pulse how much does network latency really matter john dilley
How Much Does Network Latency Really Matter?
Haseeb Budhani
CEO and co-founder
Does lower network latency make a difference to performance? We absolutely think so! When I described the Programmable Edge concept to my father, a career scientist with deep research and teaching experience, he said, "Light can circle the Earth 7 times in a second, how much difference does even a thousand miles really make?" It's a great question – he always finds challenging questions. Putting servers at the network edge reduces network latency (round trip time) for clients and I assert that this makes applications faster and more highly available.
How does latency affect web application response time?
First, I’m sure you agree that response time matters (a lot) to a web-based business. Many studies have linked response time to improved user engagement and e-commerce conversion rates and fast response time becomes more important every year. Web page response time is the total time your browser took to fetch and render the page. Allow me to dip into network queuing theory to formalize a few terms before we go on.
- Network Latency: The minimum (latent) time a packet takes to get from here to there. We normally talk in terms of round-trip time (RTT), which is the delay there and back.
- Queuing Delay: The time spent waiting in a queue – perhaps in a router as your packet moves from network to network between your browser and the server.
- Server Residence Time: How long the server takes to compute and start sending a response back to you. This includes generating dynamic content, looking up the response in a cache, or whatever.
As a developer, the residence time is your code doing its thing. You work to make this fast, and this time dominates the overall response time in desk and local network testing. Only when you push it to the open Internet do you really face latency and queuing.
The page you're reading now probably took 80-100 network requests. Mostly images, some JS and CSS, and four or so html objects across multiple domains. Some of the objects transferred over 100 KB. The total round trips for the page to load is well over 100.
Show Me The Data!
The following graphs show first the network latency, client-to-edge and client-to-origin, for a web server tested from client locations listed on the horizontal (x) axis. The green bars show network latency, coral shows edge latency.
Closing Remarks
If you objected to my counting 1 RTT for sending the web request (instead of 1/2 – since technically we don't need the response ACK) you may subtract 1/2 RTT from the "multiple RTT" on the response side. As always, if you strongly agree or disagree with the perspectives of the entire team here at Rafay, we would love to talk to you.