3.1.3  Network Topology
§A network topology refers to
i.The layout of the computers and devices in a communications network or
ii.The configuration of a network that consists of cables, computers, and other peripherals.

§It describes the physical and logical layout of the network.


                              PHYSICAL AND LOGICAL TOPOLOGY

§The physical topology
-refers to the configuration of cables, computers, and other peripherals.
§The logical topology
 -refers to the architecture, that is the way in which the network appears to the devices that use it.

NOTES:
Node
 – any device that is connected to a network.
Client
– a node that requests and uses resources available from other nodes.
Server
– A nodes that share resources with other nodes.
Switch
– central node that coordinate the flow of data by sending messages directly between sender and receiver nodes.
Hub
 – The device that provides a common central connection point for nodes on network.
Network interface cards (NIC)
– expansion cards located within  the system unit that connect a computer to a network.
HOST
                 – Any computer that provides services and connection to other computers on a network

Three  basic types of network topology:

i.Star Network.
ii.Bus Network.
iii. Ring Network.








BUS TOPOLOGY
Physical


-A bus network consists of a single central

    cable (backbone/trunk), to which all computers and

    other devices connect (node).

-The bus is the physical cable that connects the computers and other devices.
-Each devices is connected to the single bus

  cable through T-Connector.


-A terminator is required at each end of the bus

  cable to prevent the signal from bouncing back

  and forth on the bus cable.


Local
-The bus in a bus network transmit data, instructions, and information as a series of signal.
-Those signals are sent as electrical pulses that travel along the length of the cable in both direction
*When a sending device transmits data, the address of the receiving device is included with the transmission


* If the device address does not match the  intended address for the data ,the  device ignores the data.
* If the data does match the device address, the data is accepted.
* All devices receive the data  but only the receiving device accept them.

 

Advantages  Of Bus Topology


1. Bus networks are inexpensive and easy to install.


2. Computers and other devices can be attached and detached at any   point on the bus without disturbing the rest of the network.

  

3. Failure of one device usually does not affect the rest of the network

    rest of the bus network.

Disadvantages of Bus Topology

1. There might be disruption when computer or other device are added orremoved

2. Because all systems on the network connect to asingle cable or backbone , a break in the cable will prevent all systems from accessing the network .

3. It is difficult to identify the problem if the entire

    network shut down








Ring Network


On a ring network, a cable forms a closed loop

  (ring) with all computers and devices arranged

  along the ring.


* Data transmitted on a ring network travels from

  device to device around the entire ring, in one

  direction (clockwise or counterclockwise)


* Token passing is one method for sending data

   around a ring

 

* Each device takes a turn sending and receiving

  information through the

  use of a token

*The token along with any data is sent from the

  first device to the second device which extracts the

  data addressed to it and adds any data it wishes

  to send.


* Then second device passes the token and data to

  the third device, etc. until it comes back around to

  the first device again.


* Only the device with the token is allowed to send

  data . All other devices must wait for the token to

  come to them.

Advantages:

1. The transmission of data is relatively

    simple as packets travel in one direction only.

2. Cable faults are easily located, making

    troubleshooting easier.


3. The uses of token passing enables all devices in

    a ring topology to share the network resources

    fairly.

Disadvantages :

1. A failure in any cable or device breaks the

    loop and can take down the entire network.

2. Data packets must pass through every computer

    therefore, this makes it slower.

3. A ring network can span a larger distance than a

    bus network, but it is more difficult to install.

Star Network.

*All the computers and other devices on the

  network connect to a central device, thus forming

  a star.


* Two types of devices that provide a common

  central connection point to all the other devices

  on the network are a hub and a switch.

Hub / Switch


* The device that provides a common central
  connection point for other devices on a
  network.
* All data that transfers from one device to
  another passes through the hub or switch.
* The hub takes a signal that comes from any device 

  and passes it along to all

  the other devices in the network.


Advantages:

1. If one device fails, only that device is affected.

2. Devices can be added to or removed from

    network with little or no disruption.

3. Easy to troubleshoot and isolate problem.

Disadvantages:

1. If the hub or switch fails, the entire network will

    be inoperable.

2. Requires more cable than most of the other

    topologies.

3. More expensive because of the cost of the

    hub/switch.

                                            ENTER :)