What are Network Functions (NFs) in 5G?

In 5G, the network architecture is changed to ‘Service-based Architecture’ (SBA). SBA allows 5G core solution vendors to move to software-based platform. Hence, eliminating the need to be dependent on proprietary software and hardware vendors. Each software unit in 5G core network is called as the ‘Network Function’. Every NF is entitled to a particular job and acts as a producer as well as consumer for every other NF. The communication is usually done over a software-based stateless interface. Services exposed by these network functions are invoked using a standard API. 5G Core architecture has introduced the concept of CUPS (Control and User Plane Separation).

Architectural diagram of 5G core network functions and interfaces

Following are different Network Functions in 5G and their functionalities:
1. AUSF (Authentication Server Function): Performs the UE authentication. It relies on a backend service for computation and keys. UEs get authenticated only with AUSF in the home network. When the device roams in a serving network a Security Anchor Function acts as the authentication gateway between the serving network and AUSF in the home network.

2. AMF (Access and Mobility Management Function): AMF is a control plane function in 5G core that is solely responsible for registration management, mobility management, reachability management and connection management. It performs registration and de-registration of the UE with 5G core. AMF also performs NAS (Non-Access Stratum) signaling with the UE via gNodeB. Function of AMF is much similar to MME (Mobility Management Entity) from 4G core. It ensures that UE is always reachable.

3. UDM (Unified Data Manager): UDM acts as a centralized repository of the data for authorization, user registration and subscriber profiles. Function of UDM is much similar to HSS (Home Subscriber Server) from 4G. A stateless UDM can store its data in external entity called UDR (Unified Data Repository).

4. PCF (Policy Control Function): PFC maintains the unified policy framework that controls the UE’s behavior with the network. It provides policy rules to other network functions for their enforcement. PCF is similar to PCRF (Policy and Charging Rules Function) from 4G core.

5. UPF (User Plane Function): UPF is the crucial component of the 5G core. It is directly connected to the Data Networks (DN) like internet or IMS. It is responsible for packet routing, packet forwarding, QoS handling and PDU session management. It handles the downlink (DL) and uplink (UL) rate enforcement. It also performs the downlink packet buffering for the UE.

6. NSSF (Network Slice Selection Function): As discussed in the previous post(s) earlier, 5G introduces the concept of ‘network slicing’, where a piece of 5G network is dedicated to a specific use case. NSSF assists AMF with selection of a network slice to serve a particular device. It determines the NS-SAI (Network Slice Selection Assistance Information) for the device.

7. NRF (Network Repository Function): NRF is the key network function in 5G core. It acts as an internal broker for all core network functions. It maintains an updated repository of all network functions along with services provided by them with NF discovery information in an entity called ‘NF Profile’. It allows consumer NFs to discover provider NFs and keep track of other NF instances.

8. NEF (Network Exposure Function): One of the biggest advantages of 5G SBA is that it emphasizes the use of HTTP/2 based stateless APIs for communication. NEF facilitates a third-party application function (AF) by securely exposing some of the services offered by 5G core network functions. It acts as an ‘external broker’ for third-party applications having access to 5G core network information. For example, an external application may try to request information such as UE reachability from AMF. NEF does the job of retrieving this information from AMF and provide it to the external application.

The Voice of 5G

Voice is the most fundamental and an essential service when it comes to mobile communication. In 2G and 3G, voice was a primary network service and was mainly handled in circuit-switched fashion. It was only until the network architecture was changed to all-IP in 4G, an alternative solution was needed to replace traditional circuit-switched voice calls with packet-switched fashion which could deliver more sophisticated IP-based voice service. This is how Voice over LTE (VoLTE) was emerged. VoLTE offered superior call quality with a significantly reduced connection delay. However, most 4G networks had chosen an option of CSFB (Circuit Switched Fall Back) to hand over voice calls to legacy networks (2G/3G) on the fly. Most of the operators went with the CSFB approach, skipping a much more sensible approach of VoLTE entirely. Hence, the adoption of IMS has been slower. According to data, VoLTE adoption in UK is around 60%. This is more or less the same with all operators across the globe. In contrast, India’s Jio has all-IP LTE network with 100% VoLTE adoption. There is another standard called Voice over Wi-Fi (VoWiFi, or simply Wi-Fi calling) that allows offloading of the VoLTE traffic to any Wi-Fi/WLAN network, thus ensuring the superior call quality even in areas where network coverage is low.

Using IMS for enabling packet-switched mobile voice

First introduced back in 2003 in 3GPP Release 5, IMS (IP Multimedia System) is an architectural framework that delivers multimedia services over a packet-switched network. IMS is the backbone of VoLTE and VoWiFi. It uses SIP (Session Initiation Protocol) as a signaling protocol for the initiation, maintenance and termination of real-time call sessions. It can offer various services such as voice calls, video calls and SMS messaging. Even though 3GPP had put an end to the circuit-switched era in Release 15 (5Gv1) mandating operators to use IMS for 5G voice, the legacy alternative was re-introduced in Release 16 (5Gv2). Irrespectively, operators should be opting for end-to-end packet-switched voice on their most advanced 5G infrastructures (With great power comes the great responsibility!)

Voice over 5G (Vo5G) aka Voice over NR (VoNR) will need some evolutionary upgrade over existing IMS implementation (if any). This upgrade is a must in order to support the new interfaces within the Service Based Architecture (SBA) of 5G. The enhanced IMS must be cloud-native, and thus utilizing containerized OS-level virtualization leveraging numerous benefits such as auto-scaling, improved security and faster deployment. This cloud-native IMS also provides numerous 5G-specific benefits such as network slicing. A dedicated network slice for IMS will effectively isolate the 5G voice from the rest of the data traffic, enabling highly reliable and optimized voice experience.

There is a makeshift solution called EPS fallback. In case the IMS and/or the core network is not upgraded to 5G by the operator, EPS fallback allows to make the voice call over VoLTE when connected to 5G. The same approach is being used by most of the current 5G operators operating non-standalone (NSA) mode.

Readiness of the market for Vo5G

Chipmakers like Qualcomm and Mediatek have introduced chipsets with native support of VoNR, with Mediatek’s Demensity 1000 chip and Qualcomm’s third generation Snapdragon X60 modem. Phone manufacturer Oppo supports 5G voice calls with the latest smartphone Reno 3. While the availability of VoNR is currently limited to a few ones among current 5G enabled smartphones, we can expect more and more devices in 2021. Most of the current 5G phones and network operators use EPS fallback for making voice calls over 5G. Talking about the equipment vendor’s contribution to 5G voice, Ericsson has put forward some pretty interesting use cases of 5G voice calls like interactive calling.

Although there is much work to be done to enable this next-gen voice technology – 5G, in its nature, opens a huge platform unleashing a bunch of possibilities for innovation and new monetization opportunities for carrier voice (and video) calls.

What’s New in 5G Phase 2/3GPP Release 16? (Part-2)

Integrated Access and Backhaul (IAB)

Release 16 will be providing support for this new technology developed by Qualcomm. Backhaul is a portion of the cellular network that comprises the intermediate links between the cell towers and telco’s core network. Traditionally, these backhaul connections have been using methods such as microwaves, fibre and other cable connections. Since, a typical 5G network will consist of numerous antennas in form of ‘small cells’ to ensure the best performance over millimetre waves, it would be impractical and very expensive to use these traditional types of connections for backhaul. With IAB, telcos can use the same millimetre waves to communicate to user equipment as well as other reception points within the cell. Single equipment will be used for cellular as well as backhaul access, hence saving a huge amount of expenses which would be otherwise spent on traditional backhaul methods.

Cellular V2X and Sidelink

Release 16 has been focusing on enhancing the safety of autonomous driving. Sidelink enables support for sensor data sharing and coordinated driving. Sensor data from one car can be shared with another car within proximity for assisted driving. There are also many other enhancements that improve the efficiency of autonomous driving and reduce the effective power consumption when it comes to sending cellular signals to network as well as other connected vehicles.

Time Sensitive Networking (TSN)

Being another important addition to 5G standard, Time Sensitive Networking technology ensures the level of precision in environments where the same timing and low latency are critical. The use cases are advanced IoT environments like a factory or remotely operating mechanical systems. Presently, wired ethernet connections are the only way to ensure these precision demands. However, TSN will be able to meet these demands over a 5G wireless connection and ensure everything in these environments stays in sync.

Satellite Access with 5G (SatCom)

This is one of the interesting introductions in Release-16. Although more is expected in Release-17 when it comes to SatCom, it allows the extension of 5G network coverage by using satellite link. This will integrate cruise ships, airplanes and submarines with a 5G network. The satellite will provide a transparent link between UE and 5G base station (gNodeB). More on SatCom in an upcoming post!

Future Railway Mobile Communication System (FRMCS) Phase 2

5G FRMCS is eventually going to replace GSM-R, a 2G standard currently being used for train radio communication. 3GPP Release 16 has standardized certain services for FRMCS such as Mission Critical Push To Talk (MCPTT), Mission Critical Voice and Video, Mission Critical Data and Mission Critical Common Requirements (MCCoRe). To read more on FRMCS from Towards5G, click here.

Release 16 standards have paved way for operators to kick off their 5G SA deployments. 5G is more of an enabler for digital transformation of the globe and catalyst for Industry 4.0. However, the story doesn’t end here! 3GPP Release 17 is already in progress and expected in late 2021.