19. A system of interaction between a requesting entity and a responding entity on a communication network based on session initiation protocol, comprising: a memory; the responding entity including at least one SIP based resource and a processor, the responding entity being configured to process a request received from the requesting entity and provide a response to the request; the requesting entity including at least one SIP based resource and a processor, the requesting entity being arranged to invoke a service session initiation protocol uniform resource identifier by means of an invocation message patterned according to a predetermined machine-readable service description and to interpret the response provided by the responding entity according to the machine-readable service description, said machine-readable service description comprising specifications of interaction between the requesting entity and the responding entity, said specifications comprising at least a set of rules comprising abstract input/output message formats and session initiation protocol binding rules, wherein the abstract input message format comprises information relating to invoking a service by the requesting entity, and wherein the abstract output message format comprises information relating to the service provided by the responding entity, and wherein at least one of the requesting entity or the responding entity is further arranged to: receive a dynamic notification regarding an updated machine-readable service description comprising specifications of interaction; and retrieve the updated machine-readable service description including the session initiation protocol binding rules.
21. The system according to claim 19 , wherein the machine-readable service description comprises headers and information whether a message body is required, and, in the affirmative, content and format of the message body.