Today, I learned more about the TCP.
There are two type of message in TCP:
- Seq#
- Byte stream "number" of first byte in segment's data
- Ack#
- Seq # of next byte expected from other side
So, the packet which is not acknowledged yet is yellow packets. Buffer moves to the next sequence of packets.
RTT: Round Trip Time
RTT is the length of time it takes for a message to be sent plus the length of time it takes for an acknowledgment of that message to be received.
RTT consists of the propagation times between the two points of a signal.
Here are the two questions about the TCP.
Q: How to set TCP timeout value?
- Answer: Time out must be longer than RTT
- Answer: Too short premature timeout, unnecessary retransmissions
- Answer: Too long: slow reaction to segment loss
Q: How to estimate RTT?
- SampleRTT: measured time from segment transmission until ACK receipt
- Ignore retransmissions
- SanmpleRTT will vary, want estimated RTT "smoother"
- Estimated RTT will be an average of several recent measurements, not just current SampleRTT
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