Traffic Management Technologies 1625When traffic arrives at wire speed, congestion may occur for network resourcebottleneck.Besides the bottleneck of link bandwidth, congestion will also be caused byresources deficiency in normal packet forwarding, such as the deficiency ofassignable processor time, buffer and memory. In addition, congestion may occurif the arrival traffic is not managed efficiently and the assignable networkresources are inadequate.Impact Congestion may cause the following negative effects:■ Increase the delay and jitter of packet transmission, and an excessive delayleads to packet re-transmission.■ Decrease the efficient throughput of network and lower the utilization ofnetwork resources.■ Intensified congestion can occupy too many network resources (especially inmemory), and the irrational assignment of resources even can lead to resourceblock and breakdown for the system.It is obvious that congestion will make the traffics unable to obtain the resourcesin time and degrade the service performance accordingly. No one wantscongestion, but it occurs frequently in complex environments where packetswitching and multi-users applications coexist. So it needs to be treated cautiously.Countermeasure A direct way to solve resources deficiency problem is to increase the bandwidth ofnetwork; however, it cannot resolve all the problems caused by congestion.A more effective method to solve the problem of QoS is to enhance the functionsof traffic control and resource allocation in the network, and to providedifferentiated services for applications with different service requirement in orderto allocate and use resources rightly. During the process of resources allocationand traffic control, the direct or indirect factors that might cause networkcongestion should be controlled with best effort to reduce the probability ofcongestion. As congestion occurs, resource allocation should be balancedaccording to features and demands of applications, to minimize the effects onQoS by congestion.Traffic ManagementTechnologiesTraffic classification, traffic policing, traffic shaping, congestion management, andcongestion avoidance are the foundations for a network to provide differentiatedservices. Mainly they implement the following functions:■ Traffic classification: It is a prerequisite for differentiated service, to identify theinterested objects based on a certain matching rule.■ Traffic policing: polices the specification of particular traffics entering therouter. When the traffics exceed the specification, then some restriction orpunishment measures can be taken to protect the commercial benefits ofcarriers and to prevent network resources from being damaged.■ Traffic shaping: A traffic control measure of actively adjusting the output speedof traffics, generally it can enable the traffic to adapt to the network resourcessupplied by the downstream router, to prevent the unwanted packet dropping
