In a method of transmitting user data over a synchronous digital
communication network (SDH), the user data are packed in multiplex units
by a peripheral device (10; 40). If a greater bandwidth than the capacity
of the multiplex unit is required, several multiplex units are
contiguously concatenated (VC-4-4c) and transmitted in a common transport
module (STM-4). At the gateway to the synchronous communication network,
the contiguous concatenation of the multiplex units (VC-4-4c) is
converted to a virtual concatenation of multiplex units (VC-4-Nv). To
adapt the number of concatenated multiplex units to the bandwidth
actually required, only part of the multiplex units are filled with user
data, and during the conversion, those multiplex units which are not
filled with user data are omitted.