9.3 Webex Calling Call Routing Process & Translation Patterns

9.3 Webex Calling Call Routing Process & Translation Patterns

Blueprint objective 5.2 asks you to describe the call routing process in Webex Calling, and objective 5.4.d covers translation patterns. Unlike Unified CM, Webex Calling has no partitions or calling search spaces that an administrator arranges. Instead, the cloud applies a fixed decision sequence to every call, and administrators influence it through numbers, dial plans, translation patterns, permissions, and PSTN settings. Cisco's Webex Calling design sessions describe that sequence in three phases.

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1. Phase One: Source Classification

Webex Calling first decides what kind of caller it is dealing with, because later rules depend on it:

For trunk calls, the calling number (or the number in the SIP Diversion header, if present) is compared with the organization's configuration: a match on a dial plan pattern marks the call as coming from the premises PBX, and the location's settings for unknown extensions can also mark short numbers as premises calls. Anything else from the trunk is treated as an external PSTN call.

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2. Phase Two: Destination Selection

Webex Calling then works out where the dialed string should go, in this order:

1. Emergency numbers: A match on the location's emergency number is routed to the PSTN for emergency handling immediately.
2. Translation patterns: If the dialed string matches a translation pattern, it is rewritten and the lookup starts again. A pattern that does not actually change the string (for example, 6XXX rewritten to the same digits) does not loop, and Webex Calling allows at most 10 translations per call leg.
3. Outside dial digit: If the location uses an outside dial digit (such as 9) for external calls, it is removed once.
4. Feature access codes: Codes such as call park or call forwarding activation are recognized after translation patterns.
5. Internal matches, in priority order: a user's extension, then the user's enterprise significant number (routing prefix plus extension), then a telephone number in the organization. An extension wins over an overlapping ESN or telephone number, which is why Cisco advises against overlapping extensions with other number types.
6. Virtual extensions map an extension to an external number and send the call straight to the PSTN.
7. Dial plans: A match on a dial plan's enterprise or +E.164 pattern sends the call to that dial plan's trunk or route group (Section 9.2).
8. National number analysis: Using the national dialing plan of the caller's location, Webex Calling classifies the number (national, international, toll-free, and so on), converts it to +E.164 when needed, and loops back so that +E.164 translation patterns, telephone numbers, and dial plans can match.
9. Unknown numbers: Short strings that match nothing can be sent to the premises as unknown extensions (per-location setting, 2 to 10 digits), and the organization's unknown-number handling decides whether other unmatched strings go to a premises trunk or to the location's PSTN connection.

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3. Phase Three: Screening and Routing

Finally, Webex Calling checks whether the call is allowed and sends it:

• The call type found during number analysis is checked against the caller's outgoing call permissions (Section 9.4). A blocked type is rejected or sent to an authorization-code prompt or an auto-transfer number.
• Calls to a Webex meeting dial-in number are recognized and routed straight to the meeting service instead of across the PSTN.
• Allowed calls go to a user, to a trunk or route group, or to the location's PSTN connection: Cisco Calling Plan, Cloud Connected PSTN, or premises-based PSTN through a Local Gateway.

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4. Translation Patterns

Translation patterns let administrators rewrite dialed strings before routing, which Webex Calling dial plans cannot do (Section 9.2).

Typical uses:

• Abbreviated dialing: 88 translated to the IT help desk's full +E.164 number.
• Preserving dialing habits: Cisco's example translates the 10-digit Bangalore pattern 80[2-9]XXXXXXX by putting 91, India's country code, in front of the original digits.
• Migrations: Old site codes or short codes translated to +E.164 numbers so that users keep dialing the way they did on the previous PBX.

Because the lookup restarts after a translation, the rewritten number can then match a user, a dial plan, or the PSTN exactly as if the user had dialed it.

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5. Worked Example

A user in the London location dials 88:

1. 88 is not an emergency number.
2. A location-level translation pattern matches 88 and rewrites it to +442079460100; the lookup restarts.
3. +442079460100 matches a telephone number owned by a Webex Calling user in the organization, so the call stays on-net and rings that user.

If instead the user dials 02079460777, a London number that is not in the organization, national number analysis tags it as a national call for the United Kingdom location, converts it to +442079460777, finds no dial plan match, checks that national calls are allowed for the user, and sends it out through the London location's PSTN connection.