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Network Performance metrics

  • What is throughput
  • Suppose you have a serial connection of many links of varying bandwidth, which of those link determines the overall throughput?
  • Differentiate between bandwidth, throughput and goodput
  • Give the equation for the total delay experienced by a packet
  • What is the formula for transmission delay?
  • What is the formula for propagation delay?
  • What is queuing delay?
  • Give examples of the operations that may take place during nodal processing

TCP

  • Is TCP stateful or stateless?
  • Which is faster TCP or UDP?
  • Draw the packet diagram of a three-way handshake with sequence numbers
  • When does a sender start sending data? Does it wait of its ACK to reach the receiver?
  • Explain the difference between Sequence#, Acknowledgement# and SYN, ACK
  • What can be the interpreted meaning of the number sent on the ACK?
  • How are sequence numbers picked initially?
  • What is the meaning of a sequence number
  • Assume that a packet has SEQ of 35 and the sender receives an ACK with Acknowledgment number of 69. What can you say about the size of the packet?
  • What is the meaning of a congestion window?
  • Draw a Go-Back-N window
  • How does the receiver detect faults that may occur during transmission?
  • What are the two ways in which TCP recovers from delays and losses?
  • What happens when an ACK packet gets lost
  • Mention the different scenarios in which a timeout can occur?
  • What are implications of a smaller timeout period?

TCP Timeout Calculation v1

  • What is the principal way in which TCP determines timeout value?
  • How do you measure RTT?
  • How do you make updates to the estimated RTT?
  • What is the name of the method used for updating RTT?
  • What are the effect of adjusting $\alpha$ ?
  • Why not just use regular average?
  • What is the formula for Retransmission Timeout?

Karn/Patridge

  • What are two key insights of KP?
  • Why is there an ambiguity when dealing with retransmissions?
  • What happens to the RTO when there is a retransmission?

Jacobson/Karel

  • What are the key insights of JK?
  • Give the formulas used for updating in JK?
  • If there is small variance how should the RTO be in relation to Estimated RTT?
  • If there is a high variance then how should the RTO be in relation to Estimated RTT?
  • What is the value of the initial RTO?

RFC 6298

  • Mention the changes between Jacobson/Karel and RFC 6298?

TCP Congestion Control

  • How can a sender limit its sending rate?
  • How can a sender detect that there is congestion?
  • Explain the relationship between cwnd and the network congestion
  • In general what is the strategy used by TCP?
  • What is the shape of the cwnd vs time graph look like
  • What is MTU and MSS? What are their usual sizes?
  • What is slow start?
  • What is congestion avoidance?
  • How is ssthresh set after detection of congestion?
  • What happens to cwnd when congestion is detected?
  • Explain fast retransmit
  • What is fast recovery?
  • What is main difference between TCP Tahoe and TCP Reno?
  • What is TCP Cubic? and what is the main problem that it is trying to solve?