Type property defines message type. Beep protocol defines few message types:

msgMessage to "initiate" message and wait for response,

msgReply and msgAnswer to reply back to the message (you can have many msgAnswer types back, but only one msgReply),

msgError to declare an error as a result to the message,

msgEmpty to send empty message back

You should not use msgOther in your applications because it is for use by transport service, if needed.