Identify the product before calling it a carrier trunk
Webex Calling PSTN trunking for hybrid deployments is a Route List Calls feature that connects an on-premises PBX or vertical application through Webex Calling to a selected Cloud Connected PSTN provider or a local-gateway PSTN design. It is not one universal PSTN carrier, direct SIP-provider account or ordinary Webex Calling user license.
Record the Webex subscription, Route List Calls entitlement, Control Hub organization, location, selected PSTN provider, enterprise SBC, PBX, number inventory and support owners. Keep the Webex routing layer, PSTN provider order and on-premises implementation as separate evidence records.
Documented service facts
Reviewed 2026-10-09. Compare SIP trunk services →
SIP authentication
DocumentedWebex Calling documents registration-based and certificate-based trunks between the service and the premises local gateway. The registration model gives the local gateway a registration domain, trunk group, line or port and outbound proxy; losing credentials requires regeneration. Do not merge that handoff with a certificate trunk or with the separate Cloud Connected PSTN provider account. Preserve the selected trunk type, gateway, identity, secret or certificate owner and sanitized exchange.
SIP registration
DocumentedFor a registration-based trunk, Cisco says the local gateway performs SIP registration and must keep it active. Certificate-based trunks use a different trust and reachability model. An active registration establishes that trunk connection only; it does not prove a Route List number, route group, dial plan, Cloud Connected PSTN provider or completed off-net call.
Inbound delivery
DocumentedThe hybrid PSTN guide says an external call is routed through a trunk in the Route Group when the dialed number matches a number configured in the Route List. Route Lists are location-bound. Preserve the provider-assigned number, Control Hub number state, Route List membership, Route Group, inbound PBX identity and destination instead of treating tenant-wide number inventory as one route.
Routing and failover
DocumentedWebex Calling route groups can contain one to ten trunks. Equal-priority trunks are load balanced, and an unavailable higher-priority set can fall through to a lower priority. That policy does not prove diverse access, gateway, site, certificate, Cloud Connected PSTN provider or power, and it does not establish survival of an active call. Record the actual trunks, priorities, health evidence, failure trigger and restoration order.
Number and regional availability
Not verifiedThe service uses location-bound Route Lists and PSTN numbers ordered from a selected integrated or non-integrated Cloud Connected PSTN provider. The public workflow allows numbers to be added or activated, but it does not establish current inventory, port eligibility, country coverage or activation for a requested location. Bind each number and provider to a dated qualification and order.
Audio codecs and DTMF
DocumentedCisco's audio specification requires G.711 in every INVITE and warns that G.729-only offers can fail in some Webex Calling flows. It says G.711 is used with most PSTN providers. That is an offer requirement, not proof of the selected codec, packetization, bandwidth, transcoding or decoded digits on one hybrid call. Preserve both SDP bodies and observed media; obtain current DTMF requirements for the selected gateway and PSTN provider.
T.38 fax
Not verifiedThe reviewed hybrid trunking, route-group and audio pages do not establish T.38 entitlement, G.711 pass-through policy, switchover, redundancy, gateway compatibility or completed pages for the selected Cloud Connected PSTN provider and on-premises PBX. Treat fax and other non-voice devices as separate workflows and require current provider and gateway evidence.
Signaling and media encryption
Not verifiedWebex Calling distinguishes registration-based and certificate-based local-gateway trunks and exposes certificate and TLS failure states for certificate paths. The reviewed pages do not establish one universal signaling or media-protection profile through the enterprise SBC, Webex Calling and the selected PSTN provider. Record each hop, certificate and trust result, negotiated signaling transport and selected media profile without representing the PSTN leg as end-to-end encrypted.
Concurrent calls and call starts
DocumentedRoute List Calls is a concurrent-call license. Cisco documents 20 percent burst capacity before non-emergency calls are blocked, ten concurrent calls during trial and a maximum individual-subscription route-list volume of 10,000 calls. These values do not define call attempts per second, burst duration, gateway resources, codec bandwidth or PBX capacity. Preserve the accepted license count and each independent limit.
Emergency calling
DocumentedCisco says a Route List location using RedSky routes emergency calls through RedSky and requires the Route List number to be mapped in that portal; without RedSky, emergency calls route through the location's PSTN provider. The enhanced service can use location-specific methods including PIDF-LO. Complete the selected provider and location workflow, callback identity, notifications, dispatchable address and approved validation instead of inferring readiness from number membership.
Pricing model
Not verifiedCisco identifies Route List Calls as an add-on for eligible subscriptions and says Dedicated Instance includes the feature, but the reviewed public pages do not publish the selected tenant's price, term, PSTN provider charges, numbers, porting, taxes, support or overage economics. Bind the license quantity and provider commercial terms to a dated quote, subscription and bill.
Administration and support
DocumentedControl Hub exposes active off-net calls, peak concurrent usage over the previous 72 hours, blocking alerts and CDR fields for Route List Calls overage and blocking. Those records are operational evidence, not a guarantee that every call succeeds. Assign owners for tenant, location, numbers, Route List, Route Group, gateway, Cloud Connected PSTN provider, alerts, escalation and change rollback.
SMS and MMS
Not verifiedThe reviewed Route List Calls and hybrid PSTN trunking pages do not establish SMS or MMS on Route List numbers, sender registration, APIs, throughput, webhook protection, retention or price. Require a separate current messaging product and number-eligibility record from the selected PSTN provider; do not infer messaging from voice-number activation.
Trace each call through Route List and Route Group
Inbound delivery requires the called number to match a number in the location's Route List, after which a trunk in the associated Route Group carries the call toward the premises. For outbound calls, Cisco requires the calling party number in the SIP INVITE to match an E.164 number configured in the Route List. Number assignment, routing choice, trunk selection, PBX acceptance and destination remain separate checkpoints.
Route groups can hold up to ten trunks. Equal-priority trunks are load balanced, while lower-priority trunks can receive calls when the preferred set is unavailable. This is routing policy, not proof of physical diversity or established-call survival.
Keep trunk identity separate from PSTN provider identity
Webex Calling documents registration-based and certificate-based trunks between the cloud service and the local gateway. The registration model gives the gateway a specific registration handoff; the certificate model has its own trust and reachability requirements. Neither substitutes for the selected Cloud Connected PSTN provider's number, emergency, media and commercial handoff.
Preserve the exact trunk type, gateway configuration, identity headers and credential or certificate lifecycle. A green trunk or accepted registration does not prove that a Route List number is active, that the provider authorized the call or that media traverses the expected path.
Plan licensed concurrency without inventing throughput
Route List Calls licensing measures concurrent off-net calls. Cisco documents 20 percent bursting and then blocking of non-emergency calls; outbound callers in the burst receive an announcement, while calls beyond the burst are blocked and inbound calls are rejected. Control Hub can expose active calls, recent peak concurrency, alerts and CDR overage fields.
Licensed calls, active calls, call attempts per second, burst duration, SBC capacity, PBX resources and media bandwidth are different quantities. G.711 must be present in Webex Calling offers, but the selected codec and resulting bandwidth still require call evidence.
Bind emergency behavior to the Route List location
If RedSky is enabled for the Route List location, Cisco says emergency calls from that list are routed through RedSky and the Route List number must be mapped there. Otherwise emergency calls use the location's PSTN provider. A number appearing in Control Hub does not prove its dispatchable address, callback identity, notification or provider activation.
Complete the current location and provider workflow, retain an independently powered alternative path and use only the approved validation method. Public license and feature pages are not the selected subscription's commercial record; preserve current quotes, orders and bills separately.
Sources & applicability
Primary references for the technical details above. Operational examples and planning checklists are VoIP.info editorial guidance.
- Webex Calling hybrid PSTN trunking ↗
- Webex Calling trunks, route groups and dial plans ↗
- Webex Calling audio specifications ↗
- Webex Calling enhanced emergency calling ↗
- Webex Calling Route List Calls license ↗
Examples require adaptation to your topology. No live PBX or hardware testing is claimed.