The Services Gateway chassis supports Common Form-factor Modules (CFMs). A single-wide module format and a double-wide module format are available. I/O Card (IOC), Services Processing Card (SPC), and Network Processing Card (NPC) modules are in single-wide CFM format. The Switch Fabric Board (SFB) and the Routing Engine (RE) are not in CFM format, and thus have assigned slots within the chassis. With the interchangeability among the IOCs, SPCs, and NPCs, you have more flexibility and scalability when deploying your networks based on the requirements in the field. For example, if you need more ports and bigger oversubscription ratio, then you can load more slots with IOCs; on the other hand, if you need smaller oversubscription ratio for better QoS behavior, or you need more security services, then you can load more slots with SPCs and only use the on-board network interface ports.