PQ (priority queuing queue)

PQ (priority queuing priority Queue)

A very traditional but cannot but talk about the queue

PQ is a strict, hierarchical execution of the scheduling queue, it can create up to 4 different levels of the queue, is high, medium, Normal, low, and then according to the different data traffic classification, the different classification data into 4 different levels of the queue. As shown in figure x , and then 100% of the use of bandwidth, the first service in the "high" queue of data, until the "high" queue of data are all sent to complete, and then serve the "medium" queue of data, and so on, then serve the "normal" queue, and finally " Low "queue. According to this logic, the biggest feature of the PQ queue is that the high-priority queue is always serviced, so this may cause the data in the low-priority queue to be "starved" for what? If the high priority queue continues to send data continuously, then the PQ scheduler will ensure that the high priority queue data is sent to the lower priority queue to send, in other words, in the "Low" rank queue of data, must wait for "high", "medium", "normal" The data in the "Low" rank queue is sent only after all of the three queues have been sent. Therefore, the "low" ranks of the data can easily be "starved", resulting in the queue of data has not been serviced, the end result will be the application service suspension or termination.

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about priority Queues PQ Precautions :

First,Pqwhen the queue is filled, it will take a tail-dump;Pqthe queue length can be set to0, if you putPqThe queue length is set to0, this means that the length of the queue is unrestricted, until the memory of the router is exhausted, when the memory is exhausted, then the data will not be sent to the team example, in other words, the memory is not exhausted before the packet can be queued to queue, and will not discard the packet, the value of the recognition0This is not to say that the queue is not long, but remember: don't do that, because when the router's memory is exhausted, it is more serious than the packet cannot enter the team case;Pqin4the default length of each queue is: High20in40Normal60Low80, when scheduling data in a queue of the fourth to fourth different priority, it is high to low from the overall queue, but if a string of data belongs to the same level of queue, for exampleHighqueue, then in thisHighthe data in the queue will takeFifoThe logic completes the dispatch. V,Pqusing the three-layerAclor Access interface, packet size,Tcpand theUdpthe port number to classify, the data traffic that is not explicitly stated will be categorized into the "Default" class.

Note: If congestion does not occur, technically it is the hardwareTXif the queue is not filled, then the data will be fed directlyTXqueue, will not be usedPQ, keep in mind that software queuing only starts when the hardware queue is filled. PQis a very early, very traditional way of queuing, which producedPQis not described in the followingCBWFQand theLLQ, so it's used in a certain age .PQto ensure that some important services are guaranteed to be of high quality, but now usePQthe odds are low because it's going to be described later in this bookLLQ(Low latency queue), the goal is to ensure that important data is sent first and not "starved" to other queue data.

Forensics Demo: Configuring the PQ Queue and effect of data transfer

Demo Target:

1 simulates a low-speed link that can generate congestion and continuously sends high-voltage traffic across the link.

2 Forensic first-out (FIFO) queues adversely affect the important data (ICMP) transmissions assumed by the environment.

3 Configure the PQ queue to classify important data into a "high" priority queue.

4 Observe the transmission delay of important data again and determine the impact of PQ on data transmission

5 Forensics using the Debug tool different real-time data classifications were sent to different levels of the queue.

Demo Environment: still using the forensics demo: FIFO queues affect the effect of data transfer "the same experimental environment.

Demonstration steps:

R1 (config) #access-list 101 permit ICMP host192.168.2.100 host 192.168.4.2

R1 (config) #access-list 101 permit UDP anyany eq RIP

R1 (config) #priority-list 1 protocol IP highlist 101

R1 (config) #priority-list 1 Protocol Httpmedium

R1 (config) #priority-list1 protocol PPPoE Normal

R1 (config) #priority-list 1 Default Low

R1 (config) #intes1/0

R1 (config-if) #priority-group 1

R1 (config-if) #exit

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This article from the "Nameless Christ" blog, declined to reprint!

PQ (priority queuing queue)