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	English	French
	Redraw the same figure assuming that the second segment that was delivered by the sender in the figure experienced congestion. In a network that uses Explicit Congestion Notification, this segment would be marked by routers and the receiver would return the congestion mark in the corresponding acknowledgment.
	Same question, but assume now that the fourth segment delivered by the sender experienced congestion (but was not discarded).
	A TCP connection has been active for some time and has reached a congestion window of 4000 bytes. Four segments are sent, but the second (shown in red in the figure) is corrupted. Complete the time-sequence diagram.
	Footnotes	Notes de pied de page
	On Linux, most of the parameters to tune the TCP stack are accessible via :manpage:`sysctl`. These parameters are briefly described in https://github.com/torvalds/linux/blob/master/Documentation/networking/ip-sysctl.txt and in the :manpage:`tcp` manpage. Each script sets some of these configuration variables.
	packetdrill_ requires root privileges since it inject raw IP packets. The easiest way to install it is to use a virtualbox image with a Linux kernel 4.x or 5.x. You can clone its git repository from https://github.com/google/packetdrill and follow the instructions in https://github.com/google/packetdrill/tree/master/gtests/net/packetdrill. The packetdrill_ scripts used in this section are available from https://github.com/cnp3/ebook/tree/master/exercises/packetdrill_scripts
	By default, packetdrill_ uses port 8080 when creating TCP segments. You can thus capture the packets injected by packetdrill_ and the responses from the stack by using ``tcpdump -i any -n port 8080``
	The `Push` flag is one of the TCP flags defined in :rfc:`793`. TCP stacks usually set this flag when transmitting a segment that empties the send buffer. This is the reason why we observe this push flag in our example.
	The variables that are included in TCP_INFO are defined in https://github.com/torvalds/linux/blob/master/include/uapi/linux/tcp.h
	These states are defined in https://github.com/torvalds/linux/blob/master/include/net/tcp_states.h