Comp sci unit 3 terms

TCP

Transmission control protocol

Communication standard that enables application programs and computing devices to successfully exchange data packets over networks

For email/messaging, file transfers, web browsing

TCP connections:

Requires an established connection before transmitting data

Can sequence data

Can retransmit data if packets fail to arrive

Uses error-checking to guarantee that data arrives in intended state

Don’t support delivering continuous data

Can be slower than UDP

UDP

User datagram protocol

“Connectionless” communications standard that enables application programs and computing devices to exchange packets of data over networks

For: live streaming, online gaming, video chat

UDP connections:

Require no connection to start and end a data transfer

Cannot sequence or arrange data

Cannot retransmit data if packets fail to arrive

Use minimal error-checking that may not prevent all errors

Support delivering continuous data

Can be faster than TCP

IP address

Internet protocol address

Numerical label assigned to identify a device

Divided into network and host portion

Class A

Mask - 255.0.0.0

Addresses - 16,777,216

First octet - 0-127

/8

Class B

Mask - 255.0.0.0

Addresses - 65,536

First octet - 128-191

/16

Class C

Mask - 255.255.255.0

Addresses - 256

First octet - 192-223

/24

Subnet mask addresses

For each subnet mask, usable host IP addresses is less by 2

First address for network

Last address for broadcast (used to send data to all other hosts on subnet)

IPv4

uses 32-bit addresses

Represented by four 8-bit fields (octets)

Separated by periods

IPv6

Uses 128-bit addresses

Represented by eight 16-bit hexadecimal fields

Separated by colons

Public IP

Identifies you to the wider internet so that all the info you’re searching for can find you

Private IP

Used within a private network to connect securely to other devices within the same network

MAC address

Media access control address

Unique identifier assigned to a network interface controller to identify physical hardware in a network

MAC vs IP

MAC: designates the physical location of a device

IP: signifies the device’s global or internet-accessible identity

Subnet

Network inside a network

Makes networks more efficient

Data can travel a shorter distance without passing through unnecessary routers

Subnet mask

Like an IP address, but only for internal usage within a network

Used by routers to route data packets to the right place

Not indicated within data packets traversing the internet

Collision domain

Section of a network where packet collisions can occur

Collisions occur when 2 or more data packets try to occupy the same network channel at the same time, which can lead to packet loss

Problem when using hubs instead of switches

Network segmentation

Used to compartmentalise subnets to deliver unique security controls and services to each subnet

Hub

Like a router but doesn’t route frames intelligently

When it receives a signal, it will repeat it out on all connections except the one where it received the signal from

Physical (OSI) layer

Switch

Prevent collision by buffering Ethernet frames

Receives incoming data packets and redirect them to the destination on a LAN

Operates using MAC addresses to switch data on the ethernet layer

Internet (DoD) and data link (OSI) layer

Port number

Way to direct TCP/UDP connection to a specific process

Serve to identify the purpose of a connection

Come after an IP address, separated by a colon

OSI model layers

1. physical

2. data link

3. network

4. transport

5. session

6. presentation

7. application

Physical layer

Responsible for the physical cable or wireless connection between network nodes

Protocols: Ethernet, DSL, fibre optic

Data link layer

Establishes and terminates a connection between two physically connected nodes on a network

Protocols: LCP, NCP

LLC

Logical link control

Identifies network protocols, performs error checking and synchronises frames

MAC

Uses MAC addresses to connect devices and define permissions to transmit and receive data

Network layer

Breaks up segments into network packets and reassembles them on the receiving end

Routes packets by discovering the best path across a physical network

Uses network addresses (IP) to route packets to a destination node

Layer 3 routing

Use IP address to decide where to forward packets through a hardware switch

Switch/router accepts a packet, looks at its destination address and makes a routing decision

Transport layer

Takes data transferred in the session layer and breaks it into ‘segments’ on the transmitting end

Responsible for reassembling the segments on the receiving end, turning it back into data that can be used

Transport layer carries out…

Flow control - sending data at a rate that matches the connection speed of the receiving device

Error control - checking if data was received correctly and if not, requesting it again

Session layer

Creates communication channels (sessions) between devices

Responsible for opening sessions, ensuring they remain open and functional while data is being transferred

Responsible for closing them when communication ends

Session layer checkpoints

Allows devices to resume data transfer from the last checkpoint if session is interrupted

Presentation layer

Prepares data for the application layer

Defines how 2 devices should encode, encrypt and compress data so it’s received correctly

Takes data transmitted by the application layer and prepares it for transmission over the session layer

Protocols: TLS, SSL

Application layer

Used by end-user software

Provides protocols that allow software to send and receive info and present meaningful data to users

Protocols: HTTP, FTP, SMTP

OSI model

Open systems interconnection model

Based on the concept of splitting up a communication system into 7 abstract layers, with each layer dependent upon the last

Data passes through each layer in sequence

DoD TCP/IP model

Department of defence transmission control protocol/internet protocol model

Condensed version of OSI model

Basis for the current internet

Packets

Basic unit of communication between source and destination in a network

Data sent through the network is broken into packets that are recombined by the destination devices

Dividing data allows the network to easily transmit, route, keep track of and retransmit lost or corrupted data

IPv4 packets

Contains header (20/24 bytes long) and data (variable length)

Header - IP addresses of source and destination, other fields that help route the packet

Data - actual content (e.g., string of letters, part of webpage)

Data at TCP/IP model

Encapsulates/modifies data according to a 4 layer procedure

Data is sent out through the layers, converted into packets and routed to their destination

Packets are received and reassembled by the destination device into data usable by apps

Data at application layer

Unencapsulated, not modified

Sends data to the transport layer

Encapsulation details are mostly hidden from the user, process and software developer through abstraction

Segments at transport layer

Protocols start the process

Data is wrapped with a header which contains a source and destination port, checksum and session establishment

TCP - segment

UDP - datagram

Checksum

Value that represents the number of bits in the segment

Used to detect data corruption

Packets at internet layer

Data wrapped in ‘IP envelope’ which contains source and destination IP addresses, info on protocol type (TCP) and version (v4/v6) and time to live (TTL)

TTL

Time to live

Amount of time (hops) that a packet is set to exist inside a network before being discarded by a router

Frames at network layer

Packet wrapped in ethernet frame which contains info on source and destination MAC addresses, Frame Check Sequence (FCS) for error correction and header and footer that mark the start and end of frame

Data at different layers of OSI

Encapsulated as data -> segments -> packets -> frames

Physical layer: data is known as bits - the raw ‘bit stream’ of 1s and 0s over the network, transmitted as electrical or wireless signals

DoD application protocols

SMTP, FTP, HTTP, HTTPS, DHCP, DNS, PING

DoD transport protocols

TCP, UDP

DoD internet protocols

IPv4, IPv6, ARP

DoD network protocols

Ethernet (802.3), Wi-Fi (802.11)

Transmission media

Provides a physical path between a transmitter and receiver

Channel through which data is sent from one place to another

Network (DoD) and physical (OSI) layer

LAN

Local area network

Collection of devices connected together in one physical location

WLAN

Wireless local area network

Group of co-located devices that form a network based on radio transmissions

WAN

Wide area network

Collection of LANs or other networks that communicate with each other

Problems from unauthorised network access

Data breaches, which can also lead to ransomware.

Identity theft - access to one’s personal details through their personal network can give hackers substantial content to steal the identity of the person whose info they are accessing

Disruptions - shutting down systems or making it more difficult to access data

Firewall

Acts as a gatekeeper for network traffic, filtering and controlling access to prevent unauthorised access and protect against cyberattacks

Examines incoming and outgoing data based on predefined security rules, allowing legit traffic while blocking malicious or unwanted connections

Transport or internet (DoD) and network or transport (OSI) layer

Packet filtering

Involves inspecting incoming and outgoing data packets based on rules

Can be based on IP addresses, port numbers, and protocols

Can block traffic that doesn't match the established rules, preventing unauthorised access

Stateful inspection

Enhances packet filtering by keeping track of active connections and the state of the packets within a session

Allows the firewall to make more informed decisions about which packets to allow or block based on the context of the connection

Proxy services

Act as intermediaries between the client and the destination, inspecting the content before it's allowed onto the network

Can help prevent malicious content from entering the network

OSI vs TCP/IP model

Similarities - describe how info is transmitted between 2 devices, use encapsulation where data is packaged into headers and trailers that contain info about the data and how it should be handled

OSI - delivery is guaranteed

TCP/IP - more reliable

DoD layers

Application

Transport

Internet

Network

Application layer role (DoD)

Provides network services directly to user applications

Transport layer role (DoD)

Ensures reliable data transfer between devices, manages error detection and correction, flow control

Internet layer role (DoD)

Determines the best path for data to travel across networks, handles logical addressing and routing

Network layer role (DoD)

Manages the physical transmission of data over network media

Router

Determines the best path for data packets to travel across an internetwork

Utilises routing tables and protocols to make routing decisions

Internet (DoD) and network (OSI) layer

WAP

Wireless Access Point

Allows wireless devices to connect to a wired network

Acts as a bridge between the wired network and wireless clients

Network (DoD) and physical and data link (OSI) layer

Bandwidth

The maximum rate at which data can be transferred through a network

Layer 2 switching

Uses MAC address table that identifies the MAC address of the connected device and port number

Enables the switch to direct frames towards the correct destination

TCP vs UDP

TCP - reliable, provides extensive error-checking mechanisms, sequencing to ensure packets arrive in order

UDP - no acknowledgement segment, faster, simpler, more efficient, no retransmission of lost packets

TCP packet architecture

20-60 byte variable length header

Heavy-weight

Byte stream connection type

Low overhead (higher than UDP)

UDP packet architecture

8 byte fixed length header

Lightweight

Message stream connection type

Very low overhead

Subnetting

Process of dividing a large network into smaller networks

Saves IP addresses, keeps networks faster and protects sensitive data

Contains broadcast domains to minimise bandwidth consumption

Default gateway

Node that forwards the packet to other networks when there’s no routing info about the destination

DNS

Domain name system

Translates human-readable domain names into machine-readable IP addresses, enabling internet connection

Gateway

Connects 2 networks with different transmission protocols

Physical network gateway includes network interface cards (NICs), inputs and outputs and software for translating protocols

Internet (DoD) and network (OSI) layer

Network topology

Arrangement of different elements in a computer network

e.g., bus, ring, star, point to point

Network design

Efficient designs reduce the number of hops and bottlenecks, improving data flow across the network

Ping

Helps check the reachability of a server/IP address

Measures the round-trip time for messages sent from computer to destination and back

Verifies whether a device/server is active and responsive

Traceroute

Traces the path that packets take from computer to a remote server/host

Provides a detailed map of the route the data packets follow across the network

Shows how long it takes to travel from one hop (router/intermediary device) to the next

Malware

Any type of malicious software designed to harm or exploit any programmable device, service or network

Malware effects

Costs people and businesses money and can lead to data loss, identity theft and other serious problems

Ransomware

Locks up or encrypts files so user can’t access them, requiring a ransom to restore access to the files

Virus

Programs or code that self-replicates or copies itself in order to spread to other devices or areas of the network

Rootkit

Tool or set of tools used by an attacker in order to compromise a system, gain the highest level of privilege, and then hide their activity

Spyware

Enters a user’s computer, gathers data from the device and user and sends it to third parties without their consent

Backdoors

Any method by which authorised and unauthorised users are able to get around normal security measures and gain high level user access on a computer system, network or software application

Phishing

Way attackers trick users into giving them personal info, usually through fraudulent emails or text messages pretending to be from a large, trusted and known org

Reliance on software

Software systems, the algorithms that drive them and the the hardware devices they operates on are more powerful and capable than ever

Social networking

Computer networks have been used to socialise, chat and share information

Cyber safety

Refers to the ways we protect ourselves, data and others in the digital world

Cyber safety importance

Proliferation of cyber crime, ease of accessing people’s private data and overreach of governments

Internet information

Large volumes of info (which may be unsupported, unverifiable, misleading or incorrect) available through the internet

Class

Blueprint for an object

Object

New instance of a class

Attributes

Data contained within an object

Methods

Functions callable on an object or attribute

Instantiation

To create an “instance” of a class (an instance is called an object)

Using methods

Method or operation is a function that can only act on a specific class/object. Use dot notation to access an object’s methods or attributes.