What are network topologies?

In communication networks, a topology is a usually schematic description of the arrangement of a network, including its nodes and connecting lines. There are two ways of defining network geometry: the physical topology and the logical (or signal) topology.

The physical topology of a network is the actual geometric layout of workstations. There are several common physical topologies, as described below and as shown in the illustration.

In the bus network topology, every workstation is connected to a main cable called the bus. Therefore, in effect, each workstation is directly connected to every other workstation in the network.

In the star network topology, there is a central computer or server to which all the workstations are directly connected. Every workstation is indirectly connected to every other through the central computer.

In the ring network topology, the workstations are connected in a closed loop configuration. Adjacent pairs of workstations are directly connected. Other pairs of workstations are indirectly connected, the data passing through one or more intermediate nodes.

If a Token Ring protocol is used in a star or ring topology, the signal travels in only one direction, carried by a so-called token from node to node.

The mesh network topology employs either of two schemes, called full mesh and partial mesh. In the full mesh topology, each workstation is connected directly to each of the others. In the partial mesh topology, some workstations are connected to all the others, and some are connected only to those other nodes with which they exchange the most data.

The tree network topology uses two or more star networks connected together. The central computers of the star networks are connected to a main bus. Thus, a tree network is a bus network of star networks.

Logical (or signal) topology refers to the nature of the paths the signals follow from node to node. In many instances, the logical topology is the same as the physical topology. But this is not always the case. For example, some networks are physically laid out in a star configuration, but they operate logically as bus or ring networks.

Network Topology refers to layout of a network and how different nodes in a network are connected to each other and how they communicate. This slideshow describes five of the most common network topologies.

Network topologies are categorized into the following basic types:

This diagram illustrates the bus network topology. A bus topology such as10Base-2 or10Base-5 Ethernet uses a single communication backbone for all devices.

This diagram illustrates the ring network topology. A ring topology such as FDDI or SONET sends messages clockwise or counterclockwise through the shared link.

This diagram illustrates the star network topology. A star topology typically uses a network hub or switch and is common in home networks.

This diagram illustrates the mesh network topology. A mesh topology provides redundant communication paths between some or all devices (partial or full mesh).

This diagram illustrates the tree network topology. A tree topology integrates the star and bus topologies in a hybrid approach to improve network scalability.

# you can see this link

http://compnetworking.about.com/od/networkdesign/ig/Computer-Network-Topologies/

Network topology refers to the physical or logical layout of a network. It defines the way different nodes are placed and interconnected with each other; alternately, network topology may describe how the data is transferred between these nodes. There are two types of network topologies: physical and logical. Physical topology emphasizes the physical layout of the connected devices and nodes, while the logical topology focuses the pattern of data transfer between network nodes.

The physical and logical network topologies of a network do not necessarily have to be identical. However, both physical and network topologies can be categorized into five basic models:

• Bus Topology: All the devices/nodes are connected sequentially to the same backbone or transmission line. This is a simple, low-cost topology, but its single point of failure presents a risk.
• Star Topology: All the nodes in the network are connected to a central device like a hub or switch via cables. Failure of individual nodes or cables does not necessarily create downtime in the network but the failure of a central device can. This topology is the most preferred and popular model.
• Ring Topology: All network devices are connected sequentially to a backbone as in bus topology except that the backbone ends at the starting node, forming a ring. Ring topology shares many of bus topology's disadvantages so its use is limited to networks that demand high throughput.
• Tree Topology: A root node is connected to two or more sub-level nodes, which themselves are connected hierarchically to sub-level nodes. Physically, the tree topology is similar to bus and star topologies; the network backbone may have a bus topology, while the low-level nodes connect using star topology.
• Mesh Topology: The topology in each node is directly connected to some or all the other nodes present in the network. This redundancy makes the network highly fault tolerant but the escalated costs may limit this topology to highly critical networks.