A network synchronization plan is required for the synchronization of telecommunication and data networks. The master/slave principle is generally used for network synchronization. Plesiochronous operation of systems or network elements is also possible. In digital island networks with analog environment or analog connection to other networks the network frequency does not have to be absolutely accurate. It is sufficient for all the systems interconnected in a network to operate synchronously in relation to one another. However, if networks are digitally connected, absolute accuracy is essential if the connection is to be operated in plesiochronous mode, since the bit slip rate must be limited. Networks can be operated here in pseudosynchronous mode, meaning that each has free-run accuracy of 1 x 10 exp – 11.