WPT Measurements

WebPageTest is a popular tool for evaluating website performance. It offers detailed visual representations and valuable information about each request.

If you use this tool to measure asset loading speed when utilizing iSmartFrame, especially for images, you may come across a relatively long time to first byte (TTFB). This is often observed when utilizing HTTPS, specifically HTTP/2, the default protocol used by iSmartFrame for delivering assets.

HTTP/2 establishes a single connection to a domain and handles all asset requests through that connection. Furthermore, HTTP/2 prioritizes assets based on their significance in terms of user experience:

  • critical assets like JavaScript (JS) and Cascading Style Sheets (CSS) receive high priority;

  • less critical assets, like images, receive a lower priority.

Consequently, the browser used by WebPageTest receives less important resources later, even though the connection has already been established. However, it mistakenly includes the time elapsed until the actual selection for download by the browser in the calculation, leading to an extended TTFB. This behaviour is uncommon for real users browsers, which typically retrieve the resource much faster than the time indicated by WPT.

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