Hubs
Hubs, which operate at the physical
layer of the OSI Model, are the central location to which cabling from
most topologies connect. Three types of hubs include passive, active, and intelligent.
A passive hub receives information
through one of its ports, then transmits the data out through another
port to a destination location. It has no electrical power and does
not possess any signaling processing capability. Passive hubs only
allow communication from one location to another to flow across the
network, and they absorb some signal energy, causing a signal to
weaken.
An active hub receives data through one
of its ports, then works like a repeater; regenerating and re-timing
the signal before sending it out through another port to a
destination. Active hubs are also known as multi-port repeaters. Most
hubs "share" bandwidth among users - more users, less
bandwidth per user.
Intelligent hubs have even more
electronics than active hubs, and they allow network management (a
"managed" hub) or even switching (a "switching
hub", or more commonly a "switch").
MAUs
A Multistation Access Unit (MAU) allows
multiple workstations, which are connected on a Token Ring network,
the ability to communicate with each other. Although, MAUs are not a
UTP hub, they are commonly referred to as a token ring hub. Often, this device has eight ports and uses Universal Data Connectors (UDC) or RJ-45 connections.
MAUs
are not powered devices; however, occasional lights will flash when
connected to the network. MAUs also adds fault tolerance to ring
networks.
Switching Hubs
A switching hub, also called a
multi-port bridge, is a device that automatically verifies the MAC
addresses of each device connected to its ports. When a packet is sent
to its network, the switching hub checks the MAC address before
sending the data to the specified location. Unlike a standard passive
or active hub, switching hubs do not broadcast signals to each segment
on the network, but transmits data only to a specific destination. Switching Hubs (and switches) result in dedicated bandwidth per port; where as other hubs share the total bandwidth with the number of users.
Repeaters
When a repeater receives data from an
Ethernet segment, it decodes/codes the binary information, and then
retransmits the signal to the destination. Advantages of a repeater
include; the ability to extend the network a greater distance,
increase the number of devices connected to the network, added fault
tolerance by isolating breaks on a network to only that cable segment,
and the ability to link different cable types together. A disadvantage is that repeaters enlarge collision domains: If two computers send packets at the same time, a collision will occur and CSMA/CD is applied to the entire network, thereby slowing down the network.
A repeater does not manage the flow of
traffic, it only repeats signals. A maximum of four repeaters
can be installed on a single-segment Ethernet network.
Transceivers
A transceiver (transmitter-receiver) is
a device which transmits and receives data to and from the network
This device attaches to the network interface card (NIC) in two
different ways: On-Board and External.
An On-Board Transceiver is usually
"on-board" or attached to the adapter card, such as RJ-45
receptacles and BNC connectors.
An External Transceiver makes a
physical connection to the NIC using a small device, called an
adapter unit interface (AUI) or a Digital-Intel-Xerox (DIX) connector,
which is attached by an extension cable. A common external transceiver can also connect one side to an AUI interface and the other to an RJ-45 interface.
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