CHAPTER 10. QoS198 © SAMSUNG Electronics Co., Ltd.Output Queue Congestion ManagementWhen the link bandwidth is not enough for egress traffic on an interface,queues can build up and result in increased buffer consumption. Buffermanagement is needed to ensure optimum and fair usage of the limitednumber of buffers available in the system. It is needed at two levels. It isneeded at the interface level to ensure that one interface does not consume toomany buffers and affect the traffic on other interfaces. Buffer management isalso needed for traffic classes on an interface to ensure that the classes have anoptimum share of the interface’s buffers to meet their service commitments.It is important to realize that we will not create separate buffer pools for eachinterface or class. Instead we will define ‘logical’ buffer pools for eachinterface and class which is nothing but a maximum limit which indicates thenumber of buffers that the interface or class can use. The sum of these limits,plus the limits for other uses, cannot exceed the total number of buffersavailable.Following is an explanation of variables/terms used in the followingsubsections.y BCR - ‘Committed rate bytes’. Root-out class parameter. Number of bytesthat can be sent from an interface in one scheduler interval. This depends onthe bandwidth of the interface.y CR - ‘committed rate bytes’. Class parameter. Number of bytes that can besent from the class in one scheduler interval. This is configured by the user.y bcr - ‘committed rate bytes’. Class parameter. It is the number of bytes thata class can send in one scheduler interval, corresponding to its CR.y BR - ‘Burst rate bytes’. Class parameter. Maximum number of bytes thatcan be sent from an interface in one scheduler interval. This is configuredby the user.y bbr - ‘Burst rate bytes’. Class parameter. This is the number of bytes a classcan send in one scheduler interval, corresponding to its BR.
