-configuration switches support a power distribution unit, which can provide some power redundancy at additional cost. However, Cisco's chassis- based switches all support multiple power supplies (older 4000 chassis switches actually required three power supplies for redundancy and even more to support Voice over IP). Most chassis-based switches support dual supervisors as well. Speed The Cisco 6500 chassis employing Supervisor-720 (Sup-720) processors sup- ports up to 720 Gbps of throughput on the backplane. The fastest backplane in a fixed-configuration switch-the Cisco 4948-supports only 48 Gbps. (The 4948 switch is designed to be placed at the top of a rack in order to support the devices in the rack. Due to the specialized nature of this switch, it cannot be stacked, and is therefore limited to 48 ports.) Chassis-based switches do have some disadvantages. They can be very heavy, take up a lot of room, and require a lot of power. If you need the power and flexibility offered by a chassis-based switch, however, the disadvantages are usually just considered part of the cost of doing business. Cisco's two primary chassis-based switches are the 4500 series and the 6500 series. There is an 8500 series as well, but these switches are rarely seen in corporate environments. Switches Planning a Chassis-Based Switch Installation Installing chassis-based switches requires more planning than installing smaller switches. There are many elements to consider when configuring a chassis switch. You must choose the modules (sometimes called blades) you will use, and then determine what size power supplies you need. You must decide whether your chas- sis will use AC or DC power, and what amperage the power supplies will require. Chassis-based switches are large and heavy, SO adequate rack space must also be provided. Here are some of the things you need to think about when planning a chassis-based switch installation. Rack space Chassis switches can be quite large. The 6513 switch occupies 19 RU of space. The NEBS version of th