Managing Classes Of Service - Siemens RUGGEDCOM ROS User Manual

RUGGEDCOM ROS
User Guide
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, Medium, High, 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 source and 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
Each frame's CoS will be determined once the first examined parameter is found in the frame.
NOTE
For information on how to configure the Inspect TOS parameter, refer to
"Configuring Classes of Service for Specific Ethernet
Received frames are first examined to determine if their destination or source MAC address is found in the
Static MAC Address Table. If they are, the CoS configured for the static MAC address is used. If neither
destination or source 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.
After inspection, the frame is forwarded to the egress port for transmission.
2. Forwarding Phase
Once the CoS of the frame is determined, the frame is forwarded to the egress port, where it is collected into
one of the priority queues according to the assigned CoS.
CoS weighting selects the degree of preferential treatment that is attached to different priority queues. The
ratio of the number of higher CoS to lower CoS frames transmitted can be configured. If desired, lower CoS
frames can be transmitted only after all higher CoS frames have been serviced.
The following sections describe how to configure and manage Classes of Service:
• Section 5.4.1, "Configuring Classes of Service Globally"
• Section 5.4.2, "Configuring Classes of Service for Specific Ethernet Ports"
• Section 5.4.3, "Configuring Priority to CoS Mapping"
Managing Classes of Service
Section 5.4.2,
Ports".
Chapter 5
Setup and Configuration
167