3Com 10014299 manual QOS Overview

664CHAPTER 47: QOS OVERVIEW

■Differentiated service: This is is a kind of multi-service model oriented to different demands. It sorts the services into classes, and provides different qualities of services according to the various classes without the support of signal. Differentiated service adopts the following technologies:

■Traffic policing: Performing the traffic policing for one or more or all flows.

■Traffic shaping: Performing the traffic shaping for one or more or all flows.

■Queue management: Performing congestion management for the queues on the interface by employing the technologies such as FIFO, Priority Queue (PQ), Customized Queue (CQ), Weighted Fair Queue (WFQ), Class-based Weighted Fair Queue (CBWFQ).

■Congestion avoidance: It is a traffic control mechanism that, by monitoring the usage of the network resources (such as the queue or memory buffer), removes the network overload by dropping packets on its own initiative to adjust the network traffic in case of network congestion.

The QoS of the 3Com router is implemented based on the differentiated service, and has the following functions:

■Packet classification: The services with different service quality requirements are classified in the network edge. It is processed according to different packet classifications in the core network.

■Traffic policing: Two token buckets are used to indicate the allowable burst levels. Tokens are placed into each bucket at the same rate (CIR). The CBS (the C bucket) is generally smaller than EBS (the E bucket). When traffic conformance is being evaluated, if the C bucket has sufficient tokens, the traffic is said to conform to allowable burst levels. If the C Bucket is short of tokens but the E bucket has sufficient tokens, the traffic partially conforms to allowable burst levels. If both the C and E buckets are short of tokens, the traffic does not conform to the allowable burst levels.

■Traffic shaping: Performs the shaping on the flows that do not conform to the predetermined traffic characteristics, to facilitate the bandwidth matching. It may perform the shaping on each flow or all flows on the interface.

■Interface Line Rate: Provides a management approach to the network bandwidth by limiting the physical interface bandwidth.

■Congestion management: Provides various queue mechanisms to relieve and dispatch the congested packets when the interface congestion occurs.

■Congestion avoidance: Takes measures to avoid the congestion by estimating the congestion status of the network. The congestion avoidance may reduce the packet loss ratio and improve the efficiency of the network availability.

Benefits of QoS for QoS can provide controllable and predictable services for network applications and

the Network Service network traffic. Using QoS in the network can realize:

■Control of network resources. The user can control the usage of network resources. For example, the user may limit the bandwidth resource consumed in the FTP transmission on a connection, or provide higher priority for the data that are more important.