45network ProtoCols
communication can be carried out by the network. Such a phenomenon is called
network congestion collapse. To prevent the network congestion collapse, TCP pro-
vides several congestion control mechanisms. TCP is able to adjust the packet trans-
mission rate according to the packet loss rate. When many packets get lost or delayed
in a short time, instead of resending all the missing packets immediately, TCP will
resend one packet rst. If no packet gets lost during the transmission, the sender will
get the acknowledgment back from the receiver. In such a case, TCP will double the
retransmission rate. If there is still no packet that is lost during the transmission,
TCP will double the retransmission rate again. By doing th