Method and apparatus for implementing a quality of service policy in a data communications network

Abstract

A content addressable memory (CAM or L3 Table) contains flow information for each active flow of packets passing through a given node of a data communications network. The CAM has associated with each entry (corresponding to each active flow) a packet counter, a byte counter, a token bucket and a contract value. Each flow is assigned one of a plurality of output queues and optionally at least one output threshold value. A token bucket algorithm is employed on each flow to determine whether packets from that flow exceed the contract value. Such packets may be dropped or optimally modified to reflect an alternate output queue and/or alternate threshold before being sent to the selected output queue for transmission from the node. In another aspect an access control list CAM (ACLCAM) contains masked flow information. The ACLCAM provides an index to internal token bucket counters and preconfigured contract values of an aggregate flow table which becomes affected by the packet statistics. In this way flows are aggregated for assignment of output queues and thresholds, possible dropping and possible modification of packets. In another aspect the CAM contains active flow information, the ACLCAM and the aggregate flow table are combined in one system and used to produce in parallel a pair of traffic rate limiting and prioritizing decisions for each packet. The two results are then resolved to yield a single result.