## Common ground
Both options refer to devices that route or combine multiple signals, but they differ in technology and application context.
## Options at a glance
**8517.62 – Data transmission multiplexers**
- **Defining trait:** Use electrical signaling to combine or separate data streams over a single channel.
- **Typical examples:** TDM (Time Division Multiplexer) for digital audio, USB signal routing devices.
- **Best fit when:** The device handles electronic signals in data networks, computers, or digital systems.
**9013.80 – Optical fiber multiplexers**
- **Defining trait:** Use optical wavelengths (e.g., WDM) to transmit multiple signals over a single fiber using light.
- **Typical examples:** DWDM (Dense Wavelength Division Multiplexing) units in telecom backbones, fiber optic network hubs.
- **Best fit when:** The device operates in high-capacity fiber optic networks, especially for long-distance or high-speed data.
## Key differences
| Feature | 8517.62 – Data transmission | 9013.80 – Optical fiber multiplexers |
|-----------------------|------------------------------|----------------------------------------|
| Signal type | Electrical | Optical (light-based) |
| Medium | Copper wires, PCBs | Optical fiber |
| Typical use case | Internal data routing | Long-haul telecom networks |
| Technology | TDM, FDM | WDM, DWDM |
## How to choose
- Does it transmit signals using light through glass fibers? → 9013.80
- Is it used for electronic signal routing in digital systems or devices? → 8517.62
## Overlaps & pitfalls
A device might use both electrical and optical components (e.g., a fiber interface with electrical control logic), but the primary function determines the classification. If the core purpose is optical signal multiplexing, use 9013.80; if it’s electronic data routing, use 8517.62. The main function should guide the choice—no priority rule is implied in the codes