The Evolution of the Universal Mobile Telecommunications System

The Evolution of the Universal Mobile Telecommunications System

When LTE was presented in 2008 as the evolution of the Universal Mobile Telecommunications System (UMTS) technology, in addition to an increased bandwidth and data rate, it brought a profound architectural change of the operators’ infrastructure. The new standard was based on data packet switching and followed an all-IP approach for the communication between all the network’s entities, instead of the circuit-based nature of previous generations.

This new architecture is usually viewed as three separate domains: the User Equipment (UE) used to connect to the network, the radio devices (antennas and base stations) that provide the physical link for the UE to connect to, and the operator’s internal packet systems that manage the traffic between the UE and other UEs or external data networks, such as the Internet. Figure 1 provides a high-level view of such architecture.

Fig. 1

4G network high-level architecture

The UE is the equipment used by the end-user to connect and communicate with the operator’s network. It has two main components: the actual physical device (i.e., a phone or a modem) or Mobile Equipment (ME), and one element to identify the user to the network, usually stored in a Subscriber Identity Module (SIM) card provided by the operator.

The Radio Access Network (RAN) consists of a mesh of base stations, the so-called Evolved NodeBs (eNBs), which connect the users with the operator’s core network. An intelligent deployment to maximize coverage area and the separation of the control plane from the data plane of the traffic allows reducing the time needed by the UE to jump between base stations, providing a nearly seamless communication when the user moves.

Finally, the Evolved Packet Core (EPC) constitutes the core of the 4G network and provides much of the intelligence needed to run it. Instead of using a monolithic architecture, an EPC is composed of several entities tasked with different functions and services. This distribution of tasks maximizes the performance of each component and enables their replication if the need arises. The primary entities inside the EPC are the following:

  • The Mobility Management Entity (MME) that controls the connection and the user’s mobility between base stations, and maintains a single session for a particular UE between all the entities.
  • The Home Subscriber Server (HSS) that maintains the users’ database and the security of the connections.
  • One or more Serving and Packet Data Network Gateways (SGW and PGW) that connect the RAN with the EPC and the EPC with external networks, respectively.

There are also entities, for instance, to control charging and billing, connect to older mobile networks, measure and optimize the handover between base stations, etc.

The Fifth Generation of mobile networks, the so-called 5G networks, is an evolution of the 4G architecture and doubles down on the effort of separating functionality into different entities, both at the core and the RAN. It is designed to support a massive number of users with heterogeneous devices, meeting not only a high traffic demand but also Quality of Service (QoS) requirements of new and complex services. Observe that the 5G network is composed of three main subsystems similar to LTE networks, which correspond to the evolution of the UE (5G UE), the 5G New Radio (5G NR) composed of new base stations called gNodeBs (gNBs), and the 5G core network, that comprises the 5G Network Functions (NFs).

A large part of the performance improvement in 5G is achieved by decoupling, even more, the functionality of the operator’s core network into new entities. For example, the MME of 4G is split into two different network functions: the Access and Mobility Management Function (AMF), which is responsible for only handling connection and mobility tasks, and the Session Management Function (SMF) to coordinate session synchronization between other NFs. The same happens with the HSS of 4G, as it is now divided into separate functions for user data management [the Unified Data Management (UDM)], authentication procedures [the Authentication Server Function (AUSF)], and a database with user profiles and encryption key management [the User Data Repository (UDR)]. This decoupling allows each entity to be used by new services independently without the need to parse the complete messages and protocols of the previous architecture.

To support the massive number of connections expected in this mobile generation, and meet the new QoS requirements, 5G networks introduce the concept of network slices, which are private and isolated virtual networks on top of a common shared physical infrastructure. The implementation of network slices relies mainly on three technologies: Network Function Virtualization (NFV), which allows the virtualization of core and network functions, Software Defined Networking (SDN), which supports the programmability of the network to separate data and control planes into distinct network topologies, and Mobile Edge Computing (MEC), which increases the flexibility of the network by moving part of the core close to the end user. Figure 2 shows the high-level architecture of a 5G network. Thus, a 5G network slice includes exactly the network functions required by a service to achieve the expected performance, using a common infrastructure that can be dynamically configured to put some NF near the end user. The EuWireless project aims at offering network slices, called EuW slices, to its users for experimentation and service provision.

Fig. 2

5G deployment over a SDN architecture

Source – Valera-Muros, B., Panizo, L., Rios, A. et al. An Architecture for Creating Slices to Experiment on Wireless Networks. J Netw Syst Manage


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