How do I calculate network utilization for both transmit and receive

Question

How do I calculate network utilization for both transmit and receive either using C or a shell script?

My system is an embedded linux. My current method is to recorded bytes received (b1), wait 1 second, then recorded again (b2). Then knowing the link speed, I calculate the percentage of the receive bandwidth used.

receive utilization = (((b2 - b1)*8)/link_speed)*100

is there a better method?

Answer 1

Check out open source programs that does something similar.

My search turned up a little tool called vnstat.

It tries to query the /proc file system, if available, and uses getifaddrs for systems that do not have it. It then fetches the correct AF_LINK interface, fetches the corresponding if_data struct and then reads out transmitted and received bytes, like this:

ifinfo.rx = ifd->ifi_ibytes;
ifinfo.tx = ifd->ifi_obytes;

Also remember that sleep() might sleep longer than exactly 1 second, so you should probably use a high resolution (wall clock) timer in your equation -- or you could delve into the if-functions and structures to see if you find anything appropriate for your task.

Answer 2

thanks to 'csl' for pointing me in the direction of vnstat. using vnstat example here is how I calculate network utilization.

#define FP32 4294967295ULL
#define FP64 18446744073709551615ULL
#define COUNTERCALC(a,b) ( b>a ? b-a : ( a > FP32 ? FP64-a-b : FP32-a-b))
int sample_time = 2; /* seconds */
int link_speed = 100; /* Mbits/s */
uint64_t rx, rx1, rx2;
float rate;

/* 
 * Either read:
 * '/proc/net/dev' 
 * or 
 * '/sys/class/net/%s/statistics/rx_bytes'
 * for bytes received counter
 */

rx1 = read_bytes_received("eth0"); 
sleep(sample_time); /* wait */
rx2 = read_bytes_received("eth0");

/* calculate MB/s first the convert to Mbits/s*/
rx = rintf(COUNTERCALC(rx1, rx2)/(float)1048576);
rate = (rx*8)/(float)sample_time;

percent = (rate/(float)link_speed)*100;