Implementation Issue Operating system timers are very coarse- how to pace packets out smoothly? Implemented using a congestion window that limits how much data can be in the network TCP also keeps track of how much data is in transit Data can only be sent when the amount of outstanding data is less than the congestion window The amount of outstanding data is increased on a send and decreased on"“ack” (last sent -last acked)<congestion window Window limited by both congestion and buffering Senders maximum window= Min(advertised window, cwnd Lecture 19: TCP Congestion ControlLecture 19: TCP Congestion Control 8 Implementation Issue • Operating system timers are very coarse – how to pace packets out smoothly? • Implemented using a congestion window that limits how much data can be in the network. • TCP also keeps track of how much data is in transit • Data can only be sent when the amount of outstanding data is less than the congestion window. • The amount of outstanding data is increased on a “send” and decreased on “ack” • (last sent – last acked) < congestion window • Window limited by both congestion and buffering • Sender’s maximum window = Min (advertised window, cwnd)