> For the complete documentation index, see [llms.txt](https://alex-robenko.gitbook.io/commsdsl-specification/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://alex-robenko.gitbook.io/commsdsl-specification/frames/id.md).

# id Layer

The **\<id>** layer represents numeric message ID. The [frame](/commsdsl-specification/frames.md) definition must **NOT** contain more than one **\<id>** layer.

```
<?xml version="1.0" encoding="UTF-8"?>
<schema ...>
    <frame name="ProtocolFrame">
        <id name="Id">
            <int name="IdField" type="uint8" />  
        </id>
        <payload name="Data" />
    </frame>
</schema>
```

The **\<id>** layer doesn't have any extra properties in addition to [common](/commsdsl-specification/frames/common.md) ones.