CTC Union FRM220-NMC, Руководство пользователя

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Appendix A
82
A.2.16.9 Class of Service
Class of Service (COS) is a technique used to deliver Quality of Service (QoS) in a network. CoS is a way of
classifying and prioritizing packets based on classification. A "first class" priority label is assigned to data
applications - such as mission-critical data transactions, or video or voice transmissions - which require faster
turnaround, while a lower-priority label is assigned to less time-sensitive traffic, such as e-mail and Web surfing.
CoS, as defined in IEEE 802.1p, uses Layer 2 VLAN Tagging and makes use of three bits in the Ethernet
frame header that can be used to specify priority. The field specifies a priority value of between 0 and 7 inclusive
that can be used by Quality of Service (QoS) disciplines to differentiate traffic.
CoS operates only on Ethernet at the data link layer.
Where QoS mechanisms are used, an aggregate traffic stream may be classified into a number of constituent
classes, and different QoS guarantees may be provided to different classes within the aggregate. When a class has
a defined minimum bandwidth assurance, this is referred to as the
class capacity .
The 1000EAS supports either a fixed-priority (strict-priority) or weighted (fair-queuing) scheme.
In the strict priority scheme, all top-priority frames egress a port until that priority's queue is empty. Then the
next lower priority queue's frames egress. This approach can cause the lower priorities to be starved of opportunity
for transmitting any frames but ensures all high priority frames egress the switch as soon as possible.
In the weighted scheme, an 8, 4, 2, 1 weighting is applied to the four queue priorities. This approach prevents
the lower priority frames from being starved of opportunity for transmission with only a slight delay to the higher
priority frames.
The IEEE 802.3ac Tag contains IEEE 802.1p priority information, and it will override any default port CoS
policy.
The switch in the 1000EAS has four internal priority queues (0~3) which need to be mapped to the 802.1Q
QoS eight priority (0~7) levels. The switch requires that each port (two fiber and two UTP in the 1000EAS) have a
mapping for queue priority.
To configure the CoS feature, first, from the main menu go to the <L> Local Status and Configuration menu,
then select <D> Device Status and Configuration , then select <7> Tag's CoS Mapping to Internal Classify .
This is where the Class of Service priority (0~7) can be mapped to the 1000EAS internal switch's priority queues
(0~3). In the switch, 3 is the highest priority queue and 0 has the lowest priority.
*********************************************
*** CTC UNION TECHNOLOGIES CO., LTD. ***
*** FRM220-1000EAS Ver:3.273 ***
*********************************************
<< Tag CoS Mapping to Internal Classify >>
<1> :CoS 0 [1]
<2> :CoS 1 [0]
<3> :CoS 2 [0]
<4> :CoS 3 [1]
<5> :CoS 4 [2]
<6> :CoS 5 [2]
<7> :CoS 6 [3]
<8> :CoS 7 [3]
<ESC>:Go to Previous Menu.