The method of computing the available space in a packet for data stream transport comprises: a step of determining the requirements of each module of a data stream manager, for space in the packet for at least two types of header and/or extension data required by each protocol and/or service used by said module, a step of determining a maximum space requirement in the packet to meet all these requirements, by implementing different rules for combining space requirements for the different types of data and a sum of the combined requirements for the different types of data and a step of computing a difference between the space of the packet and the maximum space requirement in the packet in order to determine the available space for data stream transport.