A method for lossless encoding of collaboration messages compliant with the XMPP protocol, this encoding method being implemented by one transmitter equipment, in bidirectional communication with at least one receiver equipment in a multimedia content exchange session, said collaboration messages being: - enumeration messages used for the update of a shared dictionary during said session; - CIP messages specifying a state of presence of said transmitter equipment; - CIM messages including information intended for said at least one receiver equipment; - CIQ messages including administration or control metadata of a collaboration system in which said session is implemented; this method including: - during said session, after location of the transmitter equipment and of said at least one receiver equipment, at least: • a step of exchanging, with said at least one receiver equipment, at least one attribute of one said collaboration message capable of being used in said session and an index associated with this attribute, said at least one attribute and its index being used by said equipment to update said shared dictionary of indexed attributes, this dictionary being stored by each of said equipment throughout the duration of the session, the content of said dictionary increasing as needed during the course of said session, said enumeration messages being used for said exchange of the data of the shared dictionary; • a step of substituting, in a collaboration message intended to be sent to said at least one receiver equipment, at least one attribute by its index in said shared dictionary and sending this collaboration message to at least one receiver equipment; and - a step of destroying said shared dictionary at the end of said session, the size of said attribute being greater than the size of its index in said shared dictionary. - enumeration messages used for the update of a shared dictionary during said session; - CIP messages specifying a state of presence of said transmitter equipment; - CIM messages including information intended for said at least one receiver equipment; - CIQ messages including administration or control metadata of a collaboration system in which said session is implemented; - during said session, after location of the transmitter equipment and of said at least one receiver equipment, at least: • a step of exchanging, with said at least one receiver equipment, at least one attribute of one said collaboration message capable of being used in said session and an index associated with this attribute, said at least one attribute and its index being used by said equipment to update said shared dictionary of indexed attributes, this dictionary being stored by each of said equipment throughout the duration of the session, the content of said dictionary increasing as needed during the course of said session, said enumeration messages being used for said exchange of the data of the shared dictionary; • a step of substituting, in a collaboration message intended to be sent to said at least one receiver equipment, at least one attribute by its index in said shared dictionary and sending this collaboration message to at least one receiver equipment; and • a step of exchanging, with said at least one receiver equipment, at least one attribute of one said collaboration message capable of being used in said session and an index associated with this attribute, said at least one attribute and its index being used by said equipment to update said shared dictionary of indexed attributes, this dictionary being stored by each of said equipment throughout the duration of the session, the content of said dictionary increasing as needed during the course of said session, said enumeration messages being used for said exchange of the data of the shared dictionary; • a step of substituting, in a collaboration message intended to be sent to said at least one receiver equipment, at least one attribute by its index in said shared dictionary and sending this collaboration message to at least one receiver equipment; and - a step of destroying said shared dictionary at the end of said session,