Development Directions of Fiber Access Technology

From DSL to Fiber-to-the-Home, speeds have jumped from tens of Kbps to tens of Mbps or even hundreds of Mbps, and broadband access technology has undergone dramatic changes over the past decade. GPON has become the mainstream, EPON is catching up, and access technologies capable of delivering even higher bandwidth, such as 10GPON, are poised for takeoff.

With the booming development of broadband networks, the debate over technology choices has taken a back seat, and how to better apply xPON technology to real-world networks has become the direction of development and discussion for fiber access technology.

Common Platform Abandons the Technology Debate

Whether to choose GPON or EPON has been the most debated focus in the industry. From technical, commercial, and maturity perspectives, people have given different answers. But for operators, is there a solution that suits both the existing network infrastructure and future business development while reducing OPEX? Huawei's SingleFAN solution has led the direction of the common platform.

Wu Haijun, Chief Engineer of the Access Network Product Line at Huawei's Network Product Line, stated, "The multi-network integration, high capacity, fewer central offices, and network flattening concepts advocated by the SingleFAN solution have been highly recognized by major European operators. Reducing the number of CO sites can significantly lower construction and network maintenance costs." Wu added, "At the same time, the SingleFAN solution advocates one network for multiple uses and full-scenario coverage, using the PON network to carry all services, making it the preferred solution for integrated operators."

It is understood that the SingleFAN solution has sufficient future-oriented evolution capabilities, with adequate capacity reserved at the system capacity, software architecture, and service development levels. It provides comprehensive smooth evolution from ATM to IP, from copper access to fiber access, from PSTN to IMS, from IPv4 to IPv6, and from xPON to NGPON, maximizing investment protection.

The EPON/GPON common platform development direction led by SingleFAN has also been recognized by domestic operators and has become a basic requirement in bidding.

Solving ODN Management Challenges

In FTTx development, the access layer requires the construction of a huge fiber distribution network, namely the ODN network. The construction cost of the ODN network is high, accounting for up to 50%-70% of total investment, making it a key focus of FTTx investment. At the same time, ODN is also a challenge for FTTx management. First, compared with the simple P2P structure of copper lines, ODN mostly adopts a P2MP topology, with many splicing nodes in the network and complex network management. Second, fiber is more sensitive than copper and more prone to damage.

Therefore, efficient construction, operation, and maintenance of the ODN are crucial, requiring an intelligent and accurate management solution to ensure full utilization of the ODN network and effective protection of long-term investment. Currently, how to scientifically manage the ODN network has become a focus of attention for major operators and standards organizations such as ITU-T.

Can the two core issues of ODN management be resolved without changing the passive characteristics of the ODN, achieving automated ODN management? Huawei has proposed the iODN (Intelligent ODN) solution. In the iODN solution, ODN products have added the following intelligent features: fiber identification management, port status collection, port lookup indication, and visualization tools such as PDA.

The iODN solution enables automatic recording and management of ODN fiber connection information, ensuring accurate and timely synchronization of existing system information. At the same time, through the PDA visualization software and intelligent LED indicators on iODN devices, automated fiber lookup and precise operations can be achieved, greatly improving O&M efficiency and enabling efficient operation and maintenance of the ODN network.

In addition, based on the iODN architecture, multiple value-added applications can be developed on the existing system to achieve full-process automation of construction, operation, and maintenance.

Introducing MPLS into the Access Layer

With the advancement of FTTx, on the one hand, traditional leased line services have faced a dilemma with the retirement of ATM switches. A large number of leased line services need to be accessed with high quality assurance. If a separate access network were built to carry these services, it would impose a huge burden on operators. On the other hand, the traditional DSLAM model mainly uses VLAN configuration for service provisioning, which is limited by the number of VLAN ID identifiers (4K), bringing limitations to the development and planning of new services. Moreover, since new service development usually spans the entire network, cross-departmental coordination is extensive, and service development and delivery efficiency are low. To this end, the industry has proposed the idea of introducing MPLS technology into the access layer.

The value of MPLS in the WAN has been proven. It simplifies packet processing and improves packet forwarding efficiency. MPLS-based traffic engineering and fast reroute technologies enhance network QoS. As the metropolitan area network structure becomes flatter and OLT positions move upward, MPLS is expanding from the WAN to the MAN and access network. Currently, the MAN is gradually evolving from a TDM/ATM network architecture to an Ethernet network architecture. The adoption of MPLS technology in Ethernet-based MANs and access networks will become a trend.

At present, operators such as Deutsche Telekom and France Télécom have already required future OLT equipment to support this function. At the previous Global MPLS Forum, Huawei demonstrated for the first time a solution supporting MPLS on OLTs and passed the interoperability test conducted by the internationally authoritative testing institution EANTC, becoming the only OLT solution in this field to pass the test. The function has also been successfully activated at operators such as Accor in Germany.

However, some experts have pointed out that the MPLS protocol is more complex than traditional Layer 2 access, requiring equipment vendors to have a thorough understanding of routing protocols. For example, MPLS itself has a large number of protocols, and not all of them need to be implemented at the access layer—only a selection is needed. From a device perspective, MPLS significantly raises performance requirements for access equipment and also increases requirements for device management capabilities. From a cost perspective, MPLS at the access layer will increase equipment costs. Therefore, current demand is mainly concentrated in developed countries that focus more on operational efficiency, helping them reduce OPEX. However, from a long-term development perspective, MPLS at the access layer is a major direction for future product development.

Copper and Fiber Advancing Together

With the gradual advancement of "fiber-to-the-x, copper-to-the-y" (replacing copper with fiber), DSL access nodes are gradually moving downward, and market share will decline year by year. However, Wei Leping, Director of the Science and Technology Committee of China Telecom Group, believes that as a way to achieve the last few hundred meters of user access, DSL will have at least 10 more years of survival space. "DSL, as the main method of home access, will coexist with PON for 10 years."

These 10 years of survival space will also drive breakthrough changes in DSL technology. Currently, VDSL2 has been continuously optimized. Ultra-high-bandwidth DSL using multi-pair bonding technologies such as SuperMIMO has achieved major technical breakthroughs, providing higher bandwidth over shorter distances. This technology development direction is also aimed at better coexistence of copper and fiber technologies.

At the same time, in the mobile service field, to provide cost-effective backhaul solutions for 3G/LTE deployment, technologies such as time synchronization, bonding, and crosstalk processing have also been introduced on copper lines. In January this year, Huawei announced the launch of the world's first DSL prototype supporting 1588v2 time synchronization. This product can transmit 1588v2 high-precision time synchronization signals over DSL lines, with prototype test accuracy reaching GPS levels. This technical breakthrough means that operators have a more economical backhaul technology option during 3G/4G deployment, enabling them to leverage widely deployed copper resources to quickly overcome GPS deployment limitations.

People's demand for higher bandwidth has never ceased, so technological innovation continues. A simpler, smarter, and flatter broadband access network has begun to take shape.