QoS Scheduling Policy Design

The basic principle of traditional QoS design for wired networks is to mark or re-mark packets at boundaries of different DiffServ domains and perform bandwidth control. Devices in the same DiffServ domain only need to schedule packets in queues based on the priorities marked on edge nodes. Typically, service deployment involves traffic identification at the access layer, DiffServ model deployment at the aggregation or core layer, and bandwidth control on egress firewalls.

• Traffic identification at the access layer

  Access switches function as edge switches. The switches identify, classify, and mark data flows at the user side. In actual deployment, different interfaces on access switches are connected to different terminals. Different priorities can be allocated to different services on access switches. Then traffic of the services can be scheduled based on the priorities.

• DiffServ model deployment at the aggregation or core layer

  Interfaces on aggregation and core switches are configured to trust DSCP or 802.1p priorities and enforce QoS policies based on priorities marked at the access layer, to ensure that high-priority services are scheduled first. A switch interface trusts 802.1p priorities by default.

• Egress device bandwidth control

  Egress devices are also located in the DiffServ domain and are configured to trust DSCP or 802.1p priorities and implement QoS policies. WAN interfaces of egress devices are restricted by the egress bandwidth. Therefore, you need to consider differences when setting bandwidth parameters of WAN interfaces. Additionally, QoS policies of egress devices vary according to the enterprise WAN construction mode.

  • WAN QoS policies can be managed by an enterprise itself in the following scenarios: enterprise-built WAN, private line construction using leased fibers, and customized enterprise QoS policies applied to the carrier WAN. In this case, egress or PE devices on the campus network do not need to re-mark traffic.
  • The WAN QoS policies are not controlled by an enterprise itself. The enterprise leases the private line network of a carrier, and the carrier does not trust the packet marking on the enterprise network or the two parties have different definitions of the same packet marking. In this case, egress devices on the campus network need to re-mark traffic.

The network efficiency of WLANs is lower than that of wired networks, and STAs are more sensitive to user experience. Therefore, you are advised to consider the following aspects when designing the QoS policies for STAs:

• The maximum bandwidth of a single user can be limited based on service requirements. If multiple SSIDs are planned, the total bandwidth of non-critical SSIDs can be limited.
• In high-density scenarios, many users preempt channel resources. As a result, the Internet access quality of each user deteriorates. You are advised to enable the following functions:
  • The call admission control (CAC) function is used to control STA access based on the radio channel utilization and number or signal-to-noise ratio (SNR) of online STAs to ensure the Internet access quality of online STAs.
  • The dynamic enhanced distributed channel access (EDCA) parameter adjustment function allows APs to adjust EDCA parameters flexibly by detecting the number of STAs to reduce the possibility of collisions, improve the throughput, and enhance user experience.
• To enable STAs (especially sticky STAs) to re-associate or roam to APs with better signals, enable the function of quickly disconnecting STAs to force low-SNR or low-rate STAs to go offline.
• In scenarios requiring high multicast service experience, you are advised to enable the multicast-to-unicast conversion function to improve multicast service experience (for example, HD video on demand) to prevent the impact of low-rate STAs on multicast services.
• In scenarios where VIP user experience needs to be guaranteed, you are advised to enable preferential access of VIP users to ensure preferential access, scheduling, and bandwidth guarantee for VIP users.

In WLAN QoS design, you need to consider priority mapping between wired and wireless network packets. For example, 802.11 packets sent by WLAN clients carry user priorities or DSCP priorities, VLAN packets on wired networks carry 802.1p priorities, and IP packets carry DSCP priorities. To ensure consistent QoS scheduling of packets on wired and wireless networks, you need to configure priority mapping on network devices.

Only 802.11ax (Wi-Fi 6) APs support bandwidth guarantee.

Different enterprises attach different importance to data. For example, the Internet access and online game traffic may be considered as important traffic for portal websites while junk traffic for the financial system. For the financial industry, real-time transactions may be considered as important or even more important than voice services. Therefore, the QoS policy solution must be designed and deployed based on actual service types and QoS requirements of each enterprise. Table 3-25 lists the typical QoS policy solutions formulated based on engineers' experiences, which provide references for design personnel.