Network Topology and Types of Networks

Topologies

• Bus - This is the most simplistic topology in which the nodes of the network are individually linked to up to two successive other nodes or another node and a terminating node or terminator. This is considered now an archaic topology, because of the difficulty of troubleshooting network issues (how do you know which node is causing the connection issue?), redundancy issues (if one node fails, the network as a whole can fail), the need for terminators, and the amount of traffic created (every node between A and B must receive the packet that A sends). The nodes linked in this topology are often referred to as "daisy-chained."
  
  
• Ring - Similar to a bus network in that nodes are linked to each other, but dissimilar in that the ends of a ring network are not terminated because, well, there are no ends! A ring network is something like a "circular" network in which each and every node is linked to two other nodes. This shares the many of the same weaknesses as the bus topology, including troubleshooting difficulty, redundancy issues, and traffic created, and also adds an additional difficulty - the difficulty of adding a node to a token ring network.
  
  
• Star - This is the most typical and practical network setup. In a star network, each node maintains an individual connection to a hub, where all other nodes are connected. Traffic between two nodes, therefore, only goes through the hub and not through other nodes. This increases the redundancy of the network (one computer faltering will not cause the network to fail), increases data privacy (information does not travel through all nodes), and is a relatively easy-to-use setup. Disadvantages include reliance on the hub (a fail-point) and the amount of wiring necessary.
  
  
• Mesh/"Ad Hoc" - This is a rarely occurring configuration in which every node is connected to every other node it usually occurs only in wireless networks in "ad hoc" mode, which will be discussed later in this mode, each wireless card maintains a connection to each other wireless node it wishes to connect with, forming a "mesh" of a network. This is a relatively easy to understand option but is inefficient, requires a large amount of overhead, and is difficult to manage.
  
  
• Combined or Hybrid - This is simply a topology referring to the case where more than one topology is utilized. For example, you may have three token ring networks connected to a central hub, forming a star of token rings. This is one of many possibilities of a hybrid network.

Types of Networks (Access Models)

• Decentralized - Often referred to as "peer to peer" network, a decentralized network does not contain any distinctions between client and server. In a decentralized network, every node acts as a client and/or a server depending on the task at hand. For example, many file sharing networks are considered "decentralized" because nodes both download and upload (serve) files. The ease of adding nodes and the ease of setup is a drawing point of decentralized networks, but the pivotal downfall of these networks is their difficulty of maintenance (a setting must be changed on each node to reflect a setting change on the whole network).
  
  
• Client-Server Access - In this type, nodes can either act as "clients" or "servers," requesting or handing out information. Do not confuse the model with the star topology though the star topology often utilizes the client-server access model, this does not infer that every client-server network utilizes the star topology. In a client-server network, management is easy and the network can offer services that decentralized networks cannot, but this comes at the expense of difficulty in setup, setup cost, and server reliance.
  
  
• Centralized - A centralized network is a modified client-server network in which the clients have no individual control that is, all maintenance and setup occurs at the server level. The extreme ease of management and ability to micromanage is a drawing point of this access method, but the prohibitive cost and inflexibility of the method deter many from employing it.