Hub is network device for creating links between computers. Hubs are usually highly specialized and ordinary clients are not able to cope with their right choice. It is a device which has the ability to connect multiple network devices in the star topology. Hub is sometimes differently called multiport or multiplexer. It is worth noting that the hub works in the first layer ISO / OSI model, which is the physical layer. It transmits the signal from one port to all other. Hub does not do anything else except frame analysis of MAC and IP address. A hub repeats every electronic signal which reaches its. That creates single collision domain. In general, the hub is connected to the router as a splitter. To this, in turn, you can connect other network devices e.g. workstations, servers, network printers and others. Hub transmits the signal from the input port to all output ports, bit by bit. So you do not get too long delays. Individual hubs may be joined together in the cascade way. Workstations and other equipment stored in a single network are connected to one or more hubs to form segments. Ethernet does not tolerate large segments, namely collision domains, so it is good practice to create segments no greater than 40-50 units. All network hubs can be cascaded through a simple interface cable connection, reversed pairs. In order to facilitate this process the majority of the concentrators are equipped in the inverting slot. In this case, the hub can be connected using an ordinary cable. Each hub has a port to connect to the host (Upstream Port) and up to seven ports connect devices or subsequent hubs (Downstream Port), of which, in principle, anyone can be individually configure and control by the host computer. Generally, the hub consists of Hub Controller and Hub Repeater. Hub Repeater is a protocol that controls the connection between Upstream Port and Downstream Port. It is designed to provide a record which will be used for communication with the host.
Hubs are divided into active and passive. Now, passive hubs are very cheap devices that act as a junction box only and do not need external power supply. On the other hand, active hub further amplifies the signals from the workstation and allows to expand the connection. However, in this case the additional power source is required.
The computer connects to the hub using twisted pair, or 10Base-T. A good hub should also adapt to different network standards, such as Ethernet, Token Ring or ATM. When you buy a hub, pay attention to whether it allows you to implement other advanced features, which include the management of the network connection, maintenance of all traffic on a large network, the monitoring of its condition or monitoring of users. The modern hub models should have the function of switching ports for easy workstations reconfiguration and simultaneous management of workgroups. Interestingly, individual users who belong to the group may not necessarily be physically in the same place, because hub port can be assigned to any segment network.
The main parameters so that hubs deserve attention are: the number of USB ports, the distance between the inputs, cable length, dimensions, security and other options. Number of connectors in the hub is an important parameter utility, because it indicates how many network devices can be connected.