Overlay Subnetworks
Implementation:
Overview
In a multi-blockchain system like TON, even full nodes would usually be interested in obtaining updates (i.e., new blocks) only around a few shardchains. To this end, a special overlay subnetwork has been built inside the TON Network, on top of the ADNL Protocol, for each shardchain.
Also, overlay subnetworks are used for the operation of TON Storage, TON Proxy and so on.
ADNL vs Overlay networks
In contrast to ADNL, the TON overlay networks usually do not support sending datagrams to other arbitrary nodes. Instead, some “semi-permanent links” are established between certain nodes (called “neighbors” with respect to the overlay network under consideration) and messages are usually forwarded along these links (i.e. from a node to one of its neighbors).
Each overlay subnetwork has a 256-bit network identifier usually equal to a SHA256 of the description of the overlay network—a TL-serialized object.
Overlay subnetworks can be public or private.
Overlay subnetworks work according to a special gossip protocol.
Read more about overlays in Overlay subnetworks article, or in Chapter 3.3 of the TON Whitepaper.