Method, system, converter and switch for communication in asynchronous
transmission mode (ATM) between a source end station (13) and a
destination end station (14) by means of information cells and data cells
following the information cells, the information cells representing a
signalling message containing an information element (IE) which contains
an indication of a requested kind of traffic contract (ATC) for, in
accordance therewith, processing the data cells. When a kind of traffic
contract requested from a switch of the system or from the destination
end station is not supported, but a kind of traffic contract which is not
more unfavorable than a kind of traffic contract requested by the source
end station (13) is supported, the signalling message is converted, the
requested kind of traffic contract being replaced by the other kind of
traffic contract as the new requested kind of traffic contract, in such a
way that eventually there is converted back to the kind of traffic
contract supported by the destination end station (14), which is equal to
the kind of traffic contract requested by the source station. After each
conversion, the data cells of a traffic flow received are processed in
accordance with the kind of traffic contract to which there is converted.