General Information

Underlying protocol is Remote Frame Buffer (RFB).

2011 RFB Protocol (IETF): good summary of the state of RFB, based on actual implementation as of 2011.

Lifecycle

Stage one: handshaking, to define protocol version and type of security

ProtocolVersion message: server tells client what is the hiest RFB protocol it supports

ProtocolVersion message: client tells server what version to use

Security: server lists supported security types

Security: client specifies what security type to use

Security: based on type, do further security handshaking

SecurityResult message: server sends info re: success or failure

*NOTE: this stage is the only area of variation between versions 3.3, 3.7, and 3.8

Stage two: initialization, exchange ClientInit and ServerInit messages

ClientInit message: client tells server if it wants a shared or exclusive desktop

ServerInit message: server tells client about size of framebuffer, pixel format, and name of desktop

Stage three: normal protocol interaction

Client-to-server messages: SetPixelFormat, SetEncodings, FramebufferUpdateRequest, KeyEvent, PointerEvent, ClientCutText

*NOTE: SetEncodings is also used to check for support for extended features (pseudo-encodings)

Server-to-client messages: FramebufferUpdate, SetColorMapEntries, Bell, ServerCutText

*NOTE: FramebufferUpdate may contain a pseudo-encoding. which contains arbitrary data rather than pixel information

Open-source Implementations

TigerVNC, source on Github

LibVNC, source on Github