Integration with mobile networks

For a service provider planning to become a mobile operator, there are two alternative options for entering the mobile market. The first one, and perhaps the most straightforward one, is through acquiring a spectrum license and deploying your own mobile network.

The other market entrance option is to become a virtual mobile network operator (MVNO) and utilize the network infrastructure of an existing MNO (mobile network operator). This model allows virtual operators to offer to their customers a full range of mobile services without having to make significant investments to build and maintain a mobile network.

PortaBilling can serve as the BSS and OCS for any of these solutions and integrate with 2.5/3G and 4G mobile networks.

The integration process between PortaBilling and 2.5/3G networks includes the following major aspects:

When an MNO signs up a mobile end user (subscriber) for a service, the subscriber is provisioned as a customer with one or more accounts in PortaBilling. Each account represents an actual phone line with an assigned phone number (MSISDN) and is associated with a SIM card (identified by IMSI).

This subscriber must be recognized in the mobile operator’s network in order for them to be granted access to the service. To do this, PortaBilling communicates with the HLR (Home Location Register) mobile network component.

The HLR is a centralized repository that stores information about all of an MNO’s subscribers. Once an account is added and activated in PortaBilling, the system connects to the HLR and creates an entry with the account’s IMSI (SIM card) and MSISDN (phone number).

Real-time authorization and rating is an important requirement for providing prepaid mobile services. PortaBilling fully supports this, allowing real-time charging for services such as voice calls, SMS messages or Internet use.

In 2.5 and 3G networks, the CAMEL protocol is the de-facto standard for online charging. Therefore, PortaBilling interoperates with mobile operator networks via a CAMEL gateway (GW) that converts the CAMEL protocol to the Diameter protocol and vice versa.

The mobile network component that PortaBilling interoperates with for real-time authorization and rating is the MSC (Mobile Switching Center).

When a subscriber makes a call, MSC performs call authorization in PortaBilling to verify that the subscriber has a sufficient balance and is permitted to call that destination. Since MSC uses the CAMEL protocol, its call authorization request is first converted to Diameter Ro and then delivered to PortaBilling. PortaBilling locks funds to cover the initial period of the call and sends confirmation to MSC. When that period is over, MSC sends a request to lock funds for the subsequent period, etc. Once the call is over, MSC produces a CDR record and sends it to PortaBilling.

In the message exchange between MSC and PortaBilling, all of the protocol conversions – from CAMEL to Diameter and from Diameter to CAMEL – are done using the CAMEL GW.

A similar procedure is followed when a customer sends an SMS. In this case, PortaBilling interoperates with the SMSC (Short Message Service Center) – a mobile network component that is responsible for delivering SMS messages.

PortaBilling permits MNOs to include roaming with their service offering.

When an MNO subscriber roams to a place where their MNO is not covered, they are automatically connected to another MNO – a roaming partner – without any interruption in service.

The roaming partner generates CDRs with service usage information in the roaming area and sends them to the subscriber’s MNO in TAP files. TAP is a commonly used standard for roaming data exchange among mobile operators. The MNO then parses these TAP files to distinguish the roaming CDRs that belong to their subscriber and sends them to PortaBilling. PortaBilling processes those CDRs and charges the subscriber for all of the roaming services provided.

A similar level of integration is done with 4G/LTE networks.

To provision customer’s data, PortaBilling communicates with the following components:

• HSS (Home Subscriber Server) – this is a database that contains information about all of the MNO’s subscribers. Once a subscriber is configured in PortaBilling and assigned a SIM card and the desired product, the subscriber’s information is nearly instantly provisioned in the HSS. Now the subscriber is ready to register on the mobile network.
• PCRF (Policy and Charging Rules Function) – this component provides policy decisions for mobile network subscribers. Such policies are usually related to QoS parameters and charging rules. PortaBilling provisions customer data to PCRF to allocate the correct policy/QoS parameters to the subscriber.

For real-time session authorization and rating, PortaBilling communicates with SAE-GW (System Architecture Evolution Gateway) via Diameter (Gy) for Internet service provisioning and via Diameter (Ro) for voice calls and SMS delivery.

Once the subscriber’s session starts, SAE-GW performs real-time authorization in PortaBilling and locks the funds to cover the initial period of the session. When the session is over, SAE-GW transmits the information about the transferred data volume to PortaBilling. PortaBilling then charges the subscriber for the session.

5G is the fifth generation of mobile network technology, offering significantly higher data speeds, lower latency, and the capacity to connect a vast number of devices simultaneously. This unlocks new possibilities across various industries, such as smart homes and cities with numerous IoT (Internet of Things) devices, self-driving vehicles, or cloud gaming. You can find a dedicated article about 5G on our blog.

In this chapter, we’ll explore how PortaBilling integrates with 5G networks to perform real-time charging and credit control.

A 5G network's core (5G Core, or 5GC) includes various Network Functions (NFs), each with specific interfaces to communicate with other NFs. Unlike the traditional Diameter-based interfaces used in 4G networks, these interfaces use modern RESTful APIs over HTTP, making them easier to integrate with web services and troubleshoot.

Let’s take a closer look at some key NFs involved in charging:

• User Data Repository (UDR) – stores and manages subscriber profiles and policy-related data, similar to the Home Subscriber Server (HSS) in 4G.
• Convergent Charging Function (CHF) – handles both real-time and offline charging for 5G services, such as data usage, voice calls, and SMS. In 4G, Online Charging System (OCS) and Offline Charging System (OFCS) are used for these purposes.
• Session Management Function (SMF) – manages user internet sessions and IP address allocation. SMF communicates with CHF to enforce real-time credit control. In the 4G network, similar functions are performed by the P-GW and S-GW.
• Policy Control Function (PCF) – enables real-time policy control, such as enforcing Quality of Service (QoS) rules based on user subscriptions and inputs from PortaBilling acting as CHF. It is the 5G equivalent of the PCRF in 4G.
• Application Function (AF) – communicates with PCF to support charging, policy control, and quality management for multimedia services like voice and video calls. For example, AF communicates with the PCF for QoS enforcement.

  The actual handling of voice and video calls in 5G is managed by the IP Multimedia Subsystem (IMS), just as in 4G. In 5G networks, the VoNR (Voice over New Radio) technology is used, which is similar to VoLTE in 4G networks.

• SMS Function (SMSF) – manages the sending and receiving of SMS messages. It ensures that messages are properly routed through the Short Message Service Center (SMSC), which functions the same as in 4G.

In 5G networks, many network elements continue to support 4G charging interfaces because 5G network components evolved from 4G products. This backward compatibility simplifies integration and ensures that operators can use existing 4G interfaces and systems when transitioning to 5G. For example, in standalone 5G networks, VoNR charging is handled via the Nchf_ConvergedCharging interface, with the IMS TAS (Telecommunication Application Server) functioning as an application function (AF). However, in networks that still support 4G IMS (VoLTE), Diameter Ro may still be used for online charging.

In 5G networks, PortaBilling functions as both a Business Support System (BSS) and a Charging Function (CHF), enabling real-time and offline charging for mobile services. It integrates with the 5G Core (5GC) to support various billing models, including prepaid, postpaid, and hybrid billing.

As a CHF, PortaBilling interacts with other Network Functions (NFs) as follows:

• With SMF (Session Management Function): PortaBilling communicates via the Nchf_ConvergedCharging interface to handle real-time charging for mobile data. This includes authorizing a specific number of megabytes based on available credit or an active plan, monitoring data service usage, and enforcing charging rules.
  You need to subscribe to the Add-on Mart adapter module that facilitates online charging in a 5G network via the API.
• With PCF (Policy Control Function): PortaBilling can integrate with PCF to support content-based charging. Through the Nchf_SpendingLimitControl interface, PortaBilling informs PCF when a user reaches a defined spending or data consumption limit.
  Integration with PCF via the Nchf_SpendingLimitControl interface is available as part of PortaOne Workflows.

If your network operates 4G, VoLTE, and 5G together, PortaBilling supports 4G online charging interfaces as a built-in functionality.