Endianness in Networking
Many IETF RFCs use the term network order, meaning the order of transmission for bits and bytes over the wire in network protocols. Among others, the historic RFC 1700 (also known as Internet standard STD 2) has defined its network order to be big endian, though not all protocols do.
The telephone network, historically and presently, sends the most significant part first, the area code; doing so allows routing while a telephone number is being composed.
The Internet Protocol defines big-endian as the standard network byte order used for all numeric values in the packet headers and by many higher level protocols and file formats that are designed for use over IP. The Berkeley sockets API defines a set of functions to convert 16-bit and 32-bit integers to and from network byte order: the htons (host-to-network-short) and htonl (host-to-network-long) functions convert 16-bit and 32-bit values respectively from machine (host) to network order; the ntohs and ntohl functions convert from network to host order. These functions may be a no-op on a big-endian system.
In CANopen multi-byte parameters are always sent least significant byte first (little endian). The same is true for Ethernet Powerlink.
While the lowest network protocols may deal with sub-byte formatting, all the layers above them usually consider the byte (mostly meant as octet) as their atomic unit.
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