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Computer science A level OCR > Networks > Flashcards

Networks Flashcards

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1
Q

Network

A

Set of interconnected devices that exchange data and resources with each other

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2
Q

Internet

A

The largest public network (WAN), a network of interconnected networks. Contains a backbone, and a set of dedicated connections that connect large networks at various points in the world. Each point is connected to another regional network controlled by ISP’s.

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3
Q

WiFi

A

Wireless networking tech providing high speed internet and network connection. A family of wireless network protocols.

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4
Q

Station

A

Consists of NIC and computer

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5
Q

Wireless Access Point

A

Point where devices connect to a wireless network. Requires connection to a router.

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6
Q

Network switch

A

Connects devices on a LAN, receives and sends packets.

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7
Q

IP Address

A

A unique identifier for every device on the internet. Made up of 4 or 6 octet values.

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8
Q

URL

A

Used to specify the means of accessing a resource across a network and its location. Consists of protocol and domain name

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9
Q

Web search procedure

A

DNS server maps domain to an IP address.
If it cannot resolve, it passes the request to the root DNS.
DNS server sends the IP address to the requested web browser.

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10
Q

DNS servers

A

Domain Name system; dedicated computers with an index of domain names and their IP addresses.
When computers query a DNS server to domain, it returns an IP address for the computer to send a message to it.

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11
Q

Topology

A

Arrangement of devices that make up a network

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12
Q

Bus topology

A

Devices connected by a single cable(backbone).
Devices can be easily added, good for small networks.

Unidirectional,only one computer can transmit at a time,main cable is point of failure, performance lowers with heavy use due to collisions, poor security.

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13
Q

Star Topology

A

Contains central hub which acts as connection point for devices. Computers connected to central node. Switch communicates to specific computer intended.

Good performance, easy to isolate problems, more secure

Expensive to set up, central device is point of failure.

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14
Q

Physical vs logical topology

A

Physical: Defines how devices are physically connected
Logical: Defines how devices communicate across physical topology

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15
Q

5 internet global registries

A

Allocate IP addresses to specific domain names, which must be unique.

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16
Q

Protocols

A

Set of rules that define how data is transmitted across a network (i.e TCP/IP stack)

Must be standard across all devices for communication to work

17
Q

TCP/IP stack

A

Transmission control protocol/internet protocol consists of 4 layers:
Application
Transport
Internet
Link

18
Q

Application layer

A

Provides services for applications that want to communicate across a network. Uses high level protocols like SMTP, FTP,HTTP that set an agreed standard between end points.

Presents image data for user at destination

19
Q

Transport layer

A

Uses the TCP to establish end to end connection with receiver. Splits data into packets, numbers them sequentially, adds port number to be used based on HTTP. At receiving end, confirms if packets have been received, requests for missing packets to be resent.

20
Q

Internet layer

A

Uses the IP to address packet with source and destination IP address. Router forwards each packet to an endpoint, defined by combination of IP addresses and port numbers. Router uses routing table to instruct next hop

21
Q

Link Layer

A

Operates across a physical connection. Adds MAC address of physical NIC that packets should be sent to.

22
Q

FTP, SMTP, IMAP,POP3

A

FTP - used to transfer files
SMTP - send and receive emails
IMAP- manages emails
POP3- downloads emails

23
Q

Firewalls

A

Hardware/software that controls access to and from a network. Ports are opened to allow specific traffic (packets) to pass

24
Q

Packet filtering

A

Packets inspected by a firewall to see which port they are trying to access, if allowed through, port opened for duration of communication, otherwise firewall rejects.

25
Q

Proxy servers

A

Make a web request on behalf of users device, hiding true request’s IP address from receiver.
Enables anonymous surfing, can be used to filter undesirable online content, logs user data with their requests. Provides a cache of previously visited sites to speed access.

26
Q

Phishing

A

Using fake emails to manipulate victims into visiting a fake website to give away personal information.
Measures:
2fa,strong passwords, use of access rights, guard against SQL injection and buffer overflow, improving code quality.

27
Q

Malware

A

Malicious software, annoys users and damages their data.
Examples: trojans, viruses, worms

28
Q

Virus

A

Infects other programs ans data by self replicating. Need a user to spread

29
Q

Worms

A

Do not need a user to spread

30
Q

Trojans

A

Pretends to be harmless application. Cannot self replicate.

31
Q

Gateways

A

Alternative to routers.
Required when data is travelling from one network to another that use different protocols.
Required by networks using different transmission media.
Header data removed and reapplied using correct format of new network.
Can combine with router to create one integrated device.

32
Q

Routers

A

Forward data packets from one network to another
Shares data about available routes to destination
Looks up destination IP address in routing table to find best router to forward packets to,
Each transfer between routers=hop.

33
Q

Data packets

A

A segment of data that needs to be sent (size ~ 500-1500 bytes)
Kept small to ensure individual packets do not take time to transfer preventing other packets from moving.
Should not be too small as additional data makes transfer inefficient.

34
Q

Data packet format

A

Header- holds sender and receivers ip address, time to live/hop limit
Payload - holds data and protocol used as well as packet number
Trailer - Contains a checksum/CRC to detect transmission error. (done by obtaining a hash total calculated by adding number of 1’s in transmission)

35
Q

Packet switching

A

Packets sent across separate routes, determined by least congested route. Easily reassemble when reaching receiver. Packets that do not make it are resent.

36
Q

Circuit switching

A

Creates direct link between devices for duration of communication, even when data is not transmitted (a waste of bandwidth)
Very device specific as two devices need to transmit and receive at the same time.
Data segments are sent in order of arrival so simplification of restructuring packets at the receiving end.
Switches connecting and disconnecting circuits causes electrical interference, producing corrupt data.

Computer science A level OCR (6 decks)

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