Flow control (credit-based)
Beginner
A rule that stops a core from sending data until the next one has room to take it, so nothing is dropped.
Novice
The mechanism that decides when a packet may move to the next router. With credits, a sender keeps a count of free buffer slots downstream and only sends when that count is above zero.
Expert
Credit-based, hop-by-hop backpressure is standard on chip: it never drops packets, but a stalled destination backs traffic up through the network, which is how one hot link can slow unrelated streams.
Explained in Dataflow and spatial meshes (Architectures).
See also: Router (on-chip network), Deadlock (network).