Which protocol is responsible for network congestion control?

The correct answer is TCP (Transmission Control Protocol) because it incorporates mechanisms specifically designed to manage network congestion. TCP uses a technique called congestion control, which adjusts the rate of data transmission based on the perceived state of the network. When TCP detects signs of congestion, such as increased packet loss or delays in the acknowledgment of sent packets, it reduces the transmission rate to alleviate the congestion, preventing network overload.

Furthermore, TCP implements several algorithms, such as Slow Start, Congestion Avoidance, Fast Retransmit, and Fast Recovery, that efficiently manage how much data can be sent before expecting an acknowledgment. This proactive approach to controlling flow helps maintain the stability and reliability of data transmissions over a network.

In contrast, protocols like FTP and HTTP operate on top of TCP but do not handle congestion control themselves; they rely on TCP's mechanisms. UDP, on the other hand, does not provide any congestion control features because it is designed for speed and efficiency, prioritizing low latency over reliability.