Transmission Medium Requirement

Description

The Transmission Medium Requirement (TMR) is a technical parameter defined in the context of the 3GPP Policy and Charging Control (PCC) architecture, specifically for interactions involving the Bearer Binding and Event Reporting Function (BBERF). The BBERF is a functional entity typically located in the access gateway (e.g., Serving Gateway in E-UTRAN, PDN Gateway in non-3GPP access) that is responsible for bearer binding, uplink bearer binding verification, and event reporting to the Policy and Charging Rules Function (PCRF). The TMR is a crucial piece of information conveyed from the BBERF to the PCRF to request or report the required QoS resources for a specific service data flow or aggregate of flows.

Operationally, when a new service data flow is detected or when QoS conditions change in the access network, the BBERF formulates a TMR. This TMR contains detailed QoS attributes necessary for the PCRF to make informed policy decisions. These attributes typically include the QoS Class Identifier (QCI), Allocation and Retention Priority (ARP), Guaranteed Bit Rate (GBR) for GBR bearers, Maximum Bit Rate (MBR), and potentially Aggregate Maximum Bit Rate (AMBR). The BBERF sends this TMR to the PCRF within a Gxx session message, such as a Credit Control Request (CCR). The PCRF uses the TMR, along with subscriber profile information, service data flow filters, and operator-defined policies, to generate or modify corresponding Policy and Charging Control (PCC) rules.

The generated PCC rules, which include the authorized QoS parameters, are then provisioned to the Policy and Charging Enforcement Function (PCEF) and also communicated back to the BBERF. This allows the BBERF to perform bearer binding—mapping the authorized QoS of the PCC rule to an appropriate underlying access-specific bearer (e.g., an EPS bearer in LTE). The TMR mechanism ensures that the PCRF has accurate, real-time information about the transmission capabilities and requirements of the access network, enabling dynamic and session-aware policy control. It is a key enabler for QoS coordination between the core network's policy layer and the resource management in the radio access network.

Purpose & Motivation

The TMR concept was developed to address the challenge of centralized policy control in a multi-access, IP-flow-based network architecture introduced with EPS and enhanced PCC. Prior to PCC, QoS and bearer management were often statically configured or managed in a decentralized manner within each access network, leading to potential inconsistencies, inefficient resource use, and an inability to apply sophisticated, service-aware policies across different access types. The need arose for a standardized interface and information model to allow the access gateway (BBERF) to communicate its specific resource requirements to the central policy decision point (PCRF).

The TMR solves the problem of abstracting access-specific bearer characteristics into a generic QoS parameter set that the PCRF can process. It allows the network to dynamically request resources based on real-time service demands, such as the initiation of a VoIP call or a video stream, rather than relying on pre-provisioned static bearers. This was motivated by the evolution towards all-IP networks and the requirement for seamless service continuity and consistent QoS enforcement, whether a user is on LTE, 3G, or trusted non-3GPP access. The TMR facilitates the PCRF's role as the brain of the PCC system, providing it with the necessary inputs to make intelligent decisions that balance user experience, network efficiency, and operator policies.