Communications of the ACM

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 R TT representative of full-path network latency experienced by TCP traffic.

Understanding network delay is key to understanding some important aspects of network performance. The time taken to traverse the network between two hosts affects how responsive services are, and it affects the effective bandwidth available to end hosts. Measuring this information passively on servers can help provide a fine-grained indication of service responsiveness from the customer’s perspective, and it simultaneously offers a network-distance metric for customers that is more useful than coarse-grained and often inaccurate IP-based geolocation.