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frame-relay traffic-shaping - Access Rate definition

In http://www.cisco.com/en/US/customer/tech/tk713/tk237/technologies_configuration_example09186a00800942f8.shtml

it states that the 'access rate is the physical line speed'.

Does this mean that the access rate for a 256k fract T1 is still to be treated as 1536k or as 256k?

Just to be clear: 256k fract T1 implies 'service-module t1 timeslots 1-4'.

When I 'show frame-relay map' I see BW=128000 on one of my sub-interfaces.

Is this the CIR I purchased from the telco?

Is it therefor the value I use for 'frame-relay mincir'?

Thx,

Phil

12 REPLIES

Re: frame-relay traffic-shaping - Access Rate definition

Hello Phil,

if you have a fractional T1 of 256K, that is your access rate. The output of 'show frame-relay map' indeed tells you what your provider is giving you. The mincir should be half of the CIR. So, to put it all together, your map-class should look like this:

map-class frame-relay FR_T1

frame-relay cir 128000

frame-relay bc 16000

frame-relay mincir 64000

You also might want to have a look at the link below, which contains a very nice presentation on FRTS:

Frame Relay Traffic Shaping

http://www.internetworkexpert.com/resources/01700368.htm

HTH,

GNT

Re: frame-relay traffic-shaping - Access Rate definition

Phil,

The access rate in your scenario is 256k i.e timeslots 1-4.

The BW of 128k shown by your 'show frame-relay map' output is your CIR (guaranteed bandwidth) and you would use the 'frame-relay mincir 128k' in your map-class to define it. BW show by this command is what is set by Telco on their switch but you need to make sure the CIR is consistent with your circuit provisioning order.

HTH,

Sundar

Community Member

Re: frame-relay traffic-shaping - Access Rate definition

Sundar,

I have this actual running config:

Fract T3 of 9Mbps at hub

15 spoke sites (on sub-interfaces) with various combos of access-rate and reported BW

Examples: AR=1536 and BW=512; 1536 and 256; 256 and 128; 128 and 64

I don't understand the relationship (if any) between the remtoe access-rate and the cir and mincir values in the map-class.

Do you simply set the cir to the AR and the mincir to the BW?

If my remote AR is 1536 and the BW value is 512000 then is this config correct?

map-class frame-relay AR1536-BW512

frame-relay cir 1536000

frame-relay bc ?????

frame-relay mincir 512000

How is the bc value derived?

Thx,

Phil

Re: frame-relay traffic-shaping - Access Rate definition

Hello Phil,

Are you asking practical questions about the usage of those 2 parameters ? or the definition of the values?

cir, bw, bc and min are very different from each other and depends on what your provider has aggreed to give you.

I'd recommend you check these definitions firt:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cg/hqos_c/part20/qchpolsh.htm#wp1011592

Then check an example:

http://www.cisco.com/warp/public/125/traffic_shaping_6151.html

Vlad

Re: frame-relay traffic-shaping - Access Rate definition

Phil,

Your Bc for the above example is 48k. Bc is derived using the following forumla:

Bc = CIR * Tc/1024

1536000*32/1024 = 48000

CIR = 1536k

Tc = 32ms

Other parameters look correct in your scenario.

I recommend you a take look at an excellent resource on this topic that interetworkexpert has made available at the following URL. Hopefully, this should enlighten you on this topic.

http://www.internetworkexpert.com/resources/01700368.htm

Good Luck!!

Regards,

Sundar

Gold

Re: frame-relay traffic-shaping - Access Rate definition

As I see 2 posts that said the same will revise mine to point out.

MINCIR is only used if you use adaptive traffic shaping. If you do not turn on that option I do no think it has a effect.

As to the releationship of CIR and access rate I will try a example that is not 100% correct but illistrates the point.

If you and your provider agreeded to a cir of 10m/second and your interface is a fastethenet 100m/second. Now also assume they average the usage over 10 seconds.

Now you always transmit at 100m nomatter what since that is the physical access speed. I could transmit 100m for 1 full second and then do nothing for the next 9 seconds. I would then get a average of 10m and be within the commited rate. I could also transmit for 1/10 of a second but do it for 10 seconds in a row and still be in my committed rate.

The issue comes when the CIR rate and BC values do not agree with the provider. If you would think you had 10 seconds to average the traffic and they used 1 second in the above example the first case you would get lots of traffic marked discard eligible and in the second it would work fine.

Hopefully this does not just confuse you more. Traffic shaping and these CIR/BC/TC things take a while to figure out.

Community Member

Re: frame-relay traffic-shaping - Access Rate definition

Sundar,

Thank you and the others for their input.

However, there are conflicting responses.

One says my BW=512000 is the cir and other says mincir

I have this 'show frame-relay map':

Serial1/0.15 (up): point-to-point dlci, dlci 102(0x66,0x1860), broadcast, BW = 512000

The local loop is full 24-channel T1 = 1536kbps

I am using adaptive-shaping becn in my map-class

map-class frame-relay MyClass

frame-relay adaptive-shaping becn

frame-relay cir 512000

frame-relay bc 16000

frame-relay mincir 256000

Where Bc=cir*Tc/1024 => 512000*32/1024 = 16000

Is this correct or is mincir=512000?

If mincir=512000 then what is cir?

Thx

Phil

Re: frame-relay traffic-shaping - Access Rate definition

Phil,

I know FRTS is a confusing topic and there are many different views out there ;-)

Your map class should read as follows:

map-class frame-relay MyClass

frame-relay adaptive-shaping becn

frame-relay cir 1536000

frame-relay bc 48000

frame-relay mincir 512000

CIR = Remote site's AR

MINCIR = Telco provided CIR or guaranteed bandwidth

Bc = cir*Tc/1024 => 1536000*32/1024 = 48000

If you set your CIR to 512000 then you are limiting yourself to 512k and wouldn't be able to use any free bandwidth available during periods of no-congestion on the provider network. If you decide to leave the CIR at 512k then you don't even need the 'adaptive-shaping becn' command.

Hope that helps!!

Regards,

Sundar

Community Member

Re: frame-relay traffic-shaping - Access Rate definition

Sundar,

Thanks for the help. This resolved my issue. I think Cisco could do more to explain this QoS subject so it is better understood. In the case of a 64k fract T1 one could make the mistake of thinking the access-rate was the full 1536k and not just 64k.

Phil

Re: frame-relay traffic-shaping - Access Rate definition

Phil,

Glad it helped!

I agree Cisco's documentation on this topic is somewhat confusing and it can be improved.

Regards,

Sundar

Re: frame-relay traffic-shaping - Access Rate definition

Phil,

I have a small request for you. If the solutions posted on this forum helped resolve a problem please remember to resolve the thread. This would help others in the same boat go through the archives and identify the resolved thread to get answers to their queries quickly.

Regards,

Sundar

Community Member

Re: frame-relay traffic-shaping - Access Rate definition

I'm not sure if the Bc calculation given to you above was correct. I always thought that the Tc was always presumed to be 125ms (or 0.125 sec). In which case, the Bc calculation would be: Bc = CIR * Tc Or 192000 (1536000 * 0.125).

Regarding CIR vs. mincir, my understanding is: mincir = the CIR bandwidth that you are guaranteed by the provider. While the CIR (in map-class) = the max burst bandwidth allowed by your provider. Hence, if your provider allows you to burst up to the full T1 speed, then CIR(map-class) = 1536000. But, if your provider does not allow bursting, then your CIR(map-class) would be the same as mincir.

Personally, I also found the legacy FRTS configs to be a bit confusing. I'd rather use MQC-based FRTS. For example, the following config would be required for you (presuming 512Kb CIR, bursting up to 1024Kb):

policy-map shape512to1M

class class-default

shape peak 512000 64000 0(*)

shape adaptive

shape fecn-adapt

fair-queue

!

interface serial0.1

ip address

service-policy shape512to1M

!

Note: The numbers that follow 512000 in the "shape peak" command are Bc and then Be. Bc was calculated based on my understanding above, while Be is presumed to be 0. If your provider allows excess burst, then set this number to the number allowed by your provider. If Be allowed but the size is not known, set it to the same as Bc.

HTH.

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