What is a Network Topology?

The physical topology of a network refers to the configuration of cables, computers, and other peripherals and how they attach to one another. Physical topology should not be confused with logical topology which is the method used to pass information between workstations.

NETWORK TOPOLOGIES 

Bus Topology

·         This basic form of topology is a single cable running to all the PCs in the network.
·     Each device on the network must first listen to see if there is a quiet time on the net before
      speaking. This is called carrier sense multiple access/collision detection (CSMA/CD). Also
      called a contention-based network
·         Collisions are possible. When two devices talk at the same time, a “collision” occurs. And
      both packets get destroyed. The two devices sending the packets then arbitrate amongst
      themselves to see who gets to resend the packet first
·         Termination: Like the SCSI bus, a bus network needs to be terminated.
·         Bus network problems are not easy to diagnose
·         Bus networks most commonly use coaxial cable as the media. 

Ring Topology

·         The ring topology (also known as Token Ring) is a proprietary product from IBM. It is a much
      more efficient topology, and also more expensive. In theory, the ring topology is a closed
      circle—a physical “ring.”
·         There is a single token (a small packet) in one direction on the ring. Before a device can talk, it
      has to have the token. The device then attaches its data packet to the token. The token with
      the data travels around the ring until it finds its destination. This eliminates any chance of a
      data collision.
·         Diagnosis is fairly easy on a ring. If a device fails, the device physically before it on the ring
      sends out a signal (along with the ID on the device) in the opposite direction on the ring. You
      merely have to look at the next device in the ring. (There is no termination required.)

Star Topology

·         In a star topology, all devices are connected via a hub. There is no centralized bus (like in a
      bus network). Some might consider the hub itself to be the bus, but since you can have one
      hub connected to another hub, you would have two or more buses. That debate is not yet
      over.
·         A star network is the most popular. It is cheap and efficient. It is also fairly easy to configure
      and to diagnose. If a device is not on the net, you only need to look at the device and its
      connection to the hub. If a number of devices are not on the net, you look at the hub to which
      they are connected.
·         A star network is also a contention-based network, like a bus network. Collisions are possible,
      especially on a busy network

Mesh Topology

·         In this topology there are at least two pathways to each node. In a mesh topology
·         Although a computer or cable is lost, if there are other possible routes through the network,
      the damage of one or several cables or computers may not have vital impact except the
      involved computers. However, if there are only few cables in the network, the loss of even one
      cable or device may damage the network seriously.

HYBRID TOPOLOGIES: Hybrid topologies conformed of a Logical and a Physical topology such as:

STAR BUS TOPOLOGY:
(Physical Star/Logical Bus) The Computers Believe they are attached to each other via a BUS TOPOLOGY (LOGICAL) and abide by all the rules and regulations of a BUS TOPOLOGY however they are physically attached to a Central location STAR TOPOLOGY (PHYSICAL)

STAR RING TOPOLOGY:
(Physical Star/Logical Ring) The Computers Believe they are attached to each other via a RING TOPOLOGY (LOGICAL) and abide by all the rules and regulations of a RING TOPOLOGY however they are physically attached to a Central location STAR TOPOLOGY (PHYSICAL)