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OpenAutomation Knowledge Base
Enabling Traffic
Whether the port is actually transmitting packets is controlled both by the P_TRAFFIC parameter for the parent port and by the PS_ENABLE parameter for the stream.
While the parent port is transmitting, the parameters of any enabled stream cannot be changed.
Stream Test Payload Data (TPLD)
Each Xena test packet contains a special proprietary data area called the Test Payload Data (TPLD) which contains various information about the packet. The TPLD is located just before the Ethernet FCS and consist of the following sections:
Normal TPLD (20 or 22 bytes)
| Field | Length | Explanation |
| Sequence Number | 3 byte | Packet sequence number used for loss and misordering detection. |
| Timestamp | 4 byte | Timestamp value used for latency measurements. |
| Test Payload ID (TID) | 2 byte | Test payload identifier used to identify the sending stream. |
| Payload Integrity Offset | 1 byte | Offset in packet from where to calculate payload integrity. |
| First Packet Flag | 1 bit | Set if this is the first packet after traffic is started. |
| Checksum Enabled | 1 bit | Set if payload integrity checksum is used. |
| | 7 bit |
|
| Payload Integrity Offset (MSB) | 3 bit | Offset in packet from where to calculate payload integrity, MSB (bits 10:9:8) |
| Timestamp Decimals | 4 bit | Additional decimals for the timestamp. |
| Checksum | 8 byte | TPLD integrity checksum. |
| Total TPLD Size | 20 bytes |
|
If the Payload Checksum Offset option is enabled on the parent port, then an additional 2 byte checksum field is inserted in the TPLD sequence – just before the sequence number. This increases the total size of the TPLD to 22 bytes.
Micro-TPLD (6 bytes)
| Field | Length | Explanation |
| First Packet Flag | 1 bit | Set if this is the first packet after traffic is started. |
| | 1 bit |
|
| Test Payload ID (TID) | 10 bit | Test payload identifier used to identify the sending stream. |
| Timestamp | 28 bit | Timestamp value used for latency measurements. |
| Checksum | 8 bit | TPLD integrity checksum (CRC-8). |
The selection between the default TPLD or the micro-TPLD is done on the parent port. It is thus not possible to use different TPLD types for streams on the same port.
Disable TPLD
The TPLD function can also be completely disabled for any given stream by setting the Test Payload ID (TID) value for the stream to the value -1 (or the empty value in the XenaManager-2G GUI).