Roaming Protocol Dynamics

CoreESIM: QoS Parameters & eSIM Profile for Roaming Subscribers

3 min read

Ensuring a consistent and high-quality user experience for roaming subscribers is a critical function within CoreESIM deployments. This necessitates meticulous management of eSIM profile configurations and rigorous enforcement of Quality of Service (QoS) parameters, spanning both the Home Public Land Mobile Network (HPLMN) and Visited Public Land Mobile Networks (VPLMNs). The complexity arises from the inter-PLMN signaling and the potential disparity in network capabilities and policy enforcement across different operators.

eSIM Profile Management and QoS Enforcement in Roaming

eSIM profile configuration for roamers is governed by GSMA specifications, primarily SGP.22 (eSIM Remote Provisioning Architecture) and SGP.02 (Technical Specification). An eSIM profile, delivered by the Subscription Manager-Data Preparation+ (SM-DP+) to the eUICC via the Local Profile Assistant (LPA), contains all necessary subscription data, including International Mobile Subscriber Identity (IMSI), authentication keys, and network access parameters such as Access Point Name (APN) settings. For roamers, this profile dictates how the User Equipment (UE) attaches to the VPLMN and how traffic is routed, whether via local breakout in the VPLMN or home routing back to the HPLMN, influencing latency and overall service quality.

QoS parameters define the performance characteristics guaranteed to a specific service or subscriber traffic flow. Key parameters include:

  • Guaranteed Bit Rate (GBR) / Non-GBR: Throughput guarantees for specific services.
  • Packet Delay Budget (PDB): Maximum permissible latency for packet delivery.
  • Packet Error Loss Rate (PELR): Acceptable percentage of lost packets.
  • Allocation and Retention Priority (ARP): Priority level for resource allocation during congestion.
  • QoS Class Identifier (QCI) / 5G QoS Identifier (5QI): Standardized identifiers mapping to specific QoS characteristics and treatment at the network layer.

These parameters are typically specified in Policy and Charging Control (PCC) rules within the HPLMN’s Policy and Charging Rules Function (PCRF) or Policy Control Function (PCF).

Enforcing HPLMN-defined QoS parameters in a roaming scenario requires robust inter-PLMN interoperability. For 4G (LTE), this involves signaling over the S8 (between HPLMN P-GW and VPLMN S-GW) and S9 (between HPLMN PCRF and VPLMN PCRF) interfaces. In 5G, the N9 interface connects the HPLMN UPF with the VPLMN UPF, and Npcf connects HPLMN PCF with VPLMN PCF. The challenge lies in ensuring that the VPLMN can honor the QoS demands set by the HPLMN, especially when roaming agreements may not fully align on specific QCI/5QI mappings or resource prioritization. GSMA PRD IR.88 (LTE Roaming Guidelines) and PRD IR.38 (IMS Roaming and Interconnection Guidelines) provide frameworks for these inter-operator QoS negotiations.

The eSIM profile plays a pivotal role in this enforcement. The APN configured within the profile is crucial, as it often correlates with specific QoS policies and gateways. For instance, a dedicated APN for VoLTE roaming might be provisioned with a higher priority QCI (e.g., QCI 1 for conversational voice) to ensure low latency and minimal packet loss. Any misconfiguration or failure to activate the correct roaming profile can lead to suboptimal QoS, service degradation, or even complete loss of service. CoreESIM systems must ensure that roaming profiles are correctly provisioned, activated, and dynamically updated to reflect evolving roaming agreements and QoS requirements, thereby maintaining service integrity and subscriber satisfaction.