Managing Classes Of Service - Siemens RX1500 User Manual

Chapter 5
Setup and Configuration
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Section 5.32

Managing Classes of Service

Classes of Service (CoS) provides the ability to expediate the transmission of certain frames and port traffic over
others. The CoS of a frame can be set to Normal, Medium, High or Criticial. By default, ROX II enforces Normal
CoS for all traffic.
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:
. Inspection Phase
In the inspection phase, the CoS priority of a received frame is determined from:
• A specific CoS based upon the source and destination MAC address (as set in the Static MAC Address
Table)
• The priority field in 802.1Q tags
• The Differentiated Services Code Point (DSCP) component of the Type Of Service (TOS) field, 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.
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
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 IP and inspecting TOS is enabled, the CoS is determined from
the DSCP field. If the frame is not IP or inspecting TOS is disabled, the default CoS for the port is used.
After inspection, the frame is forwarded to the egress port for transmission.
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RUGGEDCOM ROX II
User Guide
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Managing Classes of Service