TCP Congestion Control

The congestion window and self-clocking

Additive increase and multiplicative decrease

Slow start and fast retransmit

From Reno to CUBIC

A TCP connection has CongestionWindow equal to 8000 bytes and AdvertisedWindow equal to 12000 bytes, with 2000 bytes currently unacknowledged. How many more bytes may the source send right now?

A TCP flow in steady state loses a packet every time its congestion window reaches 16 segments. Assuming the classic algorithm with halving on loss and additive increase afterward, what does the window do next?

Why does TCP's fast retransmit wait for three duplicate acknowledgments before resending the missing packet, instead of retransmitting on the very first duplicate?

A new TCP connection starts slow start with a congestion window of one segment and loses nothing for four round trip times. How many segments does the window allow in transit at the end of the fourth round trip?

TCP is often described as self-clocking. What does that description refer to?

TCP congestion control adds one state variable per connection to limit how much data the source may have in transit, the counterpart of flow control's advertised window. Give its name in camel case as used in the protocol literature.

During slow start the congestion window doubles each round trip until it crosses a remembered value, after which additive increase takes over. Give the usual name for this threshold, in camel case or as plain words.

Fast retransmit fires without waiting for a timer when the sender has seen a specific count of identical acknowledgments for the same sequence number. How many duplicate acknowledgments trigger it?

A TCP sender detects congestion once through a coarse timeout and once through three duplicate ACKs. How do the two responses differ?

Classic TCP grows its window by one segment per round trip when things go well and halves it on loss. Networking texts name this strategy with a four letter acronym. Give it.