5G bearer standards are not unified, and the three major operators have different paths

The so-called 5G commercialization requires bearer technology first. However, the industry has not yet formed a unified solution on the selection of 5G bearer technology.

At present, China Mobile is leading SPN and has entered the testing phase. It will launch an SPN line network pilot in Q3 this year. If all goes well, it will be expanded to 18 pilot cities by the end of the year. China Telecom is leading the M-OTN solution and has already established two related standards. The ITU-T G.698.4 standard (formerly G.metro) led by China Unicom was officially passed at the ITU-T SG15 plenary meeting, marking that metropolitan area WDM technology is gradually moving from standards to practical applications.

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China Mobile: Leading the SPN solution, launching the SPN line network pilot in Q3 2018

Currently, there are two schools of thought in the entire 5G construction: one is the evolutionary school, which aims to improve bandwidth capacity based on existing technologies, and the other is the innovation school, which aims to revolutionize or innovate from a technological perspective.

From China Mobile's perspective, there are four main factors to consider when designing the entire 5G bearer solution or architecture:

• ***, 5G RAN architecture, 3GPP 5G RAN functional segmentation defines a two-level architecture of CU and DU, resulting in diverse site types in the 5G stage. It is no longer mainly backhaul, but fronthaul, midhaul, and backhaul networks will be equally important and support multiple services.
• Second, in the 5G CORE architecture, UPF and MEC in the 5G network are flexibly deployed according to specific business needs. The traffic between MECs needs to be forwarded nearby, and the L3 function of the metropolitan area network needs to be sunk to the aggregation layer or even the access layer. The L3 domain increases, which has a great impact on the networking.
• Third, 5G network slicing and low-latency services in vertical industries need to reduce end-to-end latency, requiring each node to support extremely low forwarding latency, and supporting both hard and soft isolation to achieve hard and soft slicing.
• Fourth, 5G is based on the SDN architecture, and it is necessary to consider introducing controllers and orchestrators. It is necessary to achieve decoupling of each layer through standard interfaces and information models. At the same time, it is necessary to consider the performance issues of the control system when managing the large three-layer network.

Based on the above four elements, China Mobile has set three goals for the 5G network architecture: capacity increased 10 times, latency reduced 10 times, and cost per bit reduced 10 times.

To this end, China Mobile proposed the SPN overall architecture, which adopts innovative slicing Ethernet technology and segment routing technology for transport (SR-TP), integrating FlexE line interface and slicing Ethernet (SE) key technologies.

As early as during MWC2018, China Mobile released the SPN technology white paper for 5G bearer. At present, China Mobile has completed the formulation of the entire technical architecture, as well as the development and testing of SPN prototypes. The laboratory test of the line network pilot is now underway, and the real line network test will begin in June and July. If the test goes well, the SPN line network pilot will be launched in Q3 and piloted in 5 cities in Q4. At the same time, a larger-scale pilot will be carried out in 18 cities by the end of this year.

China Telecom: Leading M-OTN solutions in the 5G bearer field

Since OTN technology has the characteristics of large bandwidth, low latency and other features that seamlessly connect to 5G bearer requirements, China Telecom dominates the M-OTN solution in the 5G bearer field.

It is understood that M-OTN technology is an OTN technology optimized for mobile bearer. It is not only suitable for the fronthaul, midhaul and backhaul of 5G bearer, but also has certain value in the point-to-point application of metropolitan area network and DCI business. The main features include single-stage multiplexing, more flexible time slot structure, simplified overhead, etc. The goal is to provide a low-cost, low-latency, and low-power mobile bearer solution.

At present, the M-OTN standard promoted by China Telecom has made substantial progress and has achieved the establishment of two related standard projects.

In China Telecom's view, 5G has just begun, and it actually brings great opportunities not to wireless but to wired. Because wireless spectrum resources are absolutely limited and it is impossible to solve all problems, but wired may be the most extensive, and fiber bandwidth can be continuously tapped. Therefore, 5G bearer brings huge opportunities to the entire fiber industry.

In addition, at yesterday's "2018 5G Bearer Technology Development Seminar", Li Junjie, deputy director of the Network R&D Department of Beijing Research Institute of China Telecom Co., Ltd., proposed four "as much as possible" principles for 5G bearer solutions:

• ***, looking at 5G now, it is difficult to reconstruct an industry. We should try our best to use mature industrial chains, especially optical modules, and especially reuse data modules.
• Second, try to reduce costs based on mature technologies and equipment, because 5G costs are extremely high.
• Third, try to unify equipment and modules in China.
• Fourth, try to unify domestic technical standards, because only standardized things can be recognized by everyone and can reduce costs in the future.

China Unicom: Metro WDM technology approved, 5G faces challenges in "three-side" projects

Tang Xiongyan, a senior expert at China Unicom's Network Research Institute, pointed out: "The demonstration and testing of 5G traditional bearer solutions is the focus of China Unicom's work this year. With the development of 5G commercialization next year and the year after, 5G bearer upgrades may be carried out."

Although China Unicom does not have clear plan steps like China Mobile and China Telecom, the ITU-T G.698.4 standard (formerly G.metro) led by China Unicom was formally passed at the ITU-T SG15 plenary meeting, marking that metropolitan area WDM technology is gradually moving from standards to practical applications, and will also provide a more economical and reasonable implementation plan for the rapid deployment of 5G bearer networks.

China Unicom believes that 5G transport bearer still faces some challenges and difficulties from the perspective of network planning and construction:

• First of all, there is the uncertainty of 5G itself. The standards of 5G are different from those of 3G and 4G. At that time, we planned and built the network after the standards and equipment of 3G and 4G came out. Today, 5G is a "three-side" project with many uncertainties. Because the standards are not determined, the network architecture and other aspects cannot be completely determined.
• Secondly, 5G scenarios are diverse. EMBB, MMTC, and uRLLC have different requirements for the network, so the corresponding transport bearer needs to meet different conditions. If all extreme requirements are met, it will inevitably lead to an increase in costs. Therefore, there is uncertainty about what indicators the entire transport bearer design should meet.
• Third, the diversity of 5G transmission and bearer methods. For example, from different technical levels, optical fiber, WDM, OTN, IP-related technologies, including the SPN mentioned earlier, etc., all belong to the IT Ethernet category, as well as PON access technology and microwave technology. These technologies can all be used in 5G transmission and bearer, so how to choose these technologies remains to be determined.

In addition, we cannot ignore the differences in network status. The network traditions of various operators are different, so there must be differences in technology selection. Different bearer technologies will lead to many industrial chains.

However, Tang Xiongyan proposed that China Unicom should consider seven principles in the development of 5G bearer:

• ***, demand-driven, traditional bearer is only a supporting part of 5G, based on the principle of meeting the basic needs of 5G development. Because 5G has some very special requirements, special requirements are treated specially and do not become a universal consideration.
• Second, be pragmatic and adopt more mature technologies in the industrial chain as much as possible.
• Third, try to simplify the network structure, use simple and mature technologies, and have stable basic interfaces.
• Fourth, cost is the priority. The goal should be to minimize comprehensive cost and TCO. In particular, the cost of high-frequency devices and optoelectronic core devices should be reduced through network innovation and industrial scale-up.
• Fifth, we must proceed step by step. 5G cannot be achieved in one go, and we must not blindly invest ahead of time.
• Sixth, the 5G system is open, leaving room for future technological advances and avoiding technology and manufacturer lock-in.
• Seventh, technology collaboration. In the field of transmission and bearer, there are many mature technologies, innovative technologies are constantly emerging, there are existing networks and new networks, IP-based technologies, transmission technologies, and the coordinated development between wireless networks and transmission and bearer. Therefore, we need to consider the collaboration of multiple technologies to jointly create a better transmission and bearer environment for the development of 5G.