Updated: Aug 22, 2025
You are moving voice to the cloud for clear business reasons, so you need a build sheet that goes beyond slideware. This guide breaks down how Webex Calling really works, how you connect to the PSTN, what keeps sites alive during WAN loss, and how to run it like a production system. You will also see where a partner like Proactive adds value that most gold partners skip.
Webex Calling is a multi-tenant cloud PBX that registers apps and SIP endpoints over TLS, encrypts media with SRTP, and centralises admin in Control Hub. The service targets high uptime, published as a 99.999 per cent SLA for enterprise voice, which is the baseline many CXOs expect for critical workloads. (Source: Cisco)
You manage locations, users, numbers, devices, dial plans, and policies in one place. You can keep softphones first, add certified IP phones where needed, and phase out legacy trunks on your own timeline.
Control Hub is your cockpit. Provision users, assign numbers, push devices, and apply RBAC. Track adoption and quality with jitter, packet loss, and latency views, then drill into outliers. This is where you spot sites that need QoS tuning, codec changes, or bandwidth upgrades.
Ask yourself, do your admins have named roles, can they roll back changes, and is every site tied to a clear owner with SLAs?
You have three clean ways to reach the PSTN:
Pick per location, not per tenant. For small sites or greenfield regions, a cloud plan keeps it simple. For regulated markets or where you have contracts in place, a Local Gateway keeps numbers and interconnects stable. Cisco states that Local Gateway lets you keep your existing provider in over 180 markets, which covers most footprint plans without a carrier swap.
Questions for you: which sites must keep existing PRIs for a period, and where can you flip to a cloud calling carrier now?
Default to Opus for variable networks, fall back to G.722 or G.711 where needed, keep SRTP end-to-end, and enforce QoS at every hop. Use E.164 cleanly, normalise dial strings at the tenant edge, and keep emergency routing rules explicit per site. Alert on MOS dips, not just call failures. Capture SIP ladder diagrams when faults recur, and keep simple runbooks that any on-call engineer can follow at 2 a.m.
When the WAN drops, you still need dial tone. Survivability Gateway on IOS XE lets phones fail over and keep local calling rules in play until the site regains cloud reach. You plan for this like you plan for power, with clear tests, device registration checks, and emergency call paths that do not depend on a data centre link.
What breaks if DHCP moves, or if a firewall policy changes mid-day, and who gets paged when registrations flap, not just when they fail?
Most partners deploy and leave a runbook. Proactive builds a living runbook, adds site survivability tests into your BCP, and wires analytics to the numbers you report to the board. You get a hardened Local Gateway design on IOS XE, clean per-site PSTN choices, named owners, and a dashboard that your CIO can read without a decoder ring.
Proactive’s managed cloud calling model also covers change windows, number hygiene, capacity alerts, and quarterly reviews that tie MOS, policy changes, and adoption back to business impact.
If you want DIY, Proactive still helps with design reviews, dial plan audits, and Control Hub hardening, then hands you the keys.
Map your sites to one of the three PSTN paths, set survivability as a hard requirement, and decide what lives in multi-tenant and what needs DI for now. If you make those calls with a partner who lives in day-2 data, you will see fewer incidents and faster cutovers.
Book a 45-minute architecture review with Proactive. You will leave with a per-site PSTN plan, a survivability test sheet, and a Control Hub hardening checklist.
