By Pan Feng
With the rapid development of new services like cloud computing, streaming media, and mobile broadband, the optical network's bandwidth and efficiency must be improved. Smarter networks of higher bandwidth must be built. The fifth-generation optical network will be software-defined, and feature flexibility, orchestration, and openness.
The telecom industry is facing ever-growing demand for higher bandwidth. It is estimated that by 2018, global data traffic consumption will reach 5ZB – that’s more than 100 million DVDs per hour. Optical networks are the fundamental architecture of the telecom network. The relentless development of the telecom industry drives the evolution of optical networks. Although the 100G optical transport network (OTN) has just arrived, the industry is already anticipating what comes next. As the latest evolutionary step, the fifth-generation optical network architecture will reshape the software and hardware of optical networks.
From the start, the two main factors driving the development of the optical network industry have been bandwidth and cost. Optical networks of higher bandwidth yet lower costs are constantly being developed. In less than 50 years, the optical network has witnessed four important phases of development: Plesiochronous Digital Hierarchy (PDH), Synchronous Digital Hierarchy (SDH), Wavelength Division Multiplexing (WDM), and OTN-based coherent 100G WDM.
Advancements in hardware and software have graduated optical fiber capacity from Mbps to Tbps. System efficiency has also improved, reducing cost per bit. Further, manual control has been automated in many ways.
With the rapid development of new services like cloud computing, streaming media, and mobile broadband, the 100G OTN must be improved. Smarter networks of higher bandwidth must be built. Tbps-level networks must be exponentially enhanced. The fifth-generation optical network will be software-defined networks that feature flexibility, orchestration, and openness.
Key flexibility
The first key component is flexibility. Flexible super pipes boost network capacity. The extreme transmission capacity of a pair of optical fibers can be increased to support the huge amount of data traffic of the entire telecom network. Network flexibility includes the flexibility of the optical layer, electrical layer, and capacity. Hardware flexibility of the optical network means the hardware can be upgraded just like the upgrade of smartphones to support LTE/LTE-A. Technological upgrade of hardware can boost system speeds.
Optical layer flexibility refers mainly to a flexible grid. According to the current ITU-T DWDM standards, multiplexers (MUX) and demultiplexers (DEMUX), wavelength selective switching (WSS), and reconfigurable optical add/drop multiplexer (ROADM) are all defined based on fixed bandwidth grids such as 50GHz and 100GHz spectrum gaps. Flexible grids minimize grid gaps to 12.5GHz. The system can conduct dynamic bandwidth allocation based on service requirements. Different spectrums (37.5GHz, 50GHz, 75GHz, 100GHz, 125GHz) can be allocated and adjusted based on dynamic data transmission requirements. Flexible grids redefine the accuracy capability of optical signal scheduling, increasing spectrum utilization by 50%.
Electrical layer flexibility refers mainly to Flex OTN based on Nx100G flexible frame architecture. The evolution of traditional OTN follows a fixed pattern. For example, the rate of optical transport unit 5 (OTU 5) is four to ten times faster than that of OTU 4. If this pattern persists in the 100G era, different OTUs would support different rates, making for stark gaps. The lack of medium rates will make actual bandwidth utilization low. Flex OTN supports cross-connection and multiplexing of high-speed pipes. The baseline rate can be set as 100G and the dynamic interface OTUCn can be used to provide n x 100G rates. Flex OTN is like a flyover, achieving flexible service scheduling. After 100G became a reality, the era of flexible OTN frame architecture dawned.
Capacity flexibility: Thanks to the rapidly developing Optical Digital Signal Processing (ODSP) technology, online real-time signal modulation now supports switching of different CODEC for high-speed signals, realizing flexible switching between capacity and distance. For example, 16 quadrature amplitude modulation (16QAM) supports large capacity. Now the system can transform 16QAM into QPSK so that both large capacity and long distance can be achieved.
So far, leading operators including Vodafone, DT, Türk Telekom, BT, and MTN have all tested future-oriented flexible super-large capacity technologies, breaking many world records relating to capacity of the optical network system.
Key orchestration
The second key component is orchestration, which means the efficient collaboration between different channels of multiple layers. Multi-layer orchestration unleashes the full potentials of a system, maximizing system efficiency. The orchestration optimizes traffic usage and minimizes costs. Network orchestration includes the orchestration of the IP layer and optical layer, inter-domain NE networking management, and traffic orchestration of the wavelength of a single NE, OTN, and Ethernet (L0/L1/L2).
The value of orchestration is obvious. The costs per bit for each pipe are different. Policy-based pipe orchestration minimizes traffic cost and improves pipe efficiency and utilization.
At the beginning of 2014, Telefónica tested the orchestration between the IP layer and optical layer on commercial devices, which showed that network-level orchestration effectively improves network capacity. The lessons learned are expected to be put into commercial use within the year.
Key openness
The third key component is software-defined network openness. On the one hand, software-defined networking (SDN) enables the system's hardware capabilities; pipes become flexible and high-efficiency orchestration is achieved, unleashing hardware potentials. On the other hand, SDN opens network capabilities. The network system can be empowered through SDN technologies to meet a wide variety of customer needs, realizing system availability and scalability.
Through network resources, capability abstraction, and standard interfaces, telcos can provide innovative service such as bandwidth on demand (BoD) and virtual transport network service (VTS). BoD is a refined intelligent leased line service. Customers can flexibly adjust network features such as bandwidth and latency of leased lines based on demand, which maximizes the value of leased lines.
VTS provides virtual leased lines to customers so that they can conduct effective and visualized network management. SDN changes the operation model of optical networks to realize bandwidth monetization. SDN also enables abstraction and unification of network resources, which simplifies network operation and maintenance and reduces cost per bit.
Telefónica, SingTel, and China Telecom have conducted in-depth testing and trial use of SDN in the transport network field in preparation of commercial SDN deployment.
At the end of June 2014, Huawei shared fifth-generation optical network concepts at the Next Generation Optical Networking Forum in Nice, France. Dedicated to the research and promotion of next-generation optical networks, Huawei leads the development of global optical networks and continues to make strategic investments in the area. Working with industry partners, Huawei drives the formulation of industry standards and promotes the sustainable development of the optical network industry.
The fifth-generation optical network architecture will lead the industry into a bright new future.
