 Within the Xgrid protocol , three types of messages can be passed to other computers on the same cluster : requests , notifications and replies . Requests must be responded to by the recipient with a reply , notifications do not require a reply , and replies are responses to sent messages . They are identified by their name , type ( request / notification / reply ) and contents . Each message is encapsulated in a BEEP message ( BEEP MSG ) and is acknowledged on receipt by an empty reply ( <unk> ) . Xgrid does not leverage <unk> message / reply infrastructure . Any received message which requires a response merely generates an independent BEEP message containing the reply . The Xgrid messages are encoded as dictionaries of key / value pairs which are converted to XML before being sent across the BEEP network . 
