tcp - What are fine-grained and coarse-grained timeout -


what definitions of fine-grained , coarse-grained timeout?

i googled them, properties lectures , academic papers. still don't know mean.

tcp uses estimate of round trip time (rtt) guess when packet has received other end. if timer exceeds, packet assumed lost , retransmitted.

in tcp reno rtt computed using coarse-grained timer. means that, say, every 500ms checked whether sent packet received or not. if is, rtt time of timer, if not timer checks again in 500ms. of ourse, 500ms arbitrary value how works.

tcp vegas, example, uses fine-grained timer, using system's time @ point of sending , point of receiving segment compute rtt.

see rfc 2988 details.


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