TCP Flags, Connection Management, and Congestion Control Concepts

What flags are set during TCP's three-way handshake?

SYN, SYN-ACK, and ACK flags are set on the segments.

Which flag does a server set when a client connects to a closed port?

The RST (Reset) flag.

What flag initiates the closing of a TCP connection?

The FIN (Finish) flag.

Who typically closes a TCP connection, the client or the server?

Either the client or the server can initiate the closure.

What does a lost segment imply in TCP congestion control?

It implies congestion in the network.

What should a sender do when it determines a packet has been lost?

The sender must retransmit the lost packet.

What is bufferbloat?

An inflated queuing delay caused by large router buffers leading to long wait times.

What are the two approaches to congestion control in TCP?

End-to-end and network-assisted approaches.

Why does TCP primarily use an end-to-end approach?

Not all routers can notify senders of congestion, and relying on feedback is necessary.

What is the congestion window (cwnd) in TCP?

A control mechanism that limits the amount of data a sender can send before receiving an acknowledgment.

What happens to cwnd during a loss event?

It is reduced in size.

What are the three phases of TCP congestion control?

Slow start, congestion avoidance, and fast recovery.

How is cwnd initialized at the start of a TCP connection?

It is typically initialized to 1 MSS (Maximum Segment Size).

What occurs during the slow start phase of TCP?

cwnd doubles each time an ACK is received, leading to exponential growth.

What happens when a timeout occurs during slow start?

cwnd is reset to 1 and ssthresh is set to half of cwnd at the time of congestion.

How does congestion avoidance differ from slow start?

In congestion avoidance, cwnd increases linearly instead of exponentially.

What should happen when a triple duplicate ACK occurs?

A fast retransmit is performed, and the sender enters the fast recovery phase.

What is the role of acknowledgments in TCP congestion control?

More acknowledgments indicate successful delivery and help reduce congestion.

What is the purpose of probing for more bandwidth in TCP?

To maximize the utilization of available bandwidth when there is no congestion.