What is TCP startup throttle

TCP slow start throttles the number of packets a TCP endpoint can have in flight at any one time. Put simply, each time a packet received successfully, the sender gets permission to send two more packets. If an Http transaction has a large amount of data to send, it cannot send all the packages at once. It must send one packet and wait for an acknowledgement; then it can send two packets, each of which must be acknowledged, which allows four packets, etc. Because of this congestion-control feature, new connections are slower than tuned connections that are already have exchanged, a modest amount of data. Because tuned connections are faster, HTTP includes facilities that let you reuse existing connection.

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