Johnathan Corgan wrote: > 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 > field.
Sorry; what I meant is, should we assume that all packets are protected by CRCs? The CRC check is done after the packet is pulled from the message queue, in what I think I would say is the network layer, or the MAC "layer". I was positing that the end-to-end argument would imply that the framer (link layer) should not assume that all packets have a 4-byte CRC. -Dan _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
