  We introduce a new functional element (synchronizer for marked pairs) meant
to join results of parallel processing in two-branch fork-join queueing
network. Approximations for distribution of sojourn time at the synchronizer
are derived along with a validity domain. Calculations are performed assuming
that: arrivals to the network form a Poisson process, each branch operates like
an M/M/N queueing system. It is shown that mean sojourn time at a real
synchronizer node is bounded below by the value, defined by parameters of the
network (which contains the synchronizer) and does not depend upon performance
and particular properties of the synchronizer.
