802.1P And 802.1Q Recommendations; Network Congestion And Qos Design - Avaya 8800 Planning And Engineering, Network Design

802.1p and 802.1Q recommendations

In a network, to map the 802.1p user priority bits to a queue, 802.1Q-tagged encapsulation must be
used on customer premises equipment (CPE). Encapsulation is required because the Avaya
Ethernet Routing Switch 8800/8600 does not provide classification when it operates in bridging
mode. If 802.1Q-tagged encapsulation is not used to connect to the Ethernet Routing Switch
8800/8600, traffic can only be classified based on VLAN membership, port, or MAC address.
To ensure consistent Layer 2 QoS boundaries within the service provider network, you must use
802.1Q encapsulation to connect a CPE directly to an Ethernet Routing Switch 8800/8600 access
node. If packet classification is not required, use a Business Policy Switch 2000 to connect to the
access node. In this case, the service provider configures the traffic classification functions in the
Business Policy Switch 2000.
At the egress access node, packets are examined to determine if their IEEE 802.1p or DSCP values
must be remarked before leaving the network. Upon examination, if the packet is a tagged packet,
the IEEE 802.1p tag is set based on the QoS level-to-IEEE 802.1p-bit mapping. For bridged
packets, the DSCP is re-marked based on the QoS level.

Network congestion and QoS design

When providing Quality of Service in a network, one of the major elements you must consider is
congestion, and the traffic management behavior during congestion. Congestion in a network is
caused by many different conditions and events, including node failures, link outages, broadcast
storms, and user traffic bursts.
At a high level, three main types or stages of congestion exist:
1. no congestion
2. bursty congestion
3. severe congestion
In a noncongested network, QoS actions ensure that delay-sensitive applications, such as real-time
voice and video traffic, are sent before lower-priority traffic. The prioritization of delay-sensitive traffic
is essential to minimize delay and reduce or eliminate jitter, which has a detrimental impact on these
applications.
A network can experience momentary bursts of congestion for various reasons, such as network
failures, rerouting, and broadcast storms. The Avaya Ethernet Routing Switch 8800/8600 has
sufficient queue capacity and an efficient queue scheduler to handle bursts of congestion in a
seamless and transparent manner. Traffic can burst to over 100% within the Weighted Round Robin
(WRR) queues, and yet no traffic is dropped: if the burst is not sustained, then the traffic
management and buffering process on the switch allows all the traffic to pass without any loss.
June 2016 Planning and Engineering — Network Design
Comments on this document? infodev@avaya.com
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