Method of and apparatus for addressing a buffer memory in a transit exchange for synchronous data signals

In a TDM-system having a transit exchange connecting incoming TDM-links to outgoing TDM-links which carry data channels with different data rates having one or more time slots in a TDM-frame in accordance with the data rates of the data channels wherein the transit exchange includes a switch memory for the storage of incoming data signals in memory positions, each of which is assigned to one of the incoming data channels in the incoming links, and a buffer memory to which the data signals are transferred and stored in memory positions assigned according to the sequence numbers of the time slots belonging to the respective data channels in the outgoing links before being sent out via the outgoing links, and wherein the write-in and read-out of the buffer memory occurs alternately at a repetition rate determined by the data rate of the respective channel in such a manner that the read-out to the outgoing TDM-links occurs cyclically with each cycle encompassing the reading of a time slot having a certain sequence number for each of the links, the method of minimizing the transfer time of data signals through the transit exchange by writing into a memory position of the buffer memory data signals of a data channel which is assigned more than one memory position, the memory position being the one which is next in turn for a read-out, comprising the steps of comparing the sequence number of the time slot read out last with the sequence number of the first appropriate time slot in the TDM-frame assigned to the actual data channel whose data signals are being transferred, then if the latter sequence number is higher, writing the data signals of said actual data channel into the memory position which corresponds to said appropriate time slot, if said latter sequence number is lower, comparing said last sequence number with the sequence number of the next appropriate time slot assigned to said actual data channel, repeating said comparing steps until a higher sequence number is found, writing the data signals of said actual data data channel into the memory position of the buffer memory which corresponds to said found higher sequence number, whereas, if the found sequence number of the time slot is equal to the sequence number of the time slot read out last, or if equality has already been found during the comparision of said last sequence number with the sequence number of the first appropriate time slot assigned to said actual data channel determining whether a readout has been made from the memory position corresponding to the sequence number of said first appropriate time slot to the outgoing TDM-link which transfers said actual data channel, said determining comprising comparing the sequence number of said outgoing TDM-link with the sequence number of the TDM-link to which read-out was made last, after which, if the comparision shows that a read-out of said time slot has been made to the TDM-link which transfers said actual data channel, writing the data signals of said actual channel into the memory position which is associated with the next appropriate time slot of said actual channel, while otherwise a write-in is made to the memory position which is associated with the time slot in the process of being read.