Tutorial 7: Design Topology for an Application

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Tutorial 7: Design Topology for an Application#

Programming with low-level APIs can be tedious and error-prone. The following two tutorials demonstrate how to use OpenOptics’ high-level APIs to build optical DCNs with just a few lines of code.

In this tutorial, you will design a network topology tailored for a custom distributed application.

The application is deployed on 8 hosts in an 8-ToR (Top-of-Rack switch) network, with one host per ToR. Each host may send traffic to every other host.

The diagram below illustrates the application’s traffic pattern:

    Group A (Hosts 0–3)                    Group B (Hosts 4–7)
    ┌───────────────┐                       ┌───────────────┐
    │ dense traffic │                       │ dense traffic │
    │ within group  │                       │ within group  │
    └───────────────┘                       └───────────────┘

        h0 --- h1                              h4 --- h5
         |  X  |                                |  X  |
        h2 --- h3                              h6 --- h7

               \                                  /
                \                                /
                 \______ light traffic _________/
                between nodes in different groups

  • The applications are divided into two groups.

  • Group A = hosts 0–3; Group B = hosts 4–7.

  • Groups have denser intra-group communication and lighter inter-group communication.

  • Traffic ratio (intra-group : inter-group) = 2:1. (You don’t need to fit the topology perfectly to this ratio.)

By default, the script tutorials/7-topologies.py creates a round-robin topology across all nodes (you will modify this topology in this task):

  • Each node connects directly to one other node per time slice.

  • Across all time slices, each node has a direct connection to every other node.

Note

Run the script first and inspect the topology on the dashboard to understand the default round-robin schedule.
Then, modify the input arguments of round_robin() to check when topologies are generated.

Your Tasks#

We will use direct routing for this task. Your goal is to design a topology that:

  1. Ensures no packet loss: the schedule must include direct connections between all node pairs.

  2. Allocates more connections within groups than across groups.

  3. Bonus: After completing the above, try to reduce the maximum message RTT to within 10 time slices, if you haven’t.

Notice:#

  • Don’t change the application.

  • Don’t change the routing.

  • Don’t change the slice duration.

  • Don’t change the number of links per ToR

Note

You can complete this task using only OpticalTopo.round_robin() inside the topology generator function my_topology.

To test your design in the OpenOptics CLI:

OpenOptics> test_task7

You will see PASS if your solution satisfies all requirements.

You can also use ping between individual hosts to check connectivity and delay.

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