ToS field from IPv4 or the Traffic Class Field in the case of IPv6. Both fields are 8 bits in size. Of these 8 bits, the last 2 bits are used for end-to-end congestion notification (ECN), leaving 6 bits for the effective coding of the DSCP field. The default PHB is Best Effort (BE), meaning that no bandwidth guarantees are given to the incoming traffic. This PHB is coded in the DSCP as "000000." The highest priority traffic on the other hand is classed as Expedited Forwarding (EF, "101110"). This traffic should be routed with the highest priority. However, the ingress must be policed in such a fashion that the total egress traffic from a node is smaller than the available bandwidth. This implies making sure that no user abuses the EF class. There are four different Assured Forwarding (AF) classes with a dequeue priority between the BE and EF. Each of the four AF classes can have three drop precedence levels (low, medium, and high). The DSCPs for the AF classes are noted in the following table: 001010 010010 011010 100010 Medium 001100 010100 011100 100100 001110 010110 011110 100110 The class to which a certain flow must be mapped when in enters a DiffServ domain can be determined during the classification stage. Within the class, the drop precedence is 100 Open Radio Access Network (O-RAN) Systems Architecture and Design determined using, for example, a single-rate Tri Color Marker (srTCM) or a dual-rate Three Color Marker (see RFCs 2697, 2698). Red normally corresponds to the high drop precedence, yellow to medium drop precedence, and green to low drop precedence. It is also allowed to map the three drop precedence levels to two different levels of drop probability. In this case, both red and yellow are given the same drop probability. The AF class does not allow any packets within a microflow to be reordered. This almost always dictates that it is not possible to use three different queues to transmit the traffic (and does a priority dequeue). Instead, a mechanism such as RED is to be used to discard the packe