Network topology is the structure in which the links and nodes of the network are connected, whether it is a biological network or a computer network . Computer network topology may refer to the physical topology of the network or to the logical topology. The Physical topology deals with the design of the network in terms of the devices and the cables and their positions, while logical topology is concerned with how the data actually flow in the network regardless of the physical shape of the network.
Local area networks are one example of a network that exhibits both types of topologies (physical, logical). As any node in a local area, network connects one or more links to other nodes in the network, and the layout of these links and nodes in geometric shape determines the physical topology of the network, similarly, to the planning of information flow, (information transfer) between network nodes determines a logical topology of the network. In the sample words, the physical and logical topologies may or may not be the same in the given network.
The main types of network topologies
When studying the main types of network topologies, we distinguish five main types:
- Linear (BUS)
- star
- Ring
- Tree
- comb
Physical topology
Diagram of network nodes and the physical connections between them, for example: the configuration of wires, the location of the nodes and the connections between them, and the cabling system.
Types of Physical Topology:
node to node (PointToPoint):
It is the simplest network topology and is a permanent link between the ends of two nodes. Switched one point to another topology is the basic form of traditional telephony. The reality is that this topology is switched means that it uses directed packets or circuit switching technology. from one node to another node circuit can be set up dynamically and removed when it is not needed.
Linear (Bus):
In local area networks (LANs) that use this topology, all devices are connected through a single cable with some kind of link. A piece called a terminal must be placed at the end of each cable in a linear network to prevent the signal from bouncing back into the cable. When the signal is issued from one of the computers, it goes in both directions to the rest of the devices are connected on the serial cable until it finds out the physical or logical address of the intended receiver, but if the address of any of a network devices does not match an address of the desired receiver, the transmitted data will ignore.
Since the network consists of a single cable, its cost is low compared to the rest of the networks, but on the other hand, the cost of managing it is relatively high, in addition to the fact that when the cable breaks or breaks, this leads to the disruption of the entire network. Among the forms of this structure:
Linear Bus:
A type of network topology in which all network nodes connect to a common transmission medium that has only two ends (often called a backbone or trunk). All data exchanged by network elements passes through it and can be received from virtually all nodes simultaneously (ignoring generation delays).
Distributed Serial:
It is the type of network topology in which all network nodes are connected to a common transmission medium that has two or more parties that is created by adding branches to the main part. It shares a common transmission medium.
Star:
In local area networks (LANs) that use this topology, all machines are connected to a hub. In contrast to a linear topology, here each machine can communicate with the central axis as a point to point. All signals pass through the central axis which acts as a signal amplifier or repeater allowing the signal to reach a further distance. In this architecture, each computer has a direct connection to the hub.
Stellar topologies are among the easiest and most popular to design and implement.
One of the advantages of this topology is that it is easy to add a new node to the network, and one of its disadvantages is that the disruption of the central hub leads to the disruption of the entire network. Among the forms of this structure:
Extended star:
A form of network topology in which one or more repeaters are located between the central hub and other nodes or terminals where the repeater is used to increase the transmission distance between the central hub and the node.
Distributed star:
It is a form of network topology that is based on networks connected to each other by star topologies and connected to each other by linear topologies.
Ring:
In networks that use this topology, each computer is connected to a closed loop, and each machine has a unique address for identification purposes. The signal passes through all the computers connected in the same direction, and this network uses the token passing method to regulate the transmission tolerance in the network, where only the node that owns the token can broadcast in the network and the rest of the computers act as repeaters or repeaters of the signal. One of the most famous examples of networks that use this topology is token ring networks.
One of the disadvantages of this network is that the failure of one node in the network leads to the failure of the entire network.
Tree
In these networks, there is a central root (the first level) and it is connected to one or more node at a lower level than it (the second level) and the connections between them are node to node and also these points that are connected to the root will connect on the other hand to one or more points of a lower level by node to node (Point) To Point). For each of the nodes there is a fixed number of nodes that it connects to from the lower level, this number is called the branching factor.
Notes:
Networks with tree topologies must be at least three levels because if they consist of one root and one level, they are considered topologies Asterisk. Also, a network with a tree topology with a branching coefficient of 1 devolves into a network with linear topology.
Hybrids:
Produced when more than one topology is used in the network (eg linking between a star and a ring topology in a single network).
Boolean Topology
In contrast to physical topology, logical topology is the way a signal behaves between network nodes, or is the way data is transmitted from one device to another in the network regardless of the physical connection method.
Logical topology is not necessarily the same as physical topology, for example:
In Ethernet networks that use twisted-pair Ethernet, they follow a logical linear topology with the appearance of physical linear topology.
In IBM’s Token Ring networks, they follow a ring logical topology with the appearance of a physical star topology.
Note: Signal topology differs from logical topology where logical topology expresses the shape of the path that data takes between network nodes, while it expresses the true path of signals (optical, electronic) when it passes between nodes.