Although powerful and necessary to prevent network collapse, the congestion control mechanism of the TCP is not sufficient to avoid congestion. Since TCP sources exert a limited control of the network, and unresponsive flows, which do not slow down their sending rates when congestion occurs, may be present, the efficacy of end-to-end congestion control also relies on queue mechanisms at the routers.
Key Terms in this Chapter
Global Synchronization Problem: A phenomenon that happens when most of active TCP flows lose packets, reducing their sending rates, which can lead to network underutilization.
Round Trip Time: Time elapsed between the transmission of a packet and the reception of the corresponding acknowledgement.
Congestion Window: Range of packets that can be transmitted by a sender without leading to network congestion.
Congestion: State of the network characterized by the demand of traffic transmission exceeding its transport capacity.
Congestion Control: Traffic control mechanisms that remedy the consequences of congestion problems that have already occurred.
Congestion Avoidance: Traffic control mechanisms that attempt to avert the occurrence of network congestion.
Tail Drop: A policy, which admits packet into the router buffer whenever there is available space.
Active Queue Management (AQM): Congestion control mechanism for the early notification of incipient congestion pursued by dropping/marking packets.
Random Early Detection Policy (RED): An AQM policy recommended by the Internet task engineering force for deployment on the Internet.
Transmission Window: Range of packets that can be transmitted by a sender.