Login Sequence

Minimal Login

The bare minimum number of packets to join a server with a Notchian client is as follows.

Packet	Contents
C->S Pre-Login	Telling the server a client would like to connect
S->C Pre-Login	Gives the client the server id
C->S Login	Gives the server info about the client
S->C Login	Gives the client info about the to-be-used player and world
S->C Player Position and Rotation	Sets the players position in the world

A vanilla client will become responsive upon receiving the player's initial starting position and rotation from the server. After this, the client will continuously send Position and Look packets as needed.

This will place the player into an empty world at sunrise. The player will begin to fall shortly after connecting, since there are no solid blocks for it to collide with.

Vanilla Login

Packet	Contents
C->S Pre-Login	Telling the server a client would like to connect
S->C Pre-Login	Gives the client the server id
C->S Login	Gives the server info about the client
S->C Login	Gives the client info about the to-be-used player and world
S->C Set Compass Target Position	Makes the players compass point at their spawn
S->C Set Time	Sets the current time
S->C Set Health	Sets the shown health
S->C Fill Container	Sets the players inventory

This is followed by a bunch of Set Chunk Visibility packets to load the chunks, and Chunk packets which contain the actual chunk data, alongside the server and Client exchanging position and rotation information.

For info on how Authencation/Online Mode comes into play, check the Authentication page.