Talking about the Local area network, we should be familiar with the concept of the LAN topology that we use. There are many types of LAN topologies for different types of networks. We should also be familiar between physical topology and logical topology. Physical topology describes the layout of a network media such as copper cable, fiber optic cable, and most popular today is the wireless. While the logical topology is concerned about logical path through the network that data can take from one place to another.
See also Local area network topology in the real world deployed in industry.
The following are basic types of LAN topology:
- Bus
- Star
- Ring
- Mesh
- Hybrids
Bus Topology
The first type of LAN topology is the Bus topology which is the first type used in Ethernet network and consists of coaxial cable connected to all the computers on the LAN network. Each computer connected to the coaxial cable through a BNC-style T-connector. The following figure shows typical Bus topology.
All the computer network devices communicate through the same shared bus – so that’s why a bus is also a logical topology. Typically, collision detection (CD) or collision avoidance (CA) algorithms are used in bus topologies to arbitrate network access along with concepts such as “broadcasts” to reach every device on the cable.
Pro:
- LAN Bus topology is very simple and inexpensive to implement, there is only one main trunk.
Cons:
- LAN Bus topology requires proper termination on both ends of the bus. Improper termination will cause the network to be malfunction.
- One single trunk cable becomes a single point of failure, one break, causes all the network impact.
- Difficult in troubleshooting since you only have one single cable to share for all the computers on the network.
This type of bus LAN topology is not popular today, and it is part of the past and it is difficult today to find any types BNC type LAN adapter at the market.
LAN Star Topology
The second LAN topology is the Star topology. If you run a network cable from each computer to a centralized point such as a Switch, that is a simple concept behind the star topology. The switch handles the repeating or switching the traffic out to the other nodes on the network. The following figure shows the LAN Star topology.
Pro:
- Management is easy through the Switch at the port level. Administration and management can be done remotely by the authorized administrator. See also switch configuration.
- Any single failure of the port will not impact the whole network. See also network troubleshooting.
- Installation of the cable in each port will not disrupt LAN services
- No termination needed like in bus topology.
You should note that nearly every popular network technology today uses a star topology for its physical implementation.
Ring Topology
The third LAN topology is the Ring topology. Compared to bus and star topologies, ring topologies are more complex but they offer some attractive features. Nodes logically communicate in a ring formation, with each node communicating only directly with its upstream and downstream neighbors.
The following figure shows ring topology. Actually Ring topology is physically implemented using star topology.
In a ring topology, access to the network is controlled through a token that is passed from node to node as the arbitration mechanism. Each node takes its turn at claiming the token as the token passes from neighbor to neighbor, and when a node possesses the token, it takes its turn to transmit onto the ring. A data packet is transferred from one node to the next until it reaches its destination node. After the destination node has received the packet, it modifies the packet to acknowledge receipt and passes it on. Eventually, the packet makes it completely around the ring, and the transmitting node receives it and notes that the receipt has been acknowledged. When the transmitting node is finished, it releases the token to its neighbor, and the process repeats.
Ring topology is primary used by the Token-Ring networks.
Pro:
- No collision detection mechanism is required, so Token ring provides greater overall bandwidth use.
- Troubleshooting is easy by the fact that each node only knows its upstream and downstream neighbors.
Cons:
- The firmware required to manage the ring is somewhat complicated and must be on every network card that participates in the ring
- Expensive to implement and mostly the LANs today use Ethernet technology which dominate the market today.
Mesh Topology
Other LAN topology is a mesh topology which is an interlacing of multiple connections among several nodes. Typically, a mesh is done for one purpose: redundancy. Any serious campus network must incorporate a mesh to achieve the level of redundancy and fault tolerance that businesses demand from their data networks. There are two types of mesh: full and partial.
The following figure is a typical full mesh LAN topology, each devices has connection to each other devices on the network.
Pros:
- Partial meshes are designed to provide redundancy where it is needed
Cons:
- Except in the smallest network, a full mesh is not very practical
- The cost of the full mesh implementation is very expensive.
Hybrid Topologies
In large network environment, you can attach Switches one to another to create larger LAN to support more devices. Hybrid topologies combined the above topologies together to form three popular hybrid topologies: tree, hierarchical star, and star-wireless.
Tree Hybrid Topology
The figure below shows combination topology: the star topology combined together with the bus topology.
Pro:
- A single computer failure will not bring the entire network to halt.
- If one hub malfunctions, it disables only the workstations that are attached to it from communicating on the network. The remaining workstations on the other hubs can continue to function normally
Cons:
- If any problem with the backbone, each groups of the Switches will become segmented into individual Switch.
Hierarchical Star Topology
For large network environment you can configure switches in hierarchical star topology as shown in the following figure.
Pros:
- Can be used to build large networks.
- Switches can be configured redundantly to avoid single point of uplink failures
Cons:
- Size restrictions due to address space and timing issues without introduction of routing technology. See also Layer 3 Switching
Star Wireless
The most recent hybrid topology has arrived with the advent of wireless technology. Wireless LAN technology in its current implementation requires a user to be in the vicinity of a wireless access point attached to the wired network. See also wireless LAN for more detail.
The star topology is necessary to combine the many access points spread across a building to ensure wireless coverage. All the access points collapse back into the main star hub, where server resources would reside on the network. As wireless technologies continue to evolve, so will the topologies that support them.
