Bridges

A bridge is used to join two network segments together, it allows computers on either

segment to access resources on the other. They can also be used to divide large
networks into smaller segments. Bridges have all the features of repeaters, but can have
more nodes, and since the network is divided, there is fewer computers competing for
resources on each segment thus improving network performance.


Bridges can also connect networks that run at different speeds, different topologies, or
different protocols. But they cannot, join an Ethernet segment with a Token Ring
segment, because these use different networking standards. Bridges operate at both the
Physical Layer and the MAC sublayer of the Data Link layer. Bridges read the MAC
header of each frame to determine on which side of the bridge the destination device is
located, the bridge then repeats the transmission to the segment where the device is located.

SWITCHES

Switches are a special type of hub that offers an additional layer of intelligence to basic,
physical-layer repeater hubs. A switch must be able to read the MAC address of each
frame it receives. This information allows switches to repeat incoming data frames only
to the computer or computers to which a frame is addressed. This speeds up the
network and reduces congestion.
Switches operate at both the physical layer and the data link layer of the OSI
Model.

HUB

HUB
Networks using a Star topology require a central point for the devices to connect.
Originally this device was called a concentrator since it consolidated the cable runs from
all network devices. The basic form of concentrator is the hub.

As shown in Figure; the hub is a hardware device that contains multiple, independent
ports that match the cable type of the network. Most common hubs interconnect
Category 3 or 5 twisted-pair cable with RJ-45 ends, although Coax BNC and Fiber Optic
BNC hubs also exist. The hub is considered the least common denominator in device
concentrators. Hubs offer an inexpensive option for transporting data between devices,
but hubs don't offer any form of intelligence. Hubs can be active or passive.

An active hub strengthens and regenerates the incoming signals before sending the
data on to its destination.

Passive hubs do nothing with the signal.

Ethernet hubs

An Ethernet hub is also called a multiport repeater. A repeater is a device that amplifies
a signal as it passes through it, to counteract the effects of attenuation. If, for example,
you have a thin Ethernet network with a cable segment longer than the prescribed
maximum of 185 meters, you can install a repeater at some point in the segment to
strengthen the signals and increase the maximum segment length. This type of repeater
only has two BNC connectors, and is rarely seen these day



8 Port mini Ethernet Hub

The hubs used on UTP Ethernet networks are repeaters as well, but they can have many
RJ45 ports instead of just two BNC connectors. When data enters the hub through any
of its ports, the hub amplifies the signal and transmits it out through all of the other
ports. This enables a star network to have a shared medium, even though each
computer has its own separate cable. The hub relays every packet transmitted by any
computer on the network to all of the other computers, and also amplifies the signals.
The maximum segment length for a UTP cable on an Ethernet network is 100 meters. A
segment is defined as the distance between two communicating computers. However,
because the hub also functions as a repeater, each of the cables connecting a computer
to a hub port can be up to 100 meters long, allowing