WAN Edge QoS Design: Video and Scavenger

[cedar_lee]

Hi QoS Experts,

I am thinking QoS on WAN edge but not sure if Interactive Video better on Gold or Silver class and if scavenger class could be used and how.

Our service provider offers 4-class QoS model. The prices and performance metrics listed here are not real but close enough as some factors of QoS design. Traffic allocation to each class is totally up to us, not service provider. But service provider makes the rules that

1. Only Default class is allowed to use the unused bandwidth from other classes.
2. The rest of three classes will drop excessive traffic.

Class	DSCP	Traffic Type	Price	RTT	Jitter	Pkt Loss
Gold	46 (EF)	VoIP, Real-time Interactive Video	$15/Mbps/Mon	20ms	4ms	0.1%
Silver	26 (AF31)	Network Control/Critical Apps	$5/Mbps/Mon	30ms	8ms	0.5%
Bronze	10 (AF11)	Apps cannot be in default class	$3/Mbps/Mon	50ms	8ms	1.0%
Default	0 (CS0)	All other traffics	$1/Mbps/Mon	150ms	n/a	5.0%

Q1. Real-time Interactive Video better on Gold or Silver class?

For cost consideration, it would be better to move Real-time Interactive Video from Gold class to Silver class. For example, if 500Mbps is needed for Real-time Interactive Video, it would save $5000/Month if used Silver class.

For performance consideration, Silver class has bigger jitter than Gold.  Gold should be better.

Or, leave the audio part in Gold and move video part to Silver. For example, DSCPs of audio and video of Microsoft Lync can be marked separately on servers.

Any comment please?

Q2. if scavenger class could be used and how?

Again, to save money, we want to put majority of traffic to Default Class and use Bronze for the non-critical Applications that have to be separately from Default class. (For example, 5G BW, Gold 15% or 5%, Silver 5% or 15%, Bronze 5%, Default 75%)  At the same time, it would be great to implement something to limit the traffics that should be considered in scavenger class. However, I have only four classes from service provider and not sure if scavenger class could be used and how.

Any good advice please?

Thank you,

Cedar

[Terry Cheema]

1) Interactive Video: Technically from the above latency, jitter, packet loss - Interactive video should be fine in the silver class:

Ref: http://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoS-SRND-Book/QoSIntro.html#pgfId-46626

2) Regards to the Scavenger, just classify this traffic clearly, assign it to a class with a limited bandwidth (say 5% in Bronze class - just an example, choose based on your requirements). You will want to clearly classify this traffic and rate limit it.

So something like this:

1) Audio + Signalling (signalling can go into silver class but its not very bulky so you can put in Gold class) - Gold

2) Multimedia Conferencing\critical data: Silver

3)  Scavenger with a limited bandwidth: Bronze

4) All other data : Best Effort (assign more of bandwidth here)

Please see, above is just a suggestion based on limited information, you can refer to Cisco guide lines etc. as well, but you can only work out the accurate policy based on the review of your environment. Please do work out what type of  traffic you have, what is critical, bandwidth needs for each class and work out a policy accordingly.

-Terry

[cedar_lee]

Hi Terry,

Thanks for your comment. I understand it's not just black and white about the QoS solution because it's so flexible and multiple options might work fine in the same environment. I like your idea above. I will need to get more information by looking at my current work environment and then make a decision to choose one design among the three or four.

Thanks,

Cedar

[Joseph W. Doherty]

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Posting

Actually a QoS solution often is black and white, what often makes it gray is lack of a full understanding of how to use QoS, lack of QoS features that are needed, and/or lack of full understanding of the service needs of your traffic.

For starters, to really obtain the optimal benefit of what your providers offers it to truly understand how your provider's QoS really works, and your WAN (logical) topology and technology.

Technically, what you've posted for performance attributes of the Bronze class would meet the needs of VoIP bearer or interactive video.  Yes, the Gold and Silver classes have better SLAs, but Bronze's SLA is "good enough" (if really met) to meet their requirements.  I.e. VoIP bearer or interactive video shouldn't much, to a user, seem better in the Gold or Silver classes.

Yes, the provider's Default class could be used for scavenger traffic, but if you only relied on provider QoS, you would need to place non-scavenger class in something other than Default, such as Bronze.  From the provider's perspective, it shouldn't matter if you mix VoIP bearer or interactive video in that class, but it may matter how you feed traffic into the WAN.  (I.e. what's your QoS policy, if any?)

You could mix non-critical and scavenger in the provider's Default class, but for that to work well, you would need to control how you mix the traffic as you feed it into the provider's WAN.  You also would need to indirectly manage WAN egress if your logical topology is multipoint.

Unfortunately, as whole books have been written on QoS, it's difficult to describe, in just a few paragraphs, all that might be considered and what might be done.  (Also, much for what might/should be done depends on your environment, which I don't know.)

However, as I believe you're trying to minimize costs while meeting your traffic service requirements, I'll mention, in the past, I've (well) supported everything from VoIP, interactive video, email, web applications, SAP applications, file servers, and backups and replication across the same Internet VPN tunnel; the secret being "QoS".  I mention this, because QoS (NB: encompassing more than what your WAN provider offers) might also be your key to likewise minimizing your WAN costs while meeting your service objectives.

[cedar_lee]

Hi Joseph,

Thanks for the comment. 

You are right about that performance wise almost all the three classes, Gold, Silver and Bronze, should be able to support voice and interactive video. And I have seen voice working fine with just Bronze class in some cases.  

And agreed that QoS is difficult to describe. So far, I found the book End-to-End QoS Network Design 2nd Edition by Tim Szigeti, Robert Barton, CHristina Hattingh and Kenneth Briley Jr. is very helpful.

Now my idea is to follow Cisco modified RFC4594-based to perform 12-class traffic classification and marking by using NBAR2 on the ingress direction of LAN interfaces on the WAN routers. Then on the WAN router WAN interfaces egress direction to group the 12 classes to 4 classes. It is very flexible. I presented four options and discussed with my team. Finally we made a choice on one of them. We are happy with this design and will move forward with it.

Thanks,

Cedar