5G is a real multi-scenario integrated network and an important foundation for future “Internet of Everything” (IoT). It supports digital economic transformation of vertical industry. 5G poses higher requirements for bandwidth, latency, flexible connection, reliability and open SDN capability of transport network, which causes huge challenges to transport network architecture and technology and drives continuous transport network technology upgrade and innovation.
As a leader in 5G transport network solutions, ZTE has been actively tracing and advancing the development of standards and specifications for 5G transport networks and researching key technologies since 2015. To address transport requirements of 5G networks, ZTE innovatively proposes the Flexhaul solution which provides a unified E2E transport solution for 5G fronthaul, midhaul and backhaul services.
1) It supports the flat network architecture and implements multi-wavelength and multi-bandwidth binding based on FlexE, which flexibly expands network capacity, highly increases bandwidth expandability and greatly reduces the initial network construction costs.
2) It employs innovative FlexE channel technology to expand the FlexE from interface level to network level, meeting the requirements of 5G low latency and network slicing.
3) It adopts SDN based Segment Routing (SR) and EVPN technologies, which ensure efficient and unified control plane, to address the ubiquitous connection requirements brought by cloudification of 5G core networks and base stations (BS) as well as the Mesh networking requirements brought by L3 downshifting to BS.
4) It can slice forwarding plane, control plane and management plane of the transport network. In addition, it coordinates wireless and core network slicing to provide an E2E 5G slicing solution, meeting the multi-scenario and multi-tenant requirements of 5G vertical industry.
5) The innovative 3A time synchronization technology supports ultra-high-precision time synchronization to satisfy the application requirements of 5G BS new air interfaces, inter-station collaboration and BS positioning service.
FlexE channel Technology - Flexible Bandwidth and Ultra-Low Latency
The FlexE technology decouples service bandwidth and physical interface bandwidth, and gradually evolve service bandwidth in the order of 25G->50G->100G->200G->400G->xT through port binding and timeslot cross-connect technologies to randomly expand bandwidth while keeping equipment arichitecture unchanged.
ZTE innovatively expands the FlexE from interface level to network level, which allows FlexE Cross Connection (FlexE-XC) and end-to-end FlexE channel based on physical-layer timeslot cross-connect. The FlexE-XC avoids the traditional packet-based device from parsing customer service packets hop by hop at MAC and MPLS layers. The single-hop device forwarding latency is reduced from tens of μs to less than 1μs, laying a foundation for transporting ultra-low latency services. Because the intermediate nodes do not need to parse service packets, the end-to-end FlexE channel forms a rigid pipe with strict physical layer service isolation. In addition, the protection switching based on the FlexE channel technology can be fulfilled within 1ms, increasing the carrier-class protection to the industrial control level.
Figure 1. FlexE channel with physical layer isolation
Segment Routing Technology - Flexible Connection and Applicable to Large-Scale Networking
5G mobile backhaul uses a flat IP architecture. RAN and core network function virtualization, distributed deployment of service anchors and L3 function down-shifting tend to complicate service flows, so new technologies should be introduced to support ubiquitous connections.
The Segment Routing effectively simplifies existing MPLS technologies and is fully compatible with current MPLS networks. It supports smooth evolution from MPLS network to SDN and can easily create and manage millions of connections to support ubiquitous connections of 5G transport.
EVPN is originally to be an alternative of traditional VPLS (Virtual Private LAN Service) to provide L2VPN service. With the progress of EVPN, it extends L3VPN functions. By these, EVPN can integrate L2 and L3 service in service layer.
5G Flexhaul employs SR and EVPN based architecture. SR simplifies protocols to unify the control in network layer; meanwhile, EVPN simplifies the service solution by unifying the L2VPN and L3VPN services. This architecture solves the fronting problems of scalability, flexibility, and ease of use of the existing network, and provides minimalist network deployment. Moreover, SR and EVPN are compatible with MPLS network, and can be seamlessly integrated with SDN. It is an effective solution for 5G massive transport connections.
Figure 2. SR and EVPN based architecture
Network Slicing Technology - Flexible Network Reconstitution for a Multi-Purpose Network
The network slicing technology can slice multiple virtual networks in a hardware infrastructure. Each network slice supports logical isolation on forwarding plane, control plane and management plane, adapts to various types of services and meets different user needs. It can be fully guaranteed in bandwidth, QoS, security and other exclusive resources. Because the slices are isolated from each other, the failure of a slice does not affect the communication of other slices.
ZTE first proposed the innovative solution to the ITU-T for transport network slicing. It systematically describes network slicing model and SDN-based hierarchical control plane architecture. The entire architecture is divided into client/tenant layer, service layer, virtual network layer and physical network layer, as shown in Figure 3. The virtual network (vNet) has independent management plane, control plane and forwarding plane, and each vNet can independently support a variety of services. The services are not aware of the actual physical network, which decouple services and physical network resources. The vNet recursive slicing can support the operations of virtual operators and sub-operators, secondary leasing and other services.
Figure 3. Transport network slicing architecture
ZTE also supports the network slicing based on its own FlexE channel technology to isolate end-to-end sub-channels for different services and provide the best forwarding plane support for 5G transport network slicing.
In addition, ZTE also proposed a solution to coordinate RAN, core network and transport network through an orchestrator based on an SDN/NFV architecture so as to enable the end-to-end slicing, meeting differentiated requirements of 5G services.
3A Time Synchronization Technology - Ultra-High-Precision Synchronization and Accurate Positioning
A 5G network has ultra-high requirements for clock accuracy. 5G inter-site CA and JT technologies require less than ±130ns network synchronization between base stations. 5G short frame structure requires that air interfaces reach ±390ns time synchronization accuracy. The Internet of Things puts forward higher requirements on the clock accuracy. For example, indoor positioning requires that the time difference between air interfaces of positioning base stations is less than 10ns.
ZTE proposes the innovative triple-A time-synchronization technology (3A: Advanced time source, Accurate timestamp and Agile algorithms) to improve the synchronization accuracy of clock sources and transport devices so as to meet the requirements of 5G ultra-high-precision synchronization.
The time source based on ZTE’s common view technology supports +/-10ns timing timing accuracy, provides a complete solution for the applications of different accuracies such as 5G, indoor positioning and Internet of Things, and offers a new flexible networking mode for large-scale ultra-high-precision time synchronization networks.
Firstly, the egress timestamp accuracy can be improved for transport devices. The synchronization frame header is identified mostly at the MAC layer to record the timestamp information. The ZTE 5G Flexhaul moves the timestamp down to the place close to the physical layer to support high-precision 1588 message delivery and avoids the impact of device processing on time precision. Secondly, the time allocation mechanism in the system is optimized to automatically measure and compensate the system time so as to accurately synchronize time modules in the system. The single-node time synchronization accuracy of transport devices can be up to
With further development of 5G wireless standards, researches on the 5G transport standards are imminent. ZTE actively participates in various standards organizations to promote the 5G transport standard research. At the ITU-T SG15 plenary meeting held in February 2018, many enterprises and organizations such as China Mobile, China Telecom, China Unicom and ZTE Corporation submitted a number of 5G transport proposals. The plenary considered the proposals laid a good foundation of the research of 5G transport technologies, and unanimously agreed a new standard project of Characteristics of transport networks to support IMT-2020/5G (G.ctn5g). It marks that ITU-T takes a crucial step in studying the 5G transport standards, and it is also a significant contribution made by Chinese enterprises in promoting the 5G transport standards.
At present, ZTE promotes the pilot trials of 5G transport solutions and conducts extensive cooperation with many internationally renowned operators to fully demonstrate ZTE's leading advantages in 5G.
In August 2017, ZTE worked with Telefonica to complete the first phase of a 5G transport test at the Future Networks Lab in Madrid, Spain. The test verified the outstanding performance of the 5G Flexhaul solution regarding CPRI/eCPRI unified transport, ultra-low latency, and fast switchover.
In September 2017, the China Mobile Research Institute organized the first-phase lab test for major equipment providers of 5G transport Slicing Packet Network (SPN) prototypes. ZTE not only completed all tests successfully in compliance with China Mobile’s SPN specifications, but unveiled an excellent single-node forwarding latency lower than 0.5µs, providing strong technical support for the acceleration of 5G commercialization.
In December 2017, ZTE, in conjunction with the National Time Service Center, Chinese National Academy of Sciences, took the lead in completing the ultra-high-precision time source test based on the satellite common-view principle and providing +/-10ns timing accuracy. ZTE has introduced the satellite common view technology from scientific research on astronomical navigation to communication industry application for the first time.
In December 2017, ZTE first completed a high-precision time synchronization test organized by the China Mobile Research Institute. The single-node time synchronization performance was lower than 5ns, marking another milestone in high-precision clock synchronization.
At Mobile World Congress (MWC) Barcelona 2018, ZTE showcased the industry-leading 5G Flexhaul transport solution which is based on the innovative FlexE technology and integrates fronthaul, midhaul and backhaul transport. It meets the requirements of 5G transport network slicing, supports the unified 3G/4G/5G networking and demonstrates the performance of the key FlexE channel technology on site. The result shows that the key performance indexes reach the industry-leading level: the end-to-end protection switching time is less than 1ms and the single node forwarding latency is less than 0.5μs. The result demonstrates the outstanding performance of the 5G Flexhaul solution and products and fully meets differentiated transport needs and strict performance challenges of different types of 5G services.
During the 43rd Optical Networking and Communication conference & Exhibition(OFC) in the United States in March, 2018, ZTE was invited by OIF (Optical Interworking Forum) to attend OIF PLL Interoperability Demo 2018. This demonstration marks the breakthrough of interconnection between the FlexE interfaces of multiple manufacturers. It has attracted widespread attention an praise from the industry.
During 20th China international Optoelectronic expo (CIOE 2018) in September , 2018, CCMC held " China mobile SPN opens 5G transport new era" summit. In the summit CMCC organized 5 leading SPN equipment and instrument manufacturers including ZTE to conduct on-site demonstration of SPN interoperability. The results showed that the one-way forwarding latency of FlexE based SE-XC was significantly superior to the latency of traditional packet switching. It was also verified that FlexE based network slicing can achieve strict isolation when carrying multiple services at the same time, and its performance such as bandwidth, latency and jitter do not affect each other.
GlobalData, a well-known consulting company, spoke highly of ZTE 5G Flexhaul. They indicated that our 5G Flexhaul solution integrates fronthaul, midhaul and backhaul transport, and provides flexible on-demand deployment, hence consolidating ZTE's leading position in the 5G market.
ZTE continues to collaborate on the advancement of 5G transport with major operators in countries around the world, including China, Spain, France, Italy, Japan, Korea, Singapore and Australia. As a leader in 5G transport innovations, ZTE has set up extensive partnerships in the industry to promote the maturity and industrialization of 5G transport technologies, and to drive early commercialization of 5G.
The ZTE 5G Flexhaul solution introduces flexible architecture and innovative technologies to provide operators with a competitive and cost-effective solution. With the concept of practice, cooperation and win-win, ZTE will lead 5G transport innovations!
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