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Re: [Discuss-gnuradio] Adding/recovering packet number using packet_util

From: Dan Halperin
Subject: Re: [Discuss-gnuradio] Adding/recovering packet number using packet_utils python class
Date: Sat, 16 Jun 2007 12:18:13 -0700
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Tarun Tiwari wrote:
> Hi,
> I was wondering if we can add the packet number using current packet_utils
> python class.
> When I look into the code, I see that we introduce the preamble, access
> code, length of the packet, payoad with crc, and padding for usrp using
> make_packet function. At the same time when I look into the pkt.py , I see
> that msg.to_string() is the whitened_payload_with_crc and msg.arg1() is the
> whitener_offset for unmake_packet function in packet_utils class.
> Now, I understand that the preamble and access codes are removed by the
> timing and frequncy sync blocks in the receiver (please correct me if I am
> wrong), but I could not understand where the packet length, attached with
> the transmitted packet, went or if it was present, how do I get that?

A better way to put it is that the preamble is ignored altogether and
the access code is detected by the framer_sink, which then pulls off the
length field.

> Well, if I add the packet sequence number in the transmitted packet, how
> can
> i recover the sequence number? is it possible with current packet_utils
> python class or I need to write a new class for the same?

Why don't you just put the sequence number as part of the body of the
message and then you don't have to touch packet_utils?

- -Dan
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