Final answer:
Delay-based TCP congestion control relies on the measurement of network delays, primarily using round trip time (RTT), and may consider packet spacing or RTT changes to adjust the sending rate to keep delays stable.
Step-by-step explanation:
Delay-based TCP congestion control relies on the measurement of the delays in the network to gauge the level of congestion. This type of control assumes that as congestion within a network increases, the delays experienced by packets will also increase. Hence, it uses the round trip time (RTT) of packets, which is the time taken for a signal to go from the sender to the receiver and back again, as a primary indicator of the current network congestion state. Additionally, delay-based congestion control might consider packet spacing or changes in RTT to adjust its sending rate. Delay-based algorithms generally aim to keep the delays within the network stable by controlling the rate at which new packets are sent based on the observed RTT variations.