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Switching Hardware. Overview. Terminology: n x m switch has n inputs and m outputs Design Goals throughput (depends on traffic model) scalability (a function of n ) Ports and Fabrics ports circuit management (e.g., map VCIs, route datagrams) buffering (input and/or output) fabric
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Overview • Terminology: nxm switch has n inputs and m outputs • Design Goals • throughput (depends on traffic model) • scalability (a function of n) • Ports and Fabrics • ports • circuit management (e.g., map VCIs, route datagrams) • buffering (input and/or output) • fabric • as simple as possible • sometimes do buffering (internal)
Input Output Port Port Input Output Port Port Fabric Input Output Port Port Input Output Port Port Switching Fabric
2 port 1 Switch 2 1 port 2 Buffering • Wherever contention is possible • input port (contend for fabric) • internal (contend for output port) • output port (contend for link) • Head-of-Line Blocking • input buffering • 59% limit
Crossbar Switches 1 N 1 N
Use smaller crossbars 162=256, 42*4*2+2=130
Self-Routing Fabrics • Banyan Network • constructed from simple 2 x 2 switching elements • self-routing header attached to each packet • elements arranged to route based on this header • no collisions if input packets sorted into ascending order • complexity: n log2 n
001 011 001 110 011 111 110 111 Figure 3.32 Banyan Network 010 010
Port 0 Port 1 Port 0 Port 1 Port 2 Port 3 Port 2 Port 3 Port 4 Port 5 Port 4 Port 5 Port 6 Port 7 Port 6 Port 7 Port 8 Port 9 Port 8 Port 9 Port 10 Port 11 Port 10 Port 11 Port 12 Port 13 Port 12 Port 13 Port 14 Port 15 Port 14 Port 15 Contention 1010 1000
Port 0 Port 1 Port 0 Port 1 Port 2 Port 3 Port 2 Port 3 Port 4 Port 5 Port 4 Port 5 Port 6 Port 7 Port 6 Port 7 Port 8 Port 9 Port 8 Port 9 Port 10 Port 11 Port 10 Port 11 Port 12 Port 13 Port 12 Port 13 Port 14 Port 15 Port 14 Port 15 Sorting 1000 1010
Combination O(nlog2n) O(nlogn)
Inputs Outputs Mux Buffer Memory Demux Write Read Control Control Shared Media Switches