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IXP400 Software
Access-Layer Components: Ethernet Database (IxEthDB) API
Programmer’s Guide IXP400 Software Version 2.0 April 2005
Document Number: 252539, Revision: 007 171
Traffic class for untagged frames (unexpedited traffic) is automatically selected from the default
traffic class associated with the port. The default port traffic class is computed from the default port
802.1Q tagging information, configured as described in “Ingress Tagging and Tag Removal” on
page 165. The first three bits from the default 802.1Q tag constitute the default port user priority,
which is mapped using the priority mapping table to obtain the default port traffic class.
Note: In order to use Receive QoS processing, IxEthAcc must be configured to operate in Receive FIFO
Priority Mode. Refer to Section 9.5.3.2.
10.3.5.3 Priority to Traffic Class Mapping
In order to associate the mapping of a frames 802.1Q priority value to the receive traffic class, the
IxEthDB API maintains a Priority Mapping Table. Functions are provided to modify individual
priority mapping entries, or to define a completely new table definition.
Figure 57. QoS on Receive for Untagged Frames
Incoming frame (untagged)
Preamble Start frame Dest MAC addr Src MAC addr Len Data Pad FCS
Traffic class 3 queue
Traffic class 2 queue
Traffic class 1 queue
Traffic class 0 queue
EthAcc
Traffic class queue selector
Default port traffic
class
Rx
EthDB