a 32-bit counter;2 – the identity of the 5-bit bearer;
3 – the direction of the connection on one bit;
4 – the length of the message.
Figure 1.12. Ciphering and integrity
1.6. Network slicing
Network slicing is the embodiment of the concept of running multiple logical networks as virtually independent business operations on a common physical infrastructure in an efficient and economical way.
Virtualization is a hardware abstraction to partition network resources into distinct logical segments.
Network partitioning makes it possible to allocate a part of server hardware resources (NFVI: Network Function Virtualization Infrastructure) to network functions (VNF: Virtualized Network Functions).
Hardware capabilities are dynamically managed based on the number of users, on the one hand, and the profile of each user, on the other hand. By default, the 3GPP standard has defined four types of services:
1 – eMBB: evolved Mobile BroadBand to manage smartphone services such as high speeds, several session establishments, handover management, low latency;
2 – mMTC: massive Machine Type Communication to manage the sessions of IoT terminals (low speed, little transmission and mainly in the upstream direction, long delay);
3 – URLLC: Ultra-Reliable Low-Latency communication for critical communications requiring very low latency (less than 1 ms for the user plane) and efficient management of the handover;
4 – V2X: Vehicle to Everything for autonomous vehicles (between vehicles, with radio infrastructure, etc.).
Network slicing provides all the functionality of the 5G network, including optimization of the radio access network and core network entities to meet the service level agreement (SLA) requirements requested by the user.
Virtualization allows us:
1 – to allocate a set of material resources (storage capacity, network performance, computing capacity in terms of the number of CPUs);
2 – to deploy optimized software instances on the hardware resources. The instances correspond to the NFV network functions to be deployed:- in the radio access network by dividing the radio functions into two entities gNB-CU and gNB-DU,- in the 5G core network (AMF, SMF, PCF, etc.),- to deploy optimized network functions (content cache, video optimizer, malware detection, etc.).
The set of hardware and software resources form a Network Slice Instance (NSI). The network instance is split into an RAN Slice Instance (RSI) and a Core Network instance.
From a user point of view, the mobile requests registration on a network instance from the 5GS network. The mobile profile allows the network to define the optimized network instances through the S-NSSAI (Single Network Slice Selection Assistance Information) identifier.
The S-NSSAI indicator is composed of two fields:
1 – SST: Slice Service Type defined user profile (1: eMBB, 2: URLLC, 3: mMTC, 4: V2X);
2 – SD: Slice Differentiator to differentiate specific services within an SST service type.
The S-NSSAI indicator is stored at the UDM database for each user profile and stored in the mobile. Each mobile can subscribe to up to eight S-NSSAI. S-NSSAI indicators are integrated into the NSSAI indicator.
When requesting registration, the mobile sends the desired NSSAI flag in the RRC request. The gNB-CU entity selects the AMF entity from the NSSAI indicator if possible; otherwise, it selects a default AMF entity. The AMF entity consults the UDM entity to know the value of the NSSAI indicator that will actually be implemented. The answer depends on the customer’s profile and the radio access network (3GPP, non-3GPP or roaming).
At the 5GC core network, when the mobile wants to establish a logical connection for a data service, it sends the RRC Service Request to the AMF with the S-NSSAI flag. The AMF selects the most suitable SMF.
On NG-RAN, the gNB-CU entity selects the gNB-DU entity based on the S-NSSAI flag. The division of the network on radio access is defined by:
1 – common RRC functions (management of sharing of radio resources between slices) and specific RRC functions (DRX, eDRX, timers, QoS, etc.);
2 – PDCP, RLC, common or specific functions (header compressions, acknowledgment, etc.);
3 – sequencing (MAC function) and prioritization on the physical layer.
The objective of virtualizing the network is to provide network flexibility and dynamic adaptation to the needs of different users, in order to meet performance indicators specific to the services requested (latency, throughput, packet loss, etc.). This flexibility is provided by an orchestrator which supervises the network functions and delegates the traffic management to the radio controllers (SD-RAN – Software Defined RAN) and network controllers (SDN: Software Defined Networking). In addition, virtualization allows isolation of the different slices.
1.7. References
All standards can be downloaded from the ETSI website: https://www.etsi.org/standards.
3GPP TS 37.340
Universal Mobile Telecommunications System (UMTS); LTE; 5G; NR; Multi-connectivity; Overall description; Stage-2
Version 15.3.0 Release 15
3GPP TS 38.401
5G - NG-RAN: Architecture description
Version 15.2.0 Release 15
3GPP TS 24.501
5G - Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3
Version 15.0.0 Release 15
3GPP TS 23.003
Digital cellular telecommunications system (Phase 2+) (GSM); Universal Mobile Telecommunications System (UMTS); Numbering, addressing and identification
Version 15.5.0 Release 15
3GPP TS 33.501
5G - Security architecture and procedures for 5G System
Version 15.2.0 Release 15
For a color version of all the figures in this chapter, see www.iste.co.uk/launay/5g.zip.
