Namespace inet

Ieee8021rTagEpdHeader

class

This chunk represents an IEEE 802.1R tag header without the TPID field and with the following EtherType Protocol Discrimination (EPD) in the packet. The reason for this shifted representation is that it's often easier to look at a 802.1Q tag this way during processing. The typeOrLength field contains the EtherType as defined in the section 9.2 EtherTypes of the IEEE Std 802-2014, IEEE Standard for Local and Metropolitan Area Networks: Overview and Architecture.

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-------------------------------+-------------------------------+ | Reserved = 0 | SequenceNumber | +-------------------------------+-------------------------------+ | EtherType/Length | +-------------------------------+

Extends

Name	Type	Description
FieldsChunk	(unknown -- not in documented files)

Fields

Name	Type	Description
chunkLength
sequenceNumber	uint16_t
typeOrLength	uint16_t	This field contains the 16 bits immediately following the 802.1R tag header TCI field: I. Tag Protocol Identifier (TPID) of the following tag header: 16-bit field specifying an EtherType value that is used to identify the frame as a tagged frame and to select the correct tag decoding functions. II. This two-octet field takes one of two meanings, depending on its numeric value. For numerical evaluation, the first octet is the most significant octet of this field. a) If the value of this field is less than or equal to 1500 decimal (05DC hexadecimal), then the Length/ Type field indicates the number of MAC client data octets contained in the subsequent MAC Client Data field of the basic frame (Length interpretation). b) If the value of this field is greater than or equal to 1536 decimal (0600 hexadecimal), then the Length/Type field indicates the Ethertype of the MAC client protocol (Type interpretation).

Packet operations (observed)

action	module
insertAtFront	Ieee8021rTagEpdHeaderInserter
peekAtFront	Ieee8021rTagEpdHeaderChecker
popAtFront	Ieee8021rTagEpdHeaderChecker

Source code

//
// This chunk represents an IEEE 802.1R tag header without the TPID field and
// with the following EtherType Protocol Discrimination (EPD) in the packet.
// The reason for this shifted representation is that it's often easier to look
// at a 802.1Q tag this way during processing. The typeOrLength field contains
// the EtherType as defined in the section 9.2 EtherTypes of the IEEE Std 802-2014,
// IEEE Standard for Local and Metropolitan Area Networks: Overview and Architecture.
//
//  0                   1                   2                   3
//  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
// +-------------------------------+-------------------------------+
// |          Reserved = 0         |         SequenceNumber        |
// +-------------------------------+-------------------------------+
// |        EtherType/Length       |
// +-------------------------------+
//
class Ieee8021rTagEpdHeader extends FieldsChunk
{
    chunkLength = B(6);
    uint16_t sequenceNumber = 0;
    uint16_t typeOrLength; // This field contains the 16 bits immediately following the 802.1R tag header TCI field:
                           // I. Tag Protocol Identifier (TPID) of the following tag header: 16-bit field specifying an EtherType value that is used to identify the frame as a tagged frame and to select the correct tag decoding functions.
                           // II. This two-octet field takes one of two meanings, depending on its numeric value. For numerical evaluation,
                           //     the first octet is the most significant octet of this field.
                           //     a) If the value of this field is less than or equal to 1500 decimal (05DC hexadecimal), then the Length/
                           //        Type field indicates the number of MAC client data octets contained in the subsequent MAC Client
                           //        Data field of the basic frame (Length interpretation).
                           //     b) If the value of this field is greater than or equal to 1536 decimal (0600 hexadecimal), then the
                           //        Length/Type field indicates the Ethertype of the MAC client protocol (Type interpretation).
}

File: src/inet/linklayer/ieee8021r/Ieee8021rTagHeader.msg