This is what I found on the cisco website:
MIX-Enabled Chassis
The new Cisco 7500 MIX-enabled chassis is identical to the current Cisco 7500 classic chassis plus the addition of a new multiservice capability: the Multiservice Interchange (MIX) backplane. Future voice applications will provide seamless, end-to-end call management in both the packet and digital voice domains. A Cisco 7500 series router with the MIX-enabled chassis and the DSP-farm capabilities of the digital voice port adapters provides a high-density voice and fax gateway solution to connect private branch exchanges (PBX), the public switched telephone network (PSTN) and the WAN to create a multiservice network. In addition, MIX-enabled multichannel port adapters will combine digital voice channels with packet channels on a channelized access link to achieve access cost savings, without requiring a separate time-division multiplexing (TDM) multiplexer. This will allow DS0 channels to be switched from a channelized WAN link to interfaces connecting to PBX, video CODEC, or other TDM-oriented devices. These multiservice capabilities give customers a manageable migration path to robust, cost-effective, multiservice networks.
The relevant link is:
http://www.cisco.com/en/US/products/hw/routers/ps359/prod_bulletin09186a0080092007.html
