SD-WAN QoS – FAQ

2. What type of traffic is allocated by default to different Classes?

In the SD-WAN environment, we think of applications as falling into one of the following three classes:

Real-time –VoIP or VoIP like applications, such as Skype or ICA audio. In general, we refer to voice only applications that use small UDP packets that are business critical

Interactive – This is the broadest category, and refers to any application that has a high degree of user interaction. Some of these applications, for example video conferencing, is sensitive to latency, and requires high bandwidth. Other applications like HTTPS, may need less bandwidth, but are critical to the business. Interactive applications are typically transactional is nature.

Bulk – This is any application that does not need rich user experience but is more about moving data (i.e. FTP or backup/replication)

3. How real-time class works vs interactive:

Real-time (RT) classes are given the highest priority and gets up to 50% of the overall scheduler time. Each class can be weighted with respect to the other RT classes, for example, we could have two RT classes one that weighted to 70% and the other to 30%.

Interactive (INT) classes take the next priority and can consume the rest of the scheduler time as the traffic demands. Individual INT classes can be weighted and by default we have 4 weights (high, medium, low and very low) defined.

4. Will bulk suffer if interactive and real-time flows are there?

Yes, Bulk traffic is serviced after real-time and interactive traffic are serviced. Typically, a bulk class gets a lower sustained share % than an interactive class.

5. How QoS classes are prioritized?

Real-time (RT) classes are given the highest priority and gets up to 50% of the overall scheduler time. Each class can be weighted with respect to the other RT classes, for example, we could have two RT classes one that weighted to 70% and the other to 30%.

Interactive (INT) classes take the next priority and can consume the rest of the scheduler time as the traffic demands. Individual INT classes can be weighted and by default we have 4 weights (high, medium, low and very low) defined.

Bulk (BLK) classes takes the lowest priority and can be considered scavenge classes. They can be weighted but they can be completely starved of bandwidth if the INT/RT traffic is consuming all of the scheduler time.

6. What is the purpose of “Retransmit Lost Packets” option under WAN General, IP Rules?

If the receiving SD-WAN appliance detects a missing packet it can request that packet to be resent by the sending SD-WAN appliance.

7. What is the Criteria for the QoS calculation?

QoS is always calculated on the Send Side.

The Fair Share calculation for the services is based on Per Wan Link.

8. What is Duel Ended QoS?

The Receive side sends the Control Packets to advertise the available bandwidth before the actual Data transfer is initiated.

9. How is share provided during contention?

Please refer this article: https://support.citrix.com/article/CTX256716

10. Difference between the Drop Limit and Drop Depth:

Drop Limit: If the Estimated exceeds the threshold, the packet will be discarded. Not valid for Bulk Classes

Drop Depth (Send Buffer): The Max amount of estimated time that packets smaller than the large packet size will have to wait in the class scheduler. If the queue depth exceeds the threshold, the packet will be discarded and the statistics will be counted.



11. How Drop Limit is calculated (MS)?

Number of bytes Queued divided by Bandwidth available for the class.

12. What are transmit modes based on?

•Persistent path – Based on the latency. If there’s a latency >50mS then there will be a penalty on that path and a new path will be chosen.

•Load Balanced Path– Based on the packet Loss.

•Duplicate paths: Packets will be duplicated over the WAN links.

13. What is MOS (Mean opinion Score) under rule groups?

This Feature gathers application statistics from WAN to LAN side of the Virtual path. It Measure of the quality of the experience that an application delivers to end users. It is primarily used for VoIP applications. In SD-WAN, MOS is also used to assess the quality of non-VoIP applications.

14. What is Application QoS and how to implement it?

By default on the SD-WAN, we have pre-defined Application Family based on the type of the application in the incoming Traffic. For Example: Anti-Virus, Microsoft Office, etc…

It is also possible to create Custom application object.

15. QoS Fairness (RED):

Please refer to this Document:

https://docs.citrix.com/en-us/netscaler-sd-wan/10/quality-of-service/qos-fairness.htm

16. Do we have an option to enable Auto Bandwidth provisioning?

Yes, from SD-WAN Version 10.2.x we have an option under Site —> Wan Links —> Provisioning to enable Auto-Bandwidth Provisioning.

17. What is Auto-Bandwidth Provisioning?

When enabled, the shares for all services defined in the Provisioning section will be auto calculated and applied according to the size of Bandwidth that may be required for the remote sites.

18. How to diagnose if an issue is with SD-WAN or not with respect to QoS?

Based on Multiple factors:

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