OTN in the Metro Access and Convergence Layer: Development Trends

With the development of all-service operation, services transported in the metro access and convergence (MAC) layer have changed tremendously. Access services require high-bandwidth LTE base stations, optical line terminals with 10G uplink, and lines dedicated to gigabyte (or higher) Ethernet verification IP. Earlier networks in the MAC layer did not meet service requirements, so constructing networks in this layer has become a priority for operators.

An optical transport network (OTN) has the advantages of synchronous digital hierarchy and wavelength-division multiplexing and is a unified bearer platform for backbone networks and metropolitan area networks. OTNs provide unified, end-to-end monitoring; high bandwidth; and highly reliable transmission. Little by little, the requirements for highly efficient transmission in the trunk and metro layers are being met. This is a result of large-scale construction of unified OTN bearer platforms. Extending OTN from the backbone to the edge and metro access and convergence layer is desirable when there are insufficient optical resources and inefficiency occurs as a result of using traditional methods to expand bandwidth. OTN allows for a high degree of integration and saves money and power.

Technical Characteristics of OTN

OTN is defined by ITU-T recommendations G.872, G.709, and G.798. Although an OTN is based on WDM, it does not have the problems of a traditional WDM network. These problems include poor wavelength and subwavelength dispatching, and weak networking and protection. 

In the all-service era, every telecom operator will need to become integrated ICT service providers. Greater diversity in services means higher demand for network bandwidth, capacity, and transmission performance. An OTN meets all these requirements, and optical networking is the main trend in transport networks.

Service Bearing: From Cities to Suburbs and Towns

In recent times, OLT equipment rooms have been moved from urban areas to suburban and regional areas. This has been the driving force behind building the OTN in the MAC layer. As service requirements change, suburban transmission networks are insufficient in terms of bandwidth and transmission distance.

In the small-bandwidth era, the network between the OLT/DSLAM and BRAS has used fiber connections. However, as speed increases, a GE uplink port is insufficient for OLT/DSLAM. Two to four GE ports are bound together to provide more bandwidth, and this means that more fibers are required. Meanwhile, new services, such as IPTV, SDI, and HTV, have emerged and promoted the deployment of multi-edge gateways. This also means that more optical fibers are needed in the OLT/DSLAM uplink. All of these factors increase the burden on fiber cables. Therefore, the OTN needs to be deployed in the MAC layer for transmission between OLT/DSLAMs and BRAS/SRs. This will ease the burden on fibers, provide optical-layer network protection, improve network security, and give users a better experience.

The distance from an urban area to a suburb or town can be a hundred kilometers, and the distance covered by a ring network (used for transmission) can be even greater. If the transmission distance between two nodes is too great, relay stations must be added, and this increases network cost and may even affect networking. An OTN has high bandwidth and supports long-distance transmission.

During city-to-county bandwidth upgrades, the OTN can reduce the rapid consumption of optical fiber resources caused by fiber connection. It can also protect services and better manage bandwidth resources in the MAN MAC layer (Fig. 1).

VIP Line Access

VIP line service has become an important part of an operator’s all-service strategy. Dedicated lines are fast and provide flexible access (Fig. 2).

In most transmission networks, many devices are located in the MAC layer, and network resources need to be coordinated in order to provide services. If there is no end-to-end solution between the MAC and core layers, services cannot be properly dispatched and provided. An OTN greatly improves network transparency, channel performance, and fault monitoring. It also helps with end-to-end physical transport and the creation of a management layer.

The OTN network supports electrical cross-connection and tributary/line separation on OTU boards in order to quickly provide services. 

LTE Bearer

In recent years, services such as email, flight and weather updates, banking, shopping, and video have become available for smartphones. On the one hand, smartphones have brought convenience to daily life; on the other hand, they demand higher bandwidth and transmission rates. As Wi-Fi, LTE and LTE-A advance, wireless transmission rates are pushed higher and higher. All of these factors weigh heavily on the architecture and bandwidth of the base station network.

As they move to all-service operation, operators are using PTN/IP RAN for mobile backhaul. LTE deployment continues to increase the load on the MAN; therefore, the ability to dispatch different services must be strengthened. Combined with PTN, MSTP and PON technologies, OTN lightens the bearing pressure.

In MAC-layer applications, small OTN devices are extensively deployed. These devices are deployed on access and convergence nodes to carry services transported from the GE ports on OLTs. These devices also have a large capacity and can accommodate an LTE uplink rate of 300 Mbps to 500 Mbps. Furthermore, they can alleviate the need for greater capacity in 10 GE rings comprising PTN/IP RAN equipment.

The OTN can transform a daisy-chain network into a flat tree network and optimize the PTN/IP RAN network architecture (Fig. 3). Services are processed on the access and convergence nodes and then transported to the metro core and convergence layer through the OTN network. This creates a flat PTN/IP RAN network, increases bandwidth capacity, and improves QoS.

Conclusion

As the bandwidth requirements of fixed, mobile, and dedicated networks increases, operators are choosing to deploy OTN at the MAC layer. This increases the speed of fixed and mobile broadband networks and provides an end-to-end platform so that high-end VIP services can be rapidly provided.

An OTN in the MAC layer is a unified bearer platform that integrates fixed line, dedicated line, and mobile services. An OTN allows operators to provide all types of services, create a more competitive network, and improve customer satisfaction.