16/24-Port PoE Switch
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• The congestion consumes huge amount of network resources (especially storage resources),
improper resources allocation may result in system down.
So, we can see the congestion prevents the flows getting the resources in time and it is the
original source to lower the service performance. In the complicated environments where
there is group exchanging and multiple-user business, congestion is inevitable. So there
shall be a proper way to deal with the congestion.
6.4.2 Congestion Settlement
The direct method to solve insufficient resources is to add network bandwidth. But the
bandwidth has its limit, it cannot fix all the problems resulting from the network congestion.
The more effective way to solve network congestion is to add flow control and resources
allocation function in the network. It can provide different services according to different
business requirements, and allocate and use the resources more reasonably. During the
resources allocation and flow control process, try to control the direction or indirect factors
that may trigger network congestion, which is to reduce the occurrence rate of the congestion.
When the network congestion occurs, it can allocate the resources according to the business
type and requirements to reduce the effect of the congestion to the minimum level.
6.4.3 Queue Scheduling
Usually we adopt queue scheduling to settle the congestion management. Using the line
algorithm to categorize the flows and use the priority algorithm to send out these kinds of
flows first. Each queue algorithm is to fix the pending network flow problems; it has great
effect on the bandwidth resources allocation, delay, jitter and etc.
This series product supports two priority queue: high priority queue and low priority queue.
The priority of each packet is set according to the following four plans.
1. The physical port.
2. 802.1 Q VLAN tag.
3. TOS/DS string of the IP packet.
4. TCP/UDP port.
When there are several QoS settings, once one priority setup item becomes the high priority,
then the item will be put in the high priority line and then forward. When there are several high
priorities, for the same level, it adopts First In First Out (FIFO).
6.4.4 Priority Mode
Each received packet maps to either high priority or low priority. The packet priority setup
has three modes. See Figure 6-11.
Figure 6-11
Refer to Table 6-3 for priority mode information.
Name
Note
First In First Out (FIFO) The first received packet will be forwarded first. When QoS function is disabled
device adopts FIFO mode to process the packets.
All high before low
Device forwards the packets according to the specified priority level.
Weight round robin
Set the weight level to change the packet forwarding percentage in the high
priority and low priority.
Table 6-3
6.4.5 QoS Based on Port/802. 1 p/DSCP
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When a port is set as the high priority, the received packets are placing in the high priority
queue. Each port can set as the high priority.
Based on 802.1 p
802.1 p priority is at the 2-layer packet head. It is for the environment where there is no need
to analyze the 3rd head and shall guarantee the QoS in the 2-layer.
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In Figure 6-8, the four-byte 802.10 tag head includes 2-byte TPID ( Tag Protocol Identifier)
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displays the detailed contents of the tag head of the 802.1 Q, Priority string is the 802.1 p
priority. The priority is called 802.1 p since the priority is defined in 802.1 p specifications.
