Ethernet hub

An Ethernet hub is a type of network hardware that helps connect many Ethernet devices, like computers, so they can talk to each other as if they are on one big group. It has several ports where you can plug in cables. When a message comes in through one port, the hub sends that message out through all the other ports so everyone can see it.

Hubs work at the basic level of networking, called the physical layer. Some hubs also help manage problems when two devices try to send messages at the same time. In addition to the common RJ45 ports, some older hubs might have special connectors for connecting to very old network types.

Hubs are not used much anymore. They have been replaced by smarter devices called network switches in almost all new setups. By the year 2011, using hubs to connect networks was no longer recommended by the groups that make the rules for networking.

Physical layer function

An Ethernet hub is a simple device that connects computers together. When a message comes in through one port, the hub sends that same message out through all its other ports. This means the hub does not decide where the message should go; it just shares it with everyone connected to it.

Because the hub sends every message to all ports, messages can sometimes bump into each other. This can slow down the network. Hubs can only handle one message at a time and cannot remember messages to send later. They work best in small networks where not many messages are being sent at once.

Connecting multiple hubs

When using hubs to connect devices, there are limits to how many hubs you can use and how big the network can be. This is because devices need to be able to notice when data bumps into itself. For slower networks running at 10 Mbit/s, a rule called the "5-4-3 rule" applies. This means there can be up to five sections of cable and four hubs between any two devices. For faster networks at 100 Mbit/s, the limit is smaller — only three sections of cable between devices, and this works only with special types of hubs. Some hubs have special ports that let them connect together in ways that beat these limits, but for bigger fast networks, switches are usually needed instead.

Main article: 5-4-3 rule
Main article: Fast Ethernet

Additional functions

Most hubs can spot common issues, like too many bumps or problems on specific ports, and will stop that port from working to keep the rest of the network running. This makes hubs using twisted-pair Ethernet stronger than older types that use coaxial cables, where one bad device could mess up everything.

Hubs also make fixing problems easier because they have lights that show where something might be wrong. If needed, devices can be unplugged one by one from a hub more simply than from older cables. To make sure data moves correctly between different parts of the network, the way data is sent and the speed must be the same on each part. This means a hub cannot connect certain types of networks together, like an Ethernet network and a Token Ring network, or a slower network to a faster one.

Dual-speed hub

In the early days of Fast Ethernet, switches were expensive. Hubs could only work at one speed: either 10 Mbit/s or 100 Mbit/s. To solve this, a dual-speed hub was created. It used a small switch inside to connect the 10 Mbit/s and 100 Mbit/s parts. When a device turned on, the hub decided whether to connect it to the 10 Mbit/s or 100 Mbit/s group. This let networks mix both speeds without everyone needing to upgrade at once. These were still called hubs because they did not manage the traffic between devices of the same speed.

Fast Ethernet

Fast Ethernet hubs work at speeds of 100 Mbit/s and come in two types. Class I hubs wait for up to 140 bit times before sending the signal, which helps them change between different kinds of connections. Class II hubs wait for up to 92 bit times, letting two hubs be used together in one network area.

Gigabit Ethernet

Repeater hubs are part of the rules for Gigabit Ethernet, but we don’t see them in stores anymore because everyone switched to using better technology.

Uses

In the past, people chose hubs instead of switches because they were cheaper. By the early 2000s, the prices were almost the same. Hubs can still be helpful in some special cases.

For example, a hub can let you add a special tool to watch network traffic, or connect older types of network cables to newer ones. Hubs might also work better for some real-time networks because they can be faster in certain situations.

The first Ethernet hub, called the HP Starlan, was introduced in 1986. It helped connect computers using a new type of cable. Later models came out, but by 1994, most people started using switches instead.