Term
| Why is TCP said to be self-clocking? |
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Definition
| It uses ack to pace transmission of packets |
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Term
| What is the goal of the CongestionWindow? |
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Definition
| limit how much data the cource can trasnmit at a given time |
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Term
| What does the value of the CongestionWindow reflect? |
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Definition
| The level of congestion in the network, decereases window when congestion goes up and increases window when congestion goes down |
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Term
| What does the multiplicative decrease of the CongestionWindow mean? |
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Definition
| Halving of the window for each threat |
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Term
| What is the minimum value that the CongestionWindow can reach? |
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Definition
| cannot fall below the MSS |
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Term
| How does the additive increase of the CongestionWindow work? |
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Definition
| each time the source sends successful congestion window worth of packets it adds the equivelent of 1 pkt to the congestion window |
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Term
| In practice during additive increase how many bytes are added to the CongestionWindow? |
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Definition
| size increases by one segment in each RTT |
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Term
| Why is it much worse to have a window that is too large in contrast to too little? |
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Definition
| when too large, pkts that are dropped will be retransmitted which makes congestion even worse |
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Term
| What event does TCP consider as an indication of congestion? |
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Definition
| TCP interprets timeouts as an indication of congestion |
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Term
| Explain why additive increase is slow and what TCP does instead when it starts a connection from scratch. |
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Definition
| addative increase should be used when the sourse is operating close to the available compacity of the network TCP uses slow start |
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Term
| Why is “slow start” called slow? Slow compared to what? |
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Definition
| slow conpared to orginal behavior of tcp. Slower then an entire advertised window worth of data |
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Term
| Once slow start sees a loss, what is the value to which the CongestionWindow is dropped? |
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Definition
| multiplative to divide the congestion by 2 |
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Term
| When there are no packets in transit (so no ACK’s are coming back) and a timeout occurs, how does TCP start sending data again? (detail both the trigger mechanism and the fashion segments are sent). |
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Definition
| congestion WIN reset to 1 pkt, incremented by 1 pkt from every ack received until in reaches congestion threashold given by 1 pkt per rtt |
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Term
| What is the CongestionThreshold and how is it used? |
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Definition
| a temperary varriable to store the target window |
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Term
| Under what conditions would the CongestionWindow value stay constant during an active TCP connection? |
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Definition
| when the are no acks arriving |
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Term
| Why is that during slow start a large number of segments can be lost? |
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Definition
| TCP is trying to see how much avaliable BW is on the network. Not enough throughput is received |
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Term
| What is a duplicate ACK? When is it sent back to a TCP source? |
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Definition
| second tranmission of the ack. After tcp has seen 3 duplicative acks |
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Term
| In fast retransmit, why is that TCP waits until it sees three duplicate ACKs before retransmitting data? |
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Definition
| to make sure the pkt is actually last rather then just being delayed |
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Term
| What does fast recovery remove from TCP’s sending behavior? |
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Definition
| removes the slow start phase |
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| python I in ragnge j in range |
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