Advanced Networking

1
Advanced Networking

• Wickus Nienaber
• Daniel Beech

2
Todays 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

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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

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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

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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)

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L-R routing

• Channel that faces left is called LEFT
• Channel that faces right is called RIGHT
• Dont use the LEFT channel after using RIGHT
  channel
• Deadlock free
• Guarantees any path between any pair of nodes

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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.

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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)

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Analysis

• Deadlock free
• Guarantees any path between any pair on nodes

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Descending Layer Routing

• For use in SANs
• Implements deadlock free routing
• Reduces non-minimal paths
• Reduces traffic congestion

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Descending Layer Routing (cont)

• Divide target network in layers
• Impose deadlock avoidance conditions
• Select deterministic paths

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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)
• Sanchos traffic balancing algorithm

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Path Selection (cont)

• Selection of deterministic path
• Algorithms use Virtual Channels

• High virtual-channel first

• 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 dont hear you) and Panic