Based on RFC 4448, an Ethernet PW can operate in two different modes:
- Raw mode or VC Type 5
- Tagged mode or VC Type 4
The main difference is in raw mode the service delimiter (SD) tag (outer tag) must not be propagated and in tagged mode the service delimiter tag must be kept (or a dummy tag added if there is no SD tag) to the frame before forwarding it into the PW.
Those operations are independant from other tags manipulation that could happen at the Attachment Circuit level.
The attached document describes the different behavior per platform when we mix different AC type to different VC types: