User guide

Chapter 5
Setup and Configuration
RUGGEDCOM ROS
User Guide
152 Managing Classes of Service
1. Navigate to Spanning Tree » Clear Spanning Tree Statistics. The Clear Spanning Tree Statistics form
appears.
1
Figure 100: Clear Spanning Tree Statistics Form
1. Confirm Button
2. Click Confirm.
Section 5.4
Managing Classes of Service
Classes of Service (CoS) provides the ability to expedite the transmission of certain frames and port traffic over
others. The CoS of a frame can be set to Normal or Critical. By default, other than the control frames, ROS
enforces Normal CoS for all incoming traffic received without a priority tag.
IMPORTANT!
Use the highest supported CoS with caution, as it is always used by the switch for handling network
management traffic, such as RSTP BPDUs.
If this CoS is used for regular network traffic, upon traffic bursts, it may result in the loss of some
network management frames, which in turn may result in the loss of connectivity over the network.
The process of controlling traffic based on CoS occurs over two phases:
1. Inspection Phase
In the inspection phase, the CoS priority of a received frame is determined from either:
• A specific CoS based upon the destination MAC address (as set in the Static MAC Address Table)
• The priority field in the IEEE 802.1Q tags
• The Differentiated Services Code Point (DSCP) component of the Type Of Service (TOS) field in the IP
header, if the frame is IP
• The default CoS for the port
NOTE
For information on how to configure the Inspect TOS parameter, refer to Section 5.4.2,
“Configuring Classes of Service for Specific Ethernet Ports”.
Received frames are first examined to determine if their destination MAC address is found in the Static MAC
Address Table. If they are, the CoS configured for the static MAC address is used. If the destination MAC
address is in the Static MAC Address Table, the frame is then examined for IEEE 802.1Q tags and the priority
field is mapped to a CoS. If a tag is not present, the frame is examined to determine if it is an IP frame. If the
frame is an IP frame and Inspect TOS is enabled in ROS, the CoS is determined from the DSCP field. If the
frame is not an IP frame or Inspect TOS is disabled, the default CoS for the port is used.