What is the purpose of using an Expressway-C and Expressway-E pair in Cisco Collaboration Edge preferred architecture?

The Expressway-C and Expressway-E pair facilitates secure communication for remote users or business-to-business calls by providing firewall traversal, NAT awareness, and SIP/H.323 proxy services, allowing voice and video traffic to securely cross the enterprise network perimeter.

The Expressway pair's purpose is to enable, not block, communication for collaboration endpoints, including handling SIP signaling over ports like 5060 and 5061.

While the Expressways themselves are managed, their primary role is to enable external collaboration connectivity, not to provide general management access for internal devices.

The Expressway pair provides internet connectivity for IP-based voice and video, which is distinct from providing internet connectivity via a PSTN router that handles traditional circuit-switched calls.