In reply to chr_sue:
Actually, you could do the pk_sequence.start(this), assuming you constructed the pkt_sequence beforehand. But it is not the recommend way.
A Sequence is a functor - an object that represents a handle to a routine - the sequence’s body() task in the UVM. You typically want your test to start the top-level sequence, and have it orchestrate the flow of all the other sequences in your tests. A sequence can start other other sequences in parallel or in series, and sequences can send transaction items (uvm_sequence_item) to the driver. The driver only sees sequence_items. The sequenceRs job is arbitrate the order of sequence items that get sent to the driver, and manage the protocol between the active sequence and driver. The sequencer typically has no user code associated with it.