Automation 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).