Although obsoleted by [RFC2474], traditional use of the Type of Service octet as described in [RFC791] is still common.
idiomatic.tc defines the following fields:
ip_tos_prec are the upper three bits of ip_tos.
ip_tos_delay is the bit that, if set, indicates the desire for short delay.
ip_tos_throughput is the bit that, if set, indicates the desire for high throughput.
ip_tos_reliability is the bit that, if set, indicates the desire for high reliability.