[cisco-bba] BRAS oversubscription calculator

[Sam Meftahi]

Hi all

 

Is there any reliable oversubscription calculators, algorithms or even simple rules of thumbs.

 

TIA

 

Sam

 

________________________________

From: Andy Schutz (aschutz) [mailto:aschutz at cisco.com] 
Sent: 18 January 2005 01:16
To: Sam Meftahi; 'Benoit GRANGE'; cisco-bba at puck.nether.net
Subject: RE: [cisco-bba] ADSL shaping using Hierarchical VP

 

Sam,

 

A couple of things, I believe the 10k has a limit enforced via CLI when defining the oversubscription factor (I think it is 50).  In regards to the preservation of PQ traffic under a oversubscription scenario, the 10k is able to implement a back-pressure mechanism between the packet scheduler and the SAR indicating what traffic should be dropped in congestion conditions.  This link is a little self-serving but it validates the 10k does this correctly:

 

http://www.miercom.com/dl.html?fid=20041015&type=report

 

That said, this type of implementation can get complicated and I would advise at least consulting with your local account team on how best to implement this in your network.

 

hope that helps,

 

Andy

	-----Original Message-----
	From: Sam Meftahi [mailto:SAF at sonofon.dk] 
	Sent: Monday, January 17, 2005 12:54 AM
	To: aschutz at cisco.com; Benoit GRANGE; cisco-bba at puck.nether.net
	Subject: RE: [cisco-bba] ADSL shaping using Hierarchical VP

	Hi all

	 

	Going thru this document

	 

	http://www.cisco.com/en/US/products/hw/modules/ps2033/products_implementation_design_guide_chapter09186a0080199949.html#16529

	 

	Cisco states that oversubscribed ports could experience cell drops due to colliding cells. 

	Cells compete for same time slot provided by SAR scheduler. And this can even occur in underutilised ports links. 

	 

	Does the algorithm take into consideration all configured VCs or only the ones carrying traffic ? 

	 

	Either way, there must be a restriction on how far can a link be overbooked without triggering a high cell rate the scheduler would not cope with and starts dropping from there.

	 

	TIA

	 

	Sam    

	 

	
________________________________


	From: Andy Schutz (aschutz) [mailto:aschutz at cisco.com] 
	Sent: 14. januar 2005 17:08
	To: 'Benoit GRANGE'; Sam Meftahi; cisco-bba at puck.nether.net
	Subject: RE: [cisco-bba] ADSL shaping using Hierarchical VP

	 

	Sam,

	 

	Take a look at this link: http://www.cisco.com/en/US/partner/products/hw/routers/ps133/products_feature_guide09186a00802254b7.html

	 

	In regards to what is recommended for oversubscription factors, I don't think there is a recommended value.  It depends on customer traffic patterns and how much you want to guarantee each user.  I have heard requirements for as little of 4:1 oversubscription to as high as 50:1 as stated in above link. 

	 

	Hope that helps.

	 

	Andy

		-----Original Message-----
		From: cisco-bba-bounces at puck.nether.net [mailto:cisco-bba-bounces at puck.nether.net] On Behalf Of Benoit GRANGE
		Sent: Friday, January 14, 2005 9:31 AM
		To: Sam Meftahi; cisco-bba at puck.nether.net
		Subject: RE: [cisco-bba] ADSL shaping using Hierarchical VP

		 

		Hello,

			Which category service are u using? I am using nrt-VBR. 
			[Benoit GRANGE] We also use this one (and it is the only one supported for Hierarchical VP shaping).

			 

			Does Cisco recommend any Oversubscription or overbooking factors values for 7206VXR or 10000.
			[Benoit GRANGE] I don't know.

			Otherwise, which values is  the general ISP community using without causing any degradation?

			I thing it is really up to you (and your market constraints).

			 

			To clarify what I mean by Oversubscription, it is total SCR bandwidth exceeding line speed and not number of VCs

		You can not really oversubscribe the number of VC being really in use (you may be able to provision more than the card limit, but they may not be all used at the same time).

		 

		Having Sum(SCR) > Card badnwidth is possible in the Cisco 10k since release 12.3XI

		 

		Benoît

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