 assure correct system working and/or monitoring, but do not involve signal processing: The card detecting and terminating the service channel that brings control plan and central network manager information (e.g., the OMS and the ORS section headers) is a support card (see Section 3.2.7). Generally, some packet-oriented protocol is used on the management network, SO that frequently this card has switching abilities that are used in the management network (e.g., it can include an ethernet switch). The cards allowing fans installation and scaling, while the system scales in terms of channels, is another support card. As a matter of fact, only in the small systems the fans are included in the system mechanics without the possibility to scale them while the system scales. The power supply is another support card. Depending on the system capacity, either a single power supply can be sufficient or power supply can exist in every subrack, all dependent on a central power supply. This solution, however, is adopted only when it is really needed, due to the additional real estate and com- plexity of the power distribution structure. 6.5.1.3 Control Cards Control cards are essentially processors that run the network element agent and all the activities related to the control plane. Generally, there is a single control card, having sufficient processing capability to man- age all the needed software. Sometimes, due to different needs, every subrack has its own controller referring to the central controller via a local equipment network. The central controller is also the card allowing the local craft to be connected to the sys- tem (the local craft is a light version of the element manager that is generally installed on a portable computer and allows to configure locally the network element). Another control card is the subrack controlled. Depending on the control architecture of the system it can be a real controller or simply a switch for the equipment bus that allows different trunks of the equipment control network to b