At this week’s ITU-R WP5D meeting, a Russian contribution (5D/998) proposed a liaison statement to Global Core Specification (GCS) Proponents to clarify 5G NSA (Non-Stand Alone) and 5G SA (Stand Alone) architectures in Recommendation ITU-R M.2150 (formerly know as IMT 2020.specs). Those architectures are described in 3GPP TR 21.915 (Summary of Rel-15 Work Items).  While 5G NSA uses LTE for everything other than the RAN (5G NR), 5G SA introduces the 5G Core network which facilitates new 5G features and functions.  3GPP has decided NOT to liaison their 5G SA Core network TR’s to ITU-T for consideration as ITU recommendations for 5G non radio aspects.

Here’s the functional split between the 5G RAN (5G NR) and the 5G core network, as per 3GPP Release 15:

From 3GPP TR 21.915:

5.5.2 The 5G Core Network

5.5.2.1 Main Network Functions (NFs)

The AMF (Access and Mobility management Function) support UEs with different mobility management needs. It performs the following main tasks:

– The Non-Access Stratum (NAS) signalling termination;

– The NAS signalling security;

– The Access Stratum (AS) Security control;

– Inter CN node signalling for mobility between 3GPP access networks;

– Idle mode UE Reachability (including control and execution of paging retransmission);

– Registration Area management;

– Support of intra-system and inter-system mobility;

– Access Authentication;

– Access Authorization including check of roaming rights;

– Mobility management control (subscription and policies);

– Support of Network Slicing;

– SMF selection.

The SMF (Session Management Function) can support, together with the AMF, customized mobility management schemes such as “Mobile Initiated Connection Only” (MICO) or RAN enhancements like “RRC Inactive” state. It performs the following main tasks:

– Session Management;

– UE IP address allocation and management;

– Selection and control of UPF;

– Configures traffic steering at UPF to route traffic to proper destination;

– Control part of policy enforcement and QoS;

– Downlink Data Notification.

The UPF (User Plane Function) performs the following main tasks:

– Anchor point for Intra-/Inter-RAT mobility (when applicable);

– External PDU session point of interconnect to Data Network;

– Packet routing & forwarding;

– Packet inspection and User plane part of Policy rule enforcement;

– Traffic usage reporting;

– Uplink classifier to support routing traffic flows to a data network;

– Branching point to support multi-homed PDU session;

– QoS handling for user plane, e.g. packet filtering, gating, UL/DL rate enforcement;

– Uplink Traffic verification (SDF to QoS flow mapping);

– Downlink packet buffering and downlink data notification triggering.

The other main Network Functions are:

– The “Network Repository Function” (NRF): it provides support for NF services management including registration, deregistration, authorization and discovery.

– The “Network Exposure Function” (NEF): it provides external exposure of the capabilities of the network functions. External exposure can be categorized as Monitoring capability, Provisioning capability, Application influence of traffic routing and Policy/Charging capability.

– The “Unified Data Management” (UDM): the 5GC supports Data Storage architecture for Compute and Storage separation. The Unified Data Repository (UDR) is the master database. The Unstructured Data Storage Function (UDSF) is introduced to store dynamic state data.

5.5.2.2 Specificities of the 5G Core Network and associated NFs

5.5.2.2.1 Local hosting of services and Edge Computing

5.5.2.2.2 Network slicing

5.5.2.2.3 Unified access control

5.5.2.2.4 Support of 3GPP and non-3GPP access

5.5.2.2.5 Policy framework and QoS support

5.5.2.2.7 Other specific services

The following services are also supported by 5G SA core network:

– Short Message Service (SMS). This is supported by “SMS over NAS” (including over non-3GPP access).

– IP-Multimedia Subsystem (IMS) and its services, although, this might not be available in all initial 5G deployments. If IMS services are invoked by a UE connected to an IMS-less 5GS, this triggers a network-based handover towards an appropriate RAT and related EPS. This applies also to the support of IMS emergency services.

– Multi-Operator Core Network (MOCN), in which a RAN is shared by multiple core networks.

– Public Warning System (PWS). This is supported by either using Service-based interfaces between the Cell Broadcast Centre (CBC) Function (CBCF) and the AMF, or using an interworking function between the CBC and the AMF.

– Multimedia Priority Services (MPS). They are supported by MPS-specific exemptions for 5GS mobility management and 5GS session management.

– Mission Critical Services (MCS). They are supported by having a subscription in place for both 5G QoS profile and the necessary policies. Some standardized QoS characteristics are defined for MCS.

– PS Data Off. The 5G’s “PS data off” functionality is backward-compatible and provides Control Plane Load Control, Congestion and Overload control. This includes AMF Load balancing, AMF Load-rebalancing, TNL (Transport Network Layer between 5GC and 5G-AN) Load (re-)balancing, as well as AMF Overload Control, SMF Overload Control.

It should be noted that, in 5GS Phase 1 (3GPP Release 15), Location Services are optional and restricted to regulatory (emergency) services.  5GS Phase 2 (3GPP Release 16) was frozen in June 2020 without either URLLC in the RAN or URLCC in the Core specs completed.

References:

https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=3389

IMT 2020: Concept of Global Core Specification (GCS) and Transposing Organization(s)

by Tim Sylvester, Founder and CEO of Integrated Roadways, a smart infrastructure technology provider, with Alan J Weissberger (editor)

5G SA deployments have significantly lagged market expectations for the same reason that 5G NSA has been so rapidly deployed. 5G NSA uses existing 4G LTE signaling , core network, macro-site infrastructure, requiring only updates to its software and hardware at existing tower sites .

On the other hand, 5G SA requires a completely new Distributed Antenna System (DAS) architecture for microcell / nano or small cell deployments that need significant infrastructure with nontraditional requirements.

Unlike macro-cell deployments for 4G LTE, the position of the 5G SA millimeter wave antenna is not very negotiable – with a 5-mile service radius, a 4G LTE antenna can move considerable distances without significant changes to the service area, while a 5G millimeter wave antenna needs to be in exactly the correct spot to deliver service in a significantly smaller radius. The small cell size of 5G SA means that covering the same territory as a macro-site is essentially impossible, restricting deployments of 5G SA to dense urban areas and along highly trafficked interstate and highway routes.

5G SA requires a new core network infrastructure. Prior cell service models were iterations on technologies used in POTS and internet services that were ported to IP networks and only the final link mode changed from wired to wireless, with an emphasis on coverage area and bandwidth. But 5G SA is more than a new, higher-bandwidth link, incorporating new focuses on reliability and ultra-low latency for ehealth, autonomy, M2M services, augmented reality and other real-time or near-real time applications. This requires more than the wireless link improvements as it makes the easy “cloud” data abstraction obsolete, as these applications and databases physical storage location is relevant to maintaining reliability and ultra-low latency.

5G SA also promises network slicing, network function virtualization, cloud-native service management, distributed microservices at the edge, and software defined networking. Delivery of 5G SA has many more moving parts and stakeholders than 5G NSA and requires collaboration of many industries including automotive, tech, and health. It does not permit a monolithic delivery from a handful of parties. At the same time, the business models for ehealth, autonomy, AR, and other key 5G enabled applications are still unproven and in development, meaning that the carriers are expected to take input from many new parties and make investments in markets that are still at-risk.

Aside from the industry risks and complications, the property owners that will permit 5G SA delivery are not aligned to traditional cell service incentives or priorities. Delivering widespread millimeter wave antennas required for 5G SA networks through a DAS requires a utility or municipal license to attach equipment to each required attachment point, or development of countless private owner site leases to install antennas on private property adjacent to the desired service area. The private-owner approach is functional primarily in urban areas. It can’t be relied upon for primary delivery in non-urban interstate and highway routes that lack the necessary power and fiber drops, or in areas that traditionally only have longitudinal transmission or distribution lines, without further increasing costs to implement frequent new utility drops that service a single user. The outcome is existing approaches are very expensive and time consuming.

Regardless of FCC 1TMR requirements, municipalities and utilities are reluctant to give up that number of pole attachments and accept the visual and safety implications of accommodating that amount of visible equipment mounted overhead. These complications have resulted in permitting fees as high as $10K per antenna, as reported by Sprint in San Diego during early 5G trials (before being absorbed by T-Mobile), which makes the costs and complications of deploying infrastructure daunting to the extent of being nearly impossible. Even when tolerated, there’s no guarantee that existing poles are in the correct locations, which is why AT&T has been deploying its own utility poles to ensure they have attachment points where they need them.
There’s also the significant obstacle of locating distributed micro datacenter space proximate to the antenna attachment points as required to deploy the edge services that are natively required by 5G SA.

The hard to swallow reality for 5G deployment is public agencies are the easiest means to deploy the system, as it conceptually allows a single construction and operations contract per municipal area or interstate/highway route, instead of thousands of independently negotiated agreements with individual property owners. However, municipalities have no obligation to issue these permits, and the mandate for public works is to provide roadways and utility easements, with an institutional preference towards preserving aesthetics and limiting safety issues from overhead mounted hardware. Public agencies are responsible for roads, not responsible for delivering cell services, regardless of the desires of the cell companies. Municipal obligations are not aligned to the preferences of the 5G SA delivery industry, and there is no clear or obvious resolution available using the traditional network MSP approaches.

That said, solutions are readily available, despite their non-obvious nature and departure from traditional network MSP approaches. What the cell industry needs to deploy 5G SA widely is:

● An approach that aligns municipal incentives with 5G SA DAS needs by ensuring 5G SA deployments result in improvements to core urban infrastructure that is the obligation and primary concern of public agencies who are required to permit such improvements
● Leveraging delivery of those necessary infrastructure improvement needs alongside 5G SA capabilities in a “dig once” approach to streamline deployment and lower costs
● Incorporating the edge networking and 5G antenna delivery infrastructure into an invisible infrastructure delivery that does not occupy poles or other overhead assets

As with so many technology obstacles, the solution isn’t found within the technology itself, but found with a change in perspective and better understanding the needs of the stakeholders.

If there were a smart infrastructure technology firm that had the capacity to deploy 5G SA infrastructure as a byproduct of improving core urban infrastructure, hiding all of the antennas and edge networking assets, enabling the delivery of a fully virtualized, sliceable, edge-enabled but cloud-native open access network, the obstacles to 5G SA delivery would be resolved in a manner that is agreeable to the network MSPs, municipal authorities, utilities, and citizens.

Now that the needs for a solution have been identified, the only remaining obstacle is to identify a company that is capable of delivering on these requirements and developing partnerships between the network MSPs and the municipalities to begin widespread deployments.

About Tim Sylvester:

Tim is a computer and electrical engineer. He is the Founder, CEO and Chief Technology Officer of Integrated Roadways, a smart infrastructure technology provider. Smart infrastructure is the integration of data, communications, power, and networking systems into core infrastructure like roads, highways, and bridges.

Smart Pavement system from Integrated Roadways

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Feb 8, 2022 Update from Dave Bolan of Dell’Oro Group:

As of December 31, 2021 there were 21 known 5G SA eMBB networks commercially deployed.