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Chapter 10. EZchip Architecture, Capabil... > 10.5 Traffic Management - Pg. 424

424 CHAPTER 10 EZchip Architecture, Capabilities, and Applications 10.5 TRAFFIC MANAGEMENT There is a difference in the output phase of frame interface between NP-1 and NP-2 (and above). First and foremost, the NP-2 has an integrated Traffic Manage- ment (TM) functional unit. Second, the NP-1 interfaces with the CSIX switch fabric (or XMGII), whereas NP-2 interfaces with the SPI4.2 switches rather than the CSIX. Since we focus on demonstration and practical network processing experience in this book, we describe the NP-2's TM only very briefly, and continue with the NP-1 capabilities of traffic management, programming and usage. 10.5.1 NP-2's Traffic Management NP-2's integrated TM provides traffic management and frame queuing on both the ingress and egress paths through a full-duplex PFQ mechanism on all NP-2 interfaces. Traffic transmitted to the network links and the system switch- ing fabric as well to the host CPU can be queued and assigned with specific QoS settings. NP-2's TM enables provisioning of Service Level Agreements (SLAs) by support- ing DiffServ and IntServ services, as well as many QoS mechanisms (as described in Chapter 6), through its queuing schemes. Flow-based bandwidth control is facili- tated through programmable classification of flows, enabling Weighted Random Early Detection (WRED), priority-based and Weighted Fair Queuing (WFQ) conges- tion management, traffic metering, marking, and policing, and granular shaping and scheduling for thousands of queues in multilevel hierarchies. 10.5.2 NP-1's QoS, Scheduling and Congestion Management In this subsection we describe how to use the embedded QoS features of NP-1. 10.5.2.1 Virtual Output Queuing NP-1 implements at its output a Virtual Output Queuing (VOQ) to eliminate the Head of Line Blocking (HOLB) phenomenon often associated with switch- ing architectures. VOQ is implemented at the NP interface to the switch fabric. Up to eight priority levels can be defined for each of the switch fabric destina- tion ports (to other line cards). NP-1 maintains 1032 virtual output queues to the switch fabric, of which 1024 are unicast queues and eight are multicast queues. The unicast queues may be used for providing eight priority levels for 128 switch fabric destinations or four priority levels for 256 switch fabric des- tinations. Multicast frames are queued in the multicast queues, signifying the eight priority levels. The VOQ block schedules the frame transmission to the switching fabric. Sche- duling takes into consideration the flow control feedback received from the switch fabric. A congested switch fabric port will be masked and frames will not be for- warded to it. Scheduling has two phases: first, a priority level is selected, and then