9618 AS Level Computer Science
The Internet and the World Wide Web are not the same thing! The Internet is the physical network infrastructure connecting billions of devices worldwide, while the World Wide Web is a collection of web pages and documents accessed via the Internet using browsers.
Cloud computing refers to the delivery of computing services—including storage, processing power, networking, databases, and software—over the Internet. Instead of owning and maintaining physical hardware and software resources, individuals and organizations can access and utilize these services on-demand from a third-party provider.
Cloud storage is a method of data storage where data is stored on offsite servers. Physical storage covers hundreds of servers in many locations. Instead of saving data on a local hard disk, a user can save their data 'in the cloud'.
| Cloud Type | Description | Characteristics |
|---|---|---|
| Public Cloud | Storage environment where customer and cloud provider are different companies | Services over public internet; resources shared among multiple users |
| Private Cloud | Storage provided by dedicated environment behind a company firewall | Customer and provider operate as single entity; more control and security |
| Hybrid Cloud | Combination of private and public clouds | Takes benefits of both; sensitive data on private side |
Remember: Public = shared resources, Private = dedicated resources behind firewall, Hybrid = best of both worlds!
Software applications can be delivered to a user's computer on demand using cloud computing services. The cloud provider will both host and manage software applications—including maintenance, software upgrades, and security—for a monthly fee.
Cloud-based applications can perform tasks on the local device. This makes them different from web-based apps which need an internet connection at all times. Users can still use software even if internet connection is lost—data will be stored locally and synced when connection is restored.
| Pros of Cloud Storage | Cons of Cloud Storage |
|---|---|
| Files accessible anytime, anywhere from any device with internet | Unstable internet connection causes access problems |
| No need to carry external storage devices | Expensive for high download/upload data transfer limits |
| Provides remote backup for data loss and disaster recovery | High costs for large storage capacity requirements |
| Recovers data if hard disk or backup device fails | Potential failure of cloud storage company poses risk |
| Free storage available for small quantities | Storage limits unless paid for |
Students often confuse cloud-based applications with web-based applications. Cloud-based apps can work offline (store data locally), while web-based apps require constant internet connection to function.
Bit streaming is a contiguous sequence of digital bits sent over the Internet that requires a high-speed data communication link (such as fast broadband). Bits are transmitted serially, one after another, over a single channel.
A buffer is a temporary storage area of the computer. The data transmission rate from the file server to the buffer must be greater than the rate at which data is transmitted from the buffer to the media player.
On-demand streaming allows users to pause, rewind, and fast forward the video as required.
Since real-time streaming is live, it is NOT possible to pause, rewind, or fast forward the video!
Bit rate is defined as the number of bits transmitted per second. The rate of transmission to buffer is limited by the bandwidth of the network connection.
| Internet | World Wide Web (WWW) |
|---|---|
| Massive network of networks made up of computers and electronic devices | Collection of multimedia web pages and documents stored on websites |
| Stands for "interconnected network" | URLs specify the location of all web pages |
| Uses TCP/IP protocols | Web resources accessed by web browsers |
| Physical infrastructure | Uses the Internet to access information from servers |
The Internet is the hardware/infrastructure (networks, cables, routers), while the WWW is the software/content (web pages, documents) that runs on top of the Internet!
Telephone lines have changed from copper cables to fibre optic cables, which permit greater bandwidth, faster data transfer rates, and less risk of data corruption from interference. Video calls use Voice over Internet Protocol (VoIP) where voice is converted to digital packages using packet switching.
An IP address is a unique address for a device on a network. The Internet is based on TCP/IP protocols, and IP protocols define the rules that must be agreed by senders and receivers on the Internet.
IPv4 is the common type of addressing on the Internet. It is based on 32 bits giving 2³² (approximately four billion addresses) possible addresses.
4.3 billion addresses is not enough for the modern world as the world has 7+ billion inhabitants and many people have more than one internet-connected device!
| Class | Leading Bits | Network/Host Split | Use |
|---|---|---|---|
| Class A | 0 | 8 bits Network / 24 bits Host | Large networks |
| Class B | 10 | 16 bits Network / 16 bits Host | Medium networks |
| Class C | 110 | 24 bits Network / 8 bits Host | Small networks |
| Class D | 1110 | N/A | Multicasting |
| Class E | 1111 | N/A | Reserved for research |
IPv6 uses 128-bit addressing, which allows for approximately 3.4 × 10³⁸ addresses. It was developed to overcome the address limitation problems of IPv4.
Zero compression removes consecutive blocks of zeros using double colon (::)
Subnetting is the process of dividing a larger network into smaller sub-networks (subnets). It allows more efficient use of hostID by applying a structure to it, dividing a LAN into two or more smaller networks.
Subnetting helps reduce network traffic, improves security, and makes better use of IP addresses by reducing waste!
| Private IP Addresses | Public IP Addresses |
|---|---|
| Unique addresses assigned by network router to devices | Unique addresses assigned by ISP to network router |
| Used within private network for secure connections | Can be accessed directly over the Internet |
| More secure | Less secure |
| Can be duplicated within other networks | Must be globally unique |
| Requires NAT to access Internet | Used by DNS servers, network routers, web servers |
| Static IP Address | Dynamic IP Address |
|---|---|
| Fixed IP that never changes | Changes periodically when device reconnects |
| Manually assigned by administrator or ISP | Automatically assigned by DHCP server |
| Used by servers, websites, gamers | Used by residential users, small businesses |
| More expensive; requires extra configuration | More cost-effective; convenient for users |
| Opens network to security risks | More difficult to track network access |
Network Address Translation (NAT) is a method that allows multiple devices on a local network to share a single public IP address. The NAT box has one IP address visible over the Internet and maps private IP addresses to this public address.
Ethernet is a protocol used by many wired LANs. It was adopted as standard by IEEE and is also known as IEEE 802.3. Ethernet transmits data in frames and uses MAC addresses.
MAC address tells who you are (used in LAN to recognize each device) and IP address tells where you are on the Internet. Both work together to send a message to the correct device in the correct network!
CSMA/CD (Carrier Sense Multiple Access with Collision Detection) is a protocol used to manage collisions in Ethernet networks. When two messages use the same data channel at the same time, a collision occurs.
Students often forget that the random waiting time (backoff period) is crucial in CSMA/CD. Without random wait times, colliding devices would retry at the same time and collide again!
A URL (Uniform Resource Locator) is used to locate a resource on the World Wide Web. Web browsers use URLs to access websites.
DNS (Domain Name Service/System) is a system for finding IP addresses of a domain name. DNS servers contain a database of URLs with matching IP addresses. This eliminates the need for users to memorize IP addresses.
Name Resolution = Looking up a domain name to find an IP address. Think of it as translating a "name" humans understand to an "address" computers understand!
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| Concept | Key Points |
|---|---|
| Internet vs WWW | Internet = infrastructure; WWW = content/web pages |
| Static vs Dynamic IP | Static = fixed; Dynamic = changes, assigned by DHCP |
| Public vs Private IP | Public = Internet-facing; Private = internal network |
| MAC vs IP Address | MAC = who you are; IP = where you are |