Ideal synchronizer for marked pairs in fork-join network
  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. 
S. V. Vyshenski, P. V. Grigoriev, Yu. Yu. Dubenskaya