Flex-Slicing for 5G Transport

Release Date:2018-03-27  Author:By Chen Jie, Liao Guoqing  Click:

5G services will be differentiated and applied in multiple scenarios. For example, mobile internet services demand high bandwidth, automatic driving services require low latency and high availability, and IoT services need to support massive connections. Therefore, 5G radio access network (RAN) and core network (CN) have to be reconfigured. Based on service types, physical deployment locations of device processing units are changed, and independent end-to-end (E2E) logical networks are built for different service types on the same physical network through slicing.
5G is an open network that can meet application needs of the vertical industry and rental services. Since 5G bearer network (BN) is a part of 5G E2E service paths, BN needs to support service isolation and independent O&M for 5G slicing and to allocate different BN slices for different service types. 

Implementation of Network slicing

ZTE was the first in the industry to propose to ITU-T an innovative BN slicing solution that comprehensively describes hierarchical BN slicing architecture model and the control plane architecture.

SDN-Based Network Slicing Architecture

BN slicing refers to virtualizing network topology resources such as links, nodes, and ports to form multiple vNets (or slicing networks) as required. In terms of overall architecture, a vNet can be divided into the service layer, slicing network layer, and physical network layer (Fig. 1). With features similar to those of a physical network, a vNet has independent management plane, control plane, and forwarding plane. Each vNet can independently support various services such as L2VPN and L3VPN. 
SDN implements decoupling for the control plane and forwarding plane, makes physical networks open and programmable, and supports innovation in future network architecture and services. Through the SDN, the control plane can abstract physical forwarding resources into virtual device nodes and logical connections, perform group-based management of these virtual resources based on policies, and form independent logical slices vNets. 

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The vNet hypervisor in Fig. 1 is a special SDN controller for network slicing. It maps virtual vNet resources to physical resources and creates vNet management. The vNet controller on the service layer is the user of vNet resources and can only see vNet resources allocated to itself. It can create various services like L2VPN and L3VPN on the vNet and implement life cycle management for services. Each vNet corresponds to one independent vNet controller and supports the isolation of the control plane from the management plane. The common control function is a main component of the universal SDN controller. When network virtualization is not needed, this component can directly control the physical network. NCO is responsible for slicing orchestration policies of the vNet hypervisor and implements life cycle control for the vNet. 

Forwarding-Plane Slicing 

The forwarding plane can determine slicing methods based on service needs and use soft slicing solutions, such as the tunneling technology based on VxLAN, MPLS, and SR, and the virtualization technology based on VPN and VLAN. The forwarding plane can also use hard slicing solutions, such as FlexE, OTN, and WDM technologies. A mixture of hard and soft slicing solutions can also be used, with hard slicing ensuring secure service isolation and low latency, and soft slicing supporting bandwidth multiplexing.
Computing resources and storage resources can be sliced to form virtual NEs (also referred to as device slices). With features similar to those of a physical NE, a virtual NE has an independent forwarding plane, control plane, and management plane. Independent topological connections, isolation of CPU and memory resources, isolation of control and configuration channels, and independent deployment and upgrade of slices are supported between virtual NEs.

FlexE-Based Transport Network Slicing Solution 

FlexE can forward slices based on the PHY layer, isolate hard pipes, and flexibly allocate bandwidth. ZTE has innovatively introduced FlexE switch, OAM, and protection to successfully evolve FlexE to FlexE tunnel, a network-grade technology. FlexE tunnel extends service isolation from port level to network level and can implement E2E subchannel isolation for different services, providing the best forwarding plane support for 5G transport network slicing. Moreover, FlexE tunnel can provide a protection switching within 1 ms, boosting the protection from carrier-grade to industrial-grade. For uRLLC services, FlexE tunnel is used to solve the problems of large service granularity and low bearer efficiency in the wavelength through solution, and the problems of high latency and failure to implement physical isolation in soft slicing.

Synergy Among RAN, BN and CN Slices 

Network slicing for E2E 5G services requires synergy among RAN, CN and BN. BN slices can be defined based on the isolation and latency features of wireless services. VNIs of service VLANs and VxLANs as well as DSCPs of IP addresses can be flexibly selected as required to implement mapping between RAN services and BN slices.

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The synergy among RAN, CN and BN is implemented through the slice orchestrator based on the SDN/NFV architecture (Fig. 2). NCO is responsible for BN slice orchestration policies, and completes cross-domain transport service orchestration through the hierachical SDN controller (SDNC). Global service orchestrator (GSO) completes cross-domain service coordination and orchestration between RAN and BN and can simultaneously coordinate CN NSSMF, RAN NSSMF, and BN NSSMF to implement E2E 5G service slicing and to meet the needs of differentiated 5G services through different functional attributes of slices. 
Through BN slicing, multiple logical network services can be provided based on unified physical network facilities to meet differentiated needs of customers or specific scenarios, to share resources, and to enable rapid services provisioning. Provided that service performance and security isolation are guaranteed, BN slicing allows network resources to be shared and flexibly scheduled, implements independent subnet management, and helps operators reduce their capital expenditure. 

[Keywords] Flex-slicing, 5G transport, SDN, FlexE, Synergy

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