Network Slicing in 5G by Dr. Nishith Tripathi
Published on: 10/11/2018
Author: Dr. Nishith Tripathi, 5G Prime, Award Solutions
Network slicing in 5G enables an operator to provide custom Quality of Service (QoS) for different services and/or customers. The implementation of network slicing is operator-specific. However, standard bodies, such as 3GPP and ETSI, define suitable frameworks to facilitate the implementation of network slicing. In support of network slicing, 3GPP defines roles of the wireless device, the radio access network, the core network, and Network Slicing Management-Related Functions (NSMRF*) , while ETSI defines the role of the NFV architecture. The 3GPP NSMRF and the Network Functional Virtualization-Management and Orchestration (NFV-MANO) communicate using Application Programing Interfaces (APIs). There are numerous ways of implementing network slicing, and different degrees of virtualization and automation could be utilized. Described below is a high-level view of an example implementation for network slicing.
Implementation of network slicing can be viewed as two distinct phases: instantiation, configuration, and activation of target network slices (or network slice instances, to be more precise) in the 5G network and on-demand assignment of one or more deployed network slices to the device. During the instantiation, configuration, and activation phase, a set of 3GPP-defined control plane and user plane core network functions, such as the AMF, the SMF, and the UPF (and potentially even NG-RAN NFs, such as gNBs) are chosen, instantiated, and configured for a given network slice. Suitable resources of the cloud infrastructure required for these Network Functions (NFs) are allocated to create network slices. Once desired network slices are available in the network, a device can be assigned one or more of the deployed network slices.
Let’s discuss how network slices can be provisioned and configured, so that they can be assigned to devices later when needed. A request for a communication service, such as enhanced Mobile Broadband (eMBB), is received by the 3GPP NSMRF possibly via the OSS/BSS. One of the existing Network Slice Templates (NSTs) residing in the NSMRF may match with the service requirements. Otherwise, a new NST needs to be created. The NST includes a set of NFs with slice-specific features and optimal configurations, and the connectivity among the NFs. The 3GPP NSMRF maintains the association between the NSTs and ETSI network service descriptors. Such association facilitates the instantiation of relevant NFs. The 3GPP NSMRF provides NF application software (e.g., AMF software) and the associated NF requirements for the cloud infrastructure (e.g., those related to memory, processing power, and availability) to the NFV-MANO (more specifically, NFV Orchestrator or NFVO) using the Os-Ma interface. A deployed network slice is called a Network Slice Instance, which consists of deployed VNF instances and associated resources (e.g., compute, storage, and networking resources). The NFVO works with the VNFM and VIM to allocate cloud infrastructure resources for the relevant NFs to implement an NSI as a network service. Depending on the operator’s choice, the NFVO can provision the RAN part of the network slice along with the core network part of the network slice. Alternatively, the OAM can configure the gNBs with suitable network slice instances. All the components of a network slice instance are now available to serve users. The NSI provisioning process is repeated for different network slices. While 3GPP has defined three standard network slices of eMBB, URLLC, and MIoT to the date, operators can define numerous (e.g., hundreds) of custom network slices. Once network slices are deployed, the availability of a given NF for a given network slice (e.g., AMF for eMBB) is known to the NF itself and the network functions, such as the Network Repository Function (NRF).
Let’s turn our attention to assigning network slices to a device. Consider a 5G device that has just powered up. This 5G device finds a 5G cell and sets up a radio connection with a 5G gNB. Using the dedicated signaling connection with the gNB, the device requests one or more subscribed network slices during the registration procedure. The 5G gNB selects an AMF that supports the network slices requested by the device. The 5G gNB becomes aware of the capabilities of the AMFs during the N2 setup with the AMF. The AMF learns about the network slices subscribed by the device from the UDM. The AMF determines the allowed network slices for the device in the current registration area. If the AMF itself does not support all the slices requested by the device, then it seeks help from the Network Slice Selection Function (NSSF) to choose another suitable AMF. In such case, the NSSF provides one or more allowed network slices for the device and works with the NRF to determine the AMF set for the NSI.
The device now knows which network slices are allowed in the current registration area. The device attempts to set up a Protocol Data Unit (PDU) session in a network slice toward a target Data Network (DN), such as the internet. The PDU session enables the device to do data transfer in a network slice with a given data network. The AMF selects a suitable SMF for the network slice toward the target DN using the help of the NRF. The SMF also works with the NRF to choose a User Plane Function (UPF) for the PDU session. As part of the PDU session setup, the SMF allocates the IP address to the device. Furthermore, the end-to-end connection between the device and the UPF is established with suitable 5G QoS. This connection includes the data radio bearer between the device and the gNB, and the N3 tunnel between the gNB and the UPF.
Network slicing facilitates custom QoS for different services and customers by creating suitable logical networks. Typical network slicing implementation makes use of virtualization and automation technologies, such as NFV.
About the Authors
Dr. Nishith Tripathi is 5G Prime at Award Solutions. Nishith joined Award Solutions in 2004, and has over 20 years of experience in telecom. Nishith has brought his knowledge and experience in mobile wireless technologies to facilitate the planning, development and delivery of technical training.
Mike McKinley is a senior consultant at Award Solutions. Mike joined Award Solutions in 2008 and has over 32 years of experience in wireline and wireless core network technologies. Currently, Mike is one of the Subject Matter Experts at Award Solutions. His current focus is NFV/SDN,VoLTE, 3GPP core networks, IP convergence, and IP/Ethernet Backhaul technologies.
About Award Solutions, Inc.
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 3GPP, TS 23.501
 3GPP, TS 38.300
 3GPP, TR 28.801
 ETSI, ETSI GR NFV-EVE 012 V3.1.1 (2017-12)
*We have defined this acronym for convenience; please do not look for it on Google!