The meaning of the length field depends on the message type: Data - provides the length of bytes following the header Window update - provides a delta update to the window size Ping - Contains an opaque value, echoed back Go Away - Contains an error code
The StreamID field is used to identify the logical stream the frame is addressing. The client side should use odd ID's, and the server even. This prevents any collisions. Additionally, the 0 ID is reserved to represent the session.
The type field is used to switch the frame message type.
OptionalversionThe version field is used for future backward compatibility. At the current time, the field is always set to 0, to indicate the initial version.
The flags field is used to provide additional information related to the message type.