Physical vs. Logical Topologies

• Physical topologies describe the placement of network devices and how they are physically connected.
• Logical topologies describe how data flows throughout a network.

Wired Network Topologies

There are four main wired network topologies:

• Bus — All devices on a single cable
• Ring — Devices connected in a circular loop
• Star — All devices connected to a central device
• Mesh — Every device connected to every other device

Each topology has its own advantages, disadvantages, and use cases. Let's explore each one.

Bus Topology

• All devices are connected to a single coaxial network cable.
• Devices are connected via a vampire tap or T-Connector.
• Terminators are required at both ends of the cable to prevent signal bounce.
• Only one device can be active on the network at a time — data signals travel in both directions and are received by all devices.
• A single break in the cable can take down the entire network.
• Considered antiquated technology — rarely used in modern networks.

Ring Topology

• All devices are connected in a circular fashion.
• Each computer is connected to two other computers.
• Data travels from node-to-node, either unidirectional or bidirectional.
• Each device (node) in the ring regenerates the signal, acting as a repeater.
• Failure of a single node can take down the entire network.
• FDDI (Fiber Distributed Data Interface) uses two counter-rotating ring topologies for redundancy.

Star Topology

• All devices are connected to a central connecting device, which is usually a switch.
• Devices send data to the switch, which forwards it to the appropriate destination device.
• The most popular topology in today's networks — used in most large and small networks.
• Central device is a single point of failure — if the switch goes down, the entire network goes down.

Example: Your home or office network likely uses a star topology — all devices connect to a central router/switch.

Mesh Topology

• Each device is connected to every other device by separate cabling.
• Highly redundant and fault-tolerant — if one link fails, data can take another path.
• Expensive to install due to the large amount of cabling required.
• Commonly used in Enterprise Networks and WANs.

Two Types:

• Partial Mesh — Some devices are connected to all others, but not every device has a direct connection to every other device.
• Full Mesh — Every device is directly connected to every other device on the network.

Wired Topology Comparison

Wireless Network Topologies

Wireless networks utilise radio frequencies (RF) to communicate instead of physical cables.

There are three main wireless topologies:

• Ad Hoc — Direct device-to-device communication
• Infrastructure — Devices connect through a central access point
• Mesh — Multiple access points create a robust network

Ad Hoc Wireless Network

• A peer-to-peer (P2P) wireless network where no wireless access point (WAP) infrastructure exists.
• Devices communicate directly with one another.
• Personal area networks (PANs) are a common example of ad hoc wireless networks.

Real-World Examples:

• Apple AirDrop between iPhones
• Bluetooth file sharing between devices
• Wi-Fi Direct for printing

Infrastructure Wireless Network

• A wireless network that uses a wireless access point (WAP) as its central connecting device.
• Infrastructure wireless networks (WLANs) are commonly used in homes and small offices.
• All wireless devices connect to the WAP, which then bridges traffic to the wired network.

Example: Your home Wi-Fi network — your laptop, phone, and smart TV all connect to the Wi-Fi router (which contains a WAP).

Wireless Mesh Network

• Just like a wired mesh, wireless mesh networks utilise several wireless access points (nodes) to create a robust network that is:

• Scalable — easily add more nodes to extend coverage
• Self-Healing — if one node fails, traffic reroutes automatically
• Reliable — built-in redundancy across multiple paths

Common in larger homes and businesses.

Wireless Topologies in Everyday Life

You probably use all three wireless topologies without even realising it:

Network Interface Card (NIC)

• The network adapter installed on your network device.
• Provides the physical and electrical, light or radio frequency connections to the network media.
• It can either be an expansion card, USB device, or built directly into the motherboard.

Every device that connects to a network needs a NIC — it's the hardware that makes network communication possible.

Hubs

• Used to connect devices together within a network.
• Known as a "Multi-Port Repeater" — traffic goes in one port and is repeated (broadcasted) out every other port.
• OSI Layer 1 device — operates at the Physical layer.
• A "dumb" network device — has no intelligence about where data should go.
• Causes increased network collision errors.
• Much less efficient than a switch.
• Legacy equipment — no longer used in modern networks.

Switches

• Connects devices together just like a hub, but much smarter.
• Intelligent network device — operates at OSI Layer 2 (Data Link).
• Memorises the MAC address of each connected device via a MAC Address Table (also called a Content Addressable Memory / CAM Table).
• Pays attention to source and destination MAC addresses during communication.
• Uses ASIC (Application-Specific Integrated Circuitry), making them extremely fast.
  • Analogy: Like an automated coin-sorting machine with physical slots (hardware), rather than a person manually inspecting and sorting each coin one by one (software).
• Breaks up collision domains — traffic goes in one port and out to only the destination port.
• Standard in today's network infrastructure.

Hub vs. Switch — What's the Difference?

Wireless Access Point (WAP)

• A WAP is a bridge that extends the wired network to the wireless network.
• Just like a switch, it's a Data Link Layer 2 device.

Important: A WAP is NOT a Router

• A WAP operates at Layer 2 — it only bridges wireless devices onto the same network. It forwards frames using MAC addresses, just like a switch.
• A Router operates at Layer 3 — it connects different networks together and routes traffic between them using IP addresses.
• A WAP does not assign IP addresses, does not perform NAT, and does not route packets between networks.

Example: In an office, a WAP lets your laptop connect wirelessly to the same LAN that desktop computers are wired into. But to reach the internet (a different network), you still need a router.

People often confuse the two because home SOHO devices combine both a WAP and a router into one box.

Wireless Range Extender

• Extends the range of a wireless network by acting as a wireless repeater.
• Rebroadcasts radio frequencies from the wireless network it is associated with.

Example: If your Wi-Fi signal doesn't reach the back of your house, a range extender placed halfway can pick up the signal and rebroadcast it to extend coverage.

Note: Range extenders typically halve the available bandwidth since they use the same channel to receive and retransmit.

Routers

• Used to connect different networks together.
• Routes traffic between networks using IP addresses.
• Uses intelligent decisions (routing protocols) to find the best path to get a packet from one network to another.
• Break up broadcast domains — a broadcast is a message sent to every device on a network (e.g. "Who has this IP?"). Without a router, every broadcast reaches every device, wasting bandwidth. A router stops broadcasts from crossing into other networks, keeping each network quieter and more efficient.
• OSI Layer 3 device (Network layer).

Quick OSI Layer Reference:

• Layer 3 = Router
• Layer 2 = Switch
• Layer 1 = Hub

Networking Devices & OSI Layers

A quick way to remember which device operates at which layer:

Memory tip: "Hub = 1, Switch = 2, Router = 3" — the smarter the device, the higher the layer!

Modems (Modulators/Demodulators)

• Modems modulate one signal to another, such as digital to analog.
• For example, modulating digital pulses into an analog wave for telephone/coaxial cable transmission.

How it works:

• Modulation: Converts digital data (`1`s & `0`s) from your computer into an analog carrier wave.
• Demodulation: Converts incoming analog signals back into digital data your computer can use.

The word "modem" comes from Modulator + Demodulator.

Small Office Home Office (SOHO) Device

• An all-in-one wireless router with expanded capabilities.

A typical SOHO device combines many networking functions into a single box:

• Router — routes traffic between your LAN and the internet
• Wireless Access Point — provides Wi-Fi connectivity
• Firewall — basic network security
• Switch — wired Ethernet ports for devices
• DHCP Server — automatically assigns IP addresses
• NAT Device — translates between private and public IPs

Example: The Wi-Fi router in your home is most likely a SOHO device doing all of the above.

Media Converters

• As the name suggests, a media converter converts one media type to another.
• Layer 1 device — performs physical layer signal conversion only.
• Ethernet to fiber optic media converters are commonly used.

Example: An office building may use copper Ethernet cabling inside offices but fiber optic for the backbone between floors. A media converter bridges these two media types.

Firewalls

• Firewalls are the foundation of a defense-in-depth network security strategy.
• They protect your network from malicious activity on the Internet.
• Prevent unwanted network traffic from different networks from accessing your network.
• Firewalls do this by filtering data packets that go through them.
• They can be:
  • Network-based (hardware) — a standalone network device
  • Host-based (software) — software running on a computer system (e.g., Windows Firewall)

Types of Firewalls

DHCP Server

• Dynamic Host Configuration Protocol (DHCP) Server.
• Automatically assigns IP addresses to hosts on the network.
• Makes administering a network much easier — no need to manually configure each device.
• An alternative is static IP addressing, where you manually assign an IP to each device.

Example: When you connect your phone to Wi-Fi, a DHCP server automatically gives it an IP address like 192.168.1.105 — you don't have to type it in yourself.

Try It Yourself — Find Your IP Address

• Windows: Open CMD and type ipconfig
• Mac/Linux: Open Terminal and type ifconfig or ip a
• Look for IPv4 Address — that's the IP your DHCP server assigned to you.

Can You Get a New IP from the DHCP Server?

• Yes! You can release your current IP and request a new one:
• Windows: ipconfig /release then ipconfig /renew
• Mac: sudo ipconfig set en0 DHCP (or use System Settings → Network)
• Linux: sudo dhclient -r then sudo dhclient
• This is useful when troubleshooting network issues or when moving between networks.

Voice over IP (VoIP) Endpoints

• Most modern phone systems run over IP networks via dedicated protocols, such as the Session Initiation Protocol (SIP).
• Used in both home and office environments.
• VoIP endpoint devices can be:
  • Hardware — dedicated VoIP phones (e.g., Cisco IP phones)
  • Software — applications like Cisco Jabber, Microsoft Teams, or Zoom

Example: When you make a call on Microsoft Teams or Zoom, you're using VoIP — your voice is converted to data packets and sent over the internet.

Week 2 Summary