QoS Traffic Shaping Explained

(Andrew P) #29

Michael,
Be can be the same as Bc, but is often different. For example, with a single rate, three color policer, Bc and Be are the same, but with a dual rate, three color policer, Bc is based on the Committed Information Rate (CIR), while Be is based on the Peak Information Rate (PIR) which are often different.

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(elbert s) #30

Hi Rene,

Talking about bitrate and “Routers are only able to send bits at the physical clock rate”, I was confusing about the very basic theory of the packet, packet size and how it transmit in the network media.

If everything is sending bit by bit, how it become a “packet” and people always says how the data in a message or file is broken up into packages about 1,500 bytes long, but how it change to “a packet”? so router is sending bit or sending packet?

Thanks

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(sims) #31

Hi,
If i have one gb bandwidth and the source transmitting only 5 Mb,still do I need to work on qos
thanks

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(Andrew P) #32

Sims,
It may seem crazy in your scenario that you would have to worry about QoS, but yes, you do, if you have mission critical applications that can’t afford any type of delay. There is a sneaky phenomenon called a “micro-burst” where a sudden, very short (milliseconds) flood of traffic can overwhelm a device. If you have a mission critical application, it would be smart for you to establish a QoS policy that guarantees the bandwidth you know it needs as opposed to leaving it to chance.

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(Shantel - Networklessons.com) split this topic #33

19 posts were merged into an existing topic: QoS Traffic Shaping Explained

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(Abdus S) #34

Please help me out to implement QoS over ADSL link. I want to prioritize my voice traffic and assign 15% of BW.
Please check the config of my usual WAN link not sure what would be on ADSL.

class-map match-any Client-Signal-Class
 match precedence 3
 match ip dscp af31
 match ip dscp cs3
class-map match-any Client-VOIP-Class
 match precedence 5
 match ip dscp ef
!
policy-map 50Mb-VOIP-PMAP
 class Client-VOIP-Class
  priority percent 10
 class Client-Signal-Class
  bandwidth percent 5
 class class-default
  fair-queue
policy-map 50Mb-VOIP
 class class-default
  shape average 49000000 504000
   service-policy 50Mb-VOIP-PMAP

Not sure what would be the shaping reference BW (Here - 49000000) on ADSL link. Your prompt reply highly appreciated.

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(Rene Molenaar) #35

This example looks correct. You are shaping to 49 Mbit, with a Bc of 504000 you have a Tc of ~11ms which is fine. On Cisco IOS, you have to configure the shaper first and then use a sub-policy with LLQ like you did…10% priority queue for RTP and 5% (CBWFQ) for your signaling traffic.

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(Bogdan D) #36

Hi,

Rene, can you tell me if the Be is available at any given time or not ? If i have Bc 8000bits and Be 8000 it means that at every Tc i can send 16 000bits ?

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(Lazaros Agapides) #37

Hello Bogdan

The Be will be available only if it has been configured. If it has, then for the first Tc you will be able to send up to 16000 bits. In order for the Be to be available again, a certain time interval of inactivity, the Be will be available again to burst up to 16000 bits once again.

I hope this has been helpful!

Laz

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(Prashant W) #38

Hello Rene

I am bit confuse between policing and shaping … can you please help to understand practical difference between policing and shaping …

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(Rene Molenaar) #39

Hello Prashant,

Both policing and shaping have a common goal: to “rate-limit” exceeding traffic.

How they do it is different though. A shaper will “buffer” the traffic while a policer “drops” the traffic.

A practical example could be an ISP router that is connected to multiple customer routers. Let’s say that the routers are connected with GigabitEthernet links but the customers are only paying for a 100/100 Mbit connection.

The ISP will then use a policer to drop all incoming traffic that exceeds 100 Mbit.

On the customer end, you probably don’t want your traffic to get dropped so you can then configure an outgoing shaper that is configured for 100 Mbit. This will not drop your traffic but buffer it, which guarantees that all traffic is sent and the ISP’s policer won’t drop it.

Hope this helps!

Rene

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(Chris N) #40

Is there a way to see how much buffer space is being used, either globally or per interface, and any way to adjust this?

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(Rene Molenaar) #41

Hi Chris,

Before IOS 12.4(20)T you can use the shape max-buffers command to define the size of the queue. On newer IOS versions, you need to use the queue-limit command to set the buffer size that the shaper uses.

Rene

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(Chris N) #42

Thanks - another question, doesn’t each token represent one BYTE rather than one BIT?

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(Lazaros Agapides) #43

Hello Chris

Each token does indeed represent one bit.

I hope this has been helpful!

Laz

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(Chris N) #44

Thanks Laz, is it different for Policing then? As in this article, Rene says 1 token is a byte:

When a packet arrives the policer will check if it has enough tokens in the token bucket, if so the packet will be forwarded and the policer will take the tokens out of the token bucket. So what is a ‘token’ anyway? When it comes to policing each token represents a single byte.

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(Lazaros Agapides) #45

Hello Chris

Yes. Take a look at this Cisco documentation that compares Traffic Shaping to Traffic Policing:


The link shows a table that indicates what the Token values are, among other things. For shaping it is configured in bits per second while for policing it is in bytes.

I hope this has been helpful!

Laz

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(Vinod A) #46

Hi Rane, I want design QOS for Enterprise network (sites &DC) connected over ISP network…how to start ,what should be my approach

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(Lazaros Agapides) #47

Hello Vinod

A good place to start would probably be Rene’s lessons on QoS:


Now from here you can get into the specifics as far as how to implement QoS. But one of the things that you should look at before you even go over the technical stuff, is what do you want to achieve? What traffic do you want to provide QoS for? What kinds of speeds will be available on the enterprise network? Do you want to implement it for the WAN link or for the internal network or both? Will you be running voice and video over your network?

These are the kinds of questions you need to answer which will then lead you to the appropriate implementation of QoS. This will give you a good starting point from which to determine what to implement and how.

I hope this has been helpful!

Laz

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(Dmiry S) #48

Shouldn’t the vertical axis specify only Kb, not Kbps? So that you send some equal portions of traffic during the time intervals in milliseconds. Your picture could be read as if user sends at 128 Kbps during those time intervals. But does he really do that if we shape the rate to 64 Kbps? Thanks.

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