In this TSN network, the application is responsible for providing desired priority on data packets.
The standard method is to configure the SO_PRIORITY option on sockets using the setsockopt system call.
Here are C and Rust examples.
In the C programming language, the socket is represented by a file descriptor.
The file descriptor and the priority number are provided to setsockopt().
#include <sys/socket.h>
// Open a socket
int fd = socket(AF_INET, SOCK_STREAM, 0);
// Set the SO_PRIORITY to 6
int priority = 6;
int ret = setsockopt(fd, SOL_SOCKET, SO_PRIORITY, &priority, sizeof(priority));
if (ret < 0) { /* error */ }In the Rust programming language, a TCP connection is created by a TcpStream and the underlying file descriptor is obtained from the stream.
We call the setsockopt() from the nix library to configure the socket priority.
use nix::sys::socket::{sockopt::Priority, getsockopt, setsockopt};
use std::net::TcpStream;
use std::os::unix::io::AsRawFd;
// Create a TCP socket
let mut stream = TcpStream::connect("11.22.33.44")?;
// The the underlying file descriptor of the socket.
let fd = stream.as_raw_fd();
// Set SO_PRIORITY to 6.
setsockopt(fd, Priority, 6)?;The socket priority number ranges from 0 to 15.
The packets with higher priority number are usually processed first, depending on the actual queuing policies on the selected network device. Setting a priority greater than 6 requires the root permission, or CAP_NET_ADMIN capability to be precise.
The socket priority number is valid only within the Linux system. The ingress or egress network devices are responsible for the translation among the socket priorities and the network priorities. The network priority could be the Priority code point (PCP) field in the VLAN header, or the Type of Service field in the IPv4 header. The actual representation depends on the configuration of the network device.