A large Indian automotive components manufacturer operating 12 plants and employing over 4,500 users faced a problem that many enterprises postpone until it becomes urgent. Its on-premise PBX estate was ageing, support contracts were rising in cost, and spare parts were becoming difficult to source. Yet production schedules left no room for communication failure.
Downtime was not a technical inconvenience. It was a commercial risk. The mandate was clear: complete a cloud calling migration across all sites without disrupting factory operations, dispatch teams, or customer support desks.
Proactive Data Systems, a Cisco Preferred Collaboration Partner, was engaged at the assessment stage to analyse the existing telephony estate, network posture, and operational risk exposure. Before recommending cloud calling, Proactive conducted plant-level audits covering WAN stability, ISP redundancy, identity inconsistencies, recording gaps, and cutover dependencies. The migration strategy was shaped by this diagnostic phase rather than by product preference.
This is how the organisation executed a zero-downtime cloud calling migration at scale. Zero downtime cloud calling migration means transitioning users, numbers, and call flows to cloud-based voice without interrupting inbound or outbound calling at any site.
The company operated plants across Pune, Sanand, Hosur, and two tier-two industrial clusters. Internal coordination depended heavily on voice. Shift supervisors, maintenance teams, procurement, and logistics relied on instant connectivity.
The existing telephony estate included multiple PBX vendors, local PRI lines, and inconsistent call recording practices. Identity provisioning differed by plant. WAN links varied in quality. Some sites relied on single ISPs.
A straight PBX to cloud calling migration with a single cutover date would have exposed the group to operational shock.
Enterprise cloud calling deployment across 4,500 users meant:
Coordination of number porting across circles through licensed telecom service providers
Alignment of hunt groups and call queues
Emergency calling compliance
Recording retention standardisation
Identity provisioning at scale
In manufacturing environments, even a brief voice outage can delay dispatch, slow maintenance response, or interrupt supplier coordination.
The leadership team insisted on one condition: zero downtime during migration.
Rather than treating migration as a single technical event, the programme was structured as a phased, multi-plant cloud calling deployment and rollout.
Plants were grouped by network maturity and business criticality. WAN readiness for VoIP was validated site by site. Latency, jitter, and packet loss were tested under simulated load. Where needed, QoS policies were redefined and secondary ISP links introduced.
Identity and number mapping were centralised before any porting began. Directory attributes were standardised across locations to prevent provisioning errors during scale.
Each plant moved only after network and identity baselines were signed off.
The migration strategy relied on a parallel run model. For defined periods, legacy PBX and cloud calling operated simultaneously. Selected user groups were migrated first, including non-critical departments. Call routing rules were configured to allow fallback to legacy systems if required.
Number porting, executed by licensed telecom providers, followed a staged schedule aligned to low-traffic windows. Internal extension dialling between migrated and non-migrated sites was preserved through temporary routing bridges. This hybrid telephony migration model reduced cutover risk while preserving operational continuity.
The most sensitive phase came during migration of the two highest-volume plants, where voice traffic peaked during shift change and dispatch windows. During the first major number port window, one regional carrier delayed confirmation beyond the agreed slot. A missed window would have forced rollback and extended dual-system dependency. Instead of proceeding blindly, the migration team paused expansion to the next site, activated temporary fallback routing, and maintained legacy PBX handling for a defined user group until confirmation arrived.
No inbound calls were dropped. No production line reported loss of coordination. The following port window was executed with tighter carrier synchronisation and additional verification checkpoints.
Across the twelve-week programme:
Production ran uninterrupted across all shifts during migration. Post go-live stabilisation included active performance tracking, call quality dashboards, and a formal change control forum governing configuration updates across plants. By the end of the first quarter, call quality variance between sites had narrowed measurably and escalation tickets had declined below pre-migration levels.
After migration, the organisation achieved:
The cloud calling for manufacturing initiative did more than replace PBXs. It created a unified communication layer aligned with Industry 4.0 investments already underway.
Crucially, it demonstrated that zero-downtime cloud calling migration is achievable in complex, multi-plant environments when planning and governance match technical ambition.
Three principles emerged from this rollout:
Enterprise VoIP rollout succeeds when migration is treated as operations, not installation.
In this programme, Proactive acted as the migration lead and operational owner across all 12 plants. Proactive established a central migration war room, aligned closely with the customer’s authorised telecom providers on number porting timelines, enforced network readiness validation before each phase, and standardised identity provisioning across sites.
All number porting activities were executed by licensed service providers in accordance with Indian regulatory requirements, with Proactive overseeing technical readiness and sequencing. Cisco provided the enterprise cloud calling backbone. Proactive ensured network, identity, compliance, and governance controls were aligned before cutover and formally reviewed after go-live at every plant.
For large organisations considering PBX to cloud calling migration, the question is not whether downtime can be avoided. It is whether the rollout plan is built to prevent it.
