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qdsync Protocol

Overview

This page describes how the qdsync protocol works. Individual commands are documented below.

The qdsync protocol is a line-oriented protocol that can be implemented on top of a socket. It consists of a number of required commands and some optional commands.

State Machine

While there is no formal state machine there is an expected order of message arrival. The basic process looks like this.

• When a connection is initiated the device will send a 220 message.
• The desktop sends a USER message.
• The device responds with a 331 message.
• The desktop sends a PASS message.
• The device responds with a 230 message.
• The desktop and device can now send CALL or CALLB messages.
• The device responds to these with 200 messages (unless disabled with HELPER_INIT).
• The connection is ended when the desktop sends a QUIT message.

Additionally, once the desktop has sent the HELPER_INIT message the device expects to receive a message of some kind within the specified duration period. The HELPER_PING and HELPER_ACK commands exist for this purpose. The HELPER_QUIT command is used by the device to indicate failure to send a command in the specified time.

Commands

See also Overviews.