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The server sent many TCP Dup ack to client

asked 2020-05-03 15:05:34 +0000

codec gravatar image

updated 2020-05-04 10:18:28 +0000

Dear all,

The client uploaded the file to a server, and I see there are many TCP Dup ACK from server to client. The SLE number is the same, but the SRE number was increasing. I read the document because the server still receiving the data from the client before timeout so the SRE was increasing from the server to the client.

my questions are

  1. will the out of order retransmission slow down the sending throughput from client to server? because I saw the sender did not send out enough data to approach the TCP window size of the receiver.

  2. If the receiver's TCP window size is 128KB, the sender sent large data at one time to the receiver but out of order when delivered to the receiver. How does the receiver to handle the delivered out of order package? will put the data into the buffer to wait for previous data until the buffer is full? Any suggested document I can read to understand the detail?

Thank you!


[TCP Dup ACK 1300#1] 445 → 62113 [ACK] Seq=10598 Ack=957401 Win=65535 Len=0 SLE=958651 SRE=961151
[TCP Dup ACK 1300#33] 445 → 62113 [ACK] Seq=10598 Ack=957401 Win=65535 Len=0 SLE=958651 SRE=1022401
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answered 2020-05-04 14:27:46 +0000

jack.chen.job gravatar image

updated 2020-05-04 14:29:12 +0000

I am new to TCP traffic analyze so I will just put my understanding here, might not be correct.

  1. Yes it will slow down the sending throughput. Server send Dup Ack to Client, Client will think the packet is lost, therefor reduce congestion window ( not server side receiving window), and throughput will be reduced as well.

  2. Server should keep the received data in the buffer, the client won't send data more than the buffer size ( it will see server receiving window full). The data will not be sent to application until the missing packet is received. When TCP data is delivered to application, it's always in order.

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Asked: 2020-05-03 15:05:34 +0000

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Last updated: May 04 '20