Description
CT114 is a specific interchange circuit within the ITU-T V.24 standard, which defines the interface between data terminal equipment (DTE) and data circuit-terminating equipment (DCE). In the context of 3GPP specifications, CT114 is referenced to maintain compatibility with traditional modem-based communication systems and certain legacy network interfaces. The circuit operates as a control signal line within a serial interface, carrying binary state information (ON/OFF) that indicates the operational status of the connected DTE.
Technically, CT114 corresponds to Circuit 108 in the V.24 nomenclature, which is the Data Terminal Ready (DTR) signal. When the DTE (such as a computer or terminal) is powered on and ready to establish a connection, it asserts the DTR signal by setting CT114 to the ON state (typically a positive voltage relative to the signal ground). This signal informs the DCE (such as a modem) that the terminal equipment is operational and prepared for data transmission. The DCE monitors this signal and will typically not attempt to establish or maintain a connection if DTR is not asserted.
In 3GPP architecture, references to CT114 appear in specifications like 23.045 and 43.045, which deal with technical realization and interworking aspects. These specifications ensure that 3GPP networks can interface correctly with equipment using traditional V.24 interfaces, particularly in scenarios involving circuit-switched data services, fax transmission, or modem pooling functions. The signal is part of a broader set of control circuits (including CT106 for Request to Send, CT107 for Clear to Send, and CT108 for Data Set Ready) that collectively manage the handshaking and flow control between DTE and DCE.
The electrical characteristics of CT114 follow V.24 specifications, typically using RS-232 voltage levels where a positive voltage (between +3V and +15V) represents the ON or 'mark' state (logical 1), and a negative voltage (between -3V and -15V) represents the OFF or 'space' state (logical 0). The timing of the DTR signal assertion and de-assertion follows established modem control protocols, with specific requirements for minimum assertion duration before data transmission can begin. In 3GPP systems, this circuit might be implemented in physical interface modules, interworking functions (IWFs), or terminal adaptation functions that bridge between modern packet-based networks and legacy circuit-switched data services.
Purpose & Motivation
CT114 exists as part of 3GPP specifications to ensure backward compatibility with established telecommunications standards, particularly ITU-T V.24, which has been widely used for decades in modem communications and serial data interfaces. By incorporating this standardized interchange circuit, 3GPP systems can interoperate with legacy equipment, support traditional data services like fax and modem dial-up, and provide smooth migration paths for existing infrastructure. This addresses the practical need for telecommunications networks to support multiple generations of technology simultaneously.
The historical context stems from the widespread adoption of V.24 interfaces in data communications equipment throughout the 20th century. As mobile networks evolved from voice-centric systems to support data services, they needed to interface with existing modem pools, fax servers, and other equipment using standard serial interfaces. CT114, as the DTR signal, plays a crucial role in the handshaking protocol that establishes and maintains data connections between terminal equipment and network equipment.
Without standardized references to circuits like CT114, 3GPP networks would face significant interoperability challenges when connecting to legacy systems. The inclusion of these specifications addresses limitations in earlier mobile data implementations that might not have fully supported traditional data communication protocols. It ensures that 3GPP-based networks can serve as complete replacements for older communication systems while maintaining support for established services that businesses and consumers continue to use.
Key Features
- Standardized interchange circuit per ITU-T V.24
- Corresponds to Data Terminal Ready (DTR) control signal
- Binary ON/OFF state indication for DTE readiness
- RS-232 compatible electrical signaling characteristics
- Part of comprehensive modem control handshaking protocol
- Ensures backward compatibility with legacy data equipment
Evolution Across Releases
Initially incorporated CT114 as a reference to ITU-T V.24 Circuit 114 (DTR) in 3GPP specifications 23.045 and 43.045. This established the technical requirements for supporting legacy modem interfaces in 3G networks, particularly for circuit-switched data services and fax transmission. The implementation ensured proper handshaking between mobile equipment and traditional data communication equipment.
Defining Specifications
| Specification | Title |
|---|---|
| TS 23.045 | 3GPP TS 23.045 |
| TS 43.045 | 3GPP TR 43.045 |