9.5 PSTN Connectivity: Cloud-Connected PSTN (CC-PSTN) & Cisco Calling Plans

9.5 PSTN Connectivity: Cloud-Connected PSTN (CC-PSTN) & Cisco Calling Plans

Public Switched Telephone Network (PSTN) connectivity allows cloud collaboration users to place and receive calls to external landlines, mobile devices, and worldwide commercial numbers. Cisco Webex Calling offers three distinct architectural approaches for PSTN termination: native Cisco Calling Plans, partner-peered Cloud-Connected PSTN (CC-PSTN), and customer-managed Local Gateways (CUBE). Selecting the appropriate model requires evaluating geographical availability, operational costs, regulatory sovereignty, and hardware infrastructure.

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1. Architectural Comparison of PSTN Connectivity Models

+-----------------------------------------------------------------------------------------+
|                           WEBEX CALLING PSTN TOPOLOGY OPTIONS                           |
|                                                                                         |
|               +---------------------------------------------------------+               |
|               |                CISCO WEBEX CALLING CLOUD                |               |
|               +------------------+-------------------+------------------+               |
|                                  |                   |                                  |
|               Model 1            | Model 2           | Model 3                          |
|               Turnkey Cloud      | Direct Peering    | Premises Trunk                   |
|                                  |                   |                                  |
|         +------------------------+                   +------------------------+         |
|         v                                                                     v         |
|  +---------------+                   +---------------+                 +---------------+|
|  | Cisco Calling |                   | Cloud-Connect |                 | Local Gateway ||
|  | Plans Core    |                   | PSTN (CC-PSTN)|                 | (Cisco CUBE)  ||
|  +-------+-------+                   +-------+-------+                 +-------+-------+|
|          |                                   |                                 |        |
|          v                                   v                                 v        |
|    Global Public                      Tier-1 Carrier                     On-Premises    |
|    Telecom Grid                       Partner Network                    PRI/SIP Trunks |
+-----------------------------------------------------------------------------------------+

Model 1: Cisco Calling Plans

Cisco Calling Plans provide a fully managed, cloud-native PSTN service provided directly by Cisco Systems.

• Procurement & Billing: Procured directly through Cisco Commerce Workspace (CCW) or authorized Cisco partners. The customer receives a single consolidated monthly or annual invoice covering Webex Calling software licenses, DIDs, and telephony calling minute bundles.
• Zero Hardware Footprint: Eliminates on-premises voice routers, Session Border Controllers (SBCs), TDM PRI cards, and data center rack space.
• Rapid Provisioning: New geographic locations, DIDs, and toll-free numbers can be ordered and provisioned in Webex Control Hub within minutes.
• Coverage: Offered only in specific countries, for example the United States, Canada, the United Kingdom, Ireland, France, Germany, Belgium, Denmark, Finland, Sweden, Lithuania, and Luxembourg (Cisco's Webex blog list); check Cisco's current list before designing.
• Ideal Use Case: Greenfield deployments, branch offices with no existing telecommunications contracts, and organizations seeking to eliminate carrier vendor management.

Model 2: Cloud-Connected PSTN (CC-PSTN)

Cloud-Connected PSTN is a carrier-partner model where certified telecommunications carriers peer directly with the Webex Calling cloud over high-speed, redundant private interconnects (such as Equinix Fabric, private IP WAN, or dedicated IPsec links).

• Commercial Structure: The customer enters into a dual-contract arrangement:
  1. Software subscription and cloud PBX services contracted with Cisco.
  2. Telecommunications usage, PSTN minutes, DIDs, and regulatory compliance contracted directly with the Certified CC-PSTN Carrier (e.g., NTT, Tata Communications, Verizon, Lumen, Pure IP, Sinch, Colt, Vodafone).
• Zero Premises Hardware: Like Cisco Calling Plans, signaling and media flow directly between the Webex Cloud and the carrier cloud. No customer-owned on-premises SBC or CUBE router is required.
• Commercial Flexibility: Large multinational enterprises leverage existing Master Services Agreements (MSAs), negotiated high-volume per-minute calling rates, and specialized international calling bundles.
• Global Footprint: CC-PSTN extends PSTN connectivity into complex international markets and developing regions where native Cisco Calling Plans are not yet licensed to operate.
• API Synchronization: Certified carriers use bidirectional REST APIs integrated into Webex Control Hub to synchronize ordered numbers directly into the customer's tenant inventory.

Model 3: Premises-Based Local Gateway (CUBE)

A customer-managed Cisco Unified Border Element (CUBE) router running on Cisco IOS XE deployed on enterprise premises or private cloud. Discussed in detail in Section 9.6.

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2. PSTN Architecture Comparison Matrix

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3. CC-PSTN Onboarding & Provisioning Workflow

Provisioning Cloud-Connected PSTN in Control Hub follows an automated, API-driven lifecycle:

+---------------------------------------------------------------------------------------+
|                          CC-PSTN PROVISIONING LIFECYCLE                               |
|                                                                                       |
|   +-------------------------------------------------------------------------------+   |
|   | Step 1: Select Certified CC-PSTN Carrier Partner in Control Hub               |   |
|   |         Navigate to Calling -> Locations -> Add PSTN Connection               |   |
|   +---------------------------------------+---------------------------------------+   |
|                                           |                                           |
|                                           v                                           |
|   +-------------------------------------------------------------------------------+   |
|   | Step 2: Establish Tenant Peering Token & Authorize API Link                   |   |
|   |         Control Hub generates OAuth handshake linking Org ID to Carrier Portal|   |
|   +---------------------------------------+---------------------------------------+   |
|                                           |                                           |
|                                           v                                           |
|   +-------------------------------------------------------------------------------+   |
|   | Step 3: Order New DIDs or Initiate Local Number Portability (LNP)             |   |
|   |         Carrier validates Letter of Authorization (LOA) & schedules cutover   |   |
|   +---------------------------------------+---------------------------------------+   |
|                                           |                                           |
|                                           v                                           |
|   +-------------------------------------------------------------------------------+   |
|   | Step 4: Automated API Inventory Synchronization                               |   |
|   |         Activated numbers automatically populate Control Hub Calling inventory|   |
|   +---------------------------------------+---------------------------------------+   |
|                                           |                                           |
|                                           v                                           |
|   +-------------------------------------------------------------------------------+   |
|   | Step 5: Assign Numbers to Locations, Users, Workspaces, and Auto Attendants   |   |
|   +-------------------------------------------------------------------------------+   |
+---------------------------------------------------------------------------------------+

Step 1: Carrier Partner Selection

Within Cisco Webex Control Hub, the administrator navigates to Calling > Locations, selects the target physical facility, and clicks Add PSTN Connection. The administrator selects Cloud-Connected PSTN and chooses an authorized provider from the list of certified carriers.

Step 2: Tenant Linking via API Handshake

The administrator is redirected to the carrier's administrative portal or receives a secure authorization token. This step authenticates the enterprise's Webex Organization ID with the carrier's provisioning engine, authorizing bidirectional API data exchange.

Step 3: Number Ordering and Porting (LNP)

Through the carrier's digital portal, administrators can:

• Procure New Numbers: Instantly select available blocks of national, local, or toll-free DIDs.
• Submit Local Number Portability (LNP) Requests: To transfer existing enterprise numbers from an incumbent telecom provider to the CC-PSTN carrier, administrators submit a formal Letter of Authorization (LOA) accompanied by a recent Customer Service Record (CSR). The carrier coordinates the exact cutover date and time with the national telephone numbering authority.

Step 4: Automated Number Synchronization

Unlike legacy systems that required manual export and re-import of CSV files, certified CC-PSTN partner platforms invoke Webex REST APIs to push newly provisioned or ported numbers directly into the customer's Control Hub Calling > Numbers inventory in real time.

Step 5: Assignment and Service Activation

Once visible in Control Hub, numbers can be assigned immediately as:

• Primary user DIDs
• Workspace directory numbers
• Main company numbers
• Auto Attendant or Call Queue pilot numbers
• Emergency Callback Numbers (ECBN)

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4. High Availability & Multi-Carrier Failover Design

Mission-critical enterprise voice architectures cannot rely on a single PSTN circuit or unmonitored trunk route.

+---------------------------------------------------------------------------------------+
|                         HIGH AVAILABILITY CC-PSTN TOPOLOGY                            |
|                                                                                       |
|                     +---------------------------------------+                         |
|                     |       CISCO WEBEX CALLING CLOUD       |                         |
|                     +-------------------+-------------------+                         |
|                                         |                                             |
|                    Continuous SIP OPTIONS Keepalives                                  |
|                    Failover on SIP 503 / 504 / Transport Timeout                      |
|                                         |                                             |
|                    +--------------------+--------------------+                        |
|                    |                                         |                        |
|                    v                                         v                        |
|         +---------------------+                   +---------------------+             |
|         | CC-PSTN Carrier A   |                   | CC-PSTN Carrier B   |             |
|         | (Primary Provider)  |                   | (Secondary Provider)|             |
|         +----------+----------+                   +----------+----------+             |
|                    |                                         |                        |
|                    +====================+====================+                        |
|                                         |                                             |
|                                         v                                             |
|                           Global Public Switched Network                              |
+---------------------------------------------------------------------------------------+

Architectural Redundancy Mechanisms

1. Redundant Carrier Data Center Peering: Certified CC-PSTN carriers maintain active-active, geographically redundant Session Border Controllers peered with at least two geographically separated Cisco Webex Cloud data centers (e.g., Dallas and San Jose in North America, or London and Frankfurt in Europe).
2. SIP OPTIONS Keepalives: Webex Calling edge proxies continuously transmit SIP OPTIONS request packets to carrier edge interfaces at fixed intervals (typically every 30 to 60 seconds). If a carrier endpoint fails to reply with 200 OK within the configured timeout window, Webex Calling automatically flags the trunk as out-of-service.
3. Session Failover: For a Cloud Connected PSTN location, Webex Calling and the provider fail over between the provider's redundant SBCs. For premises-based PSTN, Webex Calling tries the next trunk in the location's route group.
4. Mixing PSTN Options: Each location has one PSTN connection, so organizations mix options site by site, for example Cisco Calling Plans in the United States, a certified provider in Asia, and a Local Gateway in India. Two CCP providers are not combined in a route group; route groups contain Local Gateway trunks.