EXACT protocol
Each source (ingress queue manager) can only have one queue allocate (QA) message outstanding for each destination port and priority level combination (one QA per queue).
The destination (egress queue manager) can only have one queue fetch (QF) message outstanding per output port.
Only one frame at a time can be fetched and reassembled per output port.
The basic EXACT protocol worked for 100 Mbps ports.
Message latency across the switch fabric was too long for 1 Gbps ports.
Result: Unable to maintain line rates, particularly for small frames.