Hubs are network components that centralize circuit connections. They started as simple wiring concentrators but have evolved into sophisticated switching centers. Hubs can be categorized by their complexity, ranging from the simplest non-switching hubs to modular multi-LAN hubs that can connect multiple network types and logically segment LANs with high-speed chassis and network management modules, providing functionality beyond just physical connectivity like bridging.

1. Hubs

2. A hub is a network
component that
centralizes circuit
connections. Hubs
started out as wiring
concentrators but have
developed into
sophisticated switching
centers.

3. Hub Complexity
One way to categorize hubs is by their level of complexity.
The Simple Hub diagram below shows the simplest type of non-
switching hub, the Multistation Access Unit (MAU). The ring-out
(RO) port of one MAU connects to the ring-in (RI) port of the
next MAU to form large rings. Network management of an MAU is
limited to front-panel LEDs in most cases and dynamic
reconfiguration is out of the question, in other words it is a
fixed configuration hub. An MAU supports one type of LAN such as
Ethernet or Token Ring.

5. The next most complex type of hub is a another fixed configuration
hub (non-switching) which allows remote network management. As with
MAUs, these hubs are straightforward and can connect only one type of
media.
Adding more sophistication and complexity is the stackable hub
which consists of modules that are stacked one on top of another and are
connected by short cables. See the Stackable Hub diagram below. Network
management capabilities exist with these types of devices but they
appear to the network as a single logical device even though physically
they are made up of separate modules.

6. Figure 8-15. Stackable Hub

7. Modular multi-LAN hubs are the most complex type of hubs.
See the Multi-Functioning Hub diagram below. This type of hub can
connect multiple types of LANs and allow users to separate LANs
into logical segments. A high-speed chassis is used to
interconnect individual LANs with network management modules.
Internetworking modules also connect to the chassis and support
bridge and router capabilities. Hubs of this type are sometimes
referred to as "collapsed backbones." If we take a close look at
the functionality of this hub we see that it provides much more
than physical layer connectivity. In fact, this example shows a
"hub" which actually has sophisticated bridging functionality.

8. Figure 8-16. Multi-functioning Hub