TCP global synchronization occurs when many TCP hosts simultaneously reduce and then increase their transmission windows after packet loss, producing cyclic network utilization. section 10.6.1
A TCP receiver advertises how much data the sender may transmit before acknowledgment. After successful delivery, the window grows; after a lost segment, it drops sharply and gradually grows again. section 10.6.1
The operational cycle is:
- Network congestion fills queues, causing tail drop when arriving packets cannot enter. section 10.6.1
- Many TCP senders detect loss and reduce their windows together. section 10.6.1
- Small windows reduce utilization; subsequent window growth restores congestion, causing more tail drop. section 10.7
RED avoids waiting for queues to become completely full by randomly dropping packets after occupancy passes a threshold. WRED adds control over which packets are dropped, but neither is suitable for loss-sensitive traffic. section 10.7
