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Interconnection Networks (notes by Ken Ryu of Arizona State)

Interconnection Networks (notes by Ken Ryu of Arizona State). Measure How quickly it can deliver how much of what’s needed to the right place reliably and at good cost and value Performance Metrics latency: time for the first bits to arrive bandwidth: sustained volume of communication

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Interconnection Networks (notes by Ken Ryu of Arizona State)

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  1. Interconnection Networks (notes by Ken Ryu of Arizona State) • Measure • How quickly it can deliver how much of what’s needed to the right place reliably and at good cost and value • Performance Metrics • latency: time for the first bits to arrive • bandwidth: sustained volume of communication • connectivity: how far is the furthest neighbor • hardware cost: can we afford to build this thing? • reliability: can links fail and the system still run? • functionality: “for free” features • combining messages • fault tolerance • Options • topology • operation mode (synchronous or asynchronous) • switching strategy (circuit, store-and-forward, cut-through) • control strategy (central or distributed)

  2. Static Connection Topologies (1) • Topology determines • degree, connections, distance (latency) • routing, cost-performance • Fully Connected Nodes • Star • Tree

  3. Static Connection Topologies (2) • Mesh and Ring • Hypercube • Shuffle Exchange

  4. Multistage Switching Networks • several stages between source and destination • provide different options in • cost • wires • blocking probability • can be combined into many hybrid options

  5. Omega Networks • logn(M) stages for M nodes and n by n cross bars • message block if the required output link is not available

  6. Benes networks • additional stages to reduce blocking • can route any disjoint src/dest pairs wo blocking • but must know requests in advance

  7. Dynamic (Fat) Trees • Tree: Disproportionate share of traffic • Idea: more resources near the root • Charles Leiserson • Used in CM-5 • More switches near the root • Theory • Given a size, the best network of the size • Proof : Leiserson’s Fat tree paper

  8. Interconnection: Combining • Try to reduce hot spots in a communication network • combine requests for the same location • really cache line • Use topology of the network to match comm ops • broadcast • flood network - everyone sends to everyone else • form a broadcast tree • reduction • put arithmetic operations into switches • CM-5 fast hardware for and,or,min,max

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