ICCSZ News As a new generation of mobile communication standards, 5G is not a hot spot in the industry. 5G network provides embB (Enhanced Mobile Broadband), uRLLC (ultra reliable low-latency communication) and MMTC (Mass IOT) three categories of business, the bearer network of the bandwidth capacity, latency and network flexibility New needs. Currently on the main solution 5G has hosted SPN over OTN, IPRAN over OTN, packet enhanced OTN. This paper focuses on the key requirements of 5G bearer network, 5G packet enhanced OTN bearer scheme and its key technologies and standards.

  5G gateway bearer bond demand

  Referring to the progress of the 3GPP standard, the functions of the 5G RAN are reconstructed into three functional entities: CU, DU and AAU. The bearer network is divided into three parts: Frontaul, Midhaul and Backhaul; 5G pairs are carried. network bandwidth, ultra-low latency, time synchronization, flexible connection of a higher demand.

  Ultra-low latency

  5G prequel, network transmission delay requirements are very high, Table 1 is a prequel, the pass, the return value of the network to allow maximum delay of the preliminary assessment.

  Due to limitations delay, uRLLC business needs CU / MEC sink network, CU and DU Joint; embB CU and DU service even with an isolated manner, the distance can not be too far away.

  High-bandwidth and flexible connectivity requirements

     5G network before the transfer between the DU and the typical bandwidth AAU (64T / R antenna, 100MHz spectral bandwidth) is 25GE, 4G era previous pass CPRI3 ~ CPRI7 increase several times the bandwidth. Sub 6GHz 5G single low frequency bandwidth of the mean S111 the base station 3 ~ 5GHz, the bandwidth increases compared to 4G-macro 10 times. 5G large bandwidth requirements bring greater challenge to the bearer network, inter-base station cooperative 5G, load balancing core network cloud deployments and Multihoming backup requirements, so that the more complex and dynamic flow rate, bearer network with sufficient bandwidth extension Ability to provide flexible business connectivity.

  Ultra-high-precision time synchronization

Runts 5G, the carrier aggregation and COMP multi-point collaboration technology introduced, to further enhance the accuracy of time synchronization requirements, the relevant standard proposal China Mobile lifting request from ± 1.5μs 4G to ± 130ns, assigned to the accuracy of time synchronization bearer network requires about ± 100ns, converted to a single node device time synchronization accuracy is expected to be less than ± 5ns.

  Network slice

  The core network and the RAN adopt the SDN/NFV-based cloud-based slicing architecture to slice according to the application scenario. Different functional slices have different requirements on bandwidth, delay, network function and reliability. 5G 5G bearer network is part of the business end of the path, we must meet the needs of eMBB, uRLLC and mMTC multi-scene needs and vertical industry and leasing business, which requires service isolation and independent operation and maintenance requirements bearer network support 5G sections of the network, as different types of traffic bearer network assign different types of slices, each slice bearer network like as a separate physical network.

  5G integrated bearer solution based on OTN evolution

  Domain TN technology combines optical and electrical transmission domain processing advantages, not only provide end rigid transparent pipe connections, and pipe flexible soft packet forwarding powerful networking capabilities, and can provide long-distance, large-capacity transmission capabilities, perfect OAM mechanism to ensure the quality of service delivery and ease of network maintenance and management.Packet Enhanced OTN proposed to meet high-bandwidth, low-latency, high-precision clock, high reliability requirements 5G carrier, on the basis of the complement SR-MPLS backhaul flexible routing forwarding bearer is to achieve efficient and cost-effective both 5G technology evolution path of good. Figure 1 is based on the general trend of the evolution of OTN 5G schematic overall carrying solutions, this solution matches OTN sinking, unified bearer traffic 5G, fixed broadband, cloud and green, and other government and enterprises. Aggregation room integrated service access, and can centrally deploy wireless concentrating equipment (DU or CU + DU), converged room grouping OTN equipment can be brought together prequel traffic to the node wireless devices, supports routing forwarding feature to the return pass business upload to the upper bearing device. For C-RAN access layer concentrated in small sites, CU & DU upstream bandwidth n × 10GE, 10G or 25G may be used to achieve the convergence room straight wavelength; DRAN site for sparse traffic service, the access point by point the relay layer 10G / 25G packet ring network.

Key technology

M-OTN technology

  Mobile-Optimized OTN (M-OTN) is a hot research topic. Recently, China Telecom and ZTE have jointly worked together to promote the standardization process of M-OTN technology in ITU-T. Single-stage M-OTN mapping ODUflex over FlexO multiplex structure, by simplifying the like OAM TCM overhead FEC optimization algorithm, FlexO-FR / SR frame structure, matching 25G, 50G, 100G low-cost optical module. ZTE creatively proposed a Cell-based FlexO solution, which has high efficiency of service mapping, eliminating the time slot granularity optimization and the computational complexity brought by the mixed time slot granularity.

  Ultra-precision time synchronization

5G ultra-precision time synchronization precision time source is directed to enhance the lifting device and OTN transmission mode, the current paths to enhance the precision time source to a single frequency for the dual-evolution, and further co-evolution parallax points to the common-mode; transmission mode and from the OTN device band, band two directions to enhance accuracy. Band means is transmitted by the optical supervisory channel wavelength of the PTP OTN, particularly Bidirectional natural ways to eliminate asymmetry delay difference, a priority scheme; to improve the accuracy of the time, to a PHY ultra high precision, We need to support and align the clock phase detection device to improve the accuracy of timestamps.

OSMC band relates FlexO management overhead bytes in AM, the need to support framer FlexO improve the accuracy of timestamps, and strictly control the delay variation due to the vertical range of the light power module, the plug.

Flexible slicing technology

Packet Enhanced OTN network needs to support bearer forwarding plane, control plane and management plane sections, forward surface support sections based on L0, L1 layer (λ, ODUk, VC) hard pipe, also requires supports L2, L3 layer (VLAN, LSP , PW, L2 / L3 VPN) soft pipe slices, each slice has its own independent logical topology, different slice has its own control and management planes, by cooperation with the wireless network and the core network sections, to provide end 5G slices solutions to meet the multi-scene 5G vertical industry applications, multi-tenant applications.

  Standard progress 5G overall carrying OTN evolution based

5G research carried OTN-based technology has been a hot work standards organization. In early September 2016 the ITU-T SG15 plenary session, some manufacturers have started using the proposed research OTN carrying radio signals, called on everyone to put forward a proposal to discuss this topic in the Q11 group. In a subsequent meeting Q11 middle, ZTE and many other domestic and foreign firms raised demand on OTN signal carrying 5G and consideration. In the next ITU-T SG15 plenary session, more and more vendors participated in the research of 5G transmission. In the OTN direction, multiple member units proposed the need to start a standard project based on OTN bearer 5G services.

At the ITU-T SG15 Q11&Q12 joint meeting in October 2017, China Telecom and ZTE Corporation proposed M-OTN technology based on OTN technology to solve 5G bearer problems. After some discussion, in February 2018 the ITU-T SG15 plenary session, M-OTN standard to make real progress, to achieve a successful project two M-OTN-related projects: "G.sup.5gotn: Application of OTN To 5G Transport (application of OTN in 5G transmission) and "G.ctn5g: Characteristics of transport networks to support IMT-2020/5G (transport network characteristics supporting IMT-2020/5G)".

ZTE with strong technical accumulation and deep understanding of 5G communication networks, 5G supports packet bearer enhanced OTN product development has made great progress; in mid-February, China Telecom Beijing Research Institute of the organization before 5G OTN bearer pass the test, The M721 device board supports the client side to simultaneously access 3 or 6 25G eCPRI 5G preamble signals and multi-channel CPRI 4G preamble signals or other service signals such as GE and 10GE. The line side supports 100Gbps or 200Gbps bandwidth. the latest M-OTN aspect, the structure of the traffic route map and FEC optimization; on key performance indicators like delay and jitter, M721 exhibit transmission equipment with nanosecond time delay and time delay of the end 1μs jitter excellent performance.

At present, ZTE is advancing, testing and piloting the SR-MPLS function of the packetized OTN products of the 5G OTN integrated bearer solution. As a leader 5G era, ZTE will continue to innovate on the technology 5G bearer, program development and equipment to provide competitive cost-effective solution for operators.