9.2 Webex Calling Routing, Trunks & Dial Plans

9.2 Webex Calling Routing, Trunks & Dial Plans

Enterprise dial plans translate user dialing habits into structured signaling paths. In Cisco Webex Calling, dial planning encompasses intra-location extension dialing, enterprise-wide multi-site routing, external PSTN breakout, and granular privilege enforcement. Collaboration engineers must configure steering codes, route groups, outgoing call permissions, and automated call handling features to construct a resilient voice infrastructure.

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1. Internal Call Routing & Dial Plans

Webex Calling categorizes internal call routing into two principal domains: intra-location and inter-location.

+---------------------------------------------------------------------------------------+
|                                 INTERNAL CALL ROUTING                                 |
+-------------------------------------------+-------------------------------------------+
| INTRA-LOCATION CALLING                    | INTER-LOCATION ENTERPRISE CALLING         |
| - Caller and callee share same site       | - Caller and callee reside in diff. sites |
| - User dials direct extension (e.g. 1001) | - Steering Code + Extension (e.g. 82-2001)|
| - Resolved locally in cloud tenant        | - Cross-site prefix translation           |
+-------------------------------------------+-------------------------------------------+

Intra-Location Calling

When an employee dials an internal extension assigned to a user or workspace within their own location, Webex Calling matches the dialed digits against the organization's extension length (2 to 10 digits). The session initiates directly across the cloud signaling plane without requiring steering codes or PSTN toll charges.

Inter-Location Enterprise Extension Dialing (Steering Codes)

When an enterprise operates multiple locations, extension numbers may overlap (for instance, extension 1001 exists in both New York and London). To facilitate direct station-to-station calling across sites without public PSTN toll charges, Webex Calling utilizes Routing Prefixes (Steering Codes).

• Routing Prefix Format: Each location's routing prefix is 1 to 7 digits and must be unique. The organization-wide prefix length includes a steering digit (for example 8) that starts every inter-location call.
• Dialing Syntax: [Location Routing Prefix] + [Internal Extension]
• Execution Mechanics:
  1. An employee in New York (Site Prefix 81) wishes to dial Alice in London (Site Prefix 82, Extension 2001).
  2. The employee dials 822001.
  3. Webex Calling inspects the leading digits, identifies 82 as the routing prefix for London, strips the routing prefix 82, and delivers the call to Extension 2001 in the London location.
• Flat Extension Dialing: If an enterprise maintains globally unique extensions across all locations (e.g., Dallas uses 1000-1999, Chicago uses 2000-2999, London uses 3000-3999), administrators can turn on Allow extension dialing between locations, so users reach other sites by extension alone.

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2. Dial Plans and Dial Patterns

Dial plans are configured at the organization level (Calling > Call Routing > Dial Plans). Each dial plan names one routing choice, a trunk or a route group, and lists dial patterns for the destinations behind it, usually an on-premises PBX such as CUCM during a migration:

• E.164 patterns: + followed by digits and optional wildcards, for example +1408555XXXX or +496100!.
• Enterprise patterns: digits followed by optional wildcards, for example 822XXX for another site's abbreviated numbers.
• SIP URI domain patterns: send user@domain calls to the trunk.

Only two wildcards exist: X matches one digit (0-9) and ! matches any sequence of digits; ! may appear only once, at the end. There are no N or [range] wildcards, and dial plans do not strip or add digits. Digit manipulation is done with translation patterns (Section 9.3) or on the Local Gateway.

A per-location setting can also send unknown extensions (2 to 10 digits that match no Webex Calling user or feature) to the premises over a trunk or route group, which preserves abbreviated dialing while a site is partly migrated.

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3. Trunks and Route Groups

Trunks establish the signaling and media pipes connecting Webex Calling to carrier networks or premises systems. Route Groups organize these trunks for resilience and capacity management.

+---------------------------------------------------------------------------------------+
|                                 ROUTE GROUP TOPOLOGY                                  |
|                                                                                       |
|                         Route Group "RG-US-Premises-PSTN"                             |
|                                          |                                            |
|              +---------------------------+----------------------------+               |
|              | Priority 1                                             | Priority 2    |
|              v                                                        v               |
|   +------------------------+  +------------------------+   +------------------------+  |
|   | Dallas LGW trunk       |  | Chicago LGW trunk      |   | Denver LGW trunk       |  |
|   | (registering)          |  | (registering)          |   | (certificate-based)    |  |
|   +------------------------+  +------------------------+   +------------------------+  |
|   Calls shared randomly between the two priority-1 trunks; Denver used only if both   |
|   priority-1 trunks are unavailable.                                                  |
+---------------------------------------------------------------------------------------+

Trunk Types

1. Registering (registration-based): The Local Gateway registers to Webex Calling with credentials shown in Control Hub, over SIP TLS to destination TCP port 8934. No inbound firewall rule is needed.
2. Certificate-based: Webex Calling and the Local Gateway authenticate each other with mutual TLS (destination TCP port 5062 toward Webex), which needs a CA-signed certificate on CUBE and an FQDN or SRV address that Webex Calling can reach.

Cloud Connected PSTN and Cisco Calling Plans are not trunks that you build; they are PSTN connection choices for a location (Section 9.5).

Route Groups

A Route Group contains 1 to 10 trunks, each with a priority level:

• Calls are distributed randomly among the trunks that share the highest available priority.
• If those trunks are unavailable, Webex Calling uses the trunks at the next priority level.
• A route group can mix trunks from different locations for geographic redundancy, and it can be the routing choice of a dial plan or of a location's premises-based PSTN connection.

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4. Outgoing Call Permissions

Every outbound call is checked against the caller's outgoing call permissions before it is routed. Section 9.4 covers the call types, their defaults, authorization codes, and the transfer and forwarding controls used to prevent toll fraud.

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5. Native Call Routing Features & Applications

Webex Calling incorporates native cloud PBX services that route incoming calls without requiring third-party contact center software.

Call Distribution Features Comparison

Auto Attendant Mechanics

• Multi-Level Menus: Callers navigate hierarchical prompts (e.g., "Press 1 for Sales, Press 2 for Support").
• Schedule Profiles: Applies different routing behaviors based on Business Hours, After Hours, and Holiday calendars.
• Key Actions: Transfer without prompt, transfer with prompt, route to voicemail, dial by extension, dial by name, transfer to external number, or repeat menu.

Hunt Group Distribution Algorithms

1. Circular (Round-Robin): Cycles through the member list, routing each new call to the agent listed immediately after the agent who answered the prior call.
2. Regular (Linear): Always rings the first agent in the directory list. If busy or unanswered, rings the second agent, progressing strictly sequentially.
3. Simultaneous: Rings all configured agent extensions concurrently. The first agent to lift the handset answers the call.
4. Uniform (Longest-Idle): Directs the incoming call to the agent who has been idle the longest since completing their previous call, balancing workload evenly.
5. Weighted: Distributes calls according to percentage weights assigned to the agents.

Call Queues

Call Queues enhance hunt groups by introducing caller hold states:

• Comfort Messages: Plays initial welcome greetings and periodic audio updates (e.g., "Thank you for holding; your estimated wait time is 3 minutes").
• Queue Capacity Limits: Defines maximum queue depth (e.g., up to 50 queued callers) and maximum wait duration (e.g., 600 seconds).
• Overflow Routing: Automatically diverts excess callers to a secondary hunt group, voicemail box, or external number when the queue exceeds capacity or timers expire.