A network topology is the arrangement of computers, cables, and other components on a network. Topology is both physical and logical: Physical topology describes how the physical components on a network are connected; Logical topology describes the way network data flows through the physical components.

There are five basic topologies:

• Bus Topology
  
  
  In a bus topology, all of the computers in a network are attached to a continuous cable, or segment, that connects them in a straight-line topology, a packet is transmitted to all network adapters on that segment.
  
  Because of the way electrical signals are transmitted over this cable, the ends of the cable must be terminated by hardware devices called terminators, which act as boundaries for the signal and define the segment. The number of computers attached to a bus affects network performance. The more computers there are on the bus, the greater the backup of computers waiting to put data on the bus. In addition, the way computers communicate in a bus topology, there may be a lot of noise. Noise is the traffic generated on the network when computers attempt to communicate with each other simultaneously.
  
  
  
  
• Star Topology:
  
  
  In a star topology, cable segments from each computer on the network are connected to a central location, or hub. A hub is a device that connects several computers together.
  
  An advantage of the star topology is that if one computer on the star topology fails, only the failed computer is unable to send or receive data. The disadvantage of using the star topology is that because each computer is connected to a hub, if the hub fails, the entire network fails. Noise is also created on a star network topology.
  
  
  
  
• Ring Topology:
  
  
  In a ring topology, computer are connected on a single circle of cable. Unlike the bus topology, there are no terminated ends. The signal travels around the loop in one direction and pass through each computer, which acts as a repeater to boost the signal and send it to the next computer.
  
  The advantage of a ring topology is that each computer acts as a repeater, regenerating the signal and sending it on to the next computer, therby preserving signal strength.
  
  Token Passing
  
  
  The method of transmitting data around the ring is called token passing. A token is a special series of bits that contain control information. Possession of the token allows a network device to transmit data to the network. Each network has only one token.
  
  The sending computer removes the token from the ring and sends the requested data around the ring. Each computer passes along the data until the packet finds the computer that matches the address on the data. The receiving computer then returns a message to the sending computer indicating that the data has been received. The sending computer then creates a new token and releases it to the network.
  
  The advantage of a ring topology is that it can handle high-traffic environments better than bus networks. In addition, the impact of noise is reduced. The disadvantage of a ring topology is that only one computer at a time can send data on a single token ring. Also, ring topologies are usually more expensive than bus topologies.
  
  
  
  
• Mesh Topology:
  
  
  In a mesh topology, each computer is connected to every other computer by a seperate cable. This configuration provides redundant paths through the network so that if one cable fails, another carries the traffic and the network continues to function. An advantage of a mesh topology is its back-up capability by providing multiple paths through the network. Because of the extra cable needed, a mech topology can be expensive.
  
  
  
• Hybrid Topology:
  
  
  In a hybrid topology, two or more topologies are combined to form a complete network design. Networks are rarely designed using only one type of topology. Two types of hybrid topologies are commonly used: star-bus and ring-star.
  
  Star-Bus
  
  
  In a star-bus topology, several star topology networks are linked to a bus connection. After a star configuration is full, you can add a second star and use a bus connection to connect the two. In a star-bus topology, if a single computer fails, it will not affect the rest of the network. However, if the central component, or hub, that connects all computers in a star fails, all computers attached to that component fail and are unable to communicate.
  
  
  Star-Ring
  
  
  In a star-ring topology, the computers are connected to a central component as in a star network. These components, however, are wired to form a ring network. Like the star-bus topology, if a single computer fails, it will not affect the rest of the network. By using token passing, each computer in a star-ring topology has an equal chance of communicating. This allows for greater network traffic between segments than in a star-bus topology.