An important part of the TCP protocol is the unique way it performs a retransmission. TCP senders retransmit packets and subsequently resume their flows, using a process called TCP slow start.
In TCP slow start, an endstation sends very few packets at the beginning of a TCP session or retransmission and gradually increases the throughput of the flow as packets are delivered to the destination without any packet drops.
NOTE Explaining TCP slow start in detail is outside the scope of this book, but you can think of TCP as a cautious protocol that intentionally starts slowly and gains speed as packets successfully reach the destination of the flow. When an endstation detects that a packet was dropped, it abruptly slows down its transmission rate and starts the slow-start process again. Two references that explain TCP slow start in detail are Stevens and Comer (see the Bibliography).
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