FS S3400-48T4SP 48 Port PoE Managed Switch User Guide

FS S3400-48T4SP 48 Port PoE Managed Switch User Guide

QoS Configuration

If you care to use your bandwidth and your network resources efficiently, you must pay attention to QoS configuration.

QoS Overview

QoS Concept

In general, the switch works in best-effort served mode in which the switch treats all flows equally and tries its best to deliver all flows. Thus if congestion occurs all flows have the same chance to be discarded. However in a real network different flows have differentsignificances, and the QoS function of the switch can provide different services to different flows based on their own significances, inwhich the important flows will receive a better service.

As to classify the importance of flows, there are two main ways on the current network:

• The tag in the 802.1Q frame header has two bytes and 3 bits are used to present the priority of the packet. There are 8 priorities, among which 0 means the lowest priority and 7 means the highest priority.
• The DSCP  field in IP header of the IP packet usesthe bottom 6 bits in the TOS domain of the IP header.

In real network application the edge switch distributes different priorities to different flows based on their significance and thendifferentservices will be provided to different flows based on their priorities, which is the way to realize the terminal-to-terminal QoS.

Additionally, you can also configure a switch in a network, enabling the switch to process those packets with specific attributes (accordingto the MAC layer or the L3 information of packets) specially. This kind of behaviors are called as the one-leap behaviors.

The QoS function of the switch optimizes the usage of limited network bandwidth so that the entire performance of the network is greatlyimproved

Terminal-To-Terminal QoS Model

The service model describes a group of terminal-to-terminal QoS abilities, that is, the abilities for a network to transmit specific networkcommunication services from one terminal to another terminal. The QoS software supports two kinds of service models: Best-Effortservice and Differentiated service

1. Best-effort service
   The best-effort service is a singular service model. In this service model, an application can send any amount of data at any necessary time with out application of permits or network notification. As to the best-effort service, if allowed, the network can transmit data without anyguarantee of reliability, delay or throughput. The QoS of the switch on which the best-effort service is realized is in nature this kindof service, that is, first come and first served (FCFS).

2. Differentiated service
   As to the differentiated service, if a special service is to be transmitted in a network, each packet should be specified with a correspon ding QoS tag. The switch uses this QoS rule to conduct classification and complete the intelligent queuing. The QoS of the switch provides Strict Priority (SP), Weighted Round Robin (WRR), Deficit Round  Robin (DRR) and First-Come-First- Served (FCFS).

Queue Algorithm of QoS

Each queue algorithm is the important basis to realize QoS. The QoS of the switch provides the following algorithms: Strict Priority (SP), Weighted Round Robin (WRR), Deficit Round Robin (DRR) and First Come-First-Served (FCFS).

1. Strict priority
   This algorithm means to first provide service to the flow with the highest priority and after the highest-priority flow comes the serviceforthe next-to- highest flow. This algorithm provides a comparatively good service to those flows with relatively high priority, but its shortageis also explicit that the flows with low priority cannot get service and wait to die.

2. Weighted round robin
   Weighted Round Robin (WRR) is an effective solution to the defect of Strict Priority (SP), in which the low-priority queues always dieout. WRR is an algorithm that brings each priority queue a certain bandwidth and provides service to each priority queue accordingtotheorder from high priority to low priority. After the queue with highest priority has used up all its bandwidth, the systemautomaticallyprovi desservice to those queues with next highest priority.

3. Weighted Fair Queuing
   Weighted Round Robin (WRR) is an effective solution to the defect of Strict Priority (SP), in which the low-priority queues always dieout. WRR is an algorithm that brings each priority queue a certain bandwidth and provides service to each priority queue accordingtotheorder from high priority to low priority. After the queue with highest priority has used up all its bandwidth, the systemautomaticallyprovidesservice to those queues with next highest priority

4. First come first served
   The First-Come-First-Served queue algorithm, which is shortened as FCFS, provides service to those packets according to their sequenceb of arriving at a switch, and the packet that first arrives at the switch will be served first.

Weighted Random Early Detection

• Congestion avoidance and traditional packet loss mechanism
  Excessive congestion may inflict damage on network resources, so network congestion should be resolved through some measures. Congestion avoidance is a sort of flow control method of positively dropping packets and regulating network flows to solve network overload via network resource monitoring. The traditional way of resolving network congestion is to drop all incoming packets when the queue length reaches its threshold. But for TCP packets, heavy packet loss may cause TCP timeout and lead to slow TCP startup and congestion avoidance, which is called as TCP

• WRED
  The WRED algorithm is adopted to prevent TCP global synchronization. WRED helps users to set the queue threshold. When thequeuelength is less than the configured threshold, the packets will not be dropped; otherwise, the packets will be dropped randomly. BecauseWRED drops packets randomly, it is avoided for multiple TCP connections to slow down the transmission speed at the same time, whichisthe reason why TCP global synchronization is avoided. WRED enables other TCP connections to maintain a relatively high transmissionspeed when the packets of a certain TCP connection begin to be dropped and their transmission speed is slowed down. No matter whattime it is, there are always some TCP connections to transmit packets with a high speed, which ensures effective bandwidth usability.

WRED cooperation is conducted when packets enter the outgoing queue and are checked for their size and packets in different ranges getdifferent treatments. The key parameters include Start, Slop and Drop priority

Average queue length

• When the queue length islessthan start, packets will not be dropped.
• When the queue length is bigger than start, the incoming packets begin to be dropped randomly. The longer the queue is, thehigher the dropping rate is.
• The rate for packet lossrises along with the increase of the queue length.

QoS Configuration Task List

In general, ONU will try its best to deliver each packet and when congestion occurs all packets have the same chance to be discarded. However, in reality different packets have different importance and the comparatively important packets should get the comparativelygood service. QoS is a mechanism to provide different priority services to packets with different importance, in which the networkcanhave its better performance and be used efficiently

This chapter presents how to set QoS on ONU.

The following are QoS configuration tasks:

• Setting the Global CoS Priority Queue  Setting the Bandwidth of the CoS Priority Queue
• Setting the Schedule Policy of the CoS Priority Queue  Setting the Default CoS Value of a Port
• Setting the CoS Priority Queue of a Port
• Setting the CoS Priority Queue Based on Dhcp
• Establishing the QoS Policy Mapping
• Setting the Description of the QoS Policy Mapping
• Setting the Matchup Data Flow of the QoS Policy Mapping
• Setting the Actions of the Matchup Data Flow of the QoS Policy Mapping
• Applying the QoS Policy on a Port
• Displaying the QoS Policy Mapping Table

QoS Configuration Tasks

Setting the Global CoS Priority Queue

The task to set the QoS priority queue is to map 8 CoS values, which are defined by IEEE802.1p, to the priority queues in a switch. Thisseries of switch has 8 priority queues. According to different queues, the switch will take different schedule policies to realize QoS.

If a CoS priority queue is set in global mode, the mapping of CoS priority queue on all ports will be affected. When priority queues areseton a L2 port, the priority queues can only work on this L2 port.

Enter the following privileged mode and run the following commands one by one to set DSCP mapping

ID of a CoS priority queue. cos1…cosn stands for the IEEE802.1p-defined CoS value.
exit| Goes back to the EXEC mode
write| Saves the settings.

Setting the Bandwidth of the CoS Priority Queue

The bandwidth of priority queue means the bandwidth distribution ratio of each priority queue, which is set when the schedule policy of the CoS priority queue isset to WRR/DRR. Thisseries of switches has 8 priority queues in total.

If this command is run, the bandwidth of all priority queues on all interfaces are affected. This command validates only when the queue schedule policy is set to WRR or DRR. This command decides the bandwidth weight of the CoS priority queue when the WRR/DRR schedule policy is used.

Run the following commands one by one to set the bandwidth of the CoS priority queue.

priority queue.. weight1…weightn stand for the weights of 8 CoS priority queues of WRR/DRR.
exit| Goes back to the EXEC mode.
write| Savesthe settings.

Setting the Schedule Policy of the CoS Priority Queue

A switch has many output queues on each of its port. This series of switches has 8 priority queues. The output queues can adopt the following three schedule modes:

• SP (Sheer Priority): In this algorithm, only when the high-priority queue is null can the packets in the low-priority queuebeforwarded, and if there are packets in the high-priority queue these packets will be unconditionally forwarded.
• In this mode, the bandwidth of each queue is distributed with a certain weight and then bandwidth distribution is conducted according to the weight of each queue. The bandwidth in this mode takes byte as its uni

Enter the following configuration mode and set the schedule policy of CoS priority queue

priority queue. sp means to use the SP schedule policy. Wrr means to use the WRR schedule policy.
exit| Goes back to the EXEC mode.
write| Saves the settings.

Setting the Default CoSV alue of a Port

If the port of a switch receives a data frame without tag, the switch will add a default CoS priority to it. Setting the default CoS value of apart is to set the untagged default CoS value, which is received by the port, to a designated value.

Enter the privilege mode and run the following commands to set the default CoS value of a port:

standsfor the corresponding CoS value.
exit| Goes back to the global configuration mode
exit| Goes back to the EXEC mode.
write| Saves the settings.

Setting the CoS Priority Queue of a Port

When a priority queue is set on a L2 port, the priority queue will be used by the L2 port; otherwise, you should conduct the configuration of a global CoS priority queue.

Enter the privilege mode and run the following commands to set the default CoS value of a port:

ID of a CoS priority queue. cos1…cosn stands for the IEEE802.1p-defined CoS value.
Exit| Goes back to the global configuration mode.
exit| Goes back to the EXEC mode.

Establishing the QoS Policy Mapping

Flow classification means to identify a class of packets with certain attributes by applying a certain regulation and take designatedactionstowardsto these packets.

Enter the privileged mode and then run the following commands to establish a new QoS policy mapping

stands for the name of the policy
exit| Exits from the global configuration mode.

Setting the Description of the QoS Policy Mapping

Enter the privileged mode and run the following commands to set the description of a QoS policy mapping. This settings will replace the previous settings.

stands for the name of the policy
description description-text| Setsthe description of the QoS policy. description-text stands for the text to describe the policy.
exit| Goes back to the global configuration mode.
exit| Goes back to the EXEC mode.

Setting the Matchup Data Flow of the Qu’s Policy Mapping

The classification rule of the QoS data flow means the filtration rule configured by the administrator according to managementrequirements. It can be simple, for example, flows with different priorities can be identified by the ToS field of the IP packet’s header, orcomplicated, for example, the packets can be classified according to the related information about the comprehensive link layer, thenetwork layer and the transmission layer, such as the MAC address, the source address of IP, the destination address or the port IDof theapplication. In general, the classification standard is limited in the header of an encapsulated packet. It is rare to use the content of apacket as the classification standard.

Enter the policy configuration mode, set the match-up data flow of policy and replace the previous settings with this data flow Accor ding to the following steps:

Setting the Actions of the Match-up Data Flow of the QoS Policy Mapping

The actions to define the data flow mean to take corresponding actions to a data flow with compliance of the filtration rule, whichincludeband width limit, drop, update, etc.

Enter the privileged mode and run the following commands to set the action of a policy, matching up the data flow. The actionwill replace the previous settings.

QoS Configuration Example

Example for Applying the QoS Policy on a Port

The following example shows how to set packet’s cos to 2 on port g0/2: ip access-list extended ipacl

permit ip 192.168.20.2 255.255.255.255 192.168.20.210 255.255.255.255 policy- map pmap
classify ip ipacl action cos 2

References

• FS.com - HPC, Data Center, Enterprise, Telecom

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