Hubs: what are they and how do they work?

Even though other options are now available for operating a network, hubs are still used. What is a hub, what is it used for (and how?), and what advantages and disadvantages does it have, especially compared to a switch?

A hub is a network device that connects various network nodes, e.g. in an Ethernet, in a star configuration. In the OSI (Open Systems Interconnections) reference model, hubs are classified as level 1 devices that operate at the physical layer. Their main task is to interconnect several computers and immediately forward received data. Hubs are usually made of plastic, run on an external power supply and contain between 4 and 16 ports, i.e. physical connections. Their maximum bandwidth is usually 10/100 Mbit per second.

A hub receives data and then sends it in full to all connected devices (hosts). All ports of the hub operate at the same speed and are located in a collision domain (which includes all connected network devices). Unlike other network devices, a hub does not offer the option to control or exclude only individual receivers. This means that all data packets are always forwarded to all computers during a transfer. This means that even those devices the data wasn’t intended for also receive the data. Since all hosts are occupied in this way, the other devices cannot send any data themselves in the meantime. Instead, simultaneous requests are processed one after the other.

If you need more hosts, you can connect one hub to another hub. This connection is created with a simple crossover cable over one of the ports. However, the number of hosts is automatically limited by the 5-4-3 rule, or repeater rule. This states that a maximum of five segments with four repeaters can be used between two end devices. In addition, the connected hosts share the entire bandwidth when a hub is used. This inevitably leads to speed losses, especially when transferring large data packets.

Hubs are an outdated technology. In addition to the speed losses mentioned above, and the lack of flexibility in terms of data transfer and the selected recipients, a hub system is also comparatively vulnerable to security issues. For example, the system cannot be quarantined and data traffic does not take place in a protected manner. Any security issues or privacy concerns immediately affect all connected hosts.

For these reasons, hubs are used less often these days. Their lack of flexibility is no longer up to date, and the lack of speed is a major obstacle with ever larger data volumes. One possible application that is still more common today is the expansion of older networks. Streaming media to multiple devices is also possible. Hubs are still used for network analysis. Here, the lack of flexibility is actually an advantage. Since all network data can be found on all ports, no additional mirror port is needed to read and analyze it.

Nevertheless, the time of hubs is by and large over. According to the 802.3 standards of the IEEE (Institute of Electrical and Electronics Engineers), hubs have been considered obsolete since 2011. In the meantime, the switch has taken their place. There are many reasons for this, since the switch is strictly speaking a further development of its aged predecessor. Unlike the hub, the switch makes it possible to send and receive data simultaneously. The bandwidth is also not limited, but is constant. While the hub always controls all hosts and delivers all data, it is possible to select individual end devices with the switch.

The switch operates at level 2 of the OSI reference model and can therefore theoretically create its own collision domains for each individual port. To enable precise targeting, the MAC addresses of the data frames are evaluated and, if necessary, end devices for which the respective data is not intended are excluded. Similar to a hub, however, switches such as MPLS have a broadcast function and can serve all connected hosts simultaneously. Due to their distinct advantages, switches were significantly more expensive than hubs for a long time which is slowly starting to change as they become more widely used.

To get a better picture, you can see the functionalities and capabilities of the hub and switch in direct comparison here:

While hubs were the only option for setting up networks for a long time, this no longer applies today. Network analysis, expansion of existing networks (without security relevance) or possibly for streaming various media are domains in which the technology is still suitable today. Also, since the prices of hubs and switches have also converged in the meantime, the more modern technology is clearly a wiser option.