A method of starting a session in a synchronization system. The maximum
size of a message that is to be sent from a synchronization server to a
mobile station for the request, and coding instructions, by which at
least one of the identifiers can be coded into a bit sequence requiring
substantially fewer bits than its ASCII presentation, are determined in
the synchronization server. Decoding instructions, by means of which the
original identifier is obtained from the bit sequence, are determined in
the mobile station. When the purpose is to transmit a request indicating
the need for starting a session to at least one mobile station, a message
is formed, is shorter or as long as the maximum size and includes the
pre-selected identifiers, at least one of which is presented as a bit
sequence defined according to the coding instructions. The mobile station
forms a session initialization message on the basis of the information
included in the message received from the server, at least part of
information being defined from the received bit sequence according to the
decoding instructions.