MCSE : Security Specialist
Hubs
A Hub is
a component that provides a common connection point for computers,
printers, and other network devices in a star topology network.
Allowing them to be managed from a central location. Also, hubs
allow you to connect and disconnect an individual computer/device
without disrupting the network. Hubs operate at the physical layer
of the OSI Model.
There
are two basic types of hubs, passive and active.
Passive
hubs simply provide a junction point, to send the data signal on to
other devices on the network.
Active
Hubs, regenerate and retransmit the data signal, because they repeat
the signal they can, increase the diameter of the network. In an
Ethernet hub the signal is regenerated to all devices at the same
time, while a Token Ring hub will only regenerate the signal to the
next to the next device in line. You can tell if a hub is active
because it requires electricity.
Active
hubs because they act like repeaters are sometimes called multiport
repeaters.
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.
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.
Routers
A
device used to connect networks of different types, such as those
using different topologies and protocols. They can operate at the
first three layers of the OSI Model. This means they can switch and
route packets across multiple networks. Routers determine the best
path for sending data.
You
can use routers, to segment a large network, and to connect local
area segments to a single network backbone that uses a different
physical layer and data link layer standard. They can also be used
to connect LAN's to a WAN's.
Brouters are a combination bridge, and router in one device.
Brouters are more cost effective as both the bridge and router are
combined together
Gateways
A
gateway is a device used to connect networks using different
protocols. Gateways operate at the network layer of the OSI model.
In
order to communicate with a host on another network, an IP host must
be configured with a route to the destination network. If a
configuration route is not found, the host uses the gateway (default
IP router) to transmit the traffic to the destination host. The
default t gateway is where the IP sends packets that are destined
for remote networks. If no default gateway is specified,
communication is limited to the local network.
Gateways receive data from a network using one type of protocol
stack, removes that protocol stack and repackages it with the
protocol stack that the other network can use.
CSU/DSU’s
A
CSU/DSU is a device that combines the functionality of a channel
service unit (CSU) and a data service unit (DSU). These devices are
used to connect a LAN to a WAN, and they take care of all the
translation required to convert a data stream between these two
methods of communication.
A DSU
provides all the handshaking and error correction required to
maintain a connection across a wide area link, similar to a modem.
The DSU will accept a serial data stream from a device on the LAN
and translate this into a useable data stream for the digital WAN
network. It will also take care of converting any inbound data
streams from the WAN back to a serial communication.
A CSU
is similar to a DSU except it does not have the ability to provide
handshaking or error correction. It is strictly an interface between
the LAN and the WAN and relies on some other device to provide
handshaking and error correction.
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