Switch Architectures Distributed buffer Output buffer Input buffer
Switch Architectures • Distributed buffer • Output buffer • Input buffer Eytan Modiano Slide 6
Distributed buffer Modular architecture Basic module is a 2x 2 switch which can be either in the through or crossed position Switch buffers: None, at input, or at output of each module Switch fabric consists of many 2x2 modules □口□ N
Distributed buffer • Modular Architecture Basic module is a 2x2 switch, which can be either in the through or crossed position • Switch buffers: None, at input, or at output of each module Switch fabric consists of many 2x2 modules N N inputs outputs Eytan Modiano Slide 7
Interconnection networks N input Log(N) stages with N/2 modules per stage Example: Omega(shuffle exchange network) 0000 2010 3011 4567 11 0 17 Notice the order of inputs into a stage is a shuffle of the outputs from the previous stage:(0, 4, 1, 5, 2, 6, 3, 7) Easily extended to more stages Any output can be reached from any input by proper switch settings Not all routes can be done simultaneously Exactly one route between each SD pair Self-routing network
Interconnection networks • N input • Log(N) stages with N/2 modules per stage Example: Omega (shuffle exchange network) 0 1 2 3 4 5 6 7 0 000 1 001 2 010 3 011 4 100 5 101 6 110 7 117 • Notice the order of inputs into a stage is a shuffle of the outputs from the previous stage: (0,4,1,5,2,6,3,7) • Easily extended to more stages • Any output can be reached from any input by proper switch settings – Not all routes can be done simultaneously – Exactly one route between each SD pair Eytan Modiano – Self-routing network Slide 8
Self Routing Use a tag: n bit sequence with one bit per stage of the network E.g., Tag= b3b2b, Module at stage i looks at bit i of the tag (b), and sends the packet up if b =0 and down if b =1 In omega network, for destination port with binary address abc the tag is cba EXample: output 100=> tag=001 Notice that regardless of input port, tag 001 will get you to output 100
Self Routing • Use a tag: n bit sequence with one bit per stage of the network – E.g., Tag = b3b2b1 • Module at stage i looks at bit i of the tag (bi), and sends the packet up if bi=0 and down if bi=1 • In omega network, for destination port with binary address abc the tag is cba – Example: output 100 => tag = 001 – Notice that regardless of input port, tag 001 will get you to output 100 Eytan Modiano Slide 9
Baseline network Another Example of a multi-stage interconnection network Built using the basic 2x2 switch module Recursive construction Construct an n by n switch using two N/2 by N/2 switches and a new stage of N/2 basic(2X 2 )modules N by N switch has Log2(N)stages each with N/2 basic (2x2) modules 2x2 N/2 X N/2 2x2 2x2 2x2 N inputs 4 x 4 switch example 2x2 2x2 2x2 N/2X NA 2x2 N/2 basic mods 2 N/2 by n/2 switches
Baseline network • Another Example of a multi-stage interconnection network • Built using the basic 2x2 switch module • Recursive construction – Construct an N by N switch using two N/2 by N/2 switches and a new stage of N/2 basic (2x2) modules – N by N switch has Log2(N) stages each with N/2 basic (2x2) modules N inputs 4 x 4 switch example 2x2 2x2 2x2 2x2 N/2 x N/2 N/2 x N/2 2x2 2x2 2x2 2x2 N/2 basic mods 2 N/2 by N/2 switches Eytan Modiano Slide 10