Data Networks: LAN, WAN, and WLAN

Data Networks

• A data network is a network that connects various computers and devices, so that they can exchange data with each other
• A typical example is the Internet, the largest data network in the world, which connects computers worldwide

Types of Data Networks

• LAN (Local Area Network) connects computers in a limited area (e.g. in a building or a school)
• LANs offer high speed and security, as they are often closed and do not have to be connected to the Internet
• An example of a LAN is a school network, where all computers are connected within the school building
• WAN (Wide Area Network) connects computers over large geographical distances
• The most famous WAN is the Internet
• WANs are often slower than LANs because they travel over long distances and are routed through different networks
• An example of a WAN is a network that connects branches of a company in different countries
• WLAN (Wireless Local Area Network) is a special type of LAN in which the connection is wireless via radio waves
• WLANs are especially popular in homes and offices because they connect mobile devices like laptops and smartphones without cables
• An example of a WLAN is the Wi-Fi in your home or at school

Network Topologies

• The topology of a network describes how the computers and devices are connected to each other
• There are several common network topologies:
• Bus topology: All computers are connected via a common cable
• When a computer sends data, it goes to all other computers on the network
• This topology is simple and inexpensive, but prone to errors
• If the central cable fails, the entire network will not work
• Star topology: All computers are connected to a central device (e.g. a switch or router)
• This topology is very robust: If a computer fails, the network remains functional
• However, the network can fail if the central node fails
• Ring topology: The computers are connected in a circle
• Each computer has exactly two neighbors
• Data travels in a certain direction through the ring
• This topology is hardly used today

Network Devices

• A data network contains various devices that ensure the smooth operation of the network
• Router: Connects different networks to each other
• It forwards data packets from one network to another, e.g. from the home network to the Internet
• Switch: Connects computers in a network with each other by forwarding the data packets directly to the correct device
• This avoids unnecessary data transmissions in the network, which increases efficiency
• Access Point: Used in WLAN networks to enable wireless connections
• It works like a "radio transmitter" that sends and receives signals to wireless devices
• Modem: Connects the home network to the Internet
• It converts digital signals from the computer into analog signals that can be transmitted via telephone lines or cables, and vice versa

IP Addresses

• An IP address (Internet Protocol Address) is a unique identifier for a device connected to a network
• Works similarly to a home address: It allows data to be sent from one device to another
• Every device on a network, be it a computer, a smartphone or a printer, needs an IP address to be identified and addressed
• There are two main versions of IP addresses:
• IPv4 is the most common and consists of four number blocks separated by periods, e.g. 192.168.1.1
• Each block can take a value from 0 to 255, which results in more than 4 billion possible addresses (2^32)
• Example: 192.168.0.10, 172.16.254.1, 10.0.0.1
• IPv6 was introduced to solve the problem of IPv4 address exhaustion
• IPv6 addresses consist of eight groups of four hexadecimal digits separated by colons, e.g. 2001:0db8:85a3:0000:0000:8a2e:0370:7334
• IPv6 can offer an almost unlimited number of addresses (2^128), which greatly improves communication between devices on the Internet
• Example: 2001:0db8:0000:0042:0000:8a2e:0370:7334
• An IPv4 address is divided into two main parts:
• Network part: Identifies the specific network to which the device belongs, defined by the subnet mask
• Host part: Identifies the specific device within this network
• Example: In the IP address 192.168.1.10, 192.168.1 could represent the network part and 10 the host part
• Subnets and subnet masks are used to better organize networks
• A subnet mask helps determine which part of the IP address identifies the network and which part identifies the hosts
• A typical subnet mask for a home network could be 255.255.255.0
• This means that the first three blocks (192.168.1) represent the network part and the last block (10) is used for the hosts in the network
• The subnet mask 255.255.255.0 means that the first 24 bits of the address are used for the network and the last 8 bits are for the hosts
• The number of possible hosts in a subnet can be calculated with the formula 2n-2 where n = number of host bits
• The subtracted value is for the network and broadcast address
• With a subnet mask of 255.255.255.0 there are 2^8-2=254 possible hosts in the network (from 192.168.1.1 to 192.168.1.254)
• Static IP address: This address remains constant and does not change
• It is manually assigned to a device
• Static IP addresses are useful for servers that should always be accessible under the same address
• Dynamic IP address: This address is automatically assigned by a DHCP server (Dynamic Host Configuration Protocol)
• The address may change when the device reconnects
• This is the more common method for most devices on a Home network, as it simplifies management
• Private IP Addresses are used in local networks and are not routable on the Internet
• They are only visible within a LAN
• Examples are: 10.0.0.0 to 10.255.255.255, 172.16.0.0 to 172.31.255.255, 192.168.0.0 to 192.168.255.255
• Public IP addresses are used on the Internet and are visible to everyone
• When your router establishes a connection to the Internet, it has a public IP address

Protocols

• A protocol is a collection of rules and standards that determine how data is sent, received, and interpreted over a network
• Protocols are critical for communication between devices and ensure that data is transmitted correctly and securely
• TCP (Transmission Control Protocol) ensures reliable data transmission
• It divides large amounts of data into smaller packets, sends them and ensures that all packets are received correctly and in the correct order
• If a packet is lost, TCP requests a retransmission
• When you send an e-mail, TCP is used to ensure that the message arrives completely and correctly
• UDP (User Datagram Protocol) is a faster but less reliable protocol
• It sends data packets without prior connection and without confirmations
• This means that packets can be lost or arrive in the wrong order
• UDP is used in online games or live streams because speed is important and occasional data losses are acceptable
• HTTP (Hypertext Transfer Protocol) is the protocol used to transfer web pages on the Internet
• It enables the retrieval of web pages and the sending of data between web browsers and web servers
• When you visit a website, HTTP is used to transfer the information from the server to your computer
• FTP (File Transfer Protocol) is used to transfer files over the Internet
• It allows users to upload or download files from one computer to another
• If you upload files from your computer to a server, you will most likely use FTP