Cisco Systems 15327 Flow Control Pause and QoS

14-9
Ethernet Card Software Feature and Configuration Guide, R7.2
January 2009
Chapter 14 Configuring Quality of Service
Ingress Priority Marking
Using the QinQ feature, service providers can use a single VLAN to support customers with multiple
VLANs. QinQ preserves customer VLAN IDs and segregates traffic from different customers within the
service-provider infrastructure, even when traffic from different customers originally shared the same
VLAN ID. The QinQ also expands VLAN space by using a VLAN-in-VLAN hierarchy and tagging the
tagged packets. When the service provider (SP) tag is added, the QinQ network typically loses any
visibility to the IP header or the customer Ethernet IEEE 802.1Q tag on the QinQ encapsulated frames.
On the ML-Series cards, the QinQ access ports (IEEE 802.1Q tunnel ports or QinQ UNI ports) have
visibility to the customer CoS and the IP precedence or IP DSCP values; therefore, the SP tag can be
assigned with the proper CoS bit, which would reflect the customer IP precedence, IP DSCP, or CoS bits.
In the QinQ network, the QoS is then implemented based on the IEEE 802.1p bit of the SP tag. The
ML-Series cards do not have visibility into the customer CoS, IP precedence, or DSCP values after the
packet is double-tagged (because it is beyond the entry point of t he QinQ service).
Figure 14-6 illustrates the QinQ implementation on the ML-Series card.
Figure 14-6 QinQ
The ML-Series cards can be used as the IEEE 802.1Q tunneling device for the QinQ network and also
provide the option to copy the customer frame’s CoS bit into the CoS bit of the a dded QinQ tag. This
way, the service provider QinQ network can be fully aware of the necessary QoS treatment for each
individual customer frame.
Flow Control Pause and QoS
When flow control and policy-map are enabled for an interface and the policy-map is configured only
with 'class-default' having policer action, flow control handles the b andwidth. For all the packets, which
match policers drop criteria, PAUSE frames are sent upstream so that far end device can reduce it's
transmit rate accordingly. If the far end device honours the received PAUSE frames, there will not be any
drops on ML card due to policer configuration. However, if the policer gets noncompliant flow, the
packets are dropped or demarked using the policer definition of the interface.
Note The above statement is valid for an interface, which has a policer with not only a class-default ( i.e with
non-default class) configured. When the policy-map is configured only with class-default, the poli cer
acts instead of allowing the flow control to drop or demark the frames.
96500
Destination Address6
Source Address6
Type=81002
Tag Control Information2
Type=81002
Tag Control Information2
Type/Length2
MAC DATA
PAD
42~1500
FCS4
Customer VLAN Tag
IEEE 802.1Q Tag
VLAN ID
CFICoS
IEEE 802.1p
(3 bits)
Service Provider Tag
QinQ Tag
VLAN ID
CFICoS
SP CoS bit
(3 bits)