2.2.4.4 Emit Upper-Level Header Format

A mapper sends an Emit frame to a responder to request that the responder transmit a set of Train or Probe frames, each with specified source and destination MAC addresses, after a specified pause time, and optionally that the responder immediately acknowledge the Emit frame with an Ack frame. The pause is used because some switches require approximately 150 milliseconds to update their port filtering databases, so back-to-back Train and Probe frames are not forwarded correctly.

Emit frames also carry inherent charge. See section 3.6.5.2 for details on how charge is accumulated from Emit frames.

The Emit frame following a Base header MUST have the following format.


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Num_Descs

EmiteeDescs (variable)

...

Num_Descs (2 bytes): This field specifies the unsigned integer count, in network byte order, of the number of EmiteeDesc items in the EmiteeDescs field. This field's value MUST be in the range 1 to 105.

EmiteeDescs (variable): This field specifies a list of EmiteeDesc items, where each EmiteeDesc item is a 14-octet structure.


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Type

Pause

Source_Address

...

Destination_Address

...

Type (1 byte): This field specifies the type of packet to emit. The following table shows valid values.

Value

Meaning

0x00

Train

0x01

Probe

Pause (1 byte): This field specifies the number of milliseconds to pause before the associated packet is emitted. The sum of the Pause values in all EmiteeDesc entries in an Emit frame MUST NOT exceed 1 second.

Source_Address (6 bytes): This field specifies the source MAC address of the packet to emit. The source MAC address MUST be either the responder's real MAC address to which the frame is sent or a MAC address from the special MAC address range 0x000D3AD7F140 to 0x000D3AFFFFFF that is specific to this protocol.

Destination_Address (6 bytes):  This field specifies the destination MAC address of the packet to emit. The destination address MUST NOT be a multicast address because these addresses could amplify traffic.