Network Topology

There are two basic categories of network topologies: Physical topologies and logical topologies.

The cabling layout used to link devices is the physical topology of the network. This refers to the layout of cabling, the locations of nodes, and the interconnections between the nodes and the cabling. The physical topology of a network is determined by the capabilities of the network access devices and media, the level of control or fault tolerance desired, and the cost associated with cabling or telecommunications circuits.

The logical topology in contrast, is the way that the signals act on the network media, or the way that the data passes through the network from one device to the next without regard to the physical interconnection of the devices. A network's logical topology is not necessarily the same as its physical topology.

Today’s network designs are based on three topologies:

1. Bus topology consists of series of computers connected along a single cable segment.

• Single cable connects all network nodes without intervening connectivity devices
• Devices share responsibility for getting data from one point to another
• Terminators stop signals after reaching end of wire
• Prevent signal bounce
• Inexpensive, not very scalable
• Difficult to troubleshoot, not fault-tolerant
• This is refer as peer-to-peer networking

2. Ring topology connects computers to form a loop.

• In Ring topology each node is connected to the two nearest nodes so the entire network forms a circle
• Data only travels in one direction on a Ring network
• Token passing is the method sending data around a ring.
• A small packet, called token, passes around the ring to each computer in turn.
• If the computer has information to send, its modifies the token, add address information and the data, and sends it around the ring.
• That information travels around the ring until it either reaches its destination or return to the sender.
• When the destination computer receives the information, it returns a massage to the sender for acknowledgement.

3. Star topology connects computers via central connection point or hub.

• In a Star topology every node is connected through a central device such as a Hub or Switch
• When a computer sends a signal, the hub receives and retransmits to all the computers or devices attached to that hub
• All the connected computers will check the destination address, but only the computer to which the data is addressed processes that data
• One major drawback about this topology is central point of failure. If the hub fails, all other computers and devices attached to that hub lose network access
• However, if one of the computer and cable fails, it has no effect on the rest of the network