The Seven Top Risks of Ageing SDH Networks

Introduced in the 1990s, SDH networks once represented a revolutionary step forward in terms of network architecture, synchronisation, and protection. With networks moving to higher bandwidth, lower cost ethernet circuits, this once industry standard technology is being replaced, but this cannot be achieved overnight, and a host of risks emerge if SDH networks are not adequately maintained or decommissioned with the proper care. Understanding these challenges is crucial for network operators.

Ageing SDH networks present a variety of risks that operators must address to ensure continued reliability and performance as an integral part of continuity and network update planning. From degradation of critical inter-dependency to the challenges of network maintenance and the impending threat of component obsolescence, understanding these risks is the first step toward developing effective strategies for network operators. The key risks are as follows:

  1. Degradation of critical inter-dependency
    SDH networks, known for their carrier-class availability and 99.999% uptime, face significant risks as they age. Long-term neglect can lead to a build-up of faults, compromising the network’s self-healing capabilities and resilience architectures. This degradation may not be obvious initially but can result in unserviced failures, putting traffic paths or entire nodes at risk. The impacts include potential loss of service, increased repair times, and higher costs. Additionally, the ability to meet service level agreements (SLAs) is put at risk, increasing the probability of major network outages and undermining the five-nines availability operators strive to maintain. This emphasises the critical importance of ongoing maintenance and servicing of SDH networks.
  2. Data integrity
    Over time, the records across operational support systems (OSS) can become out of sync with the actual network, creating challenges in maintaining and planning the decommissioning of these networks. This misalignment can lead to data errors and loss, compromising the reliability and accuracy of transmitted data. The complex nature of SDH technology, with its intricate synchronisation and fault management systems, requires deep expertise to maintain, and without adequate maintenance and timely repairs, these discrepancies cause data integrity issues, highlighting the importance of precise and up-to-date network documentation.
  3. Skills shortage
    As SDH networks transition to legacy status, the expertise required to maintain them is dwindling due to the retirement of skilled engineers and the lack of new training programs. These skilled professionals possess a deep understanding of SDH technology, having been trained extensively during its peak use years. But as they retire, the industry faces a significant knowledge gap as new engineers entering the field are more likely to be trained in modern digital technologies, rather than SDH. The specialised knowledge required to diagnose and repair SDH networks is becoming scarce and the operational training programs for SDH have largely been discontinued, making it challenging to impart this knowledge to new recruits.
  4. Reliability and product lifetimes
    The reliability of SDH nodes is a critical factor, with each node card designed to meet a target Mean Time Between Failure (MTBF) of at least 15 years. However, as these nodes approach the end of their design lifetime, the risk of failures increases. Factors such as temperature, high clock speeds, and component aging contribute to the challenges of maintaining reliable performance. The looming issue of component obsolescence adds another layer of risk, requiring careful management to ensure ongoing support.
  5. Component obsolescence
    The rapid advancement of silicon technology during the period of SDH development led to frequent retirement of old devices. This component obsolescence creates a significant challenge for operators, as unavailable components can hinder repairs. Managing the withdrawal of legacy networks becomes crucial to maintaining customer service levels and freeing up spares for redeployment.
  6. Synchronisation risks
    Synchronisation is a key component of SDH networks, crucial for stable operations. While the network can continue to carry traffic in the event of synchronisation failure, the impact includes significant jitter and wander effects, and can cause major problems and potential service outages where the network deployment relies on robust synchronisation, for example in critical infrastructure and power networks. These effects can lead to indeterminate and intermittent issues that are challenging to locate and costly to fix. Maintaining synchronisation is vital for the overall health and performance of the network.
  7. Failure to plan network decommission
    Careful planning is crucial when decommissioning a network, as the risks of not doing so are significant. Unplanned decommissioning can lead to unpredictable failures, disrupting critical services and causing potential outages. Network interdependencies, including synchronisation, DCN, and other links, must be meticulously addressed and the order in which components are decommissioned needs to be strategically planned to ensure a smooth transition. Additionally, the post-decommissioning phase requires consideration for the recovery and reuse of spare parts to mitigate risks. Updating all related systems is essential to maintain data integrity. Without careful planning, the decommissioning process can introduce severe risks that are as critical as those faced during network deployment.

The importance of planning for decommissioning can’t be underestimated. As network operators are faced with legacy technology and the promises of a digital future, embracing the complexities, acknowledging the potential single points of failure, and recognising the impacts of synchronicity risks, will help transformation. It involves meticulous planning, controlled closures, and a profound understanding of the network’s intricacies.

The risks of aging SDH networks should not just be viewed as obstacles either, they are opportunities for innovation, adaptation, and strategic evolution. By navigating them, network operators can ensure a seamless transition into the next era of telecommunications.

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