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A Level Computer Science > 4.9 Fundamentals of Communication and Networking > Flashcards

4.9 Fundamentals of Communication and Networking Flashcards

1
Q

Baud Rate

A

The number of signals sent per second

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2
Q

Bit Rate

A

The rate at which bits are transferred
Bit rate >/ baud rate

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3
Q

Bandwidth

A

The capacity of wired/wireless network communications

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4
Q

Latency

A

The delay between transfer of data and seeing the result of that instruction

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5
Q

Protocol

A

Set of rules for data exchange across a network

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6
Q

Serial (2)

A
  • one bit transmitted at once down one wire
  • external distances
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7
Q

Parallel (2)

A
  • multiple bits sent at once using multiple wires
  • internal distances
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8
Q

Serial (Adv: 3, Dis: 1)

A

Adv
- simple set up
- cheap
- reliable
Dis
- slow transmission

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9
Q

Parallel (Adv: 1, Dis: 2)

A

Adv
- faster transmission
Dis
- less reliable (skew due to interference)
- expensive

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10
Q

Synchronous Transmission (5)

A
  • data sent at regular intervals
  • synchronised by clock signal
  • clock pulse shared by receiver and sender
  • helps with skew so used in parallel
  • used for reliable, time sensitive data
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11
Q

Asynchronous Transmission (2)

A
  • bytes sent as soon as they’re ready
  • parity, start, stop
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12
Q

Bus Topology (2)

A
  • one cable: backbone
  • terminator at end of cable that reflects signal
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13
Q

Bus Topology (Adv: 3, Dis: 3)

A

Adv
- cheaper to install (less cables)
- no additional hardware
- easy to add nodes
Dis
- poor security
- main cable fail
- performance decreases heavily with traffic

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14
Q

Star Topology (1)

A
  • each device has own cable connected to switch/hub
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15
Q

Star Topology (Adv: 5, Dis: 2)

A

Adv
- easy to add
- consistent performance despite traffic
- more secure
- easy to isolate faults (single cable fails)
- no collisions
Dis
- central node goes down
- expensive to set up

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16
Q

Client-Server (1, Adv:2, Dis:1)

A
  • all data stored on dedicated server
  • adv: centralised security/backups, files/software stored securely on server
  • dis: server goes down
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17
Q

Peer-To-Peer (1, Adv:2, Dis:1)

A
  • all devices have equal status
  • adv: no specialised hardware, node goes down
  • dis: no centralised security/backups/management
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18
Q

LANs and WANs Advantages (4)

A
  • cheap, easy communication
  • share files/hardware
  • centralised file storage/install/update/back up
  • log in from any device
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19
Q

WiFi (Def, 2)

A
  • WiFi is a wireless LAN based on international standards
  • slower and less reliable than ethernet
  • Hot spots = public WiFi
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20
Q

NIC/Wireless Network Adaptor (4)

A
  • Located in device
  • Allows device to connect to wireless system
  • Allows device to communicate by sending and receiving data
  • Assigns MAC address
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21
Q

WAP (3)

A
  • Located in router
  • Allows wireless devices to connect to wired network
  • Assigns IP address
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22
Q

Network Security (5)

A
  • Doesn’t stop allowed user from using malware
  • Protects against unauthorised access
  • WPA/WPA2 -WiFi Protected Access
    • Authentication, encryption, passwords
  • SSID - Service Set Identifier
    • Unique number to identify a network
    • Must use same number to join network
    • Turn off broadcasting (only those who know exist + password can join)
  • MAC Address white list
    • List of users (MAC addresses) who can access network
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23
Q

Firewalls (7)

A
  • A system that filters network traffic to protect against unauthorised flows of data in/out of a network
  • Hardware or software
  • Isolates network traffic
  • Allows/denies based on IP address
  • Packet Filtering
    • Checks packet header to see if source/destination addresses are allowed/denied
  • Stateful Packet Inspection:
    • Looks at data inside packet
    • If any common warning signs, packet is stopped from progressing
  • Packet only allowed if passes both
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24
Q

Proxy Servers (4)

A
  • Act as ‘middle man’ between client and webserver
  • Client ←→ Proxy Server ←→ Web Server
  • Once obtained from web, copy of data stored on proxy server
  • After while, proxy server sends data back to web server to free up space
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25
Q

Malware (def)

A

Software created with intention to cause harm
Corrupts and compromises data

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26
Q

Viruses (6)

A
  • Attaches itself to program/file, by making copy of itself
  • enabling it to spread from one device to another
  • Typically executable files
  • Means cannot spread without human interaction
  • Spread through lack of awareness
  • Exploits same vulnerabilities as worms
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27
Q

Worms (5)

A
  • Similar to viruses in design
  • Doesn’t need human interaction to spread
  • Automatically self replicates
    • Automatically sends itself to everyone in address book via email
  • Exploits out of date systems - no security updates
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28
Q

Trojans (5)

A
  • Appear genuine but have hidden agenda
  • Attached to executable file
  • Create backdoors which malicious users can exploit
  • Doesn’t spread, self-replicate, cause harm
  • Exploits lack of understanding and systems with out of date anti virus software
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29
Q

Symmetric Encryption (4)

A
  • One key for both
  • Key exchanged through secured channels
  • Easy decoded
  • e.g. caesar, vernam
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30
Q

Asymmetric Encryption (keys)

A

Public key = encrypt
Private key = decrypt
Extremely secure

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31
Q

Digital Certificates (4)

A
  • Unique code to verify your identity
  • Ensures encrypted message from trusted source
  • Contains name, ID, public key, signature
  • Awarded by a certification authority (trusted organisation)
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32
Q

Digital Signatures (2)

A
  • Similar to real life signature
  • Uses mathematical functions + keys to create unique signature
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33
Q

Digital Signatures Used for (2)

A
  • Message has not been corrupted
  • Sender is who they say they are
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34
Q

Digital Signatures - Sending Messages

A
  • Hash plaintext message → message digest
  • Sender private key + digest → signature
  • Signature + plaintext message
  • Encrypt using receiver’s public key
  • Send message
  • Decrypt using receiver’s private key
  • Split signature and plaintext message
  • Sender’s public key + signature → digest
  • Rehash plaintext → message digest
  • Compare two digests to see if the same
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35
Q

MAC vs IP (5)

A

MAC
- LAN based
- Hex
- Static
- Completely Unique
- Assigned by NIC
IP
- WAN based
- Binary/Denary
- Dynamic
- Unique within Network
- Assigned by router

36
Q

IP Addresses (Purpose, Parts, 2)

A

Purpose = “To identify a device on a network using a unique number”
2 Parts:
- Network identifier (number of bits varies)
- Host (device) identifier
Largest IP address: 255.255.255.255
IPv6: 6 sections not 4, hex not binary

37
Q

Subnets (def, 2, eq)

A
  • Smaller part of a larger network
  • More efficient & secure transmission (reduces collisions/devices passed through)
  • Can send data directly without router
  • Check if devices on the same network
    • Mask AND sender IP = mask AND receiver IP (gives NetworkID)
    • Number of 1s as designated to ID
38
Q

Public vs Private IP (2)

A

Private = cannot be accessed outside of network (non-routable)
Public = needed to route over internet

39
Q

Data Packet Structure (3)

A

Header: packet size, packet number, protocol, destination and sender address, protocol identifier, port number, check sum (error checking method)
Body: Actual data of the packets
Footer: Tell receiver end of packet reached

40
Q

Packet Switching (5)

A
  • More secure and efficient
  • TCP splits into multiple packets
  • IP routes individual packets into different directions (travel through fastest route)
  • TCP checks transmission was successful
  • TCP sequences packets back inro correct order at destination
41
Q

Layers (2)

A
  • Reduces complexity of networking
  • Each layer accessed & edited separately
42
Q

Application Layer (2)

A
  • Defines TCP/IP protocols & how host programs interface with transfer layer services
  • Includes higher level protocols
43
Q

Transport Layer (4)

A
  • Purpose = permit devices on the source and destination host to carry on a conversation
  • Defines the level of service and status of the connection used when transporting data
  • Breaks data into packets
  • Main protocols used: TCP and SSH
44
Q

Network Layer (2)

A
  • Defines how data is physically sent through the network
  • Defines how bits are electrically or optically signalled by hardware devices
45
Q

Link Layer (2)

A
  • Handles the moving of data in and out of a physical link in a network
  • Used to interconnect hosts/nodes in the network
46
Q

NAT (acronym, 2)

A
  • Network Address Translation
  • Responsible for converting IP addresses as they pass over the boundary between public and private addresses space (e.g. via a router)
  • Table of requests and IPs
47
Q

CSMA (4)

A
  • Carrier Sense Multiple Access
  • Purpose is to provide error free transmission within a LAN
  • Checks that all devices & cables are clear and ready to send and receive data
  • Helps to prevent the collision of packets
48
Q

CSMA with Collision Avoidance

A

Without RTC/CS (Request To Send/Clear To Send)
- Assemble a frame
- Check is channel is idle
- If idle : transmit data
- If not: wait for random amount of time and check again
With RTS/CS
- Assemble a frame
- Check is channel is idle
- If idle: send RTS
- - Receiver received RTS
- - Sends back CTS if clear
- - Data transmitted if receiver received CTS
- - If not: wait for random time and check again
- If not: wait for random time and check again

49
Q

DHCP (Acronym, Purpose, Benefit)

A
  • Dynamic Host Configuration Protocol
  • Purpose: DHCP server automatically assigns a dynamic IP address to a computer from a pool of available addresses
  • Benefit: Takes IP back after use (helps shortage)
50
Q

DHCP Method

A
  • Device sends discovery message
  • The DHCP sends an offer out
  • The device then sends the request
  • The DHCP sends out confirmation
51
Q

TCP/IP (Acronym, 2)

A
  • Transmission Control Protocol/Internet Protocol (TCP/IP)
  • Provides error free transmission between 2 devices
  • Routes packets on a WAN
52
Q

HTTP (Acronym, 2)

A
  • Hyper-Text Transfer Protocol (HTTP)
  • Defines how data from web pages is transferred from server to client
  • Client-server method of requesting HTML files
53
Q

SMTP (Acronym, 2)

A
  • Simple Main Transfer Protocol (SMTP)
  • Sends mail to a mail server
  • Client → mail server
54
Q

POP (Acronym, 3)

A
  • Post Office Protocol (POP)
  • Used by email clients to get email from a mail server (receives mail)
  • Web server → client
  • Have to rerequest as emails deleted once read
55
Q

IMAP (Acronym, 4)

A
  • Internet Message Access Protocol (IMAP)
  • Receives: web server → client
  • Synchronises: automatic updates
  • Used to manage mail boxes
  • Messages only deleted when user explicitly requests they are
56
Q

Telnet

A

Unencrypted = not secure

57
Q

FTP (acronym, 2)

A
  • File Transfer Protocol
  • Sending files between computers
  • Client software
58
Q

SSH Process

A
  • Client initiates the connection by contacting server (client → server)
  • Server sends public key to client (client ← server)
  • Server and client agree communication rules and open a secure channel (client ←→ server)
    • May have few passes (may reject and resend new rules)
  • User can now login to the remote server host OS (client → server)
59
Q

Web Browsers (Structure 2)

A
  • Head = titles and styling scripts
  • Body = main content
60
Q

Web Names (Names, Levels, Use Over)

A
  • Website domain name: craiganddave.org
  • Fully qualified domain name: www.craiganddave.org/cryptic.pdf
  • Uniform resource locator (URL): https://www.craiganddave.org/cryptic.pdf
  • 3rd level e.g. bbc, amazon
  • 2nd level e.g. .co, .gov, .ac
  • Top level e.g. .com, .org, .net, .uk, .fr
  • Use URL over IP as it is easier to remember and to type (less errors)
61
Q

Port Numbers (4*, 5)

A

20 = FTP data
21 = FTP control instructions
* 22 = SSH remote login
* 23 = Telnet remote login
25 = SMTP
* 80/8080 = HTTP
110 = POP3
143 = IMAP
* 443 = HTTPS

62
Q

Port Forwarding (3)

A
  • A webpage coming back to a network will arrive through a port on the router
  • Router sees which device requested that page and forwards it down that specific port
  • Allows computers to exchange data directly between each other without need for complex transition step
63
Q

Thick Clients (4)

A
  • Hold the majority of the data
  • Need more RAM + decent processor
  • Share with other clients that request
  • Less reliance on server
64
Q

Thin Clients (3)

A
  • Hold only a small amount of data
  • Need less RAM + high bandwidth + very good connection
  • Request majority of data from other clients
64
Q

Domain Name Server

A
  • Client sends DN to DNS
    • DN sent to bigger DNS
    • IP address copied to DNS
  • DNS looks up corresponding IP + sends to client
    • Error message sent if DN doesn’t exist
  • Client sends IP to web server to access website
  • Website accessed by client
65
Q

Ransomware (definition)

A

Ransomware holds companies to ransom by encrypting their data and demanding a large sum of money to decrypt it

66
Q

Hackers (definition)

A

Anyone that attempts to access an IT system without permission
(you can have ethical hackers)

67
Q

Phishing (definition)

A

Phishing is to attempt to fraudulently gain information by unlawfully making claims via phone/email that the user should share personal/financial details

68
Q

Accidental Damage (4)

A
  • Accidentally delete/overwrite
  • Power cut before saving
  • Saved in wrong place/name
  • Natural Disasters
69
Q

Impacts of Threats on Individuals (4)

A
  • Stress
  • Waste Time
  • Replace/repair devices
  • Could lose photos - sentimental value
70
Q

Impacts of Threats on Organisations (4)

A
  • Loss in business
  • Damage to credibility
  • Take money + time to fix damages
  • Can be viewed as unreliable
71
Q

Reducing Threats to Data (4x2)

A

File Permissions
- password protection
- allocate right e.g. read-only

Access Levels
- users are given access to files that fulfil their role but nothing more
- fewer people put sensitive files at risk

Passwords
- secret, strong, no key words
- change every 8-12 weeks

Physical Access Control
- don’t leave unlocked devices unattended
- biometrics

72
Q

Incremental Back Up (2, Adv:2, Dis:1)

A
  • only back up files that have been changed since the last back up
  • nightly/weekly
  • doesn’t take up much storage
  • quicker
  • harder to find files to recover
73
Q

Full Back Up (3, Adv:1, Dis:2)

A
  • backs up all files
  • weekly/monthly
  • out of office hours
  • restore files more easily
  • expensive
  • takes longer
74
Q

Back Up Recovery (2)

A
  • organisation should have formalised plan
  • large organisation have a full disaster recovery plan (minimise disruption)
75
Q

LAN and WAN (definition)

A

Group of connected devices over a:
LAN: small geographical area
WAN: large geographical area

76
Q

Start and Stop Bits (definition)

A

Start: notifies receiver when data being sent
Stop: notifies when the end of a transmission has been reached

77
Q

Advantages of Proxy Servers (2)

A
  • speeds up access
  • more secure (IP hidden from webserver)
78
Q

IPv4 vs IPv6 (2x2)

A
  • IPv4 = 4 sections, binary
  • IPv6 = 6 sections, hex
    • 3.4x10^38 IP addresses
79
Q

Router (definition)

A

Device that forwards packets from one network to another

80
Q

SSH Typical Uses (4)

A
  • Providing secure remoted access for
    • Users/automated processes
  • Interactive & automated file transfers
  • Issuing remote commands
  • Managing network infrastructure
81
Q

FTP 5 Features

A
  • Local computer file manager panel
    • Shows filing structure of local machine
    • When files moved from here to panel 2: uploading from local machine to remote server
  • Remote server file manager panel
    • Shows filing structure of remote server
    • When files moved from here to panel 1, downloading files from r.s to l.m
  • FTP client to host server connection
    • Connects to remote server
  • Status Panel
    • Useful messages from remote server when connected to FTP are reported here
  • File Transfer Progress Panel
    • Shows queue of items being down/uploaded
82
Q

Physical Star vs Logical Bus (6)

A
  • Physical Star: layout (cables)
  • Logical Bus: data moves
    • data gets broadcasted to all PCs (Hub)
    • receive data -> check if it is yours
    • only 1 broadcast can happen at the same time
  • It is possible for a network to have a physical star topology, but logically the data is sent as a bus topology
83
Q

Gateways (2)

A
  • all functions of a router
    • protocol conversions
84
Q

Routers

A
  • connects network to other networks (internet)
  • in packet switching:
    • will find most efficient path
    • update NAT table with route
    • packet header: update addresses: MAC + IP of sender + receiver
  • will check which link data is to be sent on

A Level Computer Science (13 decks)

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