Networks

Mobile networks work closely with mobile devices over highly standardised air interfaces and connect to fixed telephone networks and the internet to provide voice, messaging and a wide range of services carried on their mobile packet data channels.

Currently in Australia there are three major network operators Telstra, Optus and Vodafone. The History pages on this site shows how this came to be. Each of the operators today run networks covering 3rd, 4th and 5th generation technologies WCDMA/HSPA/HSPA+/LTE/NR-NSA/NT-SA.

You can see information on the technologies deployed in Australian cellular networks and the standards which define them in the Technologies and Standards pages on this site.

Mobile networks comprise:

Radio access network
Core network and systems
Operations support systems
Content and applications delivery systems

Radio Access Networks

The radio access networks provide the connectivity from the mobile user equipment UE to the network. They employ transmission links derived on point to point radio or fibre (and in very rare cases satellite) to connect to the radio controllers for 3G and directly to the core network for 4G and 5G. The radio controllers and base stations manage the radio resources and schedule the use of the shared channels as well as managing call set up and hand-off of calls and data sessions between base stations.

Core Network

The core network provides the switching, control and management of the network. It provides core mobile features such as:

Security encryption of call set and and transmission
Equipment identity and management
Call barring and diversion
Location and roaming enablement
Voice switching and transcoding for voice calls to fixed and other mobile networks
Data routing and packet connection to data networks
SMS and MMS service management
Lawful interception capability
Number portability capability
IP Multimedia System IMS

2G and 3G Core

In the 2G and 3G era core networks comprised physical nodes dedicated to specific functions as depicted on the block diagram above. 3GPP Release 4 (2001) started the introduction of IP core network in which signalling and transport were separated and voice calls carried via IP packets.

4G EPC Core

With the introduction of 4G LTE a new core known as Evolved Packet Core (EPC) was introduced. EPC provided functions for management of mobility, home and visitor location registration, charging and packet routing which were previously managed by the various dedicated nodes shown in the block diagram above. The EPC comprises these virtualised network elements running on a handful of hardware platforms. In most cases the EPC was implemented to also control and service the 2G and 3G RAN so that the network operator had a single core to reduce the complexity of operations, maintenance, billing across the multiple networks.

The EPC function blocks defined by 3GPP were as follows.

MME (Mobility Management Entity): Tracks and manages the movement of UEs throughout the RAN. This includes recording when the UE is not active.
HSS (Home Subscriber Server): A database that contains all subscriber-related information.
PCRF (Policy & Charging Rules Function): Tracks and manages policy rules and records billing data on subscriber traffic.
SGW (Serving Gateway): Forwards IP packets to and from the RAN. Anchors the Mobile Core end of the bearer service to a (potentially mobile) UE, and so is involved in handovers from one base station to another.
PGW (Packet Gateway): Essentially an IP router, connecting the Mobile Core to the external Internet. Supports additional access-related functions, including policy enforcement, traffic shaping, and charging.

5G NR Core

The initial implementation of 5G is Non Stand Alone (NSA) and uses 4G signalling and network so lacks most of many additional benefits which 5G provides. What 5G NSA does is provide wider bandwidth carriers and mmWave capability and can run on the 4G EPC core. NR NSA was standardised as a priority by 3GPP under pressure from the mobile network operators to advance the availability of additional capacity and speed which they needed and could sell.

To gain the full benefits of 5G requires NR Stand Alone SA which in turn requires the a new core network specified by 3GPP called NR-Core. The standards spell out a set of function blocks which have universally been implemented as cloud native micro services running on cloud infrastructure using standard cloud management and dimensioning tools. The defined function blocks shown as bus connected are as follows.

SMF (Session Management Function): Manages each UE session, including IP address allocation, selection of associated UP function, control aspects of QoS, and control aspects of UP routing. Roughly corresponds to part of the EPC’s MME and the control-related aspects of the EPC’s PGW.
PCF (Policy Control Function): Manages the policy rules that other CP functions then enforce. Roughly corresponds to the EPC’s PCRF.
UDM (Unified Data Management): Manages user identity, including the generation of authentication credentials. Includes part of the functionality in the EPC’s HSS.
AUSF (Authentication Server Function): Essentially an authentication server. Includes part of the functionality in the EPC’s HSS.
SDSF (Structured Data Storage Network Function): A “helper” service used to store structured data. Could be implemented by an “SQL Database” in a microservices-based system.
UDSF (Unstructured Data Storage Network Function): A “helper” service used to store unstructured data. Could be implemented by a “Key/Value Store” in a microservices-based system.
NEF (Network Exposure Function): A means to expose select capabilities to third-party services, including translation between internal and external representations for data. Could be implemented by an “API Server” in a microservices-based system.
NRF (NF Repository Function): A means to discover available services. Could be implemented by a “Discovery Service” in a microservices-based system.
NSSF (Network Slicing Selector Function): A means to select a Network Slice to serve a given UE. Network slices are essentially a way to partition network resources in order to differentiate service given to different users. It is a key feature of 5G that we discuss in depth in a later chapter.
UPF (User Plane Function): Forwards traffic between RAN and the Internet, corresponding to the S/PGW combination in EPC. In addition to packet forwarding, it is responsible for policy enforcement, lawful intercept, traffic usage reporting, and QoS policing.

With the move to 5G NR-Core many operators have chosen to connect the legacy 4G and 5G NSA RAN to the NR-Core along with 5G SA. The Ericsson dual mode 5G core and how the move from EPC is staged is summarised in the block diagram below. The full description of how this project was carried out by Ericsson and Telstra on Telstra’s network is documented Here.

At the end of the process the dual mode cloud native 5G core supports 4G LTE, 5G NR-NSA and 5G NR-SA RAN but not 3G WCDMA. Once Telstra 3G is closed in June 2024 they can close the EPC and will have a single cloud native core which can be augmented efficiently with all 5G features including VoNR and network slicing. It can also be used for other (non wireless) access providing an easier path to provision of common features across fixed and mobile networks.

Content and Applications

In the earlier days of mobile communications the mobile content delivery and interaction was limited due to the mobile’s screen and keyboard size as well as speed and reliability of the mobile data networks. In the past 10 years mobile content and applications have taken off as a result of the roll out of 3G and 4G mobile networks with their fast packet channels and leaps in capability of mobile devices. This has resulted in the emergence of a vibrant mobile content ecosystem.

Today there is a complex web of companies from huge corporations down to individual small businesses involved in the provision of information, services and applications to mobiles. These include:

Applications developers
Apps stores
Mobile applications development platform providers
Government and private mobile information and content generators
Mobile device manufacturers
Mobile browser providers
Mobile component manufactures
Mobile operating systems developers
VoIP providers
Messaging providers
Social networks providers
Mobile banking and payment providers
Broadcasters and Publishers
Mapping and location based service providers
Streaming audio and video service providers
Online and retail shopping providers and enablers
Search providers
Mobile marketing and advertising agencies
Cloud service providers

Operations Support Systems

The operations systems support the operation of the mobile network and provide mobile services and operations capability including:

Customer billing and service activation
Over the air management of mobiles
SIM card issue and control
Customer service
Wholesale and reseller billing and control
Prepaid service
Voice Messaging
Video telephony and conferencing
Delivery of content services like streaming video and audio, ringtones
Location based services
Network management, operations and maintenance

We all love acronyms and they are used widely on this site. You can decipher most of them by reference to the list here.