Pick your source and target CUCM versions — see every meaningful feature change, deprecation, and platform requirement between them, grouped by area (licensing, security, media, APIs, deployment).
Every CUCM major/minor release changes something you'd rather know about before you start the upgrade. 12.0 made Smart Licensing mandatory (your call-home connection has to work during upgrade). 12.5 deprecated CUWL and moved everyone to Flex. 14 finally removed the 32-bit OVA templates. 15 brings TLS 1.3 + reduced OVA sizes + Webex Cloud-Connected UC improvements. This tool surfaces the deltas between any two versions so nothing surprises you mid-cutover.
Pick versions + areas, click Show delta.
Features that now exist. Most are optional; some require config.
Behavior differences. Read these carefully — they break assumptions.
Deprecated or fully removed. If you rely on them, you have a project.
Smart Licensing became mandatory in 12.0. If you're upgrading from 11.5 or earlier, you must register the cluster with Cisco Smart Software Manager (CSSM) as part of cutover. Call-home reachability is required — either direct internet (HTTPS outbound to CSSM), on-prem CSSM satellite, or license reservation mode for air-gapped. Skipping this step puts the cluster into a 90-day evaluation countdown and eventually disables provisioning.
CUWL and UCL PAK licenses went away in 12.5. Everyone moves to Cisco Collaboration Flex Plan 3.0 (Essentials / Professional / Meetings). Prior licenses are honored via migration SKUs but not renewable. The mapping — UCL Basic → Essential, UCL Enhanced → Professional, CUWL → Professional + Meetings — is mechanical, but procurement takes 2–3 weeks. Budget this into your upgrade.
TLS 1.0/1.1 support is fully removed in 14 and 15. If you have old Jabber clients, third-party SIP devices, or call-recording appliances that only speak TLS 1.0, they will stop registering after upgrade. Audit SIP Trunk Security Profiles and Phone Security Profiles before cutover to confirm all peers support TLS 1.2+.
vSphere requirements moved forward. CUCM 14 requires vSphere 6.7+, CUCM 15 requires 7.0 U3+. If your virtualization team runs on an older vSphere, either they upgrade first or you plan a fresh-install migration onto new hosts.
Webex Cloud-Connected UC is an optional add-on that publishes CUCM telemetry to Control Hub. Enabling it gives you cross-cluster analytics and quality reporting, and also unlocks hybrid services (calendar, directory) without installing Expressway-C. Requires 12.5 SU3+ or 14+ and a Webex Control Hub org.
No — it covers the changes that matter to a typical enterprise admin. For the full release-note list see Cisco.com Release Notes for each version.
IM&P version must equal CUCM version. Unity Connection can lag by one major version but shouldn't.
11.5→12.5 is bigger because of Smart Licensing mandate and Flex Plan transition. 12.5→15 is mostly additive.
7900-series phones (older, non-G2) were EoSWS in 14. Check the compatibility matrix before upgrading.
Biggest common jump — skips Smart Licensing introduction, codec modernization, security hardening
Common mid-market path. Already on Smart Licensing and Flex Plan.
Minor upgrade within the current-gen platform.
The Network & UC Health Assessment includes an upgrade-readiness review — current-version audit, target-version deltas, endpoint firmware compatibility, and a staged plan.