Classification, queueing, and scheduling
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Flow classification
The flow classifier determines into which flow each incoming packet is mapped. On
customer-role ingress ports, a number of flows can be defined, based on port, user
priority, VLAN ID, IP-ToS field, and Destination MAC ADdress. For each flow a rate
controller can be specified (CIR/PIR value).
Apart from these flows based on input criteria, a default flow is defined for packets
that do not fulfill any of the specified criteria for the flows, for example, untagged
packets that have no user priority field. Thus, untagged traffic is classified per port. All
traffic on a certain port is treated equally and attached a configurable default port user
priority value to map the traffic on the appropriate queues.
A default user priority can be specified on port level to be added to each packet in the
default flow (see “Default user priority” (p. 8-89)). Furthermore, the rate controller
behavior for the default flow can be specified. The same fixed mapping table from user
priority to traffic class to egress queue is applied to packets in the default flow as to
packets in the specified flows.
Provided that Quality of Service - Classification, Queueing and Scheduling (QoS CQS,
cf. “Quality of Service configuration options” (p. 8-82)) is enabled, each flow can be
assigned a traffic class by using QoS profiles (see “Quality of Service provisioning”
(p. 8-94)).
Each traffic class is associated with a certain egress queue (see “Traffic class to queue
assignment” (p. 8-90)).
Ingress rate control
Ingress rate control is a means to limit the users access to the network, in case the
available bandwidth is too small to handle all offered ingress packets.
A rate controller has two parameters, a provisionable committed information rate (CIR,
see below), and a committed burst size (CBS). The committed burst size is the
committed information rate multiplied by 0.11 seconds.(CBS = 0.11 seconds × CIR).
Rate control is supported for every ingress flow on every customer-role port. There is
one rate controller per flow. A “color unaware one-rate two-color marker” is supported,
which can be seen as a degenerate case of the two-rate three-color marker. “Color
unaware” means that the rate controller ignores and overwrites any dropping
precedence given by an upstream network element (network-role ports with
DiffServEdge function (E-NNI) only).
The rate controller measurement accuracy is optimized for long frame traffic. Shorter
frames are underestimated. Thus, it is recommended to dimension the transporting
network to have always a headroom of at least 10% bandwidth compared to the
committed rate (CIR) provisioned. For example: when a flow needs to be limited to 10
Mbps, it is recommended to configure approx. 9 Mbps. .
Traffic provisioning
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365-312-807R7.2
Issue 4, May 2007
Alcatel-Lucent - Proprietary
See notice on first page
8-85
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