User's Manual

Technical Notes – QoS Features on BES50

3. Traffic prioritization based on IP DSCP

This section focuses on prioritizing traffic based on the IP DSCP value in the incoming IP packets. In brief, the

user first needs to enable IP DSCP prioritization (it is disabled by default). When an incoming IP packet arrives

at an ingress port, BES50 first maps the DSCP value in the incoming IP packet to a traffic priority/CoS (value

between 0 – 7). Each traffic priority/CoS is mapped to one of the traffic classes, each traffic class will be

serviced by the scheduler.

Keep in mind that the IP DSCP field of an IP packet is 6 bits while the 802.1p field of an Ethernet frame is only 3

bits, there are a lot more IP DSCP value combination than the 802.1p value. BES50 provides a default DSCP to

CoS mapping as depicted in the following table. The DSCP to CoS mapping is also user configurable if the user

desired to use a different setting.

IP DSCP Value CoS Value

0 0

8 1

10, 12, 14, 16 2

18, 20, 22, 24 3

26, 28, 30, 32, 34, 36 4

38, 40, 42 5

48 6

46, 56 7

Table 2: BES50 IP DSCP to CoS Mapping

E.g.

• DSCP value of 40 or 0x28 maps into CoS 5, and then maps into traffic class 2 in BES50FE or traffic

class 5 in BES50GE

• DSCP value of 46 or 0x2e maps into CoS 7, and then maps into traffic class 3 in BES50FE or traffic

class 7 in BES50GE.

NOTE:

When IP DSCP prioritization is enabled, in the event that that the incoming Ethernet frame is also

tagged with an 802.1p value, BES50 will use the DSCP value in the IP packet for traffic prioritization

instead of the 802.1p value in the Ethernet frame.

Step (1) Enable IP DSCP Prioritization

BES50 has the capability to prioritize traffic based on DSCP of the incoming IP packet. By default this feature is

disabled, the user has to enable it if desired.

Each DSCP is mapped into a CoS/priority, which in turns in mapped into one of the traffic class.

Navigate to the Applications > Priority > IP DSCP Status panel