User guide

Packet Over SONET Module Installation and User Guide 3-47
Configuring QoS Functions
If you enable diffserv examination on a PoS port, then ingress IP frames are
assigned to a QoS profile based on the DiffServ code point (regardless of whether you
enabled either BCP or IPCP on the port). The existing
config diffserv examination
code-point
command maps DiffServ code points to QoS profiles. This command has
been enhanced for use with PoS ports. The syntax and description of the enhanced
config diffserv examination code-point command are given below.
Also note that, in all cases, the 802.1p priority bits of ingress frames forwarded to the
switch backplane are set based on the ingress QoS profile classification. More
specifically, the 802.1p priority value is set to qp# – 1. For example, if the packet is
classified to qp5, then the 802.1p priority value is set to 4.
When you enable MPLSCP on a PoS port, classification for MPLS labeled packets is
done based only on the EXP bits in the label stack entry of the ingress frame. The EXP
bits are used to map an ingress frame to an 802.1p priority and assigned to the
corresponding ingress queue. Before the frame is forwarded to the switch backplane,
the 802.1p bits in the frame are set based on the exp-to-dot1p mapping. You can use the
config mpls qos-mapping exp-to-dot1p command to configure the EXP to 802.1p
mapping. You can use the
config dot1p type dot1p_priority command to
configure the 802.1p to QoS mapping.
When you configure MPLSCP on a PoS port, other types of ingress commands such as
config diffserv examination code-point, config ports <portlist>
qosprofile
, and config vlan <name> qosprofile are supported only for IPCP data
frames and not MPLS labeled frames. Similarly, egress replacement commands such as
enable dot1p replacement and enable diffserv replacement are supported only
for IPCP data frame and not MPLS labeled frames.
Configuring DiffServ
All of the existing ExtremeWare DiffServ commands are supported by PoS ports with IP
frames that are encapsulated in BCP or IPCP, not MPLSCP (including the enhancements
to the
config diffserv examination code-point command, described earlier in this
chapter). PoS ports also support a DiffServ code point (DSCP) mapping function that
you configure using the
config diffserv dscp-mapping command, which is
described below. The DSCP is a 6-bit value in the IP-TOS byte of the IP packet header.
For more information on DSCPs, see “Configuring DiffServ” in the ExtremeWare Software
User Guide.