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QoS Overview
Service egress QoS policies are applied to SAPs and map forwarding classes to service egress
queues for a service. The system can allocate a maximum of 8 queues per SAP for the 8
forwarding classes. All traffic types (that is, both unicast and BUM traffic types) share the same
queue on service egress. A service egress QoS policy defines the forwarding class queue
characteristics and also defines how to remark the forwarding class to priority bits in the packet
header (for example: IEEE 802.1p bits in the Ethernet VLAN tag) in the customer traffic.
Network QoS policies are applied to access uplink ports. Access-uplink ports are typically used to
connect to the core network and forward customer traffic towards the core network. A network
QoS policy defines both ingress and egress behavior. On access-uplink port ingress, traffic that
enters through the access-uplink port is classified to map it to a forwarding Class and the user has
an option to assign a profile. Forwarding class is associated with queues on access uplink port
ingress and the profile determines the enqueuing priority for the packet, with in-profile packets
have a higher chance of getting the buffer, than out-of-profile packets. The mapping of traffic to
forwarding class queues is based on QoS marking (for example: IEEE 802.1p bits, IP DSCP bits).
The characteristics of the forwarding class queues are defined within the policy as to the number
of forwarding class queues for unicast traffic type and BUM (Broadcast, Unknown-unicast, and
Multicast) traffic type, along with the queue rate and buffer parameters (like CIR, PIR, CBS,
MBS, etc.). Each of the forwarding classes can be associated with different parameters for unicast
traffic type and different parameters for multipoint (that is,.BUM) traffic type. A network QoS
policy defines up to 8 queues per policy, with up to 2 queues per forwarding class. Unicast and
multipoint traffic can be defined to use the same queue or different queues per forwarding class. In
the case of VPLS service, four types of forwarding are supported (which is not to be confused with
forwarding classes), unicast, multicast, broadcast, and unknown. Multicast, broadcast, and
unknown types are flooded to all destinations within the service while the unicast forwarding type
is handled in a point-to-point fashion within the service. All these traffic types use the same queue
(in other words, a separate queue for multicast, broadcast, and unknown unicast traffic types
cannot be defined). On access-uplink port egress, the policy maps forwarding class and profile
state to Dot1p and /or IP DSCP values for traffic to be transmitted out of the access-uplink port.
All the access-uplink SAPs configured on the same access-uplink port use the same policy and the
same set of forwarding class queues. In other words, traffic received and transmitted through all
the access-uplink SAPs configured on a given access-uplink port are treated in the same fashion
from a QoS perspective.
Network queue policies are applied on egress of access uplink ports and map forwarding classes to
network egress queues on access uplink ports. The system allocates 8 egress queues per access-
uplink port for the 8 forwarding classes. The policy defines the forwarding class queue
characteristics (that is, CIR, PIR, CBS, MBS, etc.). All traffic types (that is, both unicast and BUM
traffic types) share the same queue on access-uplink port egress. All the access-uplink SAPs
configured on the same access-uplink port use the same policy and the same set of forwarding
class queues. In other words, traffic transmitted through all the access-uplink SAPs configured on
a given access-uplink port are treated in the same fashion from a QoS perspective.
Slope policies are applied to service ingress queues, service egress queues, access uplink port
ingress, access-uplink port, and egress queues. Each of these queuing points allocates buffers from
the buffer pool and implements WRED for congestion management. During congestion WRED is
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7210 SAS D, E, K OS Quality of Service Guide
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