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Communications of the ACM


Passively Measuring TCP Round-Trip Times

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Credit: Avinode

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Measuring and monitoring network round-trip time (RTT) is important for multiple reasons: it allows network operators and end users to understand their network performance and help optimize their environment, and it helps businesses understand the responsiveness of their services to sections of their user base.

Measuring network RTT is also important for Transmission Control Protocol (TCP) stacks to help optimize bandwidth usage. TCP stacks on end hosts optimize for high performance by passively measuring network RTTs using widely deployed TCP timestamp options carried in TCP headers. This information, if utilized, carries some distinct operational advantages for services and applications: hosts do not need to launch out-of-band Internet Control Message Protocol (ICMP) echo requests (pings), nor do they need to embed timing information into application traffic. Instead, hosts can passively measure RTT representative of full-path network latency experienced by TCP traffic.


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