Description
Reverse Charging (REV) is a telecommunications service feature defined in 3GPP TS 29.163 and other specifications, which enables the called party (callee) to bear the charges for a call rather than the calling party (caller). This functionality is typically implemented in the core network, involving signaling between the calling and called networks to negotiate and apply the reverse charging arrangement. REV operates through the Intelligent Network (IN) or IP Multimedia Subsystem (IMS) architectures, where service logic determines charging responsibilities based on subscriber profiles and service agreements.
Architecturally, REV involves components such as the Service Control Point (SCP) in IN-based systems or the Telephony Application Server (TAS) in IMS, which interact with charging systems like the Online Charging System (OCS) or Offline Charging System (OFCS). When a call is initiated, the originating network sends a signaling message (e.g., in ISUP or SIP) indicating a request for reverse charging. The terminating network validates this request against the called party's service subscription and responds with acceptance or rejection. If accepted, charging records are generated to bill the called party, often using specific charging identifiers and tariffs.
Key components include the charging triggers in the Call Session Control Function (CSCF) or Mobile Switching Center (MSC), which invoke REV service logic, and the billing systems that process the reversed charges. The technology works by modifying standard call setup procedures to include reverse charging indicators, such as the Reverse Charging Indicator in ISUP or specific SIP headers in IMS. This ensures that the charging entity is switched from the caller to the callee, supporting services like freephone (e.g., 800 numbers), where businesses pay for incoming calls to encourage customer contact.
REV's role in the network extends to various service scenarios, including premium rate services where costs are shared, or promotional campaigns where companies cover call expenses. In modern networks, REV integrates with policy control and charging (PCC) frameworks to enable dynamic charging based on real-time conditions. Evolution toward 5G and VoLTE/VoNR has seen REV adapted to all-IP environments, maintaining interoperability with legacy systems while supporting new service models. Overall, REV is a flexible charging mechanism that facilitates innovative business models and enhanced user services.
Purpose & Motivation
REV was introduced to support business models where the called party, such as a company or service provider, wishes to pay for communication costs to attract customers or provide value-added services. Prior to REV, charging was predominantly caller-pays, limiting options for toll-free or promotional calling. This feature solves the problem of enabling freephone and similar services, where businesses absorb call charges to improve customer accessibility and engagement.
Historically, REV originated in fixed-line telephony with toll-free numbers and was adopted into mobile networks as part of IN capabilities in 2G/3G eras. It addresses limitations of traditional charging by allowing flexible billing arrangements, facilitating customer service hotlines, helplines, and marketing campaigns. The creation of REV in 3GPP standards was motivated by operator and enterprise demands for standardized reverse charging mechanisms across different networks and technologies.
In the context of 3GPP, REV's standardization in Release 8 and beyond ensured interoperability between GSM, UMTS, and IMS networks, supporting seamless service delivery. It solves operational challenges like complex billing reconciliations and lack of real-time charging control. By enabling called-party pays models, REV enhances service offerings, drives traffic to businesses, and aligns with evolving communication trends toward customer-centric charging in VoIP and 5G services.
Key Features
- Enables called party to pay for call charges instead of calling party
- Supports freephone and toll-free number services (e.g., 800 numbers)
- Integrates with IN and IMS architectures for service control
- Uses standardized signaling for reverse charging negotiation (e.g., ISUP, SIP)
- Provides real-time charging capabilities through OCS/OFCS integration
- Facilitates promotional and customer service business models
Evolution Across Releases
Introduced REV in 3GPP for IMS and legacy circuit-switched networks, defining basic reverse charging procedures in TS 29.163. Initial architecture supported signaling between networks to indicate reverse charging requests and handle billing transfers, enabling freephone services in mobile environments.
Defining Specifications
| Specification | Title |
|---|---|
| TS 29.163 | 3GPP TS 29.163 |