- Rapidly configuring switch fabric is slow or expensive. Solution: replace switch fabric with fixed mesh of optical channels
- Packets can be mis-sequenced. Solution: (Full Ordered Frames First) bound the length of queues at middle stage and introduce a re-sequencing buffer at a later stage
- Periodic traffic can cause bad throughput. Solution: same as for problem #1 (replace crossbar switches by fixed optical mesh)
- Missing/failed linecards are not easily handled. Solution: presented in sections 6.2 and 6.3, they present two solutions that allow the switch to be reconfigured to scatter traffic uniformly over all present linecards in the face of some linecard failures.
The are designing for ~3 years out (in 2003), I wonder if the future aligned with their predictions.
The paper was a bit dense on technical/hardware details so I ended up being lost for most of it :-/