https://developers.google.com/web/tools/chrome-devtools/network-performance/reference#timing-explanation
Timing breakdown phases explained
Here's more information about each of the phases you may see in the Timing tab:
- Queueing. The browser queues requests when:
- There are higher priority requests.
- There are already six TCP connections open for this origin, which is the limit. Applies to HTTP/1.0 and HTTP/1.1 only.
- The browser is briefly allocating space in the disk cache
- Stalled. The request could be stalled for any of the reasons described in Queueing.
- DNS Lookup. The browser is resolving the request's IP address.
- Proxy negotiation. The browser is negotiating the request with a proxy server.
- Request sent. The request is being sent.
- ServiceWorker Preparation. The browser is starting up the service worker.
- Request to ServiceWorker. The request is being sent to the service worker.
- Waiting (TTFB). The browser is waiting for the first byte of a response. TTFB stands for Time To First Byte. This timing includes 1 round trip of latency and the time the server took to prepare the response.
- Content Download. The browser is receiving the response.
- Receiving Push. The browser is receiving data for this response via HTTP/2 Server Push.
- Reading Push. The browser is reading the local data previously received.