Information Element Data

Description

Information Element Data (IED) is the substantive content carried within the 'Value' field of an Information Element (IE). An IE is defined by its Type (or Identifier), its Length, and its Value. The IED constitutes this Value. It is the variable, instance-specific data that gives the IE its operational significance in a particular protocol transaction. For example, an IE may be defined as 'Cell Identity' with a Type ID of 0xXX and a Length of 2 octets. The IED for this IE in a specific RRC message would be the actual 2-octet binary number identifying the cell, such as 0x01A3.

The format and permissible range of the IED are strictly defined by the IE's specification. The IED can be a simple primitive type (e.g., an INTEGER, a BIT STRING, an OCTET STRING, an ENUMERATED value) or a complex, nested structure (a SEQUENCE or SEQUENCE OF other IEs). When it is a SEQUENCE, the IED itself contains a concatenation of other IEDs, each belonging to a sub-IE. The encoding of the IED follows the encoding rules specified for the IE, typically ASN.1 Packed Encoding Rules (PER), which produces a compact, unambiguous bitstream. The receiving entity decodes this bitstream based on its knowledge of the IE definition to extract and interpret the IED correctly.

The IED is the mechanism through which all dynamic network control is achieved. When a network sends an RRC Connection Reconfiguration message to a UE, the IEDs within the contained IEs specify the exact new radio bearers to establish, their QoS parameters, the physical channel configurations, and any measurement gaps. In a NAS Attach Request, the IEDs carry the UE's temporary identity, security capabilities, and requested network slice. The network processes these IEDs to make decisions about resource allocation, mobility management, and session establishment. Thus, while the IE definition provides the template, the IED provides the live, operational data that drives the network's behavior on a per-UE, per-session basis.

Purpose & Motivation

The concept of IED exists to separate the static definition of information (the IE) from its dynamic instantiation (the data). This separation is a fundamental software and protocol design principle that enhances flexibility, maintainability, and efficiency. The IE definitions are static, standardized, and baked into the protocol specifications and equipment software. The IED, however, is generated on-the-fly based on the current state of the network, the user's subscription, the requested service, and radio conditions.

This solves the problem of needing an infinite number of pre-defined, hard-coded messages. Consider a QoS parameter. The IE defines that a 'QoS Profile' is a SEQUENCE containing parameters like QCI, ARP, GBR, and MBR. The IED for a video streaming session might set QCI=2 (GBR video), GBR=5 Mbps, while for a background email sync, the IED might set QCI=9 (non-GBR). The same IE structure supports both, and countless other combinations, purely through variation in the IED. This makes the protocol immensely powerful and adaptable.

Furthermore, it enables efficient processing. Network nodes can be implemented with parsers that understand the IE structure. When a message arrives, the parser navigates the known structure to locate and extract the IED values, which are then passed to the relevant logic modules (e.g., the scheduler, the mobility manager, the policy engine). Without this structured separation, protocol messages would be opaque blobs of data, requiring complex and error-prone ad-hoc parsing for each new message type or vendor variation. The IED, within its defined IE container, provides a clean, machine-readable interface for network signaling.

Key Features

• Constitutes the variable 'Value' field within an Information Element's TLV structure.
• Format and valid ranges are strictly constrained by the parent IE's definition.
• Can be a simple data type (integer, string) or a complex nested structure of other IEDs.
• Encoded according to protocol rules (e.g., ASN.1 PER) for efficient transmission.
• Represents the instance-specific, operational data that controls network behavior.
• Is parsed and interpreted by the receiver based on its knowledge of the associated IE.

Evolution Across Releases

Defining Specifications