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Upgrading legacy networks: Transitioning from SDH/PDH to optical transceiver-based systems

In the fast-evolving world of telecommunications, legacy networks, primarily based on Synchronous Digital Hierarchy (SDH) and Plesiochronous Digital Hierarchy (PDH), are increasingly becoming outdated. These technologies, once the backbone of telecommunication infrastructures, are now seen as bottlenecks, hindering the performance and scalability required in the digital age. The transition towards optical transceiver networks promises not only significant cost savings but also considerable improvements in efficiency. Here, Marcin Bala, CEO of telecommunications networks specialist Salumanus, delves into the critical aspects of this transition and its benefits.

SDH and PDH optical networks, developed in the late 20th century, revolutionised telecommunications by providing reliable and synchronised data transmission. However, these technologies have inherent limitations.

One of the most significant limitations of SDH/PDH networks is their insufficient bandwidth capacity. PDH systems, including E-carrier (Europe) and T-carrier (North America) systems, offer bandwidths up to 565 Mbps (E4) and 44.736 Mbps (T3) respectively. These rates are inadequate for modern applications requiring high data throughput.

SDH networks, designed to improve on PDH, provide higher capacities, with rates up to 40 Gbps (STM-256). However, even this bandwidth is insufficient for contemporary needs, especially with the advent of 5G, IoT and streaming services demanding far greater data rates.

Enhancing SDH/PDH systems often requires extensive and costly hardware upgrades, involving complex configurations and extended downtime. For example, small-scale upgrades, such as replacing a few multiplexers might require only a few hours of downtime, while large-scale overhauls, like a complete transition to DWDM systems could take several days or even weeks.

Similarly, these legacy systems consume more electricity compared to optical networks, resulting in greater operational costs and larger carbon footprints. The higher power consumption also necessitates more robust cooling solutions, further increasing energy use and operational expenses.

The shift to optical transceiver-based networks
Optical transceiver-based networks present a compelling alternative to legacy SDH/PDH systems. These networks leverage advanced optical technologies to transmit data at higher speeds and over greater distances with remarkable efficiency.

Optical transceivers enable the transmission of data at speeds ranging from 10 Gbps to 400 Gbps and beyond, far surpassing the capabilities of SDH/PDH systems. They are also highly scalable, allowing for straightforward upgrades and expansions. This adaptability is crucial in meeting the dynamic needs of modern telecommunication demands, such as the development of 5G and 6G networks and VR and AR applications.

The initial investment in optical technologies can be significant, but the long-term cost savings are substantial. Lower maintenance costs, reduced power consumption, and the elimination of expensive proprietary hardware contribute to these savings.

At the same time, optical transceivers are more energy-efficient, reducing the overall power consumption of the network. This not only lowers operational costs but also aligns with global efforts towards sustainable and green technologies.

Optical networks offer superior reliability with lower latency and higher data integrity, essential for critical applications such as financial transactions, healthcare, and emergency services.

Implementing the transition

Transitioning from SDH/PDH to optical transceiver-based networks involves several strategic steps. First, a thorough assessment of the existing network infrastructure is essential. This includes identifying critical bottlenecks and areas where upgrades will have the most impact.

Choosing the right optical transceiver technology is crucial. Factors such as data rate requirements, distance and compatibility with existing systems must be considered. Similarly, a gradual implementation will help mitigate risks. Starting with the most critical segments of the network allows for smoother integration and troubleshooting. Continuous monitoring of the upgraded network also allows for ongoing optimisation and ensures that the anticipated benefits in efficiency and cost savings are realised.

At Salumanus, we help companies transition from legacy equipment to optical solutions designed for their specific needs. We provide a wide range of transceivers, including SFP+, QSFP, QSFP28, QSFP-DD modules and coherent plugs.

Nevertheless, some customers still require PDH/SDH technology in their networks. To allow them to upgrade their infrastructure, Salumanus provides dedicated SFPs to emulate SDH or PDH solutions. The PDH/SDH multiplexers are packed into a SPF form factor module, meaning that customers are only required to keep an SFP slot empty in any of their IP device in the network. This would also allow them to increase energy efficiency of their devices with a small SFP consuming less than 2W.

The transition from SDH/PDH to optical transceiver-based networks is not merely an upgrade but a necessary evolution to meet the growing demands of today’s digital landscape. The benefits of enhanced bandwidth, scalability, cost efficiency, energy savings and improved reliability make optical technologies an indispensable component of modern telecommunications.

To find out more about the solutions and range of transceivers Salumanus provides, visit