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Checksum is the 16-bit ones' complement of the ones' complement sum of a pseudo header of information from the IP header, the UDP header, and the data, padded with zero octets at the end (if necessary) to make a multiple of two octets. [7] In other words, all 16-bit words are summed using ones' complement arithmetic. Add the 16-bit values up.
For example, in the IP suite, the contents of a web page are encapsulated with an HTTP header, then by a TCP header, an IP header, and, finally, by a frame header and trailer. The frame is forwarded to the destination node as a stream of bits , where it is decapsulated into the respective PDUs and interpreted at each layer by the receiving node.
Template {{APHD}} is used to create augmented packet header diagrams. Template parameters [Edit template data] Parameter Description Type Status table header 1 (start) Generates the header. Example start String suggested offset 1 (numerical) If this parameter is numerical then it is interpreted as the octet offset of this 4 octet-sized table row, which is displayed in the left header. The bit ...
TCP and UDP, have a checksum that covers all the data they carry, as well as the TCP or UDP header, plus a pseudo-header that contains the source and destination IP addresses of the packet carrying the TCP or UDP header. For an originating NAT to pass TCP or UDP successfully, it must recompute the TCP or UDP header checksum based on the ...
Similar headers are used in Usenet messages, and HTTP headers. In a data packet sent via the Internet, the data (payload) are preceded by header information such as the sender's and the recipient's IP addresses, the protocol governing the format of the payload and several other formats. The header's format is specified in the Internet Protocol.
For example, UDP is run by a datagram service on the internet layer. IP is an entirely connectionless, best effort, unreliable, message delivery service. TCP is a higher-level protocol running on top of IP that provides a reliable connection-oriented service.
The middle section of the frame is payload data including any headers for other protocols (for example, Internet Protocol) carried in the frame. The frame ends with a frame check sequence (FCS), which is a 32-bit cyclic redundancy check used to detect any in-transit corruption of data.
For example, in Point-to-Point Protocol, the packet is formatted in 8-bit bytes, and special characters are used to delimit elements. Other protocols, like Ethernet, establish the start of the header and data elements by their location relative to the start of the packet. Some protocols format the information at a bit level instead of a byte ...