Computerphile released a video explaining the mechanisms of Transmission Control Protocol (TCP) congestion control, specifically focusing on Slow Start and Additive Increase Multiplicative Decrease [1].

These mechanisms are critical to the stability of the global internet. Without effective congestion control, data packets would overwhelm network nodes, leading to systemic collapses known as congestion collapse.

Presenter Richard G. Clegg leads the technical breakdown in the second part of a series on network basics [1]. The presentation, which was filmed and edited by Sean Riley and supported by Jane Street, examines how TCP manages the flow of data between two devices to ensure efficiency without crashing the connection [1].

Clegg said the "Slow Start" phase is where a sender begins by transmitting a small amount of data and increases the volume as acknowledgments are received. This allows the network to determine the available bandwidth without immediately flooding the path [1].

Once a certain threshold is reached or packet loss is detected, the protocol shifts to Additive Increase Multiplicative Decrease (AIMD) [1]. Under this system, the sender increases the data rate linearly but slashes it significantly when congestion is detected, a strategy designed to quickly alleviate network pressure [1].

This approach prevents the "all-or-nothing" failure of network links. By reacting to packet loss as a signal of congestion, TCP creates a self-regulating loop that balances speed with reliability across diverse hardware and distances [1].

“TCP creates a self-regulating loop that balances speed with reliability.”

The explanation of AIMD and Slow Start highlights the fundamental trade-off in networking between maximizing throughput and maintaining stability. By utilizing these algorithms, TCP ensures that the internet remains functional even as traffic spikes, preventing a single high-bandwidth user from destabilizing the shared infrastructure for all others.