 that it can all be done writing and executing software that runs on the network processor. The continuous content awareness of the NP-1 enables the programmer to code layers 2 to 4 switching and routing applications with Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. OTHER NPU ARCHITECTURES 150 NETWORK PROCESSORS granular flow classification. It also enables the programmer to handle layers 5 to 7 deep packet processing to address needs such as content switching, TCP offloading, security, and even traffic analysis. The QX-1 is a single-chip traffic manager that can be used to extend the QoS features of the NP-1 when networks must be built with stringent requirements for advanced services provisioning. QX-1 can be used in either the ingress or egress path. It was designed to achieve optimal interoper- ability and performance when interfaced with the NP-1, whose companion chip it was designed to be all along. A switching system that is built on a combination of the NP-1/QX-1 chips can provision QoS in accordance with the DiffServ model. In fact, QX-1 enables groupings of flows and queues to offer per-hop behavioral (PHB) QoS options. Features such as multiple queues that are flexibly mapped per destination port as well as a hierarchical scheduler are used for the implementation of all DiffServ services including Expedited Forwarding (EF), Assured Forwarding classes (AF1-AF4), and Class Selector (CS). In a typical system that combines the NP-1 and the QX-1 chips, the general partitioning of the tasks between the two units is as follows. The NP-1 network processor executes classification over the seven layers, handles forwarding decisions, learns new information that must be kept in tables and updates all existing tables, handles policing (using single-rate three-color marker [srTCM]/two-rate three-color marker [trTCM] token bucket), performs p