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Webex Calling Design

This chapter details the technical design for migrating from CUCM to Webex Calling, covering architecture, location configuration, dial plans, PSTN integration, and coexistence strategies.

FICTIONAL NUMBER DISCLAIMER -- All telephone numbers, DID ranges, toll-free numbers, and ITN numbers in this document are fictional and used for illustrative purposes only. Ranges used: India +91-XX-4960-XXXX, India Toll-Free 1800-266-10XX, UK Freephone +44-800-096-XXXX, Germany Freephone +49-800-096-XXXX. Do not dial these numbers.

Feature Gaps

Several CUCM features have no direct equivalent in Webex Calling and require redesign or accepted workarounds. These are documented in the Feature Gap Bridge -> chapter, which must be read alongside this design chapter.

Chapter Overview

Sections

2.1 Architecture Principles ->
Complete design for CUCM to Webex Calling migration including location strategy, dial plan design, PSTN integration, feature migration, and coexistence architecture

2.2 Location Configuration ->
Webex location configuration by region, number management, emergency services, announcement languages

2.3 Dial Plan Design ->
Enterprise dial plan, site code assignments, extension ranges, inter-site dialing, external routing

2.4 PSTN Integration ->
PSTN connectivity strategies by region, Local Gateway deployment (India), Cloud Connected PSTN (EMEA/Americas), trunk configuration

2.5 Feature Migration ->
CUCM feature mapping to Webex Calling, hunt groups, call pickup, voicemail, mobility features, paging/intercom

2.6 Coexistence Design ->
CUCM-Webex coexistence architecture, call routing during migration, SIP trunk configuration, number portability, rollback procedures

Design Principles

Architecture Goals

  1. Minimize Disruption: Zero-downtime migration with phased cutover approach
  2. Feature Parity: Maintain or improve existing CUCM features in Webex
  3. Regional Compliance: India DoT/TRAI, EMEA GDPR, Americas standard policies
  4. Operational Simplicity: Cloud-native management, reduced on-premises infrastructure

Multi-Region Strategy

Region Calling Region PSTN Strategy Data Residency
India APAC (Mumbai + Chennai DCs) Local Gateway APAC region
UK UK (London) Cloud Connected PSTN UK region
EU EU (Frankfurt) Cloud Connected PSTN EU region
Americas US Cloud Connected PSTN US region

Key Design Decisions

Location Strategy

  • 12 Webex Locations mapping to physical sites
  • Remote/WFH users assigned to nearest office location
  • Emergency Services configured per country regulations
  • Number Management maintains existing DID ranges

Dial Plan Design

  • 4-digit extensions for all sites (existing scheme retained)
  • Site codes for abbreviated inter-site dialing (existing scheme retained)
  • E.164 normalization for all outbound calls
  • Least Cost Routing via PSTN route groups

PSTN Integration

India (7 Sites) - Local Gateway per telecom circle (Mumbai, Chennai, Bangalore, Delhi, Noida, Hyderabad) - Zone/Edge configuration for toll bypass compliance - SIP trunks to Tata/Airtel per circle - ITN numbers for remote/WFH users (exempt from toll bypass)

EMEA (2 Sites) - Cloud Connected PSTN via IntelePeer UK/EU - NO Local Gateway required (no PSTN routing regulations) - Data residency compliance via calling region selection

Americas (2 Sites) - Cloud Connected PSTN via IntelePeer US - Standard enterprise PSTN configuration

Coexistence Architecture

During migration, CUCM and Webex Calling will coexist using SIP trunks:

+-------------------------------------------------------------+
|                  COEXISTENCE ARCHITECTURE                    |
+-------------------------------------------------------------+
|                                                             |
|  +--------------+        SIP Trunk        +--------------+ |
|  |     CUCM     |<---------------------->|Webex Calling | |
|  |   (Legacy)   |                         |   (Cloud)    | |
|  +------+-------+                         +------+-------+ |
|         |                                        |         |
|         v                                        v         |
|  +--------------+                         +--------------+ |
|  | Migrating    |                         |  Migrated    | |
|  |    Users     |                         |    Users     | |
|  +--------------+                         +--------------+ |
|                                                             |
+-------------------------------------------------------------+

Design Validation

Before proceeding to implementation:

  • Webex location design reviewed and approved
  • Dial plan validated with business units
  • PSTN strategy confirmed for all regions
  • Compliance requirements met (India/EMEA)
  • Feature parity documented and accepted
  • Coexistence call flows tested

Next Steps

After completing the design:

  1. Review Contact Center Design for WxCC architecture
  2. Review Compliance & Security for regional compliance details
  3. Proceed to Implementation for deployment