[Discuss-gnuradio] access code and preamble

[Nelson Odiwuor]

Hi all,
I was going through the pkt.py and packet_utils.py just to try and understand how packets are generated. Is it right to say that preamble has not being added to the payload?
"(packed_preamble, ignore) = conv_1_0_string_to_packed_binary_string(preamble)"

If it is being added how is it helpful on the receiver side because i don't see where it has been used or extracted. I know that it can be used to contain the training sequence for channel estimation but i doubt it has been used for the same here.  I can only see the access code correlator to mark the beginning of payload and no correlator for the preamble. Is it right to assume that the access code correlator alone can be suffice?  What is the significance of '\x55' at the end of the packet before introducing usrp pad? I am asking because according to my understanding it should make the end of payload(post amble) but I don't see a correlator for it. 

Kind regards,
Nelson