5G Primer Part 1: Basic Architecture

February 22, 2019 Curt Schwaderer, Technology Editor

All major mobile operators are actively promoting their 5G advancements – If you believe the commercials, 5G is being rolled out and turned up, enabling higher bandwidth applications and machine-to-machine interactions.

While it’s true that 5G rollout does appear to be underway, it’s not an “all or nothing” proposition. Like most innovations, rollout is a phased process.

The advanced 5G features and capabilities for IoT, intelligent edge, and AI/IVR are very real and attention should be paid to 5G network architecture in order to take advantage.

This is the first in a series of pieces that look at 5G from the ground-up starting with the physical architecture and working our way up through virtualization and network slicing. If you find this informative or have additional questions or comments, please feel free to reach out to me at curt.schwaderer@opensysmedia.com.

5G Generalized Physical Architecture

A look at a generalized 5G architecture is shown in the figure below. There are three physical components:

  • Radio Access Network (RAN). This is the wireless network part of the network that connects to mobile devices.
  • Evolved Packet Core (EPC). This forms the core part of the mobile network and serves as the bridge between the RAN and the Internet or other IP-based services.
  • IP Multimedia Subsystem (IMS). Most people think of this as the Voice over LTE (VoLTE) component, but by design, it’s more general than that. The purpose of the IMS is to provide IP application services within the mobile network infrastructure be it voice over IP or some other IP-based communications service.

The physical components organization in 5G is really no different than that of 4G/LTE. The 5G difference lies in the capabilities of the 5G RAN and the organization of the EPC towards a higher level of virtualization.

Radio Access Network

One of the key features introduced with 5G is that it defines three different spectrum bands that serve a specific purpose:

  • Low-band (sub 1GHz). This is also the spectrum used by LTE today. It’s the best option to maximize coverage, but the maximum bandwidth tops out at about 100Mbps.
  • Mid-band (sub 6GHz). Mid-band provides higher bandwidth to 1Gbps and lower latency, which is critical to many IoT or machine-to-machine applications. However, reception through buildings and objects is a problem. 5G addresses this by using multiple input, multiple output (MIMO) macro cells to increase the number of simultaneous users. A technology called “Beamforming” is also a new innovation in 5G where the antenna sends a directed signal to every connected device with monitoring capability to increase signal quality.
  • High-band (>6GHz) or mmWave. This gets the majority of the press when it comes to 5G because it provides peak data rates up to 10Gbps with extremely low latency. As you might expect, the price you pay is very limited distance (less than one square mile) and poor object/building penetration. It does however fit a nice sweet spot between technologies like WiFi and its low and mid-band predecessors.

Another key feature of the RAN is the capability to incorporate edge routing. Routing traffic between devices and intelligent edge components or between devices dramatically reduces latency involved with routing at the EPC.

Evolved Packet Core (EPC)

The 5G EPC also has some innovations and I’ll cover them in more detail in my next piece. In general, the 5G EPC is being updated to better manage and integrate voice, data, and internet connectivity. The key innovations in the EPC are:

  • Complete separation between control plane (connection set-up/teardown) and user plane (the communications content). Some applications have few devices but very high bandwidth requirements. Others use a massive number of sensor devices each requiring very low bandwidth. The separation of user and control plane allows the network to flexibly allocate resources to one or the other depending on the need.
  • Virtualization. Defining Virtualized Network Functions (NFV) with the ability to run VNFs and standard server platforms reduces cost and increases flexibility in contrast to the previous generations of fixed-function EPC hardware components.
  • Network Slicing. This is somewhat analogous to the virtualization of compute, memory, and storage components only slicing the physical network resources into logical network functions. Each network slice consists of network resources dedicated to serving a specific customer or service. Network slices are also isolated and insulated from one another so one poorly behaving system cannot disrupt service from others. Previous generations of mobile networks just treated the pipes as bandwidth that everyone shared. 5G breaks these resources into virtualized network slices that can be allocated, used and isolated. This is especially important with the advent of IoT where control of IoT devices and frameworks is not possible at this time.

The EPC is undergoing change, but it’s more about “under-the-hood” improvements and efficiencies in order to carry the increased burden of the improvements within the RAN.

IP Multimedia Subsystem (IMS)

I’ll address the IP Multimedia Subsystem in more detail at a later date. The high-level view is this component implements specific IP-based applications and services within the mobile network.

The most well-known use case for the IMS is Voice over LTE (VoLTE). Previous generations of mobile networks (and even 4G/LTE) implement mobile voice and short message service (SMS) as circuit-switched data – not IP. As the network evolves toward end-to-end IP, the first application that needs to be addressed are these two services. So the first defined IMS involves components that communicate with mobile phones using Voice over IP (VoIP) technology instead of the old circuit switched methods. This finally breaks the divergent paths between the old circuit switched voice and SMS and the new IP based data services of previous mobile network generations. By moving to VoLTE, the entire circuit switched part of the network can now be eliminated saving hardware and maintenance costs.

Where is 5G Today?

Today mobile operator focus is on deploying the new RAN spectrums. This will enable 5G-enabled devices to use the network and they will be connecting with the 5G RAN, but they will be running over the older 4G/LTE EPC. The industry calls this “5G Non-Standalone” or 5G. This moves the bottleneck to the EPC until the 5G EPC is deployed. The industry uses the term “5G Standalone” or 5G SA to note a network where the RAN and EPC are both 5G.

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