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

• Minimal Cost (least amount of hops)

• Balance network traffic

• Avoid Congestion

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

Regular vs. Irregular Topologies

• Regular– Network has graph structure (ring, meshes,

hypercube, etc)– Easier to optimize

• Irregular– Abnormal shape– Discovering topology is a challenge

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

Up/Down Routing (cont)

• Non-minimal paths

• Leads to congestion

L-turn Routing

• Attempts to solve unbalanced traffic issue• Adaptive Routing• Used in Irregular networks

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

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)

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

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

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.

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

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)

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

nodes

Descending Layer Routing

• For use in SANs

• Implements deadlock free routing

• Reduces non-minimal paths

• Reduces traffic congestion

Descending Layer Routing (cont)

• Divide target network in layers

• Impose deadlock avoidance conditions

• Select deterministic paths

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

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

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

AutoNet

• 100 Mbits LAN

• Packet Switched Network

• Cut-through forwarding

• 30 switches , 100 hosts

• Low latency, 2 microseconds per switch

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”