Lesson
Hubs
Learning objective
Explain that a hub repeats an incoming signal to its other ports and why hubs are now mostly historical.
What is a hub?
A hub is a simple central device that connects several hosts on one shared Ethernet network. Each host uses a cable connected to one of the hub's ports.
Think back to the hosts in the previous lesson: their Ethernet adapters need somewhere to connect. A hub provides several cable sockets, called ports, so those hosts can join one local network. It is a network hub, not a USB hub.
A hub works with the signal arriving on a port. It does not identify the intended recipient and it does not choose the best outgoing port.
Meet the device
Follow the cables below. The laptop connects to port 1; the workstation, printer and server connect to ports 2, 3 and 4. The arrows show one transmission from the laptop, copied toward every other host. On a small screen, swipe across the diagram to see the receiving hosts.
Lines are Ethernet cables; arrows show this transmission's direction. Each numbered socket is a hub port. The hub repeats the signal to every other port—not back to the sender. Only the server accepts this frame because it is addressed to the server.
How a hub handles a signal
When a signal enters one port, the hub repeats that signal through every other active port. If a laptop is connected to Port 1 and three other hosts use Ports 2, 3, and 4, all three hosts receive a copy.
The hub behaves like a loudspeaker in a room: it repeats what it receives so everyone connected can hear it. The receiving hosts determine whether the information is useful to them.
This is why a hub is called a multiport repeater: multiport means several ports, and repeater means it repeats incoming signals. It operates at the Physical Layer (Layer 1), rather than reading destination addresses to decide where to send a frame.
For a message addressed only to the server, all three receiving hosts see the signal. Their network adapters examine the frame: the server accepts it, while the workstation and printer normally discard it because it is not addressed to them. The receiving hosts make that decision—not the hub.
Watch a hub repeat a signal
Follow one signal from a laptop into a hub. Notice that the hub sends a copy toward the workstation, printer, and server even though the server is the intended host.
Watch a hub repeat one signal
Press Play, then follow the signal from the laptop to the hub and every connected host.
Follow one laptop signal as the hub repeats it toward every other connected host.
Active: Laptop
Packet inspector
Inside the packet
Host or device decision
No frame is crossing a link during this step.
- Current device
- Laptop
As you watch, notice the copies leave the hub together. The workstation does not pass the message to the printer; each receives its own copy directly from the hub.
Shared network behaviour
Every device connected to the hub shares the same communication space and the same available capacity. This is called shared bandwidth: more active devices must share the network rather than receiving a separate connection of their own.
If two hosts transmit at the same time, their signals can interfere with one another. This is called a collision. For this introductory lesson, remember only that a hub creates one shared environment in which simultaneous transmissions can conflict.
More active senders share this capacity. A collision means overlapping transmissions interfere; the sending hosts must try again. The detailed recovery process belongs in the Physical Layer module.
Hub-based Ethernet uses half-duplex communication: only one host can transmit successfully at a time, and a host cannot send and receive simultaneously. The other hosts receive while that one host sends. We will study collision detection and recovery later.
Why switches replaced hubs
Modern Ethernet networks normally use switches instead of hubs. A hub repeats a signal everywhere, while a switch can be more selective about where it sends network traffic.
That difference makes switches more efficient for modern local networks. How switches make their decisions will be taught later; here, the important distinction is hub: repeat to every other port.
| Hub | Switch |
|---|---|
| Repeats incoming signals through every other active port | Can forward a frame to the port leading to a known destination |
| All attached hosts share capacity | Separate links can carry traffic independently |
| Useful for understanding older shared Ethernet | The usual choice for modern Ethernet networks |
A switch does not always send to only one port: some traffic still needs to reach multiple ports. The Switches lesson will explain that distinction.