Qos Examples And Recommendations; Bridged Traffic - Avaya 8800 Planning And Engineering, Network Design

QoS design guidelines
Severe congestion is defined as a condition where the network or certain elements of the network
experience a prolonged period of sustained congestion. Under such congestion conditions,
congestion thresholds are reached, buffers overflow, and a substantial amount of traffic is lost.
When severe congestion is detected, the Ethernet Routing Switch 8800/8600 discards traffic based
on drop precedence values. This mode of operation ensures that high-priority traffic is not discarded
before lower-priority traffic.
When you perform traffic engineering and link capacity analysis for a network, the standard design
rule is to design the network links and trunks for a maximum average-peak utilization of no more
than 80%. This means that the network peaks to up to 100% capacity, but the average-peak
utilization does not exceed 80%. The network is expected to handle momentary peaks above 100%
capacity, as mentioned previously.

QoS examples and recommendations

The sections that follow present QoS network scenarios for bridged and routed traffic over the core
network.

Bridged traffic

When you bridge traffic over the core network, you keep customer VLANs separate (similar to a
Virtual Private Network). Normally, a service provider implements VLAN bridging (Layer 2) and no
routing. In this case, the 802.1p-bit marking determines the QoS level assigned to each packet.
When DiffServ is active on core ports, the level of service received is based on the highest of the
DiffServ or 802.1p settings.
The following cases describe sample QoS design guidelines you can use to provide and maintain
high service quality in an Avaya Ethernet Routing Switch 8800/8600 network.
Bridged trusted traffic
When you set the port to core, you assume that, for all incoming traffic, the QoS setting is properly
marked. All core switch ports simply read and forward packets; they are not re-marked or
reclassifiied. All initial QoS markings are performed at the customer device or on the edge devices.
The following figure describes the actions performed on three different bridged traffic flows (that is
VoIP, video conference, and e-mail) at access and core ports throughout the network.
June 2016 Planning and Engineering — Network Design
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