with ISP’s network. Reads the recipient’s IP address in each packet and forwards it on to recipient using fastest, least congested route to next router. This continues until destination is reached. routers use routing tables to store and update locations of other network devices and most efficient routes to them. Uses routing algorithm. When router is connected to internet, IP address of port connecting it must be registered with internet registry bc it must be unique across the internet

96
Q

routing algorithm

A

Finds optimum route between network devices. This routing algorithm can become a bottleneck in network traffic since decision making process is complicated. Shortest path algorithm: Dijkstra’s algorithm.

97
Q

hop

A

traversing between one router and another across a network

98
Q

gateway

A

routes packets between networks if the protocols differ. strips header data, leaving raw data only. new data is added in the format of the new network before packet sent again.

Computing A level (19 decks)

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