The following table shows common decimal, hex and binary values for TOS, broken down into the meaning of the parts of that byte including DSCP values when interpretting that byte as DSCP.
So, there you have it, one byte in a packet header, two ways to look at it…
Stays the same (link layer and routing protocol keep alive)
Stays the same (used for IP routing protocols)
Express Forwarding (EF)
RFC 2597 defines the assured forwarding (AF) PHB and describes it as a means for a provider DS domain to offer different levels of forwarding assurances for IP packets received from a customer DS domain. The Assured Forwarding PHB guarantees a certain amount of bandwidth to an AF class and allows access to extra bandwidth, if available. There are four AF classes, AF1x through AF4x. Within each class, there are three drop probabilities. Depending on a given network’s policy, packets can be selected for a PHB based on required throughput, delay, jitter, loss or according to priority of access to network services.
Classes 1 to 4 are referred to as AF classes. The following table illustrates the DSCP coding for specifying the AF class with the probability. Bits DS5, DS4 and DS3 define the class; bits DS2 and DS1 specify the drop probability; bit DS0 is always zero.
001010 AF11 DSCP 10
010010 AF21 DSCP 18
011010 AF31 DSCP 26
100010 AF41 DSCP 34
001100 AF12 DSCP 12
010100 AF 22 DSCP 20
011100 AF32 DSCP 28
100100 AF42 DSCP 36
001110 AF13 DSCP 14
010110 AF23 DSCP 22
011110 AF33 DSCP 30
100110 AF43 DSCP 38
RFC 2598 defines the Expedited Forwarding (EF) PHB: “The EF PHB can be used to build a low loss, low latency, low jitter, assured bandwidth, end-to-end service through DS (Diffserv) domains. Such a service appears to the endpoints like a point-to- point connection or a “virtual leased line.” This service has also been described as Premium service.” Codepoint 101110 is recommended for the EF PHB, which corresponds to a DSCP value of 46.
Again, vendor-specific mechanisms need to be configured to implement these PHBs. Refer to RFC 2598 for more information about EF PHB.