# ADR 0007: Synthetic LC Service Options

## Status
Proposed

## Context
Legacy HBLink used `0x20` in synthetic LC service options. Later MMDVMHost evidence indicates `0x20` was an early OVCM bit-position mistake; standards-clean OVCM is `0x04`.

## Decision
Synthetic group voice LC uses normal service options `0x00` by default. OVCM is `0x04` if explicitly selected. HBLink `0x20` is legacy compatibility only. Real inbound LC is preserved.

## Rationale
FreeDMR should not set reserved service-option bits in newly generated LC. Real inbound LC should not be rewritten without a deliberate reason.

## Consequences
Generated fallback LC becomes cleaner. Some legacy interop assumptions may need live RF testing.

## Compatibility
`0x20` may remain as a named legacy compatibility option, not as the default or as a traffic marker.

## Testing Requirements
Codec/unit tests must assert synthetic LC defaults to `0x00`, OVCM uses `0x04`, real inbound LC is preserved, and `0x20` is only used when explicitly configured for compatibility.