OTN and 100G: The Inevitable Choice for Future Optical Networks

Optical network data transmission has entered a new era of large-granularity service. Business growth and mature optical transport networks (OTNs) have triggered this revolution in data transmission. As the number of fixed broadband users increases, IPTV networks are being deployed on a large scale, and a variety of broadband applications are emerging. The requirement for bandwidth in the backbone transport network is growing rapidly.

According to data released by the Optical Internetworking Forum (OIF), average annual growth in operator traffic is much higher than the annual growth in operator revenue. The cost per unit of traffic has to be reduced to relieve pressure on revenue. The most effective means of lowering TCO is to improve transmission capacity. Through the joint efforts of the IEEE, ITU-T, and OIF, 100G standards have been drafted. Vendors worldwide have released or will soon release 100G products, and the 100G era is just around the corner.

OTN Status Quo and Trends

OTN is an important transport-layer technology designed for next-generation high-speed transport networks. It leverages the advantages of traditional SDH/SONET and WDM and is compatible with them. In 1998, the ITU-T put forward the OTN concept and defined its architecture. With broadband data services and increasingly mature optical transport technologies, it is inevitable that OTN will be used to build more efficient and reliable transport networks.

On the optical layer, OTN can process large-granularity services, similar to a WDM system. On the electrical layer, OTN uses asynchronous mapping and multiplexing so that the most cost-effective space division technology can be used for key cross connections. The MSTP network on core and backbone layers of an incumbent MAN is suitable for transporting TDM services, but the demand for data services is skyrocketing. Therefore, the WDM network needs to be built and expanded to accommodate fast-growing data traffic.

IP-based services are uploaded to the incumbent WDM network over the POS or Ethernet interface. This may cause problems in networking, protection, and OAM. When conditions permit, the WDM network can be upgraded to support G.709 OAM functions. A newly built WDM system that has no MSTP network must support the G.709 OAM functions and protection switching based on the optical layer. In other words, OTN takes over corresponding functions of the MSTP network. Leveraging MSTP technical advantages, OTN can better meet the need for growth of broadband business.

OTN Deployment in MAN

100M access will be a basic requirement for broadband networks in the future. To accommodate high-speed service growth, an optical network is required to provide the necessary bandwidth and to also allow for fast and flexible traffic grooming and complete OAM.

In the IP era, traditional network architecture can no longer meet the explosive growth in demand for data services. In current MANs, IP services have gradually become the largest service type, and there is also growing demand for some large-granularity services. These changes call for intelligent, IP-based, large-capacity, and highly integrated MANs. Operators also have a pressing need for OTN deployment in MANs. OTN is deployed in the convergence layer and can be extended to the access layer (Fig. 1). OTN is a basic plane that can carry optical line terminals (OLTs), convergence switches, MSTP, and packet networks. However, there is still a clear boundary between the OTN deployed at the convergence or access layer and the MSTP/packet network. OTN is only suitable for carrying GE traffic or above, and small-granularity services are carried over the MSTP/packet network.

40G vs. 100G

Operators are not optimistic about their current 40G deployments and application prospects, so 100G has become their focus of attention.

Standardization

The deferral of 40G standards has resulted in the emergence of multiple 100G solutions that are not compatible with each other. Moreover, 40G deployments need additional components that are complex and cannot be widely deployed. The related 100G standards, however, have basically matured as a result of the joint efforts of the IEEE, ITU-T, and OIF. These standards lay a solid foundation for widespread 100G deployment.

Service application

40G POS encapsulation is currently used for 40G links of backbone routers in China. Although 40GE systems are well-developed, OTN devices supplied by mainstream vendors have limited cross-connect capacity. This means a 40GE system cannot be applied to the 40G link side. 40G can be only used for grooming subwavelength traffic rather than grooming full services. Problems associated with system integration, power consumption, and heat dissipation have to be solved for 40G. Because IP services have moved from 10GE to 100GE, and the related 100G technologies have matured, the demand for 40G is shrinking dramatically. 100G will edge out 40G sooner or later and become an evolution trend of OTN at the link side.

Industry chain

The focus of leading optical component suppliers has shifted to 100G, which means less investment in 40G R&D. A shortage of 40G suppliers has led to an increase in the prices of optical components and has restricted the healthy growth of the 40G market. 100G has therefore been highly recognized and supported by technical experts, equipment suppliers, and chip vendors. Because of the long return on investment (ROI) period that stems a more than ten-year window for 100G applications, all parties in the industry chain are investing in 100G. This helps reduce 100G equipment cost. Some operators believe that the price of one 100G system is less than that of two 40G systems. With the growth of the industry chain, the cost of 100G equipment will sharply reduce over the next ten years.

In today’s booming 3G and LTE markets, OTN has played an important role in the full-service bearer sector because it has high cross-connection capacity and is capable of flexible traffic grooming. At present, 10G OTN remains the mainstream technology for optical bearer networks, and 40G OTN is a technology for transitioning from 10G to 100G.

Operators worldwide are trialing commercial 100G networks. This lays a sound foundation for 100G applications. To meet the growing need for IP bearer networks, and to keep pace with the rapid development of transport network technologies, the Chinese telecom industry plans to increase investment in OTN and 100G and speed up R&D, standardization, and applications of OTN and 100G equipment. OTN and 100G will be the inevitable choice for backbone and metro core networks in coming years.