Also known as ethernet hub, is a physical device for connecting multiple ethernet devices together acting as if it’s a single segment. These ethernet devices are connected using twisted pair or any other suitable media to the hub. Hub operates at Physical Layer of the OSI model.
Hub can also be called a multi-port repeater. This is due to the fact that a hub will repeat the signals received from one port to all other ports excluding the port it received the signals from. For example, in a 10 port hub, if signal is sent from port # 10 then hub will repeat the signal to all other ports except port # 10.
In a hub every device connected to it will receive the broadcast traffic and thus makes it inefficient for larger networks. But for small networks with less than 20 computers, using a hub can be cost effective. All the devices connected to the hub are part of the same broadcast domain and also collision domain. That means, only one device can transmit the data at any given point of time and other system when try to transmit will result in a collision.
A ethernet network utilizing a hub behaves like a shared-medium, that is only one device can successfully transmit at a time and each host remains responsible for collision detection and retransmission.
Advantages of a Hub
- A protocol analyzer connected to a hub allows it to see all the traffic on the segment but not when it comes to a switch as it will separate the ports into different segments.
- Some computer clusters require each member computer to receive all of the traffic going to the cluster. A hub will do this naturally; using a switch requires implementing special tricks.
- A cheap hub with a 10BASE2 port is probably the cheapest and easiest way to connect devices that only support 10BASE2 to a modern network. (Cheap switches don’t tend to come with 10BASE2 ports.)
Disadvantages of a Hub
- The need for hosts to be able to detect collisions limits the number of hubs and the total size of the network.
- For 10 Mbit/s networks, up to 5 segments (4 hubs) are allowed between any two end stations.
- For 100 Mbit/s networks, the limit is reduced to 3 segments (2 hubs) between any two end stations, and even that is only allowed if the hubs are of the low delay variety.
- Some hubs have special (and generally manufacturer specific) stack ports allowing them to be combined in a way that allows more hubs than simple chaining through Ethernet cables, but even so a large Fast Ethernet network is likely to require switches to avoid the chaining limits of hubs.