Network topology (Network Topology) is to determine the positional relationship and connection mode between network nodes according to the traffic volume and required information flow characteristics. Network topology refers to the physical layout of various devices interconnected by transmission media, and refers to the specific physical (real) or logical (virtual) arrangement of members that make up the network.
Why choose the right network topology? The cost of communication lines accounts for a considerable part of a communication system, so designing an optimal network topology not only saves the cost of the entire communication network economically, but also ensures the reliability and robustness of the network. At the same time, it also contributes to indicators such as flow control, link capacity allocation, and network delay.
There are mainly five types of network topologies, namely star structure, ring structure, tree structure, network structure and bus structure. The network structure can be divided into different forms such as hypercube, irregular, block and full interconnection.
1. Star topology
The main feature of the star network is that it has a central control node, in which any node only needs two hops at most to complete the communication with any node in the network. A schematic diagram of a star topology is shown in the figure below.
Advantages: Network construction and maintenance are relatively easy, the delay is small, and the network structure is simple.
Disadvantages: As the scale of the network increases, its reliability will deteriorate; the central control node is the bottleneck of this type of network. Once the central node is paralyzed, it means that the entire network is paralyzed.
2. Ring topology
In the ring network, each node is connected end-to-end to form a closed ring, information can only be transmitted point by point along the ring, and any node on the ring can request to send information. A characteristic of this type of network is that information has a fixed direction of information transmission, and the communication path between two nodes is unique. If one of the nodes is broken and the line is blocked, it will automatically transmit in the opposite direction, with high reliability. A schematic diagram of a ring topology is shown in the figure below.
Advantages: suitable for real-time services; the transmission direction of information is fixed.
Disadvantages: When the number of nodes on the ring network is large, there will be conflicts, which will affect the transmission rate; expansion is inconvenient.
3. Tree topology
A tree-type network is a typical hierarchical structure network. This type of network requires shorter communication lines, is easy to expand, and has a lower cost of establishing a network. Except for the final leaf node, when other non-master nodes or non-trunk lines fail, it will only affect the local network. But once the highest-level master node is damaged, the entire network will also be paralyzed, which is similar to the star network. This type of network is suitable for hierarchical networks because it has the same hierarchical structure as the military system, so it is more commonly used in military communications. A schematic diagram of the tree topology is shown in the figure below.
Advantages: It is convenient to expand nodes; the structure is simple; the link supports two-way transmission.
Disadvantages: If a high-level node fails, it will have a greater impact on the entire link.
4. Mesh topology
Mesh network, also known as distributed structure network, is the most complex network, but it is also the most robust network. Network nodes generally have multiple paths to communicate with each other. Therefore, each node must have a routing strategy and flow control. The management of the entire network is relatively complicated, and the cost of building this type of network is relatively high. The most typical mesh network is fully interconnected, that is, any node has a direct connection with other nodes, as shown in the figure below.
In this way, the network has better trafficability and less delay, but the corresponding cost is higher and the flexibility is worse. If the network already has N nodes, if you want to add a new node in the network, you must add N lines, and the construction cost is relatively high. Therefore, in actual network design, a compromise point will be found between network reliability and economy, so as to build a network that meets the performance index with the minimum cost.
Advantages: high reliability.
Disadvantages: high cost; complex network structure; difficult to maintain and expand.
5. Bus topology
All the nodes of the bus-type network are connected to a common bus. At both ends of the bus, signals are reflected by terminators. Each node is connected to the bus by a T-shaped connector. If any node in the network has a problem, it will not cause damage to other nodes, and the network is still unobstructed. Only when the bus fails, will it affect the network. This type of network has the characteristics of easy expansion, and the network physical structure is simple. The schematic diagram of the bus topology is shown in the figure below.
Advantages: easy to expand nodes; high channel utilization.
Disadvantages: The bus fails and the entire network is paralyzed.
Reference article:
Research and performance analysis of OPNET-based short-wave cooperative communication system-Lin Guanying