SD-WAN QoS - FAQ
Article ID: CTX256721
Updated On:
Description
1. What are the different QoS components?
- IP Rules
- QoS classes
- Application QoS.
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:
- Need to check the Actual bandwidth compared to the Physical Rate configured on the WAN Link.
- Type of Traffic.
- Isolate if is a Network issue based on the Latency, Loss, Jitter and Rate limit.
- Check if it is hitting the Rule configured.
- Need to check if it is falling under the correct Class defined.
- iPerf - to verify the Bandwidth
- SDWAN Center.
- Diagnostic Tool on SD-WAN
Provisioning Groups contains the list of Services on any given WAN link where the Bandwidth is allocated at the group level before segregating down to individual Services.
Services allows the User to view and allocate bandwidth settings for individual services within the Group.
21. What is the difference between the Permitted Rate and Physical Rate?
Permitted Rate: The amount of bandwidth that SD-WAN devices are permitted to use for Upload/download, which cannot exceed the defined physical upload/download rate of the WAN Link.
Physical Rate: The Actual bandwidth raw rate of the physical cable associated with the WAN link.
22. What are the Default Minimum Kbps by Service Type?
- Virtual Path: 80 kbps (including Dynamic Virtual Path type)
- Internet/Intranet: 100 kbps
23. How Dynamic virtual path is provisioned?
It is provisioned the same way as Static Virtual path. Need to set the Min (kbps) and Max (kbps) for an individual Dynamic Virtual Path. Once it is set, the Fair (kbps) per Dynamic Virtual Path will be recalculated to reflect the new settings.
24. What is the difference between the initial and sustained Share in Classes section?
For real-time classes:
* Initial Rate: Maximum rate at which packets leave the queue during the initial period.
* Sustained Rate: Maximum rate at which the packets leave the queue after the initial period.
* Initial Period: The time period in milliseconds to apply an initial rate before switching to a sustained rate.
For interactive classes:
* Initial Share %: The maximum share of virtual-path bandwidth during the initial period.
* Sustained Share %: The maximum share of virtual-path bandwidth after the initial period.
* Initial Period: The time period, in milliseconds, during which to apply initial percentage of the available bandwidth before switching to the sustained percentage. Typically, 20 Ms.
Interactive classes use the remaining bandwidth after the real-time traffic has been serviced.
For bulk classes, you can specify only the Sustained Share%, which determines the remaining virtual path bandwidth to be used for a bulk class.
Issue/Introduction
Frequently Asked Questions on SD-WAN QoS
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