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5G Lab – Building and Connecting to Our Own 5G Network

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5G Lab – Building and Connecting to Our Own 5G Network

Published: 2023/08/08

10 min read

According to the GSMA Mobile Economy Europe 2022 report, commercial 5G services have been introduced in most European countries, and approximately 60% of regional operators have established 5G networks. The report predicts that by 2025, there will be 311 million 5G connections in Europe, representing a 44% adoption rate. The adoption of 5G continues to surge in North America as well – J.P. Morgan predicts 5G will provide substantial enterprise opportunities. By 2030, the revenue generated by 5G in North America is projected to surpass $180 billion. 

With 5G adoption on the rise, Software Mind has created a 5G Lab where our telecom software development experts can provide the necessary tools, components and infrastructure for private 5G networks. These resources facilitate the development of advanced apps and unique solutions, enable the testing of existing 5G solutions and the designing of new ones. Software Mind’s team has vast experience developing signaling products, including roaming solutions and advanced voice services. We also want to contribute to the software community, which is creating new ideas for what has never been a more open network than 5G. 

Read on to learn about Software Mind’s 5G Lab’s private, fully functioning 5G network. Get details about the network’s performance, authentication procedures for subscribers and the process for establishing Internet and voice connectivity.

Our Mission: To connect a mobile phone to our 5G Lab 

Software Mind 5G Lab

Our goal is to show everything that occurs inside the 5G network when a mobile device, also called UE (user equipment), connects to the network and starts data transmission.

In each step of the procedure and between each network element, there is an opportunity to develop and implement new applications.

The main components of a 5G network

This article will explore the fundamental components of an end-to-end 5G network infrastructure, depicted in the picture below. 

5G Lab 2

The main protocols you’ll see on a 5G network

Protocols used in 5G network

NGAP The Next Generation Application Protocol plays a brief but significant role. It is mainly used for the Access and Mobility Management Function (AMF) to control the gNB aspects such as “UE Context” set-up and transfer to make physical mobility possible and set QoS flows for adjusting traffic resources. The NGAP protocol closely resembles the S1AP protocol used in LTE, as some message names are identical. However, NGAP has been extended to include additional message types for 5G. 

GTP The GPRS Tunnelling protocol is crucial as it helps transport traffic (also known as “User Plane Data”) from the Radio, through the Core and up to its final destination, which is typically the Internet or an IMS network for voice calling services (and often SMS and USSD as well). 

HTTP 5G Core Network elements use HTTP, REST conventions and JSON data to exchange messages between network elements. This is a significant change compared to LTE, where a much less common protocol (Diameter) was used. 

PFCP – The Packet Forward Control Protocol is used to control the data gateway and orchestrate the creation of the data tunnel from the base station and another data network. 

Developing applications for 5G signaling becomes easier using this new protocol stack, which was one of the main objectives of the described change.

Read more: Automating legacy telecom platforms

Where do we get signal from? Our own radio

Every mobile network (from a user’s point of view) starts with a radio base station5G Lab is no different. We have arranged the setup of radio devices, radio software and test SIM cards ready to connect to our 5G core network.In addition, we can incorporate any other 5G core network intended for testing purposes or commercial use.
5G Radio
The picture above shows the radio equipment that we are currently using. On the right is a versatile short-range radio module configured to be used on 5G frequencies. On the left is a GPS module essential for obtaining accurate date and time information. 

We use OpenAirInterface (OAI) to power our radio (RAN) infrastructure software. It is an open-source software platform that provides a complete implementation of 3GPP standards. It enables the research, testing and deployment of new technologies and protocols in wireless communications. 

The gNB software runs on a small computer like the one shown in the picture below, allowing the Software Mind 5G Lab to have its own 5G network. 

gNB software runs on a small computer

Test SIM cards used in the 5G Lab

The SIM cards used during the testing process are programmable, meaning our engineers can insert any key or subscriber identity for testing purposes.

Test 5G SIM cards

5G Lab 7

The mobile device and base station

What will happen if User Equipment is turned on in the 5G Lab (in this case, a mobile phone)? 

When searching for networks in the phone’s settings, our service provider name (SM-LAB 5G) will appear in the list of available options

Service provider name (SM-LAB 5G) will appear in the list of available options

What happens inside the network? Meet the AMF.

5G Lab 9

The Access and Mobility Management Function will: 

  • Create a UE Context, 
  • Obtain a subscriber identifier from the UE, 
  • Find the subscriber, 
  • Authorize access to the network. 

The aforementioned UE Context is also retrieved from the AMF when the mobile device moves around and changes the radio base station. The UE context acts as a chain that holds everything together as a subscriber physically moves. 

After starting a UE Context, the next step will need to be to find and perform the authentication of the subscriber. 

Let’s identify the subscriber

The AMF asks the mobile device to provide their subscriber identifier.

AMF asks the mobile device

The subscriber identifier in our case is the IMSI number stored on the SIM card.

Authenticating the subscriber – the AUSF and UDM

The authentication process is mutual (the network authenticates the subscriber, and the subscriber also identifies the network). If there’s no success, it would have to release the UE Context, and the subscriber wouldn’t get access to the network (obviously, that’s not our case). 

Authenticating the subscriber

The AMF retrieves and performs authentication with the help of the Authentication Server Function. 

The AUSF now needs to generate the authentication tokens, which are needed to connect to the subscriber database, called the UDM. This is the location of the subscriber identifier, along this their keys that are stored in the UDM and on their SIM card or eSIM profile. 

In production systems it is not uncommon to find the AUSF, UDM and UDR together as a single element. However, in the Software Mind 5G Lab, they are separate elements that match as much as possible to the 3GPP specification and enable us to test many different new applications. 

Before we talk about how the UE makes its final request to get access to the network (a.k.a. being “Registered”), it would be nice to explain what Network Slicing is. 

On LTE, there is no Network Slicing, while in 5G standard the registration process and access to different Network Slices are performed together.

Learn about Network Slices

5G introduces a more versatile type of dedicated networking: Network Slicing.

First, let’s have a look at how dedicated networking was achieved so far:

On LTE an APN and custom QoS per APN/customer would be the most often used solution to divide our network for specific subscribers and requirements into a basic level. Of course, there were other solutions such as using MOCN (Multi-Operator Core Network), but everything was core-centric, and often we only had control where the traffic terminates, which was only part of the data path.

Dedicated Packet Networks (APN)

With 5G, a Network Slice enables operators to more efficiently divide their network resources, from the radio aspect, through the transport, and of course, to a breakout to other networks.

Network Slices 5G

While on the LTE network, the most common division of the network was done at the core. On our 5G network, we can create new, independent data paths starting from the radio.

The concept of APN still exists on 5G as seen above, but now it’s called DNN (Data Network Name), which works at a “lower level.To do so, a Network Slice has to be selected first. 

Use case examples for Network Slices

Gaming and vehicle automation with low connection delays (lowlatency): 

An operator can lease a user plane function (UPF) on-premises at an enterprise customer’s site to enable ultra-low latency and private connectivity around their physical location for automated vehicles controlled through our 5G.  

Internet of Things: 

Devices with low data transfer requirements, such as payment terminals, rental and tracking of public bikes, can benefit from having a separate, dedicated slice for a guaranteed quality of service without affecting the rest of the network. 

Fixed broadband access: 

Splitting and providing a local break out for network traffic can be used to provide regional, high performance fixed broadband access through our 5G network and a 5G CPE (router). 

Now it’s the time to ask for Registration 

So far, we have achieved the following: 

1. Created a UE context, 

2. Obtained the subscriber’s identity, 

3 Performed mutual authentication.  

Now, the UE requests to have the much desired “Registered” status, yet it sends another request which is forwarded to the AMF by the gNB.

The AUSF will not be involved anymore in the rest of the process. It will be replaced with a new element which will be described shortly: the Network Slice Selection Function (or NSSF).

Network Slice Selection Function (NSSF)

On 5G, registration is also used to acquire access to Network Slices. The AMF sends to the UE the slices it has access to.

The AMF sends to the UE the slices

At least one Network Slice has to be selected. The AMF queries the UDM for the subscribed Network Slices for our subscriber.

The AMF queries the UDM

With that information, the AMF additionally selects a PCF and creates policy data context for the subscriber.

The function of the PCF is to store, keep track and distribute in realtime policy information such as access to certain DNNs, Slices and which QoS (bandwidth, latency…) should be applied for each session. The PCF will be queried and updated several times during the lifetime of the subscriber’s registration to the network. 

The AMF sends policy info

The PCF comes into play when, for example, we have to change, in realtime, a subscriber’s available bandwidth because the subscriber ran out of available data allowance. It takes care of distributing and updating the serving network elements to apply our new policy. 

Our mobile device just got access to one network slice of the type “eMBB” we configured in the network. This one slice will be used to create two data channels (PDU Sessions) to carry Internet and telephony services (IMS) data. 

The AMF forwards the reply to the UE: You have access to the Network Slice for Enhanced Mobile Broadband, with identification number ‘1’.

The AMF gives OK to the registration

Keep reading to see what else is necessary to enable data transmission.

Requesting a PDU Session

 On 5G, “registered” means we are granted access to a network and at least one Network Slice. However, we have yet to be able to access the Internet or make phone calls. What else needs to be done?

Because 5G is a data-only network, to fully make use of the services, a data session needs to be established (known as a PDU Session). 

The mobile devices carry the initiative to start a PDU Session. For that, it sends a message to the AMF, a socalled “PDU Session Establishment Request”.

PDU Session Establishment Request

Let’s Cook a PDU Session 

Before starting, the AMF contacts the Network Slice Selection Function (NSSF). The NSSF may have a word to say on whether a given slice is indeed still available or not due to, for example, some network conditions. 

Here, operators could implement different application logic for allowing or not allowing access to different network slices. 

Checking for slice aviability

Now it’s time to get help from the SMF to create a PDU Session. 

The AMF checks if there are any existing data sessions. If not, it creates a new one for each DNN requested.

Contacting the SMF

The SMF will now help to prepare the data session. But, how? 

First, it retrieves the current policy configuration for a subscriber from the UDM (traffic priority/QoS, maximum bandwidth, etc.).

Retrieving policy configuration for a subscriber

Once the SMF has the policy information, it contacts the PCF and updates it with the current policy information. From now on, the PCF will stay updated with information for that particular subscriber, and if the policy changes, the PCF will keep the other network elements up to date.

SMF contacts the PCF and updates it with the policy information

We are almost at the end of the journey. There is one more thing we need to do before confirming the creation of the PDU data session: establish the User Plane connection between the gNB base station and the User Plane Function (UPF). 

The UPF is at the “edge” of the operator’s network. It is the gateway where network traffic flows from and to other networks, such as the Internet. 

To control the UPF, the SMF uses the PFCP protocol, which is in use since LTE between the SGW (Serving Gateway) and PGW (PDN Gateway) and it is also used in 5G. 

Creating a PFCP session

The UPF will then use the parameters sent using the PFCP protocol to create a data “tunnel” between the UE and the data network.

PFCP protocol creates a data "tunnel"

Once the SMF gets confirmation from the UPF in a “PFCP Session Establishment Response” message, ask the AMF to forward the confirmation to the UE. 

AMF notifies the UE

The final step: confirmation of the PDU Session establishment

Almost there! The AMF now notifies the UE that the PDU Session Establishment Request the UE sent a while ago is established, and data transmission can start.

PDU Session created

And with this last step, our mobile device is ready and connected to the network! At this point is when you start seeing the data transmission. We can now make phone calls and use the Internet.

We can now make phone calls and use the Internet

A word from Software Mind

This article tried to explain, in simple terms, a very complex process. The complexity directly relates to how many new possibilities 5G creates for operators to implement new services.  

At Software Mind, our team conducts research and develops top-class applications for each step of the different processes mentioned above, which has led to exciting advancements in the telecommunications industry that have opened doors to various new services for users.  

If you are looking to fully leverage the power of 5G solutions, contact us using this form, and let us be your partner in this journey. 

About the authorJorge Espinosa

System Engineer

A systems engineer passionate not only about the technical aspects of the telco industry, but also topics related to the telco business as a whole. He has vast experience with 3GPP and GSMA standards, such as the latest generation packet core (5G, LTE), voice platforms (IMS, VAS) and business applications (BSS). Jorge works with a great and knowledgeable team focused on delivering modern and highly customized solutions and support to partners and clients.

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