Alcatel-Lucent 7950 Quality Of Service Manual page 181

forwarding class is not explicitly defined in the rule, the forwarding class is inherited based on previous
rule matches.
Default
priority {in|out|use-de} — All frames that are assigned to this forwarding class will be considered in or out
of profile based on this command or to use the default. In case of congestion, the in- profile frames are
preferentially queued over the out-of-profile frames
Values
dscp
Syntax dscp dscp-name [dscp-name...(upto 8 max)] fc fc-name [priority {low | high}]
no dscp dscp-name [dscp-name...(upto 8 max)]
Context config>qos>sap-ingress
Description
This command explicitly sets the forwarding class or subclass or enqueuing priority when a packet is
marked with the DiffServ Code Point (DSCP) value contained in the dscp-name. A list of up to 8 dscp-
names can be entered on a single command. The lists of dscp-names within the configuration are managed
by the system to ensure that each list does not exceed 8 names. Entering more than 8 dscp-names with the
same parameters (fc, priority) will result in multiple lists being created. Conversely, multiple lists with the
same parameters (fc, priority) are merged and the lists repacked to a maximum of 8 per list if dscp-names are
removed or the parameters changed so the multiple lists use the same parameters. Also, if a subset of a list is
entered with different parameters then a new list will be created for the subset. Note that when the list is
stored in the configuration, the dscp-names are sorted by their DSCP value in ascending numerical order,
consequently the order in the configuration may not be exactly what the user entered.
Adding a DSCP rule on the policy forces packets that match the DSCP value specified to override the
forwarding class and enqueuing priority based on the parameters included in the DSCP rule. When the
forwarding class is not specified in the rule, a matching packet preserves (or inherits) the existing
forwarding class derived from earlier matches in the classification hierarchy. When the enqueuing priority is
not specified in the rule, a matching packet preserves (or inherits) the existing enqueuing priority derived
from earlier matches in the classification hierarchy.
The DSCP value (referred to here by dscp-name) is derived from the most significant six bits in the IPv4
header ToS byte field (DSCP bits) or the Traffic Class field from the IPv6 header. If the packet does not have
an IP header, dscp based matching is not performed. The six DSCP bits define 64 DSCP values used to map
packets to per-hop Quality-of-Service (QoS) behavior. The most significant three bits in the IP header ToS
byte field are also commonly used in a more traditional manner to specify an IP precedence value, causing
an overlap between the precedence space and the DSCP space. Both IP precedence and DSCP classification
rules are supported.
DSCP rules have a higher match priority than IP precedence rules and where a dscp-name DSCP value
overlaps an ip-prec-value, the DSCP rule takes precedence.
The no form of the command removes the specified the dscp-names from the explicit DSCP classification
rule in the SAP ingress policy. As dscp-names are removed, the system repacks the lists of dscp-names with
7950 XRS Quality of Service Guide
None
in — All frames are treated as in-profile.
—
out All frames are treated as out of profile.
— T
use-de he profile of all frames is set according to the DEI bit.
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