This counts the total number of BFD control packets transmitted by this session since it was established, which for BFD are the periodic hello-like packets exchanged at a configured interval to prove liveness to the peer. An admin uses this counter, alongside the received count, as a basic sanity check that the session is actively exchanging keepalives rather than sitting idle, since a healthy long-lived BFD session should show a steadily climbing transmit count roughly proportional to its uptime and configured interval. For example, a session up for one hour with a 50ms transmit interval that should show roughly 72,000 transmitted packets but instead reports far fewer would suggest the local BFD process is not actually sending at the configured rate.