Standard Topologies
[BUS] [STAR]
[RING] [MESH] [HUBS]
BUS
- The Bus Topology
is often referred to as a “Linear Bus” because the computers are connected in
a straight line
- This is the simplest and
most common method of networking computers
Communication on the Bus
- Computers on a Bus
Topology Network communicate by addressing data to a particular computer
and sending out data on the cable as electronic signals.
Sending the Signal
- Network data in the form
of electronic signals is sent to all the computers on the network.
- Only the commuter whose
address matches the address encoded in the original signal accepts the
information.
- All other computer
rejects the data.
- Only one computer at a
time can send messages.
- Computers on a bus
either transmit data to other computers on the network or listen for data from
other computes on the network.
- Computers are not
responsible for moving data from one computer to the next
- If one computer fails,
it does not affect the rest of the network.
- Bother ends of each
cable segment on the network must be plugged into something – Any open cable
ends not plugged into something must be terminated to prevent signal bounce
- A break in the cable
will occur if the cable is physically separated into two pieces or if at least
one end of the cable becomes disconnected.
Signal Bounce
- Because the data, or
electronic signal, is sent to th4e entire network, it travels from one ed of
the cable to other, if it is not stopped after it has had a chance to reach
the proper destination address it will bounce back and forth casing the
network to stop.
Terminator
- A Terminator
absorbs the signal sent by computer once the signal reaches the end of the
cable.
Network Expansion
- A component called a
Barrel Connector can connect two pieces of cable together to make a longer
piece of cable.
- Using too many
connectors can prevent the signal from being correctly received
- A device called a
Repeater can be used to connect two cables.
- A Repeater actually
boosts the signal before it sends the signal on its way.
Standard Topologies
§
In the Star Topology, cable
segments from each computer are connected to a centralized component called a
“Hub”.
§ Signals are transmitted from the
sending computer through the hub to all computers on the network
§
If the Hub fails, the entire
network goes down.
Standard Topologies
- The Ring Topology
connects computers on a single circle of cable
- There are no terminated
ends
- The signals travel
around the loop in one direction and pass through each computer, which can act
as a repeater to boost the signal and send it on to the next computer
Token Passing
- One method of
transmitting data around a ring is called Token Passing – “ A token is
a special series of bits that travels around a token-ring network”
- The Token is passed from
computer to computer until it get to a computer that has data to send
- The sending computer
modifies the token, puts an electronic address on the data, and sends it
around the ring
- The data is read by each
computer it reaches the computer with the destination computer
- The receiving computer
returns a message to the sending computer indication that the data has been
received – After verification, the sending computer creates a new token and
releases it on the network
-
The token actually travels at roughly the
speed of light – A token can circle a ring 200 meters (656 feet) in diameter
about 447,376 times per second
Standard Topologies
MESH
-
A Mesh Topology network offers superior
redundancy and reliability
-
In a Mesh Topology each computer is
connected to every other computer by separate cabling – This configuration
provides redundant paths throughout the network so that if one cable fails,
another will take over the traffic
Active Hubs
-
Active Hubs regenerate and retransmit signals
in the same way as a repeater does
-
Active hubs require electrical power to run
Passive Hubs
-
Passive Hubs are only connection points and do
not amplify or regenerate the signal, the signal only passes through the hub
examples are:
-
Wiring panels
-
Punch-down blocks
-
Passive hubs do not require electrical power
to run
Hubs operate at the Layer 1 of the OSI/RM,
which is the Physical Layer
*Note: A Repeater, which is a
low-level device that amplifies electronic signals on network cables, is the
same thing as a HUB
Advantages/Disadvantages of choosing one Topology
over the other
Topology
|
Advantages |
Disadvantages |
|
Bus |
Use of cable is economical.
Media is inexpensive and easy to work with.
System is simple and reliable.
Bus is easy to extend. |
Network can slow down in heavy traffic.
Problems are difficult to isolate.
Cable break can affect many users. |
|
Ring |
System provides equal access for all
computers. Performance is even despite many users. |
Failure of one computer can impact the rest
of the network.
Problems are hard to isolate.
Network reconfiguration disrupts operation. |
|
Star |
Modifying system and adding new computers is
easy. Centralized monitoring and management are possible.
Failure of one computer does not affect the
rest of the network. |
If the centralized point fails, the network
fails. |
|
Mesh |
System provides increased redundancy and
reliability as well as ease of troubleshooting. |
System is expensive to install because it
uses a lot of cabling.
|
Marvis Strickland
Tech Instructor @ New Horizons Computer
Learning Center
This site was last updated on 12/23/2002
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