Network Topology, network tutorials for beginers

Network topology

Hi friends, today we are going to talk about network topology

The Network topology describe the physical and logical design of the network Physical topologies describe how the cables are run.

Logical topologies describe how the network messages travel.

There are several types of topology.

• Bus topology
  
  
• Ring topology
  
  
• Mash topology
  
  
• Star topology
  
  
• Bus topology

BUS TOPOLOGY

A bus is the simplest physical topology.

It consists of a single cable that runs to every workstation.

This topology uses the least amount of cabling, but also covers the shortest amount of distance. If we want to increase the distance should use a repeater.

Each computer shares the same data and address path.

With a logical bus topology, messages pass through the trunk, and each workstation checks to see if the message is addressed to itself.

If the address of the message matches the workstation’s address, the network adapter copies the message to the card’s on-board memory.

Disadvantages of bus topology

• it is difficult to add a workstation
• have to completely reroute the cable and possibly run two additional lengths of it.
• if any one of the cables breaks, the entire network is disrupted. Therefore, it is very expensive to maintain.

 

STAR TOPOLOGY

• A star topology connects all cables to a central device called a hub or switch.  
• A physical star topology branches each network device off a central device called a hub or switch, making it very easy to add a new workstation.
• Also, if any workstation goes down it does not affect the entire network. (But, as you might expect, if the central device goes down, the entire network goes down.)
• Some types of Ethernet and ARCNet use a physical star topology. Figure 8.7 gives an example of the organization of the star network.

Advantages and disadvantages of star topology

• Star topologies are easy to install. A cable is run from each workstation to the hub. The hub is placed in a central location in the office.
• Star topologies are more expensive to install than bus networks, because there are several more cables that need to be installed, plus the cost of the hubs that are needed.

Ring topology

• A ring topology connects one host to the next and the last host to the first.
• This creates a physical ring of cable.
•  Each entity participating in the ring reads a message, then regenerates it and hands it to its neighbor on a different network cable.

Disadvantages of ring topology

• The ring makes it difficult to add new computers.
• If cable will be damaged the whole network will be dropped.
• Physical ring topology systems don’t exist much anymore, mainly because the hardware involved was fairly expensive and the fault tolerance was very low.

MESH TOPOLOGY

• A mesh topology is implemented to provide as much protection as possible from interruption of service.
• Each host has its own connections to all other hosts.
•  Although the Internet has multiple paths to any one location, it does not adopt the full mesh topology.

Advantages and disadvantages

• Because of its design, the physical mesh topology is very expensive to install and maintain.
• Cables must be run from each device to every other device. The advantage you gain from it is its high fault tolerance.
• With a logical mesh topology, however, there will always be a way of getting the data from source to destination.
• It may not be able to take the direct route, but it can take an alternate, indirect route. It is for this reason that the mesh topology is still found in WANs to connect multiple sites across WAN links. It uses devices called routers to search multiple routes through the mesh and determine the best path.
• However, the mesh topology does become inefficient with five or more entities.

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