Question
In Section 3.5.4, we saw that TCP waits until it has received three duplicate ACKs before performing a fast retransmit. Why do you think the TCP designers chose not to perform a fast retransmit after the first duplicate ACK for a segment is received?
Answer
Suppose packets n, n+1, and n+2 are sent, and that packet n is received and ACKed. If packets n+1 and n+2 are reordered along the end-to-end-path (i.e., are received in the order n+2, n+1) then the receipt of packet n+2 will generate a duplicate ack for n and would trigger retrans- mission under a policy of waiting only for second duplicate ACK for retransmission. By waiting for a triple duplicate ACK, it must be the case that two packets after packet nare correctly received, while n+1 was not received. The designers of the triple duplicate. ACK scheme probabl- y felt that waiting for two packets (rather than 1) was the right tradeoff between triggering a quick retransmission when needed, but not retran- smitting prematurely in the face of packet reordering.
Discussions
Nitish Srivastava
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By waiting for a triple duplicate ACK, it must be the case that two packets after packet nare correctly received, while n+1 was not received. The designers of the triple duplicate. ACK scheme probabl- y felt that waiting for two packets (rather than 1) was the right tradeoff between triggering a quick retransmission when needed, but not retran- smitting prematurely in the face of packet reordering.
Improvemnt :
By waiting for a triple duplicate ACK, it must be the case that two packets after new packet correctly received, while n+1 was not received. The designers of the triple duplicate. ACK scheme probabl- y felt that waiting for two packets ( rather than 1) was the right tradeoff between triggering a quick retransmission when needed, but not retransmitting prematurely in the face of packet reordering.
Nitish Srivastava
nitish068
---
By waiting for a triple duplicate ACK, it must be the case that two packets after packet nare correctly received, while n+1 was not received. The designers of the triple duplicate. ACK scheme probabl- y felt that waiting for two packets (rather than 1) was the right tradeoff between triggering a quick retransmission when needed, but not retran- smitting prematurely in the face of packet reordering.
Improvemnt :
By waiting for a triple duplicate ACK, it must be the case that two packets after new packet correctly received, while n+1 was not received. The designers of the triple duplicate. ACK scheme probabl- y felt that waiting for two packets ( rather than 1) was the right tradeoff between triggering a quick retransmission when needed, but not retransmitting prematurely in the face of packet reordering.
Nitish Srivastava
nitish068
---
By waiting for a triple duplicate ACK, it must be the case that two packets after packet nare correctly received, while n+1 was not received. The designers of the triple duplicate. ACK scheme probabl- y felt that waiting for two packets (rather than 1) was the right tradeoff between triggering a quick retransmission when needed, but not retran- smitting prematurely in the face of packet reordering.
Improvemnt :
By waiting for a triple duplicate ACK, it must be the case that two packets after new packet correctly received, while n+1 was not received. The designers of the triple duplicate. ACK scheme probabl- y felt that waiting for two packets ( rather than 1) was the right tradeoff between triggering a quick retransmission when needed, but not retransmitting prematurely in the face of packet reordering.
Nitish Srivastava
Post the discussion to improve the above solution.