This is true when point-point retransmitting protocols are stacked,
not when end-end protocols are stacked on point-point. For example:
when reliable PPP (effectively LAP-B) is running thru a modem doing LAP-M.
The retransmit times are very close and this is where the problem comes
in. The PPP will retransmit while the LAPM is filling the window (the REJ
got lost), then LAPM will retransmit. OTOH, end-end protocols have *much*
larger timeouts so the link level retransmits just looks like a stalled/
congested link.