Tripp Lite NGI-M05-C1, Руководство пользователя, Страница: 58 / 254

58
6. Advanced Settings
6.1. Bandwidth Control
6.1.1. QoS
Each egress port can support up to 8 transmit queues. Each egress transmit queue contains
a list specifying the packet transmission order. Every incoming frame is forwarded to one
of the 8 egress transmit queues of the assigned egress port, based on its priority. The egress
port transmits packets from each of the 8 transmit queues according to a configurable
scheduling algorithm, which can be a combination of Strict Priority (SP) and/or Weighted
Round Robin (WRR).
Typically, networks operate on a best-effort delivery basis, which means that all traffic has
equal priority and an equal chance of being delivered in a timely manner. When congestion
occurs, all traffic has an equal chance of being dropped.
When you configure the QoS feature, you can select specific network traffic, prioritize it
according to its relative importance, and use congestion-management and congestion-
avoidance techniques to give preferential treatment. Implementing QoS in your network
makes network performance more predictable and bandwidth utilization more effective.
The Switch supports 802.1p priority queuing. The Switch has 8 priority queues. These
priority queues are numbered from 7 (Class 7) — the highest priority queue — to 0 (Class
0) — the lowest priority queue.
The eight priority tags specified in IEEE 802.1p (p0 to p7) are mapped to the Switch’s
priority queues as follows:
Priority : 0 1 2 3 4 5 6 7
Queue : 2 0 1 3 4 5 6 7
Priority scheduling is implemented by the priority queues stated above. The Switch will
empty the four hardware priority queues in order, beginning with the highest priority queue,
7, to the lowest priority queue, 0. Each hardware queue will transmit all of the packets in
its buffer before permitting the next lower priority to transmit its packets. When the lowest
hardware priority queue has finished transmitting all of its packets, the highest hardware
priority queue will begin transmitting any packets it may have received.
QoS Enhancement
You can configure the Switch to prioritize traffic even if the incoming packets are not
marked with IEEE 802.1p priority tags or change the existing priority tags based on the
criteria you select. The Switch allows you to choose one of the following methods for
assigning priority to incoming packets on the Switch:

802.1p Tag Priority - Assign priority to packets based on the packet’s 802.1p
tagged priority.