Before revision:  A key research challenge in designing large (in number of input/output ports N) input-queued crossbar switches is to develop crossbar scheduling algorithms that can compute "high quality" matchings - i.e.  those that result in high switch throughput (ideally 100\\%DIF < ) and low queueing delays for packets - at line rates.
After revision:  A key research challenge in designing large (in number of input/output ports N) input-queued crossbar switches is to develop crossbar scheduling algorithms that can compute "high quality" matchings -- i.e. those that result in high switch throughput (ideally 100\\%DIF < ) and low queueing delays for packets - at line rates.