100 Gb/s Dense Wavelength Division Multiplexing (DWDM) Networking deployment In Transnet


Utility Telecom and Information and Communication Technology needs are changing rapidly requiring the change in how we implement networks. Industry 4.0 applications will create significant increase in required speeds on utility networks. Transnet having a wide range of systems for Mission Critical Applications and Enterprise Network services requires a very high capacity, robust and scalable backbone network to ensure all the data capacity needs for the organization are catered for. A high capacity DWDM network has been seen as a critical enabler for Transnet to ensure sustainability of the business.

1. Background

Since the early 1990s, telecommunications transmission networks especially in the utilities have been dominated by a technology called Synchronous Digital Hierarchy (SDH). In optical transmission

networks using SDH, the telecommunications data is transmitted between nodes using optical fibre cable. At its inception, SDH offered the ability to transmit what were then deemed high data rates: the adding and dropping of data at nodes; high fault tolerance; and

interoperability that allowed the aggregation of multiples of lower bandwidth traffic such as E1s (2 Mb/s) second), and even Integrated Services Digital Network (ISDN) lines. SDH offers the following bandwidth rates: STM-1 (155 Mb/s); STM-4 (622 Mb/s); STM-16 (2.5 Gb/s); STM-64 (10 Gb/s).

The Transnet telecommunications transmission backbone network, based on SDH, was built in 2004-2008. The existing

telecommunications transmission backbone network is based on SDH, and has capacity of STM-16 except for the route between Johannesburg and Durban where the capacity is STM-64.

2. SDH Challenges

The challenge of SDH is that it provides insufficient maximum bandwidth (10 Gb/s) for modern telecommunications needs. Since the advent of the Internet, and the extensive bandwidth requirements of Rail, Pipeline and Port operations for Mission Critical Communications and for Transnet wide Enterprise / ICT services, the limitations of SDH have become more pronounced. Advances in technology, as well as increases in bandwidth requirements for Transnet have created a situation whereby SDH as a technology has become insufficient to meet Transnet’s future bandwidth requirements. SDH has over the past ten years been superseded by Dense Wavelength Division Multiplexing (DWDM).

In DWDM networks, the singular SDH optical signal that gets transmitted over fibre is broken down into multiple optical signals of different colours, with each colour represented by a different wavelength of the optical signal. These multiple optical signals with different wavelengths (called lambdas or ƛ) are then transmitted in one single fibre. This enables DWDM to carry multiples of what SDH carries in the same fibre. DWDM networks offer capacities of multiples of either 10 or 40 Gb/s per wavelength (ƛ) on client interfaces. Suppliers of DWDM equipment already provide systems that can provide 100 and 400 Gigabits per second per wavelength as line speeds. DWDM systems that are already available on the market are able to transmit 160 wavelengths ((ƛ) per fibre.

Transnet 4.0 based on Industry 4.0 is a strategic direction for Transnet where significant amount of sensor networks will be deployed in the operating environment. The implementation of this strategy will result in significant increase in data utilization in Transnet which requires a robust and scalable backbone transmission network.

3. Need for Network Upgrade

Transnet operates essential telecommunication networks which include Radio communications, track side equipment for condition monitoring, train control systems, Supervisory Control and Data Acquisition (SCADA), Pipeline Process Control and tele-control / tele-protection and optical transport networks are critical for these services. The world of technology is forever changing and Transnet must adapt to the rapid changes in the technology environment. Transnet also has a wide range of Enterprise services that are critical for the operations. All these business needs require a suitable technology to meet current and future bandwidth requirements. The technology choices made must be scalable for easy adaptability as bandwidth requirements increase.

4. Technology Selection

Network analysis, architecture and design have traditionally been considered art, combining an individual’s particular rules on evaluating and choosing network technologies; knowledge about how technologies, services and protocols can be meaningfully combined; experience in what works and what doesn’t; along with (often arbitrary) selections of network architectures. However, as with other types of art, success of a particular network design often depends primarily on who is doing the work, with results that will serve organizational needs. The design of a network must be logical, reproducible and defensible. Using this framework, the DWDM at 100Gb/s minimum capacity was seen to be a favourable technology choice for Transnet based on the following aspects:

  • Providing sufficient capacity for the entire Transnet network
  • Provide capacity for Transnet digital initiatives
  • Transmission presence in the business strategic areas (TERACO Data Centres and undersea cable landing stations)
  • Commercialization for managed bandwidth on the spare capacity simplified
  • Enhancing the robustness of Transnet network

5.Design Principles used for the DWDM Network

  • The 100Gb/s Dense Wavelength Division Multiplexing (DWDM) must operate at discrete wavelengths in the C-band anchored at 193.1 THz frequency grid as per ITU-T Rec.G.694.1, at 50GHz channel spacing.
  • The System must have Reconfigurable Optical Add Drop Multiplexing (ROADM) subsystem with multi-degree capabilities.
  • The DWDM System should be based on Generalized Multi-Protocol Label (Lambda) Switching (GMPLS) Control plane.
  • The DWDM system must have a high capacity switching fabric at minimum 1.2 Tb/s for the ROADM sites in the network
  • The System should support Automatic Protection Switching (APS) and must include the following parameters:a. System should Support colourless and directionless technology
    b. System should provide Robust Forward Error Correction Mechanisms
    c. System should support Multilayer restoration approach.

6. Future Proofing and Roadmap

Transnet DWDM network is highly scalable, resilient and reliable providing the following roadmap features:

  • The network to be upgradable to 400Gb/s capacity in order to cater for future Transnet bandwidth requirements without significant changes to the current platform.
  • The network has a roadmap to integrateSoftwareDefined Networking (SDN) without significant platform changes.
  • Multiple service technologies (including SDH, Ethernet, MPLS and OTN) will be supported simultaneously on the same system with no changes to the common equipment at the optical layer.
  • The DWDM system has a roadmap to support Optical Burst Switching (OBS) and Optical Packet Switching (OPS).
  • The features of the roadmap for Transnet DWDM Network are anticipated to cater for possible future network growth.

7. Proposed Network Dimensioning

As the central rings in Transnet have four directions, it is anticipated that this rings will have a capacity of a minum 200Gb/s upgradable to 400Gb/s should the need arise.

8. Conclusion

Having looked on all aspects of competing technologies and requirements of Transnet as an organization, we believe that DWDM is a network that is fit for purpose which would be able to cater for Transnet needs for now and the future. The network will support Transnet 4.0 strategy due to its capacity and robustness. The deployment of this network is expected to be completed by 2021.