Packet Format

TWAMP Light defines the Session-Sender test packets sent by the Controller to the Responder and the Session-Reflector test packets reflected by the Responder to the Controller as probes for performance measurement.

Figure 1 shows the format of the Session-Sender test packet. Table 1 describes the fields of the packet.

Figure 1 Session-Sender test packet format

**Table 1** Fields in a Session-Sender test packet
Field	Description
Sequence Number	Packet sequence number generated based on the transmission sequence.
Timestamp	Interval for sending test packets.
Error Estimate	Error detection.
Member ID	MAC address or number of the member link interface that sends the packet.
Packet Padding	Packet padding field.

Figure 2 shows the structure of the Session-Reflector test packet. Table 2 describes the fields of the packet.

Figure 2 Format of a Session-Reflector test packet

**Table 2** Fields in a Session-Reflector test packet
Field	Description
Sequence Number	Packet sequence number generated based on the transmission sequence.
Timestamp	Timestamp when the test packet is reflected.
Error Estimate	Error detection.
MBZ	The value of this field must be 0.
Receive Timestamp	Timestamp when the test packet is received.
Member ID	MAC address or number of the member link that sends the packet.
Sender Sequence Number	The value is copied from the Sequence Number field of the Session-Sender test packet.
Sender Timestamp	The value of this field is copied from the Timestamp field in the Session-Sender test packet.
Sender Error Estimate	The value of this field is copied from the Error Estimate field in the Session-Sender test packet.
Sender Member ID	The value is copied from the Member ID field of the Session-Sender test packet.
Sender TTL	TTL value of the packet.
Packet Padding	Packet padding field.