fasts_wp - Fast Switched Backplane for a Gigabit Switched...

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1 Fast Switched Backplane for a Gigabit Switched Router Nick McKeown Department of Electrical Engineering Stanford University, Stanford, CA 94305-9030 1 Table of Contents 1 Table of Contents . .................................................................................................... 1 2 Abstract. ................................................................................................................... 2 3 The Architecture of Internet Routers. ...................................................................... 2 4 Why we need fast backplanes. ................................................................................. 6 5 Switched Backplanes: An Overview . ...................................................................... 7 5.1 Crossbar Switch. .................................................................................................................. 7 5.2 Fixed vs. Variable Length Packets. ...................................................................................... 9 5.3 Input Queueing and Virtual Output Queueing. .................................................................. 11 5.4 Crossbar Scheduling Algorithms. ...................................................................................... 13 5.5 The i SLIP Algorithm. ........................................................................................................ 13 6 Unicast Traffic: Performance Comparison. ............................................................ 15 7 Controlling Packet Delay. ...................................................................................... 15 8 Supporting Multicast Traffic. ................................................................................. 19 8.1 Scheduling Multicast Traffic . ............................................................................................ 21 8.2 ESLIP: Combining Unicast and Multicast . ....................................................................... 22 9 Concluding Remarks. ............................................................................................. 27 10 References. ............................................................................................................. 29
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2 2 Abstract There is a new trend in the architecture of high performance Internet routers: congested, shared backplanes are being replaced by much faster switched backplanes that allow multiple packets to be transferred simultaneously. In this paper, we’ll see why the demand for router performance means that switched backplanes are needed now, and study the technical problems that must be solved in their design. In particular, we focus on the switched backplane developed for the Cisco 12000 GSR. This router has a high- performance switched backplane architecture capable of switching 16-ports simultaneously, each with a line rate of 2.4Gb/s. The backplane uses a number of new technologies that enable a parallel, compact design providing extremely high throughput for both unicast and multicast traffic. Inte- grated support for priorities on the backplane allows the router to provide distinguished qualities of service for multimedia applications. 3 The Architecture of Internet Routers We begin by revisiting the general architecture of an IP router, as illustrated in a simplified form in Figure 1. We find it convenient to separate the router’s functions into two types: Figure 1: The key common architectural components of a router. In high performance systems, the forwarding decision, backplane and output link scheduling must be performed in hardware, while the less timely management and maintenance functions are performed in software. Forwarding Decision Forwarding Decision Output Link Scheduling Output Link Scheduling Forwarding Table Management, Network Management, and System Management Backplane
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3 1. Datapath Functions: operations that are performed on every datagram that passes through the router. These are most often implemented in special purpose hardware, and include the forward- ing decision, the backplane and output link scheduling. 2. Control Functions: operations that are performed relatively infrequently. These are invariably implemented in software, and include, the exchange of routing table information with neighbor- ing routers, as well as system configuration and management.
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This note was uploaded on 09/13/2009 for the course EE 6345 taught by Professor Cantrell during the Spring '09 term at University of Texas at Dallas, Richardson.

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fasts_wp - Fast Switched Backplane for a Gigabit Switched...

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