Methods and devices for encoding and decoding messages

A communication apparatus comprising:

• a memory;
• a computer processing unit coupled to the memory which executes the following:
• generating, in a case where a plurality of information items which are to be notified into a same message to another communication apparatus includes both of a registered information item which is registered in an index table and a non-registered information item which is not registered in the index table when the communication method is initiated, wherein the index table is a table for associating one or more information items and one or more respective index values, a message for notifying said registered information item and said non-registered information item to said another communication apparatus, the message comprising a header includes all of (i) an index value respectively associated with the registered information item in the index table, (ii) the non-registered information item, and (iii) registration information indicating whether the non-registered information item has to be registered in the index table, wherein the index table is a table for associating one or more information items and one or more index values, and
• transmitting the generated message to said another communication apparatus.