TCP global synchronization

TCP global synchronization in data networking can happen to TCP/IP flows during periods of congestion because each sender will reduce their transmission rate at the same time when packet loss occurs.

When using tail drop (FIFO) queuing, packets are indiscriminately dropped when congestion occurs. These dropped packets are usually from different senders which causes each to reduce its transmission rate at the same time. After some time, senders will use the slow-start algorithm to increase their transmission rate on the assumption that the congestion experienced earlier will no longer be present. This pattern of each sender decreasing and increasing transmission rates at the same time as other senders is referred to as global synchronization and leads to inefficient use of bandwidth. Connectionless protocols such as UDP do not experience global synchronization because they ignore (or are not aware of) packet loss. Random Early Detection (RED) is used to reduce global synchronization's effects on link utilization.

References

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