Response time is comprised of five major components namely DNS time, connection time, SSL Handshake Time, first byte and Download time.
Let us consider a scenario to further explain these terms:
A website zoho.com is monitored by Site24x7. Firstly, we will resolve the domain names in our location- monitoring servers which is the DNS time. This is the time taken to resolve the domain that is being monitored, i.e., fetch the IP address.
Once the domain name is resolved, we will send a HTTP request to the server. Connection time here includes the time taken to send the HTTP request and to receive the HTTP response. Once the connection is established, the time taken to securely negotiate the SSL handshake is captured for all HTTPS based URLs.
The server will start sending the response, likely the content on zoho.com in the form of packets and this is where the first byte and the download time comes into picture. First byte time is the time at which the first packet or byte was received by Site24x7 after successful connection with the target server. First byte time is the kind of measure to check how fast the server is responding to our request. If the first byte time is high, it means the server is slow. Last byte time is the time at which we have received the response completely from the target server (Zoho server).
The difference between the last byte time and the first byte time is the download time that depends on the size of the content and the speed of the server.
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