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Advanced Networking

Advanced Networking. Wickus Nienaber Daniel Beech. Today’s Topics. Routing Algorithms (Dan) Up/Down routing (Wickus) L-turn routing (Wickus) Descending layers (Dan) Path Selection (Dan) Autonet (both). Routing Algorithms. Select a “path” between two machines

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Advanced Networking

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  1. Advanced Networking Wickus Nienaber Daniel Beech

  2. Today’s Topics • Routing Algorithms (Dan) • Up/Down routing (Wickus) • L-turn routing (Wickus) • Descending layers (Dan) • Path Selection (Dan) • Autonet (both)

  3. Routing Algorithms • Select a “path” between two machines • Minimal Cost (least amount of hops) • Balance network traffic • Avoid Congestion

  4. Routing in High Performance Networks • Usually local area networks • High bandwidth, low latency • Wormhole or Virtual Cut Routing is used • Deadlock free • Used in high performance computing or SANs • Strict/High network requirements • Internet or Ethernet routing fails

  5. Regular vs. Irregular Topologies • Regular • Network has graph structure (ring, meshes, hypercube, etc) • Easier to optimize • Irregular • Abnormal shape • Discovering topology is a challenge

  6. Up/Down Routing • Prevents Deadlock • Assigns a direction to links • Use of spanning tree

  7. Up/Down Routing (cont) • Non-minimal paths • Leads to congestion

  8. L-turn Routing • Attempts to solve unbalanced traffic issue • Adaptive Routing • Used in Irregular networks

  9. Building a L-R tree • Build a BFS spanning Tree • Like up/down • Assign width to every node • Increasing number is order of visit (width) • Width is horizontal distance from root

  10. Building L-R (cont) • Assign horizontal directions to channels • Left Direction: the channel with the largest width • Right Direction to the rest • Assign vertical directions to channels • Up down direction (vertical direction). Done based on distance from root. • Channels that are not in the spanning tree are added to the L-R tree (dotted lines)

  11. L-R routing • Channel that faces left is called LEFT • Channel that faces right is called RIGHT • Don’t use the LEFT channel after using RIGHT channel • Deadlock free • Guarantees any path between any pair of nodes

  12. No Root Traversal • Node 3 – 8: • L-R (3  7 6  8) 4 hops • Up/Down (3  1  0 2  6  8) 6 hops • Node 7 – 2: • Up/Down (7  6  2) 3 hops • L-R (7  1  3  0  2) or (7  3  1 4  2) 4 hops

  13. L-turn routing • LU/LD/RU/RD • Left up/down is channels facing up/down in L-R tree • Right up/down is channels facing up/down in L-R tree • Same depth channels: the right hand side node is assumed closer to the root.

  14. Restrictions in L-turn routing • No left-up channel after using the channel except left up channel. • Cyclic dependencies not including any left-up channels, does not allow the turn from left-down channel to the right direction in the cyclic channel

  15. Cyclic Dependence detection • Algorithm: • Nodes with: • a. Two or more right-up channels • b. One or more right up channels and one or more right down channel exists • Search these nodes for cycles and mark the channels prohibited • Algorithm runs in 0(n2)

  16. Analysis • Deadlock free • Guarantees any path between any pair on nodes

  17. Descending Layer Routing • For use in SANs • Implements deadlock free routing • Reduces non-minimal paths • Reduces traffic congestion

  18. Descending Layer Routing (cont) • Divide target network in layers • Impose deadlock avoidance conditions • Select deterministic paths

  19. Descending Layer Routing (cont) • Deadlock Avoidance Methods • (UD)* Up down scheme (down to up not allowed) • (UD-DU)* if sub network is even down to up not allowed, if odd up to down not allowed • UD-(DU)* In network 0 down to up not allowed on all other networks up to down not allowed

  20. Path Selection Algorithm • Pick the paths between nodes • Choose a path among set of valid paths • Goal is to select the optimal path • Random Selection • Smaller port-UID selection (low port first) • Sancho’s traffic balancing algorithm

  21. Selection of deterministic path Algorithms use Virtual Channels High virtual-channel first Path Selection (cont) • High physical-channel first • Low virtual-channel first • Low physical-channel first

  22. AutoNet • 100 Mbits LAN • Packet Switched Network • Cut-through forwarding • 30 switches , 100 hosts • Low latency, 2 microseconds per switch

  23. Autonet (cont) • Point to point links • Distributed Spanning Tree • UP/Down routing • Flow control via “start/stop” commands • “Idhy” (I don’t hear you) and “Panic”

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