Traffic congestion occurs when multiple users compete for the same resources (such as the bandwidth and buffer) on the shared network. For example, a user on a local area network (LAN) sends data to a user on another LAN through a wide area network (WAN). The WAN bandwidth is lower than the LAN bandwidth. Therefore, data cannot be transmitted at the same rate on the WAN as that on the LAN. Traffic congestion occurs on the router connecting the LAN and WAN, as shown in Figure 1.
Figure 2 shows the common traffic congestion causes.
Traffic congestion is derived not only from link bandwidth restriction but also from any resource shortage, such as available processing time, buffer, and memory resource shortage. In addition, traffic is not satisfactorily controlled and exceeds the capacity of available network resources, also leading to traffic congestion.
As shown in Figure 3, traffic can be classified into the following based on the device location and traffic forwarding direction:
Generally, upstream traffic is not congested because upstream traffic does not bother with traffic rate mismatch, traffic aggregation, or forwarding resource shortage. Downstream traffic, instead, is prone to traffic congestion.
Traffic congestion has the following adverse impacts on network traffic:
Therefore, traffic congestion is the main cause of service deterioration. Since traffic congestion prevails on the PSN network, traffic congestion must be prevented or effectively controlled.
A solution to traffic congestion is a must on every network. A balance between limited network resources and user requirements is required so that user requirements are satisfied and network resources are fully used.
Congestion management and avoidance are commonly used to relieve traffic congestion.