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cksum is a command in Unix and Unix-like operating systems that generates a checksum value for a file or stream of data. The cksum command reads each file given in its arguments, or standard input if no arguments are provided, and outputs the file's 32-bit cyclic redundancy check (CRC) checksum and byte count. [1]
This means you need to know when a 'one' bit starts to distinguish it from idle. This is done by agreeing in advance how fast data will be transmitted over a link, then using a start bit to signal the start of a byte — this start bit will be a 'zero' bit. Stop bits are 'one' bits i.e. negative voltage.
The checksum was the sum of all 128 data bytes in the packet modulo 256. The complete packet was thus 132 bytes long, containing 128 bytes of payload data, for a total channel efficiency of about 97%. The file was marked "complete" with a <EOT> character sent after the last block. This character was not in a packet, but sent alone as a single byte.
An Adler-32 checksum is obtained by calculating two 16-bit checksums A and B and concatenating their bits into a 32-bit integer. A is the sum of all bytes in the stream plus one, and B is the sum of the individual values of A from each step. At the beginning of an Adler-32 run, A is initialized to 1, B to 0. The sums are done modulo 65521 (the ...
For each byte of the input stream Perform 16-bit bitwise right rotation by 1 bit on the checksum; Add the byte to the checksum, and apply modulo 2 ^ 16 to the result, thereby keeping it within 16 bits; The result is a 16-bit checksum; The above algorithm appeared in Seventh Edition Unix. The System V sum, -s in GNU sum and -o2 in FreeBSD cksum:
On devices like modems, bytes may be more than 8 bits long because they may be individually padded out with additional start and stop bits; the figures below will reflect this. Where channels use line codes (such as Ethernet , Serial ATA , and PCI Express ), quoted rates are for the decoded signal.
Each packet requires 20 bytes of IPv4 header information and 20 bytes of TCP header information, leaving 1460 bytes per packet for file data (Linux and macOS [1] are further limited to 1448 bytes as they also carry a 12-byte time stamp). The data is transmitted over Ethernet in a frame, which imposes a 26 byte overhead per packet.
A bytestream is a sequence of bytes. Typically, each byte is an 8-bit quantity, and so the term octet stream is sometimes used interchangeably. An octet may be encoded as a sequence of 8 bits in multiple different ways (see bit numbering) so there is no unique and direct translation between bytestreams and bitstreams.