IBB blocks allowed in flight — unacknowledged — at once. Each block costs a
full IQ round trip, so an unwindowed sender moves exactly one block per RTT:
4 KiB / 100 ms ≈ 40 KB/s however fat the pipe. Eight in flight multiplies
that by eight, and the receiver's ack-withholding is still what stops a
sender outrunning a slow consumer — the window only sets how much slack it
has before that bites.
IBB blocks allowed in flight — unacknowledged — at once. Each block costs a full IQ round trip, so an unwindowed sender moves exactly one block per RTT: 4 KiB / 100 ms ≈ 40 KB/s however fat the pipe. Eight in flight multiplies that by eight, and the receiver's ack-withholding is still what stops a sender outrunning a slow consumer — the window only sets how much slack it has before that bites.