Overview… test payloads
At the end of each packet generated for a stream is a special signature called a test payload. They are the key to distinguishing traffic streams at the receiving ports as well as performing integrity checks and timing measurements.
The test payloads contain various sequence numbers, time stamps, and checksums which are inserted automatically. They also contain a test payload identifier, or TID, which is chosen by the user and specified as part of the stream definition:
The test payloads belonging to each TID value are analyzed separately at the receiving port. In particular, the number of packets belonging to this TID are counted, and it is verified that the sequence numbers are unbroken.
Test payload identifiers should be assigned to be globally unique for every stream generated for every port of every chassis across the entire testbed. This is the easiest way to prevent any ambiguity at the receiving ports.
It is certainly invalid to use the same TID for more than one stream arriving at a particular port, since that port will assume they belong to a single stream and the sequence numbers will be jumbled.
However, it is perfectly valid to multi-cast or broad-cast a stream of packets containing test payloads: each receiving port will perform its own counting and checking of the received packets, and any weak path to a particular receiver can be detected and diagnosed.