Block Propagation Grid

The SNP spec specifies that nodes need to announce their blocks only to specific peers - not to the whole network. Our interpretation of the SNP spec leads to the following grid for block propagation:

There are three grids consisting of the previous, current and future validator set. They are topologically identical. This example is simplified and uses eight instead of 31 for the grid size.

You can see the authoring validator in red and propagating to its first order peers through red edges. The second order propagation edges are in green and the third order are all nodes. The third order edges are not drawn for visibility of the others.

Example

Assuming the validator with index 32 (grid coordinate (1, 1)) wants to propagate a block. It would have to send it to these first-order grid neighbors:

[{0, 1}, {2, 1}, {3, 1}, {4, 1}, {5, 1}, {6, 1}, {7, 1}, {8, 1}, {9, 1}, {10, 1}, {11, 1}, {12, 1}, {13, 1}, {14, 1}, {15, 1}, {16, 1}, {17, 1}, {18, 1}, {19, 1}, {20, 1}, {21, 1}, {22, 1}, {23, 1}, {24, 1}, {25, 1}, {26, 1}, {27, 1}, {28, 1}, {29, 1}, {30, 1}, {1, 0}, {1, 2}, {1, 3}, {1, 4}, {1, 5}, {1, 6}, {1, 7}, {1, 8}, {1, 9}, {1, 10}, {1, 11}, {1, 12}, {1, 13}, {1, 14}, {1, 15}, {1, 16}, {1, 17}, {1, 18}, {1, 19}, {1, 20}, {1, 21}, {1, 22}, {1, 23}, {1, 24}, {1, 25}, {1, 26}, {1, 27}, {1, 28}, {1, 29}, {1, 30}]

Translating to the following indices:

[1, 63, 94, 125, 156, 187, 218, 249, 280, 311, 342, 373, 404, 435, 466, 497, 528, 559, 590, 621, 652, 683, 714, 745, 776, 807, 838, 869, 900, 931, 31, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61]

Additionally, they also send it to the same validator indices of the previous and future epoch.