Why does Cisco UCM use DNS?

While DNS might be used by components involved in SSO, UCM itself doesn't primarily use DNS to connect endpoints to SSO services; SSO integration details are typically handled by identity providers.

DNS SRV records can be used for endpoint registration or service discovery, but UCM's primary use of DNS is broader than just providing SRV resolution to the endpoints it registers.

DNS provides name-to-IP resolution; it does not directly provide certificate-based security for media. Certificate-based security uses Public Key Infrastructure (PKI) and X.509 certificates.

Cisco UCM relies on DNS to resolve FQDNs for various purposes, most notably when communicating with SIP trunks, intercluster trunks, and other external systems or gateways that are configured using FQDNs instead of direct IP addresses. This allows for more flexible and resilient deployments, as IP addresses can change without requiring updates to the UCM configuration, as long as DNS is correctly updated.