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The Internet checksum, [1] [2] also called the IPv4 header checksum is a checksum used in version 4 of the Internet Protocol (IPv4) to detect corruption in the header of IPv4 packets. It is carried in the IPv4 packet header , and represents the 16-bit result of the summation of the header words.
When UDP runs over IPv4, the checksum is computed using a pseudo header that contains some of the same information from the real IPv4 header. [7]: 2 The pseudo header is not the real IPv4 header used to send an IP packet, it is used only for the checksum calculation. UDP checksum computation is optional for IPv4.
A checksum is a small-sized block of data derived from another block of digital data for the purpose of detecting errors that may have been introduced during its transmission or storage. By themselves, checksums are often used to verify data integrity but are not relied upon to verify data authenticity .
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]
BSD checksum (Unix) 16 bits sum with circular rotation SYSV checksum (Unix) 16 bits sum with circular rotation sum8 8 bits sum Internet Checksum: 16 bits sum (ones' complement) sum24 24 bits sum sum32 32 bits sum fletcher-4: 4 bits sum fletcher-8: 8 bits sum fletcher-16: 16 bits sum fletcher-32: 32 bits sum Adler-32: 32 bits sum xor8: 8 bits ...
Version: 4 bits; Version == 2 Extension header version. Reserved: 12 bits; Reserved == 0 Reserved. Checksum: 16 bits Checksum over this header and all extension objects. This field itself is included, so it is set to zero while performing the calculation. Extension objects have the following general structure:
The advantage of choosing a primitive polynomial as the generator for a CRC code is that the resulting code has maximal total block length in the sense that all 1-bit errors within that block length have different remainders (also called syndromes) and therefore, since the remainder is a linear function of the block, the code can detect all 2 ...
A typical ROHC implementation will aim to get the terminal into Second-Order state, where a 1-byte ROHC header can be substituted for the 40-byte IPv4/UDP/RTP or the 60-byte IPv6/UDP/RTP (i.e. VoIP) header. In this state, the 8-bit ROHC header contains three fields: a 1-bit packet-type flag (set to '1' only for longer ROHC headers)