# Discussion of Using a Single DC Stream for Multi DC Application Data Transmission

## Overview

This contribution from China Mobile discusses potential issues with the current DC (Data Channel) application data transmission mechanism and proposes enhancements to support multiple DC applications over a single DC stream.

## Problems with Current DC Mechanism

### Resource and Implementation Limitations

- Current standard requires each DC application to establish a dedicated ADC (Application Data Channel) with its server or peer terminal before data transmission
- Theoretical support exists for numerous DC channels per call session, but practical implementations face constraints:
  - Resource consumption and power usage limitations
  - Current chip implementations support only up to 4 ADC bearers per session
  - Limited number of bearers cannot flexibly support diverse DC applications with different QoS requirements and destination endpoints

### Latency and User Experience Issues

- Each DC application opening requires DC bearer negotiation, introducing 100-500 ms delay
- Sequential application switching (closing DC application 1 and immediately opening DC application 2) can cause negotiation conflicts with non-robust terminal implementations

### Signaling Conflicts

- DC applications designed for immediate service upon call answering (e.g., call captioning, translation, background replacement, real-time transcription) face high risk of signaling conflicts
- When both calling and called parties have subscribed to related services, simultaneous DC negotiation requests at call answer time create conflict scenarios

## Proposed Solution

### Core Suggestion

Support a common DC channel shared among multiple DC applications with the following approach:

- **For ordinary data interaction**: DC applications can directly request data transmission without first establishing a dedicated DC bearer
- **For special requirements**: DC applications with specific transport protocol or QoS requirements still need to establish dedicated ADC before data transmission

### Solution 1 Details

- Define a generic ADC with fixed stream IDs
- Enable DCSF (Data Channel Selection Function) to support distribution of data from multiple DC applications
- Extend the ADC concept to allow ADC channels with specific stream IDs to carry data for multiple DC applications

## Proposal

Study whether to use and how to enhance DC to support multiple DC Application Data Transmission in a single DC stream.