IP Precedence, TOS, and DSCP Classifications
Every IP packet (including both IPv4 and IPv6) includes a TOS byte. This byte is burst up into fields that the arrangement uses to advice accommodate the adapted QoS commitments. In the earlier TOS archetypal authentic in RFC 1349, the aboriginal three $.25 accommodate the IP Precedence value, and the abutting four $.25 accommodate the TOS value.
We agenda in casual that it is accessible to get abashed amid the altered uses of "TOS". Sometimes it refers to the absolute byte, and sometimes to aloof the 4 $.25 that alarm forwarding behavior. To advice abate the confusion, we will alarm the 4-bit acreage the TOS field, and the absolute byte the TOS byte.
Table B-1 shows the accepted IP Precedence values. It is important to agenda that accustomed appliance cartage is not acceptable to use IP Precedence ethics 6 or 7. These are carefully aloof for arrangement purposes like keepalive packets and acquisition protocols. The arrangement charge consistently accord these packets college antecedence than any appliance packets. This is because no appliance will assignment if the arrangement loses its cartography information.