Client Background
Our client, a leading global financial services company, relied heavily on a contact centre and auto dialler to manage customer interactions. Their systems were built on a legacy ISDN 30 infrastructure approaching end-of-life. The network operator had even warned of potential suspension due to excessive traffic on the local exchange. Without a stable telephony platform, operations and customer communications were at serious risk.
Challenge
The client needed a modern, resilient, and scalable solution to replace ISDN while ensuring continuity of critical services. The objectives were:
- Eliminate reliance on ageing ISDN infrastructure
- Guarantee business continuity and compliance with regulatory standards
- Deliver a future-proof platform capable of supporting international growth
- Reduce cost per channel and improve operational efficiency
Immervox Approach
Immervox proposed and delivered a structured migration programme to SIP trunking and VoIP, followed by the establishment of dual data centres in Germany to support international expansion. The programme was delivered through three phased projects:
Project 1: Migration to SIP with Site-Based SBCs
- Replaced ISDN with SIP using Session Border Controllers (SBCs) and dedicated internet circuits
- Installed dual SBCs and four diversely routed DIA circuits for resilience
- Designed and executed a detailed migration roadmap, including department-level test plans
- Piloted migrations with selected departments, then completed phased overnight cutovers across the business
Outcome: A seamless transition from ISDN to SIP within two weeks, delivering immediate reliability improvements, full service continuity, and significant cost savings.
Project 2: Establishment of Dual German Data Centres
- Built mirrored data centres in Germany with no single point of failure
- Implemented four new DIA circuits and configured new SIP trunks and SBCs
- Migrated dialler traffic from the UK to Germany with minimal downtime
Outcome: A resilient, dual-site infrastructure ensured redundancy, compliance, and improved global performance.
Project 3: Expansion to Support European Operations
- Added further DIA capacity and created dedicated VLANs for each country (Poland, Slovakia, Netherlands)
- Configured trunk groups, number ranges, and service allocations for each region
- Ported all original numbers after a three-month stability period
Outcome: A centralised European telephony hub improved efficiency, reduced fragmented infrastructure, and delivered scalable growth.
Results and Impact
- Resilience and Continuity: 99.99% uptime delivered through dual SBCs and dual-site failover design
- Value for Money: SIP migration reduced channel costs by over 30% compared to ISDN, while removing dependency on ageing exchanges
- Future-Proofing: Modern SIP architecture enabled rapid expansion across multiple countries without service redesign
- Operational Assurance: Phased migrations avoided downtime, ensuring uninterrupted customer service
- Compliance and Security: All solutions were delivered to meet GDPR and regulatory requirements
Relevance to the Council
Although this programme was delivered for a financial services organisation, the challenges mirror those faced by many public sector bodies: replacing obsolete ISDN systems, maintaining service reliability for critical functions, and ensuring taxpayer value through cost-effective, future-proof technology. Immervox’ s proven expertise in planning, managing, and delivering complex migrations ensures public sector organisations can modernise communications with confidence, resilience, and transparency.
