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fix(mesh): add exponential backoff and jitter to retransmits #10433

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fix(mesh): add exponential backoff and jitter to retransmits #10433

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11 changes: 9 additions & 2 deletions src/mesh/NextHopRouter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -349,9 +349,16 @@ int32_t NextHopRouter::doRetransmissions()
void NextHopRouter::setNextTx(PendingPacket *pending)
{
assert(iface);
auto d = iface->getRetransmissionMsec(pending->packet);
// Two nodes that NAK each other will otherwise re-collide on near-identical
// schedules; spread successive attempts with exponential backoff plus jitter.
uint32_t base = iface->getRetransmissionMsec(pending->packet);
uint8_t attempt = (NUM_RELIABLE_RETX - 1) - pending->numRetransmissions;
uint8_t shift = attempt < 3 ? attempt : 3; // cap multiplier at 8x
uint32_t backoff = base << shift;
Comment on lines +354 to +357
uint32_t jitter = base ? random(base / 2 + 1) : 0;
uint32_t d = backoff + jitter;
pending->nextTxMsec = millis() + d;
LOG_DEBUG("Setting next retransmission in %u msecs: ", d);
LOG_DEBUG("Setting next retransmission in %u msecs (attempt %u): ", d, attempt);
printPacket("", pending->packet);
setReceivedMessage(); // Run ASAP, so we can figure out our correct sleep time
}
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