This tutorial describes the main differences between Physical Topology and Logical Topology. Learn what physical topology and logical topology are and how they differ from each other.
Network topology defines how the network is structured and how the devices on the network communicate. It consists of two parts; physical and logical. The physical part describes the physical layout of the network while the logical part describes how data flows in the network. Both, physical and logical parts are also known as physical topology and logical topology.
Physical part (topology) + Logical part (topology) = Network topology
The following image shows how physical topology and logical topology work in network topology.
Physical topologies
Physical topology defines the physical layout of the network. It describes how the devices in the network are physically connected and what happens when a node on the network fails. It also specifics the arrangement of cabling and how cables connect one device to another in the network.
The most common physical topologies are the following.
Bus Topology: -
In this topology, devices connect in a line. Coaxial cables are used to connect devices in the sequence.
Star Topology: -
In this topology, devices connect to a centralized device. A Hub or a switch is used as the centralized device.
Hybrid Topology: -
When a bus topology is used to extend the star topology, it is known as hybrid topology.
Mesh Topology: -
In this topology, devices directly connect. There are two types of mesh topology: partial mesh and full mesh. In partial mesh, only some devices have direct connections while in the full mesh all devices have direct connections.
To learn the above topologies in detail, you can check the following tutorial.
Network Topologies Explained with Examples
This tutorial describes physical topologies in detail along with their advantages and disadvantages.
Logical topologies
Logical topology defines the logical layout of the network. It describes how the devices in the network communicate with each other and how data is transmitted. The three main logical topologies are bus topology, ring topology, and switched topology.
Bus topology
Bus topology uses the one-to-all method. In this method, when a device transmits a message, the message reaches all the nodes of the same link. All nodes read the message and determine whether the message is intended for them. A node processes the message only if it is intended for it. A node uses the destination address of the message to determine whether the message is intended for it. Each message has a destination address. If the message is not intended for the node, the node discards the message.
Ring topology
Ring topology uses the one-to-one method. In this method, each node receives data only from one node and transmits data only to one node. Data is passed sequentially from node to node. A token mechanism is used to determine the node that can transmit data. Only one node can transmit data at a time. A node can transmit data only if it has the token. After transmitting data, the node passes the token to the next node. When a node receives data, it checks whether the data belongs to it. If the data is not intended for it, it passes the data to the next node.
The following image shows how data is transmitted in both topologies.
Switched logical topology
Switched topology creates end-to-end connections on demand. In this method, there is always an electrical connection between nodes and the switch. When the switch receives a data packet, it checks the source address and destination address of the packet and creates a logical connection between the sender node and the receiver node. When the transmission is over, the switch terminates the logical connection.
The following table describes how network topology uses logical topology and physical topology.
The following table describes how network topology uses logical topology and physical topology.
| Network Topology | Physical Topology | Logical topology | Description |
| Ethernet | Bus or star | Bus | This is the classical implementation of Ethernet network topology. In this implementation, logical bus topology is implemented as a physical bus or star topology. When it is implemented as a physical star topology, a Hub is used in the center of the topology. Regardless, whether you use a physical star or bus topology, data transmitted from a node is received by all other nodes. |
| Wireless LANs | Star | Bus | In this implementation, devices connect through a central access point. Only one device can transmit data at a time and all devices listen to the transmission. Since data transmitted by one device is received by all other devices, a Wireless LAN is considered as a logical bus topology. |
| Token Ring and FDDI | Ring | Ring | This implementation uses an MAU (Multi-station access unit) to connect devices. MAU creates a logical ring, so data is passed from node to node in a pre-defined sequence until it reaches the destination device. |
| Ethernet | Switched | Star | This is the modern implementation of Ethernet network topology. This implementation uses a physical star topology running a switched logical topology. In this implementation, the switch dynamically creates logical circuits between two devices whenever they exchange data. Almost all modern networks use this implementation. |
Conclusion
Network topology defines the layout of the network. It consists of physical topology and logical topology. Physical topology describes the physical layout of the network while logical topology defines data flows on the physical layout.
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