What is Topology?
Network topologies describe the methods in which all the elements of a network are mapped. The topology term refers to both the physical and logical layout of a network.
In this network topology tutorial, we will explain:
- What is Topology?
- Type of Network Topology
- Point to Point
- Bus Topology
- Ring Topology
- Star Topology
- Mesh Topology
- Tree Topology
- Hybrid Topology
- How to select a Network Topology?
Domain 4: Communication and Network Security [Designing and Protecting Network Security]
Eric Conrad, ... Joshua Feldman, in CISSP Study Guide [Third Edition], 2016
Star
Star topology has become the dominant physical topology for LANs. The star was first popularized by ARCNET, and later adopted by Ethernet. Each node is connected directly to a central device such as a hub or a switch, as shown in Figure 5.17.
Figure 5.17. Star Topology
Exam Warning
Remember that physical and logical topologies are related, but different. A logical ring can run via a physical ring, but there are exceptions. FDDI uses both a logical and physical ring, but Token Ring is a logical ring topology that runs on a physical star, for example. If you see the word “ring” on the exam, check the context to see if it is referring to physical ring, logical ring, or both.
Stars feature better fault tolerance: any single local cable cut or NIC failure affects one node only. Since each node is wired back to a central point, more cable is required as opposed to bus [where one cable run connects nodes to each other]. This cost disadvantage is usually outweighed by the fault tolerance advantages.
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Types of Network Topology
Network Topology is the schematic description of a network arrangement, connecting various nodes[sender and receiver] through lines of connection.
star network
A star network is a local area network [LAN] topology in which all nodes -- personal computers [PCs], workstations or other devices -- are directly connected to a common central computer that is often referred to as a hub.
Andrew Froehlich, West Gate Networks
10 Aug 2021
What is a star network?
A star network is a local area network [LAN] topology in which all nodes -- personal computers [PCs], workstations or other devices -- are directly connected to a common central computer that is often referred to as a hub. Therefore, a star network is often referred to as a hub-and-spoke network topology.
Every workstation connected to the hub is indirectly connected to each workstation using the hub as an intermediary device. Star networks are typically deployed at the access layer of enterprise networks. The access layer uses a centralized network switch to connect all endpoints to the rest of the LAN.
This image shows the central hub of a star network and all of its interconnecting devices.This graphic shows a star network consisting of a central hub. Each workstation is shown as a PC or laptop with the central hub interconnecting all devices. The lines that interconnect endpoint PCs and laptops are the spokes of the star topology. In the real world, a star network can consist of either wired or wireless connections. In this specific case, each spoke is connected to a hub by a wired connection.
How does a star network work?
Because a star network uses a centralized hub, that hub is responsible for controlling communications between devices. However, there are different ways that a central hub can manage these communications. For example, an Ethernet hub is a network device that simply listens to a communication destined for a device on a different spoke and then retransmits -- or broadcasts -- the message out to all spokes. This is the simplest form of a network hub, as it only must repeat the message to all other connected spokes. But this method can become inefficient quickly, as each communication is sent out to all spokes, as opposed to only the spoke the message was intended for.
If too many devices begin communicating on a network hub, the amount of broadcast traffic can quickly reduce network throughput. It also places the Ethernet hub where it physically looks like a star network topology but operates like a traditional bus network topology.
An Ethernet switch, on the other hand, may look like an Ethernet hub from a physical cabling perspective, but it is far more sophisticated when it comes to how the centralized device handles the transmission of communications to the intended spoke device. Ethernet switches eliminate the need to broadcast communications out to all spokes on the star network. Instead, the Ethernet switch maintains a media access control [MAC] address table. This table statically or dynamically maps the physical MAC address to the port or spoke where the spoke endpoint resides. Therefore, if an Ethernet switch knows the MAC address and specific spoke that the MAC address lives on, it can use this information to send a communication directly out to a single spoke, as opposed to broadcasting the communication to all spokes -- unnecessarily using network bandwidth. Ultimately, an Ethernet switch accomplishes the same goal as an Ethernet hub with the added benefit of better network transport efficiency.
Comparing star network topologies with other topologies
The star network topology works well when workstations are deployed randomly throughout a building or facility. With the hub-and-spoke design, it is easy to add or remove workstations, as all cabling is pulled and connected to a central hub.
From a cabling perspective, if the workstations are reasonably close to the vertices of a convex polygon and the system requirements are modest, the ring network topology may serve the intended purpose at a lower cost than the star network topology. If the workstations lie nearly along a straight line, the bus network topology may be best.
In a star network, a cable failure on a single spoke will only affect the spoke endpoint that it links to the central computer. All the other workstations will continue to function normally with the exception that they will not be able to communicate with the device that resides on the failed spoke. In other words, a star network is powerful from this perspective, as a failure on one spoke does not affect communications of other spokes that are in a functioning state. However, the caveat is that, if the central hub were to fail, all spokes on the star network also fail. If any workstation goes down, none of the other workstations will be affected. Therefore, if network redundancy is required, a mesh network topology may be a preferable option.
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Related Terms
- full-duplex
- patch panel
- route summarization [route aggregation]
Why is this relevant for C2G?
Our network cabling products - copper and fiber - provide the links between the nodes within the topology.
Overview
A network topology describes how computers, printers, and other devices [i.e. nodes] are connected to the network. The following topologies are most commonly used to build most networks.
Bus Topology
A bus topology exists when all of the nodes on the network are connected to a single cable. This single cable is commonly referred to as a backbone. Bus topology was used for early 10Base-2, ThinNet, and 10Base-5, ThickNet, coaxial cable Ethernet networks. In this topology messages sent from a node are broadcast to all nodes on the network. Only the intended recipient node accepts and processes the message. This type of network topology is relatively easy to install and inexpensive. This topology requires that both ends of the backbone cable be terminated. If the backbone is not terminated, then signal is likely to bounce back from the end of the cable causing data collisions and noise that may disrupt the network. The main drawbacks to this type of network topology are a limitation on the amount of computers that can be connected to the network, and the fact that only a single backbone cable is used to connect all of the nodes. Network using a bus topology are limited to only a few dozen computers. If the network exceeds this size performance, problems will likely result. If there is a failure in the backbone cable connecting all of the nodes, then the entire network will become unstable and potentially cease to function. This topology is not typically used in modern networks.
Bus Topology
Ring and Double Ring Topology
A ring topology exists when all of the nodes on the network are connected in a circle. Each node in the network acts as a repeater keeping the signal strong as it travels through the network. A node will generate a signal that is addressed to a specific computer on the network, and then the signal will be sent through the network in either a clockwise or counterclockwise direction. It is important to note that all signals on a network using this type of topology must travel in the same direction. This reduces the amount of data collision and noise on the network. The signal will continue through each node until it reaches the intended destination node. Typically this type of network will use a Token Ring protocol, which allows only one computer to transmit a signal at any given time. The main drawback of this type of topology is that if there is a failure of any of the nodes or cables connecting the nodes, then the network will become unstable and potentially cease to function. The solution to this drawback is a double ring topology. The double ring adds a secondary cable for redundancy in the case of a failure.
Ring Topology
Double Ring Topology
Star and Extended Star Topologies
The star and extended star are the most popular topologies for Ethernet networks. This type network is easy to setup, relatively inexpensive, and provides more redundancy than other topologies, i.e. bus topology. The star topology is configured by connecting all of the nodes on the network to central device. The central connection allows the network to continue functioning even if a single node or cable fails. The major drawback to this topology is that if the central device fails, then the network will become unstable or cease to function. The star topology is most suitable for small, centralized networks. The extended star topology adds sub-central devices that are connect to the central device. This type of topology is advantageous for large networks and provides functionality for the organization and subnetting of the IP address allocation within the network. The extended star topology is most suitable for large networks that may span an entire building.
Star Topology
Extended Star Topology
Tree/Hierarchical
The tree/hierarchical topology is configured by integrating multiple star topologies on a bus topology and using a central "root" node. The major drawback to this topology is that if the "root" node fails, then the network will become unstable or cease to function. This type of topology holds the advantage over a bus or star topology because it is able to better support future expansion of the network. However, this type of network is not commonly used because of the vulnerability of the topology.
Tree/Hierarchical Topology
Mesh Topology
This topology is divided into two different types; full-mesh and partial mesh. A full mesh topology provides a connection from each node to every other node on the network. This provides a fully redundant network and is the most reliable of all networks. If any link or node in the network fails, then there will be another path that will allow network traffic to continue. The major drawback to this type of network is the expense and complexity required to configure this topology. This type of topology is only used in small networks with only a few nodes. A partial mesh topology provides alternate routes from each node to some of the other nodes on the network. This type of topology provides some redundancy and is commonly used in backbone environments, networks where services are vital, and in wide area networks, WANs. The most notable partial mesh network is the Internet.
Mesh Topology
Partial Mesh Topology
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Types of Network Topology
The arrangement of a network that comprises nodes and connecting lines via sender and receiver is referred to as network topology. The various network topologies are: