ced FlexWAN. The primary differences between the two versions are CPU speed, memory capacity, and connection to the crossbar fabric bus. Enhanced FlexWAN modules use the same WAN port adapters used in the Cisco 7600-series routers. The module is layer-3-specific, and requires either a Supervisor-2 with an MSFC, or a Supervisor-720 to operate. When running in hybrid IOS mode, the FlexWAN interfaces are not visible to layer two with CatOS. Communication Media Modules. The Communication Media Module (CMM) provides telephony integration into 6500-series switches. This fabric-enabled module has thee slots within it, which accept a variety of port adapters. The port adapters available for the CMM include Foreign eXchange Service (FXS) modules for connection to analog phones, modems, and fax machines; T1/E1 CAS and PRI gateway modules; conferencing and transcoding port adapters that allow conferencing services; and Unified Survivable Remote Site Telephony (SRST) mod- ules that will manage phones and connections should the connection to a Unified Call Manager become unavailable. The port adapters can be mixed and matched in each of the CMMs installed. A 6500-series chassis can be filled with CMMs and a supervisor, providing large port density for VoIP connectivity. CatOS Versus IOS Cisco Catalyst switches originally did not run IOS-the early chassis-based switches were CatOS-based. The reason for this was that the technology for these switches came from other companies that Cisco acquired, such as Crescendo, Kalpana, and Grand Junction. CatOS may appear clunky to those who have used only IOS, but there are some distinct advantages to using CatOS in a switching environment. One of these advan- tages can also be considered a disadvantage: when a Catalyst 6500 runs CatOS, and also has an MSFC for layer-3 functionality, the MSFC is treated like a separate device. The switch runs CatOS for layer-2 functionality, and the MSFC runs IOS for Chapter 17: Cisco 6500 Multilayer Switches layer-3 and above functionality. This separati