e to a card in another backplane. After physical connection, the way in which the bus is physically implemented onto the backplane has to be defined. In general, two types of transmission schemes are used in today's backplanes-serial and parallel. These can be differentiated as follows: In a parallel transmission scheme, the driver attached to the bus places bits of data in parallel signal lines onto the bus. In serial transmission, all data is sent point-to-point in a serial stream on a single data line. In a serial backplane, to achieve the same data rates of an analogous parallel backplane, data must be sent at much higher speeds. However, differently from other network elements, like routers or switches, in DWDM systems the sig- nal does not travel along the backplane bus; thus, the backplane speed frequently has not to be very high. Often, the backplane speed is dictated by the need of performing protection switching in the required time of a few milliseconds and to do that a speed on the order of several Mbit/s is sufficient. Serial backplanes can be implemented using special serializer and deserializer devices that convert a parallel data stream to a high-speed serial data stream and then convert it back to parallel data at the backplane output. Each design type has the advantages and disadvantages summarized in the following. When designing a backplane, it is important to select a scheme satisfying the needs of the system where it has to be installed. The main advantages of the parallel design can be summarized as follows: Individual lines can be configured for control signals enabling a fast reaction time and a high degree of system and device control. This property could be very important when real-time protection switching commands have to be transmit- ted, especially in complex protection schemes like OChSPring. No time delay is required for serializing and deserializing data blocks. Besides the property described in the point aforementioned, this renders the parallel design suitable for machines driv