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Foundry NetIron M2404C and M2404F Metro Access Switches
Configuring HQoS (Rev.03)
QoS/HQoS Implementation
© 2008 Foundry Networks, Inc.
Page 20 of 98
•
Flow classification
using enhanced and flexible Access Control Lists (ACLs). The
classification rules can be defined per SAP (access port or VLAN). Up to 256 conditions can
be defined on most access ports. The conditions can be based on various parameters from the
Ethernet and IP header, including IP and MAC addresses, Ethertype, VPT, IP Protocol, IP
ToS, UDP/TCP Ports and some ICMP and IGMP parameters.
•
Flow filtering
, which allows protecting the device and other network resources in the service
provider’s network from being attacked/flooded by traffic of unwanted origin or type, which in
turn frees more resources for recognized traffic and increases its QoS.
•
Mapping to Forwarding Class (FC) and Color
. FC will determine one of 8 egress queues
(per internal connection port), while the Color (Green or Yellow) will be used to determine
WRED dropping probability. The mapping can be performed in “trusted” or “un-trusted”
mode.
o
Trusted
mode means the Provider trusts the Customer’s edge equipment to mark the
traffic using VPT/DSCP, and device maps either VPT or DSCP (as configured) directly to
FC and Color.
o
Un-trusted
mode means the FC and Color will be determined according to other fields in
the Ethernet/IP headers, as specified by the ACL.
•
Policing
. A Single-Rate Three-Color Marker (SRTCM) is implemented per Access Control
Group (a group of ACLs or flows). It allows changing the initial mapped Color of traffic
exceeding the specified thresholds (CIR, CBS and EBS). Currently the only action that can be
performed on the excess traffic is marking it Yellow, which means that this traffic is likely to
be dropped later by WRED/Tail-drop in the case of congestion or over-subscription.
•
Marking/Remarking
o
Marking of VPT field according to the internal FC and Color. Egress VPT is not affected
by the results of policing.
o
Remarking of DSCP field according to the internal FC and Color. Egress DSCP is affected
by the results of policing (if Color was changed).
Once the initial QoS operations (Classification, Filtering, Mapping, Policing and Remarking) have
been performed, the packets are assigned to VCs and are encapsulated using VC labels.
At this stage the Packet Processor also decides to which of the internal connection links each
packet will be sent. This decision is performed based on an intelligent load-balancing algorithm,
based on service/VC. That is, traffic that belongs to the same service is sent to the same internal
connection port. The distribution of services between the two internal connection ports is done
automatically by the application software.
Before the traffic is sent to the chosen internal connection port, the following additional QoS
mechanisms are applied:
•
Queuing
. The traffic is queued according to the FC in one of 8 egress queues per internal
connection port. The queues use
deep buffering
, which allows for better congestion control
and less dropped traffic due to congestion.
•
A
WRED or Tail Drop (TD)
dropping mechanism can be defined per port, based on one of 3
available profiles (each profile defines a single dropping mechanism for all 8 queues and its
parameters for each one of the 8 queues, and then the complete profile can be attached to a
port). The profiles are color-aware and so the algorithms are able to start dropping Yellow
traffic before any Green traffic is dropped.
•
Scheduling
. Scheduling between the queues is performed according to either Strict Priority
(SP) or Weighted Round-Robin (WRR) algorithm. These algorithms can be hybrid (some
queues SP, other WRR) in order to assure that both mission-critical traffic will be scheduled