IP and MAC layers have restricted memories to send packets. Consequently, both will limit the length of messages. This restriction requires TCP to package variable-length bytes into several segments before serving them to the IP layer. Each segment should be in an appropriate length. Here is a simple diagram showing…

Handshake has a purpose — exchanging information to establish a connection. Why we need a connection? The answer relates to the role TCP plays. It is easier to understand it by looking at our day-to-day activity — visiting a web page. Browser initializes a GET HTTP request. With the help…

DNS message is relatively simple: the browser queries a domain name and gets an IP address. If a DNS server doesn’t recognize the domain name, it will pass the query along to the following DNS server. Later, when receiving a response, it carries the response to the browser. Interesting in…

Though HTTP/3 is still in draft today, teams such as Shopify and Medium have implemented it in production. Here is a screenshot of Medium homepage requests. Most of them are through the HTTP/3 protocol noting as h3-29. The h3 stands for HTTP/3, and the 29 is the implemented draft's version. …

TLS helps improve security. Now it is time for performance enhancement, the focus of HTTP/2 design. The first challenge is making it compatible with HTTP/1.x. To achieve it, HTTP/2 inherits semantics from HTTP/1.x, including request methods, status codes, headers, etc. Most importantly, it inherits the scheme design. There is no…

The ultimate goal of the TLS handshake is safely exchanging the master secret for future secure communication. TLS 1.2 Handshake It takes 4 steps to complete the handshake before sending the first encrypted request from a browser: Client Hello Server Hello Client key exchange and generate the master secret Finished Let’s take a…

HTTP is the abbreviation of Hypertext Transfer Protocol. Its name tells us a lot. Protocol

An HTTP request is expensive. Whenever possible, we reach out to cache, which keeps (almost) the latest resource. Cache lives at every node of the network, including clients (in our context, browsers), proxy servers, and origin servers Two-players: browser and origin server Cache-Control from the server If you have saved an edit in a Medium post, you want other…

In the early era of the network, people send files in single-digit KB size. In 2021, we enjoy hi-res MB-size images and watch 4K (soon 8K) video in several GB. Even with a good internet connection, it still takes a while to download a 5GB file. …