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Re: [Discuss-gnuradio] Problem in framer_sink

From: Johnathan Corgan
Subject: Re: [Discuss-gnuradio] Problem in framer_sink
Date: Sun, 11 Mar 2007 14:50:17 -0700
User-agent: Thunderbird (X11/20070306)

Dan Halperin wrote:

> Is the CRC actually required? In the version of the code I'm using on
> the lab machines (which is from early January), the framer_sink only
> uses the length field to form the packet and the CRC is checked later.
> We actually do the CRC after doing some ECC on the bits themselves.

The CRC only applies to the actual data payload; it gets appended at the
end.  But the len field that gets put (twice) into the header is the
length of the payload + CRC.

On receive, if the len field is corrupt, the received packet will fail
CRC, because the last four bytes of the payload will be some arbitrary
value, not the actual CRC field (and the packet won't have the right
contents anyway.)  So no strong protection is really needed for the len

Johnathan Corgan
Corgan Enterprises LLC

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