Why is "Typing..." Instant?
Even from 10,000 miles away, the signal arrives in a blink.
Persistent Sockets + Speed of Light.
Even from 10,000 miles away, the signal arrives in a blink.
Persistent Sockets + Speed of Light.
It’s fast because the connection between your phone and the server is already open (a persistent TCP socket). It doesn't need to "dial" or establish a handshake when you start typing. The "typing" notification is a tiny data packet that travels through fiber optic cables at about 200,000 km/s (roughly 2/3 the speed of light).
Experience the journey of a single byte.
Unlike loading a webpage (which opens and closes connections), WhatsApp keeps a TCP socket open permanently. It's like a dedicated phone line that never hangs up, so data can flow instantly.
WhatsApp uses a custom binary protocol (FunXMPP). A "typing" notification is just a few bytes. The backend runs on Erlang, a language built for massive concurrency, handling millions of users per server. link
Internet cables use fiber optics. Light travels through glass at roughly 200,000 km/s. Even a round trip from London to Sydney (~34,000km) only takes about 0.3 seconds physically.