Qos And Queues; Qos And Filters - Avaya 8800 Planning And Engineering

QoS design guidelines

QoS and queues

Egress priority and discard priority are used in egress queue traffic management. Egress
priority defines the urgency of the traffic, and discard priority defines the importance of the
traffic. A packet with high egress priority should be serviced first. Under congestion, apacket
with high discard priority is discarded last.
In a communications network, delay-sensitive traffic, such as voice and video, should be
classified as high egress priority. Traffic that is sensitive to packet loss, such as financial
information, should be classified as high discard priority. The egress priority and discard priority
are commonly referred to as latency and drop precedence, respectively.
Each port on the Avaya Ethernet Routing Switch 8800/8600 has eight (or 64, depending on
the module) egress queues. Each queue is associated with an egress priority. Some queues
are designated as Strict Priority queues, which means that they are guaranteed service, and
some are designated as Weighted Round Robin (WRR) queues. WRR queues are serviced
according to their queue weight after strict priority traffic is serviced.
For more information about queue numbering and priority levels, see Avaya Ethernet Routing
Switch 8800/8600 Configuration — QoS and IP Filtering for R and RS Modules, NN46205-507.

QoS and filters

Filters help you provide QoS by permitting or dropping traffic based on the parameters you
configure. You can use filters to mark packets for specific treatment.
Typically, filters act as firewalls or are used for Layer 3 redirection. In more advanced cases,
traffic filters can identify Layer 3 and Layer 4 traffic streams. The filters cause the streams to
be remarked and classified to attain a specific QoS level at both Layer 2 (802.1p) and Layer
3 (DSCP).
Traffic filtering is a key QoS feature. The Avaya Ethernet Routing Switch 8800/8600, by default,
determines incoming packet 802.1p or DiffServ markings, and forwards traffic based on their
assigned QoS levels. However, situations exist where the markings are incorrect, or the
originating user application does not have 802.1p or DiffServ marking capabilities. Also, the
administrator may want to give a higher priority to select users (executive class). In any of
these situations, use filters to prioritize specific traffic streams.
You can use Classic and Advanced filters to assign QoS levels to devices and applications.
To help you decide whether or not to use a filter, key questions include:
1. Does the user or application have the ability to mark QoS information on data
2. Is the traffic source trusted? Are the QoS levels set appropriately for each data
3. Do you want to prioritize traffic streams?
276 Planning and Engineering — Network Design
packets?
source? Users may maliciously set QoS levels on their devices to take advantage
of higher priority levels.
November 2010