User's Manual

Technical Notes – QoS Features on BES50

Default QoS Behaviour of BES50FE and BES50GE

BES50 provides a set of default (out of the box) settings that are captured in the following table:

Traffic Prioritization Method Default Status Default CoS/Priority Value

Default port priority

Enabled 0

802.1p bit (tagged Ethernet

frame)

Enabled Taken from 802.1p value of the incoming

tagged Ethernet frames

IP DSCP

Disabled N/A

ACL based

Disabled N/A

Table 5: Default QoS Settings of BES50

Without modifying the default settings, the followings describe the default QoS behaviour of both BES50FE and

BES50GE:

• If the incoming Ethernet frame is a tagged frame, BES50 will take the 802.1p value specified in the

VLAN tag as the CoS/priority value. This CoS value is used to put the incoming frame into one the of

traffic classes (see Table 1: BES50 Priority to Traffic Class Mapping).

• If the incoming Ethernet frame is an untagged frame, BES50 will use the default port priority value ‘0’ as

the CoS/priority and maps the frame into one of the traffic classes (see Table 1: BES50 Priority to Traffic

Class Mapping).

o For BES50FE, CoS value of ‘0’ maps into traffic class 1. For BES50GE, CoS value of ‘0’ maps

into traffic class 2.

o This means that only tagged Ethernet frames with 802.1p value of either 1 or 2 will have lower

priority than the untagged Ethernet frames.

• The IP DSCP value specified in the IP header has no effect on the default QoS behaviour of BES50

switches. Incoming traffic is prioritized based on either the 802.1p value of the tagged Ethernet frames

or the default priority value of ‘0’ for all the untagged Ethernet frames.

• Since both BES50GE and BES50FE do not alter the CoS value, there is no 802.1p re-marking of any

Ethernet frames switched through BES50.

• By default, IP DSCP re-marking is disabled on both BES50FE and BES50GE.

Default QoS Behaviour on BCM Traffic

Since both BCM50 and BCM450 do not have VLAN capability, all the Ethernet frames transmitted from the BCM

must be untagged Ethernet frames. When a BCM (either BCM50 or BCM450) is connected to a BES (either

BES50FE or BES50GE) with default QoS settings, all the traffic transmitted from BCM will map to the same

traffic class. Effectively there is no service differentiation among the traffic transmitted from the BCM.

In the presence of Ethernet traffic from other L2 devices, only tagged Ethernet frames with 802.1p value of

either 1 or 2 will have lower priority than the traffic transmitted from BCM.

Default QoS treatment on the Ethernet frame sent to BCM is solely depending on whether the frame is tagged

when it arrives at the ingress port of the BES50. The BES50 behaviour is captured in the section titled “Default

QoS Behaviour of BES50FE and BES50GE”.