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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]
The bit time has nothing to do with the time it takes for a bit to travel on the network medium but has to do with the internals of the NIC. To calculate the bit time at which a NIC ejects bits, use the following: bit time = 1 / NIC speed To calculate the bit time for a 10 Mbit/s NIC, use the formula as follows:
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.
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:
The “fixed-length” password is split into two 7-byte halves. These values are used to create two DES keys, one from each 7-byte half, by converting the seven bytes into a bit stream with the most significant bit first, and inserting a parity bit after every seven bits (so 1010100 becomes 10101000 ).
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.
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.
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.