Link Characteristics

Description

Link Characteristics (LC) in 3GPP standards refer to the quantifiable attributes that define the behavior and quality of a transport link interconnecting network functions, such as between a Radio Network Controller (RNC) and a Core Network node, or between different core network elements. These characteristics are not a single protocol or function, but a conceptual framework used across various specification domains to model, configure, and monitor the underlying transport network that carries user plane and control plane traffic. Key parameters typically encompass bandwidth (maximum and available throughput), transfer delay (one-way and round-trip), delay variation (jitter), packet loss rate, bit error rate, and availability/reliability metrics. These are often defined in the context of IP transport or ATM transport in earlier releases.

The specification of Link Characteristics is crucial for several operational processes. During network planning and dimensioning, engineers use LC parameters to ensure transport links are provisioned with sufficient capacity and quality to meet the service level agreements (SLAs) for the overlying 3GPP services. In operational phases, Network Management Systems (NMS) and Element Managers (EM) collect performance measurements related to these characteristics to monitor link health, detect degradation, and trigger alarms or corrective actions like traffic rerouting. Furthermore, LC parameters are used in algorithms for load balancing, congestion control, and routing decisions within the network. For instance, the Iu interface characteristics between RNC and MSC or SGSN directly impact the perceived quality of voice calls and data sessions.

From an architectural perspective, Link Characteristics are defined in technical specifications covering transport network aspects (e.g., TS 25.414 for Iu interface, TS 29.122 for T8 interface), management (TS 32.855 for performance management), and service requirements (TS 26.110 for codec-specific delay budgets). They form part of the information models used by management interfaces like Itf-N. The characteristics are often associated with a Network Resource Model (NRM) object representing a transport link, allowing management systems to get and set thresholds, and receive notifications when characteristics deviate from expected ranges. This enables a closed-loop automation where the management system can correlate service degradation (e.g., high VoIP packet loss) with specific link performance issues (e.g., high jitter on a backhaul link).

Purpose & Motivation

The concept of Link Characteristics was formalized to address the growing complexity of separating the radio network and core network functionalities from the underlying transport infrastructure. In early mobile networks, transport was often a dedicated, predictable TDM network. With the migration to packet-switched IP transport, the characteristics of links became variable and less predictable due to statistical multiplexing and shared resources. This introduced challenges in guaranteeing end-to-end Quality of Service (QoS) for real-time services like voice and video. Defining standardized Link Characteristics provided a common language for equipment vendors, network operators, and management system developers to specify requirements, configure parameters, and measure performance consistently.

Its creation was motivated by the need for effective network management and service assurance. Without a standardized model for link properties, it would be impossible to automate fault and performance management or to implement advanced traffic engineering. Link Characteristics enable operators to translate high-level service KPIs (e.g., call drop rate, video streaming MOS) into measurable transport network KPIs. They also solve the problem of multi-vendor interoperability in management planes, as different network elements can report performance data using the same characteristic definitions. This is essential for integrated network management in modern, disaggregated networks where the RAN, transport, and core may come from different suppliers.