In IEC 61850-8-1, Annex C, it is mentioned, that the use of VLAN support is optional. If the mechanism is used, the VLAN ID (VID) shall be set by configuration; if the mechanism is not used, it shall be set to 0.
This specification is ok. However, it has to be noted, that a switch supporting VLANs will alter the tag with a VID=0 by replacing this with the configured default VID, which can not be 0. As a consequence, a device that is not supporting the VLAN mechanism, may expect to receive frames with a VID=0. If the device can not be configured to receive a specific VID, it has to ignore the value of the VID field.
Proposal
Add a note to that paragraph that gives this hint. I.e. the note could read as follow:
NOTE 3: As a switch supporting VLANs will alter tags with a VID=0 by setting the VID value to the configured default VID value for that port, an IED receiving tagged frames shall not expect this frame having a specific VID. That means, if an IED is not supporting to be configured to receive messages with a specific VID, it has to ignore the value of the VID field.
Consider to add a further note, that it is recommended to support VLAN configuration in IEDs for sending messages.
Discussion
Created
Status
31 Mar 06
In Force (green)
24 Feb 06
Ballot Period
changed to final proposal
24 Feb 06
Ballot Period
agreed.
16 Feb 06
Discussion (red)
The VLan header may also be removed from the switch since VLan is only used for Switch to Switch communication. Therefore, the Stack shall not only ignore the value of the VID filed but also be prepared to receive non-VLan Taged messages.