ifi- cation is performed in routers or hosts, and it is combined with other actions. It is based on one or more fields in the packet header, the payload contents, and the input interface. Classification is generally done in hardware at line rate. Chapter 8 The Internet and IP Infrastructures Queue Management Queue Classification Scheduling and Conditioning Device Router Figure IP QoS mechanisms Conditioning involves policing and shaping. Policing checks conformance to a configured or signal traffic profile. In-profile traffic (i.e., traffic that meets the config- ured profile) is injected into the network. Out-of-profile traffic may be marked, delayed, or discarded. Shaping removes jitter but at the expense of some latency. Policing and shaping are performed at the network ingress or logical policing points. Traditional first-in, first-out (FIFO) queuing provides no service differentia- tion and can lead to network performance problems, such as increased delay, jitter, packet discard, and SO on. IP QoS requires routers to support some form of queue scheduling and management to prioritize outbound packets and control queue depth or to minimize congestion. Several techniques are used for queue manage- ment and scheduling. The main approach to queue management is a technique called random early detection (RED). RED monitors time-based average queue length and drops arriving packets with increasing probability as the average length increases. No action is taken if the average length is less than the minimum thresh- old, and all packets are dropped if the average length is greater than the maximum threshold. The queue-scheduling process decides which packet to send out next. It is used to manage bandwidth resources of the outbound interface. The different solutions involve tradeoffs in function and complexity. Queuing Mechanisms Although there are no standards for QoS, most router implementations provide some sort of non-FIFO queuing mechanism that is implementation specific. There are four common mechanisms: Fair Que