Case Study of Legacy Communication Migration to IP Networks in Japan

Hierarchy (PDH) and Synchronous Digital Hierarchy (SDH) has been discontinued, and maintenance parts are becoming increasingly scarce. As a result, sustaining legacy systems is no longer feasible, making the transition to IP-based communication a pressing requirement.

The migration process involves substantial technical challenges, including meeting strict realtime and reliability requirements, ensuring coexistence with legacy equipment, and designing appropriate bandwidth. To address these issues, risk-mitigation strategies were adopted, such as deploying multiple models of IP converters, connecting devices to two independent IP networks, and applying delay compensation through jitter buffers. Field tests confirmed that network delay and jitter remained well within the limits required for these applications. The project spanned approximately 900 sites, which were classified into Core, Metro, and Access tiers, and full-scale implementation began in fiscal year 2022. By utilizing existing generalpurpose IP networks, expanding bandwidth where necessary, and employing a multivendor architecture, the migration achieved both flexibility and operational efficiency. These measures are expected to reduce future equipment requirements and operational workload.